Dimitrios Pournarkas

Abstract

Gelled non-toxic bicontinuous microemulsions have great potentials in transdermal drug delivery. The bicontinuous microemulsion provides optimum drug solubilisation and promotes skin permeation, while the gel network provides mechanical stability and an easy application. For the first time, we have formulated such a gelled non-toxic bicontinuous microemulsion consisting of H2O, isopropyl myristate (IPM), the non-ionic sugar-based surfactant Plantacare 1200 UP (C12G1.4), 1,2-octanediol, and the low molecular weight gelator 1,3:2,4-dibenzylidene-D-sorbitol (DBS). In this study, we solubilised both hydrophobic and hydrophilic model drugs in the non-toxic bicontinuous microemulsion, namely lidocaine and diclofenac sodium salt. We found that the microemulsion allows for the solubilisation of designated amounts of both model drugs in the same formulation. Interestingly, the combination of both drugs led to the unexpected stabilisation of a scattering one-phase formulation without adding the surfactant Plantacare 1200 UP. Furthermore, the drug-loaded microemulsions were gelled by DBS without altering the phase behaviour. Finally, we found the rheological behaviour of the drug-free and drug-loaded microemulsions to be quite similar. These results suggest that the drug-containing gelled bicontinuous microemulsion is an orthogonal self-assembled system with a high potential for the use in transdermal drug delivery.

Abstract

Gelled non-toxic microemulsions have great potential in transdermal drug delivery: the microemulsion provides an optimum solubilizing capacity for drugs and promotes drug permeation through the skin barrier, while the gel network provides mechanical stability. We have formulated such a gelled non-toxic microemulsion consisting of H2O – isopropyl myristate (IPM) – Plantacare 1200 UP (technical-grade alkyl polyglucoside with an average composition of C12G1.4) – 1,2-octanediol in the presence of the low molecular weight gelator (LMWG) 1,3:2,4-dibenzylidene-d-sorbitol (DBS) at an oil-to-water ratio of ϕ = 0.50. The study at hand aimed to develop gelled non-toxic microemulsions that can contain both oil- and water-soluble drugs and are either water- or oil-based, depending on the application. To accomplish this, we varied the oil-to-water ratio from being water-rich to oil-rich, i.e. 0.2 ≤ ϕ ≤ 0.8. Phase studies were carried out along the middle phase trajectory, and a suitable LMWG was identified for all ϕ-ratios. Electrical conductivity measurements showed that the structure can be tuned from water- to oil-continuous by adjusting the amount of 1,2-octanediol and ϕ-ratios. The existence of the gel network was visualized by freeze-fracture electron microscopy (FFEM) at three different ϕ-ratios. We found that all systems from ϕ = 0.35 to ϕ = 0.80 form strong gels with nearly the same rheological behavior, while the system with ϕ = 0.20 is a much weaker gel. We attribute this behavior on the one hand to the microemulsion microstructure and on the other hand to the solvent-dependent gelation properties of DBS, which can be described by the Hansen solubility parameters (HSPs).

Abstract

Hydrogen spillover is mechanistically poorly understood, due to the H˙ donor complexity. We show that HV(CO)4dppe (1) transfers H˙ to MoO3 in separate H+ and e− transfer steps. This is analogous to hydrogen spillover from Pt to MoO3 and suggests that 1 is a good model for H˙ adsorbed on Pt.

Abstract

Polystyrene (PS) nanofoams, prepared following the nanofoams continuity inversion of dispersions (NF-CID) principle, were utilized for the synthesis of nanoporous organic/inorganic hybrid materials. The pore size and morphology of the PS foams were found to depend on the NF-CID parameters: temperature, exposure time, and the expansion process. With this knowledge, PS foams with a pore size of 1 µm were mineralized with ZnO from a methanol precursor solution comprising zinc acetate dihydrate. Scanning electron microscopy (SEM) coupled with energy-dispersive X-ray (EDX) was used to characterize both the pure PS nanofoam and the hybrid material. The formation of a ZnO layer on the pore walls of the polymer foams was confirmed, while the general structure of the foam was retained. Uniaxial compression measurements revealed larger values of the E modulus and the yield stress for the porous PS/ZnO hybrid material compared to the pure polymer foam.

Abstract

We present a systematical investigation of gelled lyotropic liquid crystals (LLCs). This new class of soft materials combines the anisotropy of LLCs with the mechanical stability of a physical gel. The studied LLC system consists of sodium dodecyl sulfate as a surfactant, n-decanol as a cosurfactant, and water as a solvent. At room temperature, four liquid crystalline phases (lamellar Lα, nematic Nd and Nc, and hexagonal H1) are formed depending on the composition. We were successful in gelling the lyotropic lamellar phase with the low-molecular-weight organogelator 12-hydroxyoctadecanoic acid (12-HOA). The obtained gelled lamellar phase shows optical birefringence, elastic response, and no macroscopic flow. However, we were not able to obtain gels with hexagonal or nematic structure. These findings can be explained twofold. When gelling the hexagonal phase, the long-range hexagonal order was destroyed and an isotropic gel was formed. The reason might be the incompatibility between the gel fiber network and the two-dimensional long-range translational order of the cylindrical micelles in the hexagonal phase. Otherwise, the lyotropic nematic phase was transformed into an anisotropic gel with the lamellar structure during gelation. Evidently, the addition of the gelator 12-HOA to the lyotropic system considerably widens the lamellar regime because the integration of the surface-active 12-HOA gelator molecules into the nematic micelles flattens out the micelle curvature. We further investigated the successfully gelated Lα phase to examine the impacts of the gel network and the remaining monomeric gelator on both the structure and properties of the gelled lamellar phase. Small-angle X-ray scattering results showed an arrested lamellar layer spacing in the gelled state, which indicates a higher translational order for the gelled lamellar phases in comparison with their gelator-free counterparts.

Abstract

The bending rigidity of surfactant membranes in novel bicontinuous CO(2)-microemulsions of the type H(2)O/NaCl-scCO(2)-Zonyl FSH/Zonyl FSN 100 was determined using both high pressure small angle neutron scattering and neutron-spin echo spectroscopy. As an important result it was found, that the stiffness of the membrane increases solely by an increase of the pressure.

Abstract

The efficiency of an amphiphile in solubilizing water and oil into a thermodynamically stable mixture is limited by the extensions of liquid crystalline phases. New results on microemulsions from polymer blends show that almost the same holds for high molecular weight systems. This review compares these findings. It also draws attention to the effect of homopolymers and hydrophobically modified polymers on microemulsions, emphasizing the importance of polymer adsorption on the membrane properties. The recently-discovered efficiency boosting of amphiphilic block co-polymers in highly dilute microemulsions is one useful consequence of the effect.

Abstract

N-alkyl glycosides were found capable of solubilizing chlorinated oils into microemulsions. Interestingly, ternary systems with such polar oils frequently applied in organic syntheses show a temperature dependent phase inversion within the experimental window, which is absent with n-alkanes as oil-component. For comparison the utility of the well-known class of n-alkyl polyglycolethers is also examined. The investigations show important differences, though, in the variation of the phase behavior whether the ‘hydrophobicity’ of the oil is changed by variation of the hydrocarbon chain length or by varying the polarity. In addition, our studies point out variations of the Krafft-boundary in the glyco-surfactant systems by the addition of different chlorinated hydrocarbons. In a set of preliminary reaction experiments in these ternary microemulsions the epoxidation of olefins with manganese-dihydrosalen-catalysts is studied.

Abstract

Microemulsions with supercritical CO2 are promising alternatives for organic solvents, especially if both polar and non-polar components need to be dissolved. However, only fluorinated surfactants, which are known to be environmentally unfriendly, are appropriate to formulate well-structured microemulsions. While most approaches to increase the environmental performance of CO2-microemulsions deal with the design of new surfactants with a reduced degree of fluorination, we discovered that the partial substitution of CO2 by cyclohexane enables a considerable reduction of fluorinated surfactants. Thereby, the most efficient solubilization of the CO2/cyclohexane mixture, which turned out to be pressure-dependent, was found at a cyclohexane-to-CO2 mass ratio between 1 : 6 and 1 : 4. In order to elucidate this unexpected effect a systematic Small Angle Neutron Scattering (SANS) contrast variation study was performed. The analysis of the recorded scattering curves by the Generalized Indirect Fourier Transformation (GIFT) clearly shows that the scattering length density profiles differ considerably from CO2-microemulsions without cyclohexane. Instead of a nearly constant scattering length density, a density profile that varies systematically over half of the droplet radius was detected. These results clearly indicate that the observed efficiency boosting is caused by the formation of a depletion zone of cyclohexane close to the fluorinated amphiphilic film.

Abstract

We synthesized platinum (Pt), bismuth (Bi), and lead (Pb) nanoparticles by using water-in-oil microemulsions as templates. The microemulsion chosen consisted of H2O/salt–n-decane–AOT/SDS–1-butanol while the salt was either the metal precursor (H2PtCl6, Bi(NO3)3, or Pb(NO3)2) or the reducing agent (NaBH4). As the size and the structure of the resulting nanoparticles are expected to depend on the size and structure of the templating microemulsion, we studied the phase behaviour of the templating microemulsion, i.e. the composition ranges in which spherical water-in-oil microemulsions are formed. The challenge was to find those conditions under which the microemulsions containing the metal precursor and the reducing agent, respectively, had the same size and structure. Nanoparticles of the metals (Pt, Bi, and Pb) were then synthesized by mixing these two microemulsions. The size and structure of the resulting particles were characterized by scanning electron microscopy (SEM) and X-ray powder diffractometry. Average crystallite sizes of D ≈ 5, 25, and 25 nm were found for Pt, Bi, and Pb particles, respectively. According to SEM images, these particles form clusters of several hundreds of nanometers

Abstract

Microemulsions of the type H2O–scCO2–surfactant are potential candidates for novel solvent mixtures in the field of green chemistry. Furthermore, scCO2-microemulsions are highly interesting from a fundamental point of view since their properties such as the bending elastic constants can be strongly influenced solely by varying the pressure without changing the components. With this motivation we studied the phase behavior and the microstructure of water-rich scCO2-microemulsions. Such microemulsions were formulated using the technical grade non-ionic surfactants Zonyl FSO 100 and Zonyl FSN 100. At elevated pressures the temperature dependent phase behavior of these systems follows the general patterns of non-ionic microemulsions. Small angle neutron scattering experiments were conducted to determine the length scales and the topology of the microstructure of these systems. Having determined the exact scattering length densities and the composition of the respective sub-phases by a systematic contrast variation we could show that these systems consist of CO2-swollen microemulsion droplets that are dispersed in a continuous aqueous-phase. The scattering data were analyzed using a newly derived form factor for polydisperse, spherical core/shell particles with diffuse interfaces. The underlying analytical density profiles could be confirmed applying the model-free Generalized Indirect Fourier Transformation (GIFT) to the scattering data. Following the general patterns of non-ionic microemulsions the radius of the microemulsion droplets is found to increase almost linearly upon the addition of CO2.

Abstract

In this work we investigate the thermodiffusion behavior of microemulsion droplets of the type H2O/n-alkane/C12E5 (pentaethylene glycol monododecyl ether) using the n-alkanes: n-octane, n-decane, n-dodecane, and n-tetradecane. In order to determine the thermodiffusion behavior of these microemulsion droplets, we apply the infrared thermal diffusion forced Rayleigh scattering (IR-TDFRS) technique. We measure the Soret coefficient (ST) as function of the structure upon approaching the emulsification failure boundary (efb) and as a function of the radius of the spherical o/w microemulsion droplets close to the efb. By varying the chain length of the n-alkanes, we are able to study the thermodiffusion behavior of spherical o/w microemulsion droplets of different sizes at the same temperature. In the investigated range a linear dependence of the Soret coefficient as function of the radius was found. By use of a proposed relationship between the Soret coefficient and the temperature dependence of the interfacial tension, the transition layer l could be determined for the first time. Additionally, small angle neutron scattering (SANS) experiments are performed to determine the size and to prove that the shape of the microemulsion droplets is spherical close to the efb. Accordingly, the scattering curves could be quantitatively described by a combination of a spherical core–shell form factor and sticky hard sphere structure factor.

Abstract

Bicontinuous microemulsions gelled with a low molecular weight gelator have been shown to be an orthogonally self-assembled system. With the mechanical stability provided by the gel network, gelled non-toxic bicontinuous microemulsions have the potential to be an efficient transdermal drug delivery carrier. However, up to now no suitable system has been formulated for transdermal drug delivery. To fill this gap, we formulated and characterized a gelled non-toxic bicontinuous microemulsion suitable for the mentioned application. Starting from a previously studied scouting system, namely, H2O–n-octane–n-octyl β-d-glucopyranoside (β–C8G1)–1-octanol, the co-surfactant and the oil were replaced by non-toxic components. Subsequently, the expensive pure surfactant was replaced by cheap technical-grade surfactants (Plantacare® series) to make the system economical. Having formulated the non-toxic microemulsion H2O–IPM–Plantacare 1200 UP–1,2-octanediol, three low molecular weight gelators were studied with regard to the gelation of both the scouting system and the non-toxic system. The chosen gelators were 12-hydroxyoctadecanoic acid (12-HOA), 1,3:2,4-dibenzylidene-d-sorbitol (DBS), and N,N′-dibenzoyl-l-cystine (DBC). We found that only DBS gels the non-toxic microemulsion. The gelled non-toxic bicontinuous microemulsion H2O–IPM–Plantacare 1200 UP–1,2-octanediol was characterized with oscillatory shear rheometry and small-angle neutron scattering (SANS) at a DBS concentration of 0.3 wt% to verify that the system is indeed a gel and that the microstructure of the microemulsion is not altered by the gel network.

Abstract

Neutron Spin Echo and Dynamic Light Scattering techniques are used for an extensive investigation of the bicontinuous phase in water/decane microemulsions. The dynamical behavior of different surfactant systems, decyl polyglycol ether (C10E4), C10E4 mixed with polyethylenepropylene/polyethyleneoxide amphiphilic block-copolymers-(PEPx/PEOy), and sodium-bisethylhexylsulfosuccinate (AOT) is investigated under comparable conditions. At scattering wave numbers q large compared to the inverse of the structure length scale, q0=2π/d, always stretched exponential relaxations ∝e−(Γqt)β with Γq∝q3 are found, as predicted theoretically. The relaxation rate increases almost linearly as function of the bicontinuous structure correlation scale—ξ≃d/2. The apparent bare bending modulus κ determined by fitting theoretical predictions to the experimental high-q data yields values of about 1.3kBT—as inferred from previous small angle neutron scattering (SANS) studies and from other methods. The effect of increasing rigidity of the surfactant layers by anchoring amphiphilic block-copolymers, predicted theoretically and revealed experimentally in structural investigations, could not be clearly resolved due to its small influence on the dynamics. At structural length scales, the relaxation rate in water–oil contrast shows a minimum corresponding to the maximum of the static structure factor. At length scales much larger than the typical structure length the relaxation is single-exponential with a q2 dependent rate. In this regime we find indications of the additional membrane interaction due to the presence of block-copolymers.

Abstract

We predict theoretically the thermodynamics and relaxation kinetics of solutions of cylindrical branched micelles. Using a recently developed theory in combination with the experimental data, we explain the unusual, inverted temperature dependence of the phase separation observed in wormlike micelles and dilute microemulsions. We extend the model to treat the temperature dependence of the relaxation kinetics and explain the observations.

Abstract

The physical behavior of the binary phase systems of the non-ionic polyoxyethylene detergent Agrimul NRE 1205 and water was investigated. This technical detergent can be used for the large-scale recovery of biomolecules in detergent based aqueous two-phase systems. The phase diagram was determined. It shows significant and unexpected differences to highly purified detergents. Very similar to neat detergents the phase diagram can be influenced by auxiliary chemicals thus shifting the entire phase diagram in general to lower temperatures. This was demonstrated by lowering the cloud-point by various additions. The concentration factor, as an important parameter of a first capture step in purification was investigated and modeled. Auxiliary chemicals, temperature change and change in detergent concentration also influence the viscosity and density of the phases. These experimental data are shown. They can help to explain the separation behavior of proteins. In large-scale separations aqueous two-phase systems are separated using disc-stack centrifuges. It is demonstrated that this is not a feasible method for detergent-based aqueous two-phase extraction and the physical reason is presented.

Abstract

Hypothesis Many efforts have been made to formulate water-IL microemulsions. One of the most intensely studied systems is H2O – 1-butyl-3-methylimidazolium hexafluorophosphate (BMImPF6) – 4-octylphenol polyethoxylate (TX-100) and it is not questioned that this system forms microemulsions. The nanostructures observed for traditional microemulsions are postulated with the surfactant being adsorbed at the interface such that the hydrophilic EO sides intrude into the water domains, while the hydrophobic hydrocarbon chains are immersed into BMImPF6. However, the high polarity of BMImPF6 and the observation that BMImPF6 mixes well with oligoethylene oxides but hardly with non-polar solvents like toluene or alkanes are not in line with this picture. Experiments We re-studied the ternary system H2O – BMImPF6 – TX-100 by measuring phase diagrams, determining tie-lines, and carrying out ROESY NMR and PFG NMR measurements. Findings We found that the hydrophobic part of the surfactant interacts neither with water nor with BMImPF6, while both solvents interact with the hydrophilic part of the surfactant. We suggest that the surfactant is not adsorbed at the interface between water and the IL, but forms normal spherical or elongated micelles or even continuous aggregates with the hydrocarbon chains forming the interior of the aggregates.

Abstract

In this work we present a systematic study on the microstructure of soft materials which combine the anisotropy of lyotropic liquid crystals with the mechanical stability of a physical gel. Systematic small-angle neutron (SANS) and X-ray (SAXS) scattering experiments were successfully used to characterize the lyotropic lamellar phase (Lα) of the system D2O – n-decanol – SDS which was gelled by two low molecular weight organogelators, 1,3:2,4-dibenzylidene-D-sorbitol (DBS) and 12-hydroxyoctadecanoic acid (12-HOA). Surprisingly, a pronounced shoulder appeared in the scattering curves of the lamellar phase gelled with 12-HOA, whereas the curves of the DBS-gelled Lα phase remained almost unchanged compared to the ones of the gelator-free Lα phase. The appearance of this additional shoulder strongly indicates the formation of a synergistic structure, which neither exists in the gelator-free Lα phase nor in the isotropic binary gel. By comparing the thicknesses of the 12-HOA (25–30 nm) and DBS (4–8 nm) gel fibers with the lamellar repeat distance (7.5 nm), we suggest that the synergistic structure originates from the minimization of the elastic free energy of the lamellar phase. In the case of 12-HOA, where the fiber diameter is significantly larger than the lamellar repeat distance, energetically unfavored layer ends can be prevented, when the layers cylindrically enclose the gel fibers. Interestingly, such structures mimic similar schemes found in neural cells, where axons are surrounded by lamellar myelin sheets.

Abstract

Some soft matter systems behave similarly and some differently. Understanding this is one of the significant challenges in the field. For example, while the splay and bend elastic constants for thermotropic and lyotropic nematic liquid crystals are similar, the twist elastic constant is nearly an order of magnitude smaller in lyotropic nematics. Unfortunately, complete elastic data on lyotropic nematics are restricted to one polymer and two chromonic systems, omitting the most common and highly studied lyotropic surfactant systems. This article reports that a surfactant system of disk-like micelles also possesses an extremely small twist elastic constant, demonstrating that this property is general for lyotropic liquid crystals. The reason likely stems from the higher flexibility of molecular assemblies compared to molecules.Recent measurements of the elastic constants in lyotropic chromonic liquid crystals (LCLCs) have revealed an anomalously small twist elastic constant compared to the splay and bend constants. Interestingly, measurements of the elastic constants in the micellar lyotropic liquid crystals (LLCs) that are formed by surfactants, by far the most ubiquitous and studied class of LLCs, are extremely rare and report only the ratios of elastic constants and do not include the twist elastic constant. By means of light scattering, this study presents absolute values of the elastic constants and their corresponding viscosities for the nematic phase of a standard LLC composed of disk-shaped micelles. Very different elastic moduli are found. While the splay elastic constant is in the typical range of 1.5 pN as is true in general for thermotropic nematics, the twist elastic constant is found to be one order of magnitude smaller (0.30 pN) and almost two orders of magnitude smaller than the bend elastic constant (21 pN). These results demonstrate that a small twist elastic constant is not restricted to the special case of LCLCs, but is true for LLCs in general. The reason for this extremely small twist elastic constant very likely originates with the flexibility of the assemblies that are the building blocks of both micellar and chromonic lyotropic liquid crystals.All data supporting the findings of this study are available within this article and/or SI Appendix, with corresponding DLS raw data and evaluation deposited at DaRUS, the University of Stuttgart data repository (https://doi.org/10.18419/darus-746) (60).

Abstract

Abstract Microemulsions provide a unique opportunity to tailor the polarity and liquid confinement in asymmetric catalysis via nanoscale polar and nonpolar domains separated by a surfactant film. For chiral diene Rh complexes, the influence of counterion and surfactant film on the catalytic activity and enantioselectivity remained elusive. To explore this issue chiral norbornadiene Rh(X) complexes (X=OTf, OTs, OAc, PO2F2) were synthesized and characterized by X-ray crystallography and theoretical calculations. These complexes were used in Rh-catalyzed 1,2-additions of phenylboroxine to N-tosylimine in microemulsions stabilized either exclusively by n-octyl-β-D-glucopyranoside (C8G1) or a C8G1-film doped with anionic or cationic surfactants (AOT, SDS and DTAB). The Rh(OAc) complex showed the largest dependence on the composition of the microemulsion, yielding up to 59 \% (90 \%ee) for the surfactant film doped with 5 wt\% of AOT as compared to 52 \% (58 \%ee) for neat C8G1 at constant surfactant concentration. Larger domains, determined by SAXS analysis, enabled further increase in yield and selectivity while the reaction rate almost remained constant according to kinetic studies.

Abstract

Experimental evidence of corresponding states in water, n-alkane(), and n-alkyl polyethylene glycol ether systems is presented. Striking similarities in both the phase behaviour and the interfacial tensions for a variety of systems are highlighted. For some selected systems the trajectories of the middle phases in the three-phase regime are precisely determined. Projections of the middle-phase trajectories onto the - plane of the phase prism shape nearly perfect parabolae, whereas the projections onto the T - plane exhibit a sigmoidal shape. Here is the surfactant volume fraction, and is the oil-in-water-plus-oil volume fraction. It is found that the trajectories collapse into single curves, if the surfactant concentration scale is reduced by the maximum of the parabolae, , which is the surfactant volume fraction of the symmetric microemulsion, and if the temperature axis is reduced by the difference of the upper and lower critical endpoint temperature, . It is found that the maximum length scale set by the surfactant volume fraction can be used to reduce the interfacial tension scale, that is plotting versus the reduced temperature scale. These reductions yield a remarkable superposition of the interfacial tension data of 17 different systems, the carbon number of the oil k ranging from 8 to 14, the hydrophilic surfactant head j from 3 to 6 and the surfactant tail length i from 8 to 12.

Abstract

A new variant of the three-phase extraction technique (denoted as 3PHEX) for purifying nonionic alkyl polyglycolether (CiEj) surfactants is presented. Both the 3PHEX and its extension take advantage of the phase behavior of the ternary systems water–oil–CiEj. The conventional 3PHEX technique is used to extract simultaneously water- and oil-soluble impurities by removing the excess phases, keeping the microemulsion phase. The new variant, in contrast, aims at extracting surface-active ionic impurities into the microemulsion phase. Knowledge of the phase behavior permits choosing conditions where the microemulsion phase is small while the oil excess phase is large, minimizing the loss of surfactant. The oil excess phase contains most of the nonionic surfactant in monomerically dissolved form which is gained from it by distillation. The otherwise difficult to separate surface-active ionic impurities partition preferentially into the microemulsion phase, which is discarded. Thus, the new procedure is called “inverse” 3PHEX. The efficiency of the new method is demonstrated by measuring the lower miscibility gap (including the lower critical temperature Tc) and surface tension isotherms, which are both sensitive and suitable indicators for the presence of impurities.

Abstract

Microemulsion formulations based on non-toxic alkyl glucosides (CmGn) are of interest for applications in pharmaceutical and cosmetic products. In this work we demonstrate the favorable properties of quaternary microemulsions consisting of water - oil - C8G1 - alcohol. As alcohols we used n-octanol as well as the non-toxic geraniol (C10H17OH). Microemulsions with geraniol are potential candidates for pharmaceutical applications. We show for the first time by simultaneous phase behavior, SANS and interfacial tension measurements a quantitative correlation between the curvature and the composition of the interfacial film. We can relate the behavior of quaternary, temperature-insensitive microemulsions based on alkyl glucosides to that of ternary nonionic systems which exhibit a temperature-dependent curvature of the film. Thus, we are able to compare directly the effect of the temperature and the concentration of alcohol in the interfacial film. Both are important tuning parameters for the curvature, helping to formulate microemulsions with the desired properties in practical applications

Abstract

We examine the enhancement of the solubilization capacity of medium-chain surfactants in microemulsions of ternary base systems water - n-alkane - CjEj by block copolymers of the poly-(ethylenepropylene)-co-poly(ethyleneoxide) (PEP-PEO) type. The effect is an enormous increase of the swelling of the middle phase microemulsion by water and oil. The magnitude of the effect depends slightly but systematically on the chain length of the surfactant forming the base system and on the chain length of thealkane. Interestingly, the less efficient the base system the larger the boosting effect. Furthermore, the lamellar phase, which usually develops as surfactants become more efficient, is suppressed, the more the less efficient the surfactant of the base system.

Abstract

In this study we present a systematic investigation of the phase behaviour of microemulsions containing near- or supercritical solvents. The starting point of this study are microemulsions of the type water/NaCl-propane-polyethyleneglycol mono-n-alkyl ether at a pressure of p = 220 bar. Replacing propane stepwise by supercritical carbon dioxide the typical phase behavior of microemulsions systems can still be observed using scCO(2) as the only nonpolar solvent. Thus, increasing the temperature a phase inversion from a CO(2)-in-water to a water-in-CO(2) microemulsion via a balanced CO(2) microemulsion is found for the first time. Such mixtures of water and scCO(2) are expected to be versatile solvents in green chemistry. In addition, the formulation of supercritical microemulsions is the initial step in the Principle Of Supercritical Microemulsion Expansion (POSME) (DE Pat., 102 60 815 B4, 2008), which is a promising new approach for the production of low-cost nanocellular foams. In contrast to conventional foaming procedures, this approach suggests the formation of nanofoams by expanding micelles swollen with a supercritical blowing agent, thereby ensuring the unhindered formation and growth of bubbles without mass transport.

Abstract

Recently, it turned out that nanostructured reaction media containing highly inert solvents as tetrahydrothiophen-1,1-dioxide (sulfolane) are beneficial for strongly oxidizing or reductive reactions. Because of their ability of solubilizing polar and nonpolar solvents with a large nanostructured interface in particular microemulsions provide such interesting reaction media. Starting from the pseudoternary microemulsion H2O–n-octane–C12E4/C12E5 (polyoxyethylene n-alkyl ether), water was successively replaced by the highly inert tetrahydrothiophen-1,1-dioxide (sulfolane). We found that an increasing sulfolane content drives the system beyond the tricritical point. Replacing the already long chain surfactants C12E4 and C12E5 by a mixture of the even longer chain surfactants C18E6 and C18E8, we were able to prepare nonaqueous sulfolane microemulsions for the first time. We also teach how in a second step the phase behavior of the hydrophilic sulfolane–n-octane–C18E8 system can be tuned at constant temperature (as required by the reaction conditions) by addition of the hydrophobic cosurfactant 1-octanol (C8E0). The change in curvature that occurs by adding 1-octanol is demonstrated measuring the size of reverse micelles by DLS. We found that the radius varies from at least 8 to 16 nm, a suitable sizes for inverse nanoreaction vessels.

Abstract

In a previous study we investigated the phase behavior of microemulsions consisting of the ionic liquid ethylammonium nitrate (EAN), an n-alkane and a nonionic alkyl polyglycolether (CiEj). We found the same general trends as for the aqueous counterparts, i.e. a transition from an oil-in-EAN microemulsion via a bicontinuous microemulsion to an EAN-in-oil microemulsion with increasing temperature. However, unlike what happens in the corresponding aqueous systems, in EAN-in-oil microemulsions only a very small amount of EAN was detected by NMR-measurements. This is why we investigated the phase behavior and microstructure of EAN-rich n-dodecane-in-EAN microemulsions and oil-rich EAN-in-n-octane microemulsions. We found that the ionic liquid emulsification failure boundary has an extraordinarily small slope, which suggests that the amphiphilic film loses its ability to solubilize EAN with an increase in temperature by only a few degrees. The analysis of the small angle neutron scattering (SANS) curves unambiguously shows that this behavior is due to the fact that the EAN molecules form a substructure with a characteristic length scale of Λ ≈ 8 Å inside the EAN-in-oil droplets. In more detail, the analysis of the SANS data with the GIFT method revealed a transition from spherical to cylindrical structures approaching the respective critical endpoint temperatures. By using the respective form factors and combining them with a Gaussian spatial intensity distribution to account for the EAN sub-structure we were able to describe the scattering curves nearly quantitatively.

Abstract

With an appropriate tuning parameter a microemulsion can be forced to undergo a phase inversion, i.e. to invert the curvature of the amphiphilic film. In microemulsions consisting of water, an n-alkane and a nonionic alkyl polyglycolether (CiEj) temperature is an appropriate parameter since the surfactant head groups dehydrate with increasing temperature. Recently we were able to show that this also holds true for ethylammonium nitrate (EAN)–n-alkane–CiEj systems. However, the temperature sensitivity is weaker which is why we decided to use a hydrophobic cosurfactant to induce a phase inversion in the EAN-containing microemulsion. We studied the quaternary system EAN–n-octane–C12E3−1-octanol as a function of the alcohol concentration at T=15°C and found the same trends as for the aqueous counterparts. (1) Studying the phase behavior as a function of the alcohol content (δ) and of the total surfactant concentration (γ), one finds that the phase boundaries resemble the shape of a fish. (2) Measuring the interfacial tension σ between the IL- and oil-rich phase, one observes a minimum in the center of the three-phase region. (3) NMR self-diffusion measurements reveal a transition from an oil-in-EAN microemulsion to a bicontinuous microemulsion and finally to an EAN-in-oil microemulsion.

Abstract

We studied the thermal diffusion behavior of the nonionic surfactant solutions C12E6/water and C12E5/water at different concentrations and temperatures using thermal diffusion forced Rayleigh scattering (TDFRS). Two different types of TDFRS setups have been applied. In the classical TDFRS, we use an argon laser to write the optical grating into the sample by using a small amount of ionic dye to convert the optical grating into a temperature grating. In the other setup, called IR-TDFRS, we use an infrared laser as the writing beam, which utilizes the water absorption band to convert the optical grating into a temperature grating. The measurements by IR-TDFRS show a one-mode signal for all concentrations and temperatures, while the signal in the classical TDFRS consists of two modes for higher temperatures and lower surfactant concentrations (Ning, H.; et al. J. Phys. Chem. B 2006, 110, 10746). We find good agreement between the Soret coefficient determined in the IR-TDFRS and the one derived from the first fast mode in the previous studies. The Soret coefficient of the nonionic solutions is positive and enhanced at the critical point. In general, the Soret coefficient of the micelles tends to increase with temperature. We found that the presence of the second mode observed in the classical TDFRS is related to the addition of the ionic dye, but even with the ionic dye it is not possible to observe a second mode in the IR-TDFRS. The origin of the second mode is discussed in terms of charged micelles and an inhomogenous dye distribution in the temperature gradient.

Abstract

This contribution presents the direct determination of the bending elasticity of the surfactant film in an oil-continuous microemulsion by means of neutron spin-echo spectroscopy and dynamic light scattering. The investigated system is CE/water dispersed in n-octane. The values obtained for the bending elastic constants are compared to results from indirect determinations based on the spinning drop method. While good agreement is found for , the values computed for differ slightly when the calculation is based on polydispersities obtained from small angle neutron scattering experiments. Better agreement is reached using the polydispersities calculated from dynamic light scattering data. Furthermore, problems which seem to be specific for oil-continuous systems are addressed.

Abstract

Lamellar phases consisting of water and oil with intervening surfactant monolayer interfaces (eventually containing low molecular weight amphiphilic block-copolymers) are studied. Structural and dynamical investigations of oriented lamellar phases at the length scale of the intermembrane distance and beyond are performed using small-angle neutrons scattering and neutron spin-echo spectroscopy. The data analysis in terms of static and dynamic structure factors for a stack of elastic interfacial membranes yields information of the membrane curvature elasticity and membrane interactions in terms of phenomenological parameters such as the bending elastic modulus κ and compression modulus ¯B, and on the dissipation related to the viscosity η. The influence of the block-copolymers anchored to the surfactant monolayers is studied for a series of lamellar phase microemulsions containing equal volume fraction of surfactant and polymer, by varying only the polymer molecular weight. Based on numerical evaluations and fits to the data the conditions of applicability of the available theoretical concepts are discussed

Abstract

Carbon dioxide (CO2) is a renewable carbon source that is easily available in high purity and is utilized as a co-monomer in the direct ring-opening polymerization of epoxides to obtain aliphatic polycarbonates. In this work, degradable aliphatic polycarbonate diblock copolymers (mPEG-b-PBC) are synthesized via catalytic copolymerization of CO2 and 1,2-butylene oxide, starting from monomethoxy poly(ethylene glycol) (mPEG) as a chain transfer reagent. The polymerization proceeds at low temperatures and high CO2 pressure, utilizing the established binary catalytic system (R,R)-Co(salen)Cl/PPNCl. Amphiphilic nonionic diblock copolymers with varying PBC block lengths and hydrophilic–lipophilic balance values between 9 and 16 are synthesized. The polymers are characterized via NMR and Fourier transform infrared spectroscopies as well as size exclusion chromatography, exhibiting molecular weights ranging from 2400 to 4100 g mol–1 with narrow dispersities (Đ = Mw/Mn) from 1.07 to 1.18. Furthermore, the thermal properties, i.e., Tg, Tm, and Td, are determined. Surface tension measurements prove that the amphiphilic polymers form micelles above the critical micelle concentration, whereas small-angle neutron scattering shows that they are of nearly spherical shape. Adding small amounts of the synthesized mPEG-b-PBC polymers to different microemulsion systems, we found that the polymers were able to strongly increase the efficiency of medium-chain surfactants to solubilize polar oils.

Abstract

This study deals with the microemulsion phase behavior of technical-grade non-ionic surfactants of the alkyl polyglycol ether type CiEj. In contrast to the monodisperse CiEj, technical-grade surfactants have a broad distribution of the degree of ethoxylation and a certain content of unreacted alcohol. By varying both the degree of ethoxylation of the surfactant and the chain length of the n-alkanes, it was possible to show that the fundamental phase behavior of technical-grade surfactants is similar to that of the monodisperse CiEj. The distortion of the three-phase region at low surfactant concentrations towards higher temperatures and quantitative differences can be explained by the molecular weight distribution of the surfactant. The results presented here offer a way to solve industrial emulsification tasks by performing only a few characteristic experiments.

Abstract

The manifold applications of porous materials, such as in storage, separation, and catalysis, have led to an enormous interest in their cost-efficient preparation. A promising strategy to obtain porous materials with adjustable pore size and morphology is to use templates exhibiting the appropriate nanostructure. In this study, close-packed polystyrene (PS) nanoparticles, synthesized by emulsion polymerization, were used to produce porous PS and ZnO inverse opals. The size and distribution of the polystyrene nanoparticles, characterized by dynamic light scattering (DLS), small-angle neutron scattering (SANS), and scanning electron microscopy (SEM), were controlled via the concentration of sodium dodecyl sulfate (SDS). Systematic measurements of the water/styrene-interfacial tension show that the critical micelle concentration (CMC) of the ternary water--styrene--SDS system, which determines whether monodisperse or polydisperse PS particles are obtained, is considerably lower than that of the binary water--SDS system. The assemblies of close-packed PS nanoparticles obtained via drying were then studied by small-angle X-ray scattering (SAXS) and SEM. Both techniques prove that PS nanoparticles synthesized above the CMC result in a significantly unordered but denser packing of the particles. The polystyrene particles were subsequently used to produce porous polystyrene and ZnO inverse opals. While the former consists of micrometer-sized spherical pores surrounded by extended open-cellular regions of mesopores (Rpore ≈þinspace25 nm), the latter are made of ZnO-nanoparticles forming a structure of well-aligned interconnected pores.

Abstract

Self-propelled particulate systems manifest certain collective behavior of living matter, which have been the subject of intense research over the past decades. One of the elegant methods for realizing such active motions is by means of custom synthesized Janus particles suspended in a catalytic medium that can be triggered upon illumination by ultraviolet light. In this work, the evolution of the particle dynamics from passive diffusive to active ballistic behavior upon light illumination was probed by multispeckle x-ray photon correlation spectroscopy (XPCS). This technique enables not only studying the emergence of active motions in three dimensions (3D) but also deciphering different contributions to the overall dynamics. Using a combination of homodyne and heterodyne analysis, the ensemble averaged mean velocity, velocity fluctuations and diffusion coefficient of particles were determined in the thermodynamic limit. Results revealed a gradual transition from diffusive to ballistic dynamics with systematic increase of the catalytic activity. At the intermediate region, the dynamics is dominated by Gaussian velocity fluctuations and an enhanced relaxation rate with a weaker wave vector dependence similar to superdiffusive behavior. For the highest activity, the dynamics became purely ballistic with Lorentzian-like distribution of velocity fluctuations. Presented results demonstrate that different aspects of active dynamics can be investigated in 3D over a broad range of Péclet numbers and other control parameters by means of multispeckle XPCS.

Abstract

In contrast to their more common counterparts in aqueous solutions, inverse ISAsomes (internally self-assembled somes/particles) are formulated as kinetically stabilised dispersions of hydrophilic, lyotropic liquid-crystalline (LC) phases in non-polar oils. This contribution reports on their formation in bio-compatible oils. We found that it is possible to create inverse hexosomes, inverse micellar cubosomes (Fd3m) and an inverse emulsified microemulsion (EME) in excess squalane with a polyethylene glycol alkyl ether as the primary surfactant forming the LC phase and to stabilise them with hydrophobised silica nanoparticles. Furthermore, an emulsified L1-phase and inverse hexosomes were formed in excess triolein with the triblock-copolymer Pluronic® P94 as the primary surfactant. Stabilisation was achieved with a molecular stabiliser of type polyethylene glycol (PEG)-dipolyhydroxystearate. For the inverse hexosomes in triolein, the possibility of a formulation without any additional stabiliser was explored. It was found that a sufficiently strong stabilisation effect was created by the primary surfactant alone. Finally, triolein was replaced with olive oil which also led to the successful formation of inverse hexosomes. As far as we know, there exists no previous contribution about inverse ISAsomes in complex oils such as triolein or plant oils, and the existence of stabiliser-free (i.e., self-stabilising) inverse hexosomes has also not been reported until now.

Abstract

The competition between the bimolecular nucleophilic substitution (SN2) and base-induced elimination (E2) reaction and their intrinsic reactivity is of key interest in organic chemistry. To investigate the effect of suppressing the E2 pathway on SN2 reactivity, we compared the reactions F− + CH3CH2I and F− + CF3CH2I. Differential cross-sections have been measured in a crossed-beam setup combined with velocity map imaging, giving insight into the underlying mechanisms of the individual pathways. Additionally, we employed a selected-ion flow tube to obtain reaction rates and high-level ab initio computations to characterize the different reaction pathways and product channels. The fluorination of the β-carbon not only suppresses the E2-reaction but opens up additional channels involving the abstraction of fluorine. The overall SN2 reactivity is reduced compared to the non-fluorinated iodoethane. This reduction is presumably due to the competition with the highly reactive channels forming FHF− and CF2CI−.

Abstract

To investigate the kinetics of biochemical transformations in confined environments, compartments with a radius of the order of 10–50nm are needed. Giant water-in-oil microemulsions provide such nanoscale reaction compartments and allow furthermore to control the degree of compartmentalization by an external tuning parameter such as temperature. With this motivation we investigated the phase behavior and the microstructure of oil-rich microemulsions. In this approach we focused on oil-rich microemulsions of the ternary system D2O-cyclohexane(d12)-C12E6. Measurements of the phase behavior revealed that up to 20wt% of water can be solubilized by less than 3wt% of surfactant. Small-angle neutron scattering experiments were performed to determine the length scales and microstructure topologies of the oil-rich microemulsions. To analyze the scattering data, we derived the form factor for polydisperse spherical Gaussian shells with a scattering contribution of the droplet core. The quantitative analysis of the scattering data with this form factor shows that the radius of the largest droplets amounts up to 36nm.

Abstract

New microemulsions containing an amphiphilic block copolymer have been prepared. We found that the addition of such polymers to conventional microemulsions causes several highly interesting effects. The most important one is an enormous increase in surfactant efficiency, i.e. solubilization capacity. Efficiency increases by factors of 10-20 are easily achieved. At the same time the HLB temperature of the base system with pure surfactant remains almost constant. In the case of technical-grade nonionic surfactants the phase behavior of the efficiency-enhanced systems follows the temperature shift exhibited by the system without polymer. The occurrence of lamellar phases, which are usually found in highly efficient systems, can be suppressed. Investigations of many microemulsion systems with variation of both the polar and the nonpolar component as well as the surfactant and the amphiphilic polymer provide evidence that the effects described above can be found in a large variety of pure and technical-grade microemulsion systems and thus seem to be based on a common universal mechanism.

Abstract

Using neutron spin-echo (NSE) spectroscopy in combination with dynamic light scattering (DLS), we performed an extensive investigation of the bicontinuous phase in ternary water--surfactant--oil microemulsions, with extension to lamellar and droplet phases. The dynamical behavior of surfactant monolayers of decyl-polyglycol-ether (C10E4) molecules, or mixtures of surfactant with long amphiphilic block-copolymers of type poly-ethylene propylene/poly-ethylene oxide (PEP--PEO) was studied, under comparable conditions. The investigation techniques provide access to different length scales relative to the characteristic periodicity length of the microemulsion structure. Information on the elastic bending modulus is obtained from the local scale dynamics in view of existing theoretical descriptions and is found to be in accordance with small angle neutron scattering (SANS) studies. Evidence for the modified elastic properties and additional interaction of the amphiphilic layers due to the polymer is more pronounced at a larger scale. Experiments on oriented lamellar phases, and also droplet phases, with anchored block-copolymers offer more insight into the effective layer--layer interaction and efficiency boosting associated with the polymers.

Abstract

Degreasing of animal skins is an important step in leather making. A huge quantity of surfactants is used for this process, which leads inevitably to environmental problems. The development of eco-friendly degreasing agents and processes is therefore desirable. For a better understanding of this process, the fundamental physico-chemical principles must be investigated. Only after such knowledge of the principles has been obtained is the development of a novel class of eco-friendly degreasing agents feasible. At present, the fundamentals are not well understood. In this paper we present our latest research results on the physico-chemical principles of water-based degreasing. In cooperation with the University of Cologne, we were able to determine that degreasing takes place in two distinct steps. The first step, under the proper conditions, is the formation of a nanophase for solubilizing the grease in the skin. The second step is the conversion of this nanophase into a macroemulsion for transporting the grease out of the skin and subsequently away from it. This knowledge led us to the development of a novel class of degreasing agents in a more eco-friendly degreasing process.

Abstract

The formation kinetics of oil-rich, nonionic microemulsions were investigated along different mixing pathways using a fast stopped-flow device in combination with the new high-flux small-angle neutron spectrometer D33 (ILL, Grenoble, France). While the kinetics along most pathways were too fast to be resolved, two processes could be detected mixing brine and the binary cyclohexane/C10E5 solution. Here, too, the formation of large water-in-oil droplets was found to be faster than 20 ms and therewith faster than the accessible dead time. However, subsequently, both the disintegration of the large water-in-oil droplets (600 Å) and the uptake of water by swollen micelles (50–60 Å) could be resolved. Both processes occur on the time scale of a second. Strikingly, the total internal interface forms faster than 20 ms and does not change over time.

Abstract

Abstract The role of liquid confinement on the asymmetric Rh catalysis was studied using the 1,2-addition of phenylboroxine (2) to N-tosylimine 1 in the presence of RhCl(C2H4)22 and chiral diene ligands as benchmark reaction. To get access to Rh complexes of different polarity, enantiomerically pure C2-symmetric p-substituted 3,6-diphenylbicyclo3.3.0octadienes 4 and diastereomerically enriched unsymmetric norbornadienes 5 and 6 carrying either the Evans or the SuperQuat auxiliary were synthesized. A microemulsion containing the equal amounts of H2O/KOH and toluene/reactants was formulated using the hydrophilic sugar surfactant n-octyl β-d-glucopyranoside (C8G1) to mediate the miscibility between the nonpolar reactants and KOH, needed to activate the Rh–diene complex. Prominent features of this organized reaction medium are its temperature insensitivity as well as the presence of water and toluene-rich compartments with a domain size of 55 Å confirmed by small-angle X-ray scattering (SAXS). Although bicyclooctadiene ligands 4 a,b,e performed equally well under homogeneous and microemulsion conditions, ligands 4 c,d gave a different chemoselectivity. For norbornadienes 5, 6, however, microemulsions markedly improved conversion and enantioselectivity as well as reaction rate, as was confirmed by kinetic studies using ligand 5 b.

Abstract

During our studies on emulsion-templated monodisperse polymer foams we found significant differences in the finestructure if the locus of initiation is changed. This motivated us to study the phase behavior of the liquid template. Our studies indicate that the template consists of droplets of three different length scales: The water droplets generated via microfluidics (∼70 μm) are surrounded by a continuous phase in which a w/o emulsion (≤100 nm) coexists with a w/o microemulsion (∼5 nm). We speculate that the w/o-emulsion droplets act as seeds for the porous finestructure observed in AIBN-initiated polymer foams. We have experimental evidence that the w/o emulsion inverts to an o/w emulsion with progressing polymerization. This explains the granular texture observed in KPS-initiated polymer foams. The control of the finestructure is important in the preparation of tailor-made polymer foams because it directly impacts the material’s density and thus, in turn, its mechanical stability.

Abstract

The wetting transitions of water, n‐alkane, and n‐alkyl polyglycol ether (CiEj) systems are examined in order to locate the transition between weakly structured mixtures and microemulsions. Using small angle neutron scattering (SANS) we determine the local structure and relate it to the phase behavior and wetting transitions observed by macroscopic measurements. We measure the SANS of the mixtures across the transition along two different experimental paths. One path begins with well‐structured mixtures, and the effective chain length of the surfactant combination C6E2/C4E1 is decreased by increasing the C4E1 fraction. The other path starts with equal amounts of water and oil mixed by the strong amphiphile C8E3. The local structure of these ‘‘good’’ microemulsions is weakened by increasing the temperature and concomitantly the oil/water volume ratio approaching the upper critical endpoint. As in previous studies analyzing the scattering experiments quantitatively permits determination of the amphiphilicity factor which is a measure of the strength of the surfactant. We confirm predictions that the amphiphilicity factor measured at the wetting transition becomes more negative as the temperature interval between the transition and the critical endpoint decreases.

Abstract

Dynamic self-assembled structures found in complex fluids containing surfactant, water, and oil range from spherical and cylindrical aggregates to bicontinuous microemulsions and ordered liquid crystalline phases. These structures are extensively used as templates for the synthesis of nanomaterials. However, the topology of the initial structures and in particular their characteristic length scales often undergo significant changes during polymerization. Increasing the microemulsion viscosity should slow down its reorganization kinetics and, therewith, help to maintain the microemulsion nanostructure during the polymerization process. In this work, we report on systematic phase behavior studies of a new class of highly viscous microemulsions that comprise of surfactant, polymerizable oil, and concentrated water/(sucrose/trehalose) solutions. It is found that the substitution of H2O by sucrose/trehalose shifts the phase boundaries of nonionic microemulsions to lower temperatures, while the opposite trend holds for ionic microemulsions. Our systematic studies revealed that hydrophilic nonionic alkyl glycosides are the most suitable candidates for the preparation of highly viscous and polymerizable microemulsions.

Abstract

The effect of amphiphilic block copolymers on ternary microemulsions (water, oil and non-ionic surfactant) is investigated. Small amounts of PEP-PEO block copolymer lead to a dramatic expansion of the one-phase region where water and oil can be solubilized by the mediation of surfactant molecules. Small-angle neutron-scattering experiments employing a high-precision two-dimensional contrast-variation technique demonstrate that the polymer is distributed uniformly on the surfactant membrane, where it modifies the membrane curvature elasticity. Furthermore, a new approach to determine the bending rigidity of an amphiphilic membrane is proposed, which is precise enough to measure the logarithmic scale dependence of the bending rigidity and its universal prefactor in bicontinuous microemulsions.

Abstract

Phase diagrams of ternary H2O – cyclic oil – CiEj (alkylpolyglycol ether) systems have been determined for cyclic oils such as cyclohexane, ethylbenzene and toluene, and mixtures of cyclohexane with toluene. In order to solubilize these polar oils the hydrophilic surfactants C10E6 and C10E8 were used. From precise volume measurements of the middle phase at the phase inversion temperature (PIT) the monomeric solubility of the surfactant in oil was obtained permitting to quantify the fraction of surfactant in the internal interface of the bicontinuous microemulsion. Specially in toluene systems comparatively large monomeric solubilities were found, a fact which is responsible for the observed inefficiency of the CiEj surfactants in solubilizing aromatic oils. As an exercise how to handle mixed oils, we demonstrate for the cyclohexane-toluene pair how the three-phase body of the cyclohexane system gradually changes to that of the toluene system as function of the oil mixing ratio. The penetrating nature of toluene clearly is visible from the quantitative analysis.

Abstract

Elastic properties of surfactant membranes can be described in terms of the bending rigidity κ and the saddle splay modulus small kappa, Greek, macron. Phase diagram measurements and neutron scattering experiments allowed the determination of these parameters. Recent simulations showed that the bending rigidity, which is deduced from the characteristic length scales in the microemulsion, is a mixture of small kappa, Greek, macron and κ. By combining neutron spin echo (NSE) spectroscopy, small angle neutron scattering (SANS) and phase diagram measurements, we show that also experimentally the different contributions can be separated. For supercritical CO2 microemulsions and bicontinuous microemulsions with additives, the prefactors of the small kappa, Greek, macron and κ contributions are determined and compared to those from simulations.

Abstract

In our previous work we were able to prove that gelled bicontinuous microemulsions are a novel type of orthogonal self-assembled system. The study at hand aims at complementing our previous work by answering the question of whether gelled lyotropic liquid crystals are also orthogonal self-assembled systems. For this purpose we studied the same system, namely, water–n-decane/12-hydroxyoctadecanoic acid (12-HOA)–n-decyl tetraoxyethylene glycol ether (C10E4). The phase boundaries of the nongelled and the gelled lyotropic liquid crystals were determined visually and with 2H NMR spectroscopy. Oscillating shear measurements revealed that the absolute values of the storage and loss moduli of the gelled liquid crystalline (LC) phases do not differ very much from those of the binary organogel. While both the phase behavior and the rheological properties of the LC phases support the hypothesis that gelled lyotropic liquid crystals are orthogonal self-assembled systems, freeze–fracture electron microscopy (FFEM) seems to indicate an influence of the gel network on the structure of the Lα phase and vice versa.

Abstract

CO2-microemulsions show strong pressure dependent properties. Using time-resolved SANS to investigate the kinetics of structural changes upon periodic pressure jumps of adjustable amplitude, we found that the compression-induced formation of cylinders occurs on a timescale of one second, whereas the expansion-induced disintegration into CO2 swollen spherical micelles is much faster.

Abstract

Microemulsions are thermodynamically stable, macroscopically isotropic mixtures of at least two immiscible components and a surfactant. Their general features, i.e. the complex phase behavior, the ultralow interfacial tensions, and the multifarious nanostructure, have been systematically elucidated in the last century. However, the efficient solubilization of long-chain n-alkanes and waxes, which plays a significant role in enhanced oil recovery, washing, and cosmetics, remains a challenge. Thus, in this work the influence of the n-alkane chain length k on the phase behavior of ternary (symmetric) microemulsions containing equal volumes of water and oil was studied. Using n-alkanes ranging from n-dodecane (C12H26) to n-dotriacontane (C32H66) and pure n-alkyl polyglycol ether (CiEj) surfactants, we found that the efficiency of the respective surfactant decreases linearly with increasing k, while the phase inversion temperature (PIT) shows a logarithmic dependence. The influence of a technical wax on the phase behavior was studied by means of the systems H2O–SASOLWAX 5805 (Sasol)–C16E6 yielding an equivalent alkane carbon number (EACN (SASOLWAX 5805)) of 30.8. Finally, the pure CiEj surfactants were replaced with technical grade counterparts of the Genapol series (Clariant) finding that the solubilization efficiency of the long-chain Genapol O 080 is comparable to the pure C16E6 surfactant. Using small-angle neutron scattering (SANS) the microstructure of the formulated microemulsions was studied near the so-called optimum (X̃) point. The scattering curves prove that microemulsions containing long-chain n-alkanes and waxes are also bicontinuously structured at the phase inversion temperature (PIT). Interestingly, a high degree of structural ordering is found reflected by values of the amphiphilicity factor fa ranging between −0.83 and −0.87.

Abstract

Nowadays, the development of chemical processes using environmentally friendly solvents is of high importance. As an alternative to conventional reaction media based on organic solvents, we show a novel aqueous surfactant-based process concept which is used for the three step synthesis of the fungicide Boscalid®. By applying three phase microemulsion systems for the Suzuki coupling reaction, the first step within the Boscalid® synthesis, a simple product and catalyst separation can be achieved, whereby the water-soluble homogeneous Pd/SPhos catalyst complex can be reused several times. Together with an easily recyclable heterogeneous PtIr@TiO2 catalyst, which is applied for the hydrogenation reaction in the second step, followed by base-assisted condensation to the final product Boscalid® in the third step, overall yields up to 90% are achievable for the whole reaction sequence. This result was obtained without any purification step in between that requires the use of further solvents. In this way the total synthesis costs can be reduced and solvent wastage can be avoided.

Abstract

The use of smart colloidal microgels for advanced applications critically depends on their response kinetics. We use pressure jump small angle neutron scattering with supreme time resolution to study the rapid volume phase transition kinetics of such microgels. Utilizing the pressure induced microphase separation inside the microgels we were able to resolve their collapse and swelling kinetics. While the collapse occurs on a time scale of 10 ms, the particle swelling turned out to be much faster. Photon correlation spectroscopy and static small angle neutron scattering unambiguously show, that the much slower collapse can be associated with the complex particle architecture exhibiting a loosely-crosslinked outer region and a denser inner core region. These insights into the kinetics of stimuli-responsive materials are of high relevance for their applications as nano-actuators, sensors or drug carriers. Moreover, the used refined pressure jump small angle neutron scattering technique is of broad interest for soft matter studies.

Abstract

Coupling microfluidics and small-angle neutron scattering (SANS), we investigate the influence of shear flow on a model bicontinuous microemulsion of D2O/n-octane/C10E4, examining the role of membrane volume fraction in the transformation towards a lamellar structure. We employ a contraction-expansion geometry with flow velocities in excess of 10 m s−1 and spatially map the microfluidic field using a small SANS beam, illuminating down to 10 nL sample volumes. The shear-induced, progressive, bicontinuous-to-lamellar transition is found to be promoted by additional extensional flow (>103 s−1), while fast relaxation kinetics (<2 ms) return the scattering pattern to isotropic shortly after the constriction. Further, increasing the domain size of the bicontinuous structure (determined by the membrane volume fraction) appears to amplify its response to shear. Hence, the structural changes within the dilute bicontinuous microemulsions simply scale with the volume fraction of the membrane. By contrast, the stronger response of the microemulsion with the smallest domain size, located near the bicontinuous/lamellar coexistence, indicates an influence of an already more ordered structure with fewer passages. Our findings provide insight into the high shear behaviour of microemulsions of both academic and industrial relevance.

Abstract

Gelled non-toxic bicontinuous microemulsions have a great potential for transdermal drug delivery as the microemulsion facilitates the solubilization of both hydrophilic and hydrophobic drugs, while the gel network provides mechanical stability and thus an easy application on the skin. In our previous study, we formulated a gelled non-toxic bicontinuous microemulsion: we gelled the system H2O–isopropyl myristate (IPM)–Plantacare 1200 UP (C12G1.4)–1,2-octanediol with the low molecular weight organogelator 1,3:2,4-dibenzylidene-d-sorbitol (DBS). However, a large amount of Plantacare 1200 UP (12 wt \%) is needed to form a bicontinuous microemulsion. To solve this problem, we studied a new class of surfactants, namely, alkanoyl methylglucamides (MEGA), which have been rarely used for the formulation of microemulsions. The phase behavior of microemulsions stabilized by MEGA-8/10, MEGA-12/14-PC, and MEGA-12/14-HC was compared with that of systems stabilized by alkyl polyglucosides. We found that even with 2 wt \% MEGA-12/14-HC, a bicontinuous microemulsion can be formed, which is 1/6 of the amount of Plantacare 1200 UP. The bicontinuous microstructure of the non-toxic microemulsion H2O–IPM–MEGA-12/14-HC–1,2-octanediol was confirmed by small-angle neutron scattering. Furthermore, the phase boundaries remained unchanged when gelled by DBS. The rheological properties of the gel were studied by oscillatory shear rheometry. Finally, freeze-fracture electron microscopy images show the coexistence of gel fibers and bicontinuous oil and water domains. These results suggest that the new gelled non-toxic bicontinuous microemulsion is an orthogonal self-assembled system.

Abstract

Using bicontinuous microemulsions as templates opens a new field for the design of novel structures and thus novel materials, but has significant challenges due to the very small composition and temperature windows in which microemulsions are bicontinuous. In previous work we had shown that we can take a ternary base system (water−n-dodecane−C13/15E5), add monomer and cross-linker (N-isopropylacrylamide and N,N′-methylenebisacrylamide) to the water phase, and add a gelator (12-hydroxyoctadecanoic acid) to the oil phase while remaining in the one-phase region of the phase diagram. It was also possible to allow the gelator to form an organogel by changing the temperature such that we crossed the sol−gel line, which fell within the one-phase region. In this work, we show conclusively that addition of the monomers and the gelator does not affect the microemulsion microstructure and that, even in the gelled state, the polymerizable microemulsion is indeed bicontinuous. 1H NMR self-diffusion, conductivity, and small-angle neutron scattering measurements all confirm the bicontinuous nature of the gelled polymerizable microemulsion.

Abstract

The equilibrium microstructures in microemulsions and other self-assembled systems show complex, connected shapes such as symmetric bicontinuous spongelike structures and asymmetric bicontinuous networks formed by cylinders interconnected at junctions. In microemulsions, these cylinder network microstructures may mediate the structural transition from a spherical or globular phase to the bicontinuous microstructure. To understand the structural and statistical properties of such cylinder network microstructures as measured by scattering experiments, models are needed to extract the real-space structure from the scattering data. In this paper, we calculate the scattering functions appropriate for cylinder network microstructures. We focus on such networks that contain a high density of network junctions that connect the cylindrical elements. In this limit, the network microstructure can be regarded as an assembly of randomly oriented, closed packed network junctions (i.e., the cylinder scattering contributions are neglected). Accordingly, the scattering spectrum of the network microstructure can be calculated as the product of the junction number density, the junction form factor, which describes the scattering from the surface of a single junction, and a structure factor, which describes the local correlations of different junctions due to junction interactions (including their excluded volume). This approach is applied to analyze the scattering data from a bicontinuous microemulsion with equal volumes of water and oil. In a second approach, we included the cylinder scattering contribution in the junction form factor by calculating the scattering intensity of Y junctions to which three rods with spherical cross section are attached. The respective theoretical predictions are compared with results of neutron scattering measurements on a water-in-oil microemulsion with a connected microstructure.

Abstract

In dieser Arbeit werden Mikrostrukturuntersuchungen mit Neutronenkleinwinkelstreuung (SANS) und Grenzflächenspannungsmessungen von 19 Wasser - n-Alkan - Alkylpolyglykolether(CiEj) - Systemen beschrieben, zueinander in Beziehung gesetzt und quantitativ analysiert. Die Kenntnis der Formen und Größen der Mikrostrukturen ermöglicht die Bestimmung des Krümmungszustandes des amphiphilen Tensidfilms und damit die Analyse des Grenzflächenspannungsexperiments in Form der biegeelastischen Energie des Films. Mittels dieser Beschreibung können die Grenzflächenspannungskurven sämtlicher Systeme aufeinander skaliert werden. Die wenigen „kritischen“ Parameter, die für die Skalierung benötigt werden, sind die maximale Domänengröße, die Temperaturempfindlichkeit (Tu-Tl) und die mittlere Temperatur ((Tu+Tl)/2, die der Phaseninversionstemperatur PIT entspricht. Daher liegt es nahe, daß wir in Zukunft zu einem Gesetz der „Korrespondierenden Zustände“ für Mikroemulsionen kommen können.

Abstract

We investigated thermally induced phase transitions between the so called sponge- (L3) and lamellar phase (La) in the well known water (D2O) - oil (n-decane) - nonionic surfactant (n-dodecylpentaoxyethylene; C12E5) system. Due to the radically different topology of the two phases, bilayer fusion events must occur in the process of passage formation necessary for the La to L3 transition, while respectively fission takes place in the reverse case. These phenomena were studied for the first time employing the quadrupolar splitting effect of 2H-NMR spectroscopy. Additional SANS experiments were performed recently. We found a strong dependence of the phase transition kinetics on bilayer volume fraction fB+C and the driving force DT. Also, the mechanisms of the sponge to lamellar transition and the reverse case are distinctly different. While in the former case a nucleation process with subsequent growth of the lamellar regions was found, the later was characterized by locally uncorrelated passage formation.

Abstract

The interfacial tensions between water- and oil-rich phases in microemulsion systems have been measured for a series of ternary water-alkane-CiEj systems. It is found that interfacial tensions vary over orders of magnitude with temperature displaying a pronounced minimum for each surfactant. The center of the three-phase temperature interval, Tu-T1, i.e. the phase inversion temperature (PIT), corresponds to the temperature Tm of the minimum in interfacial tension. Increasing the surfactant chain length the minimum value decreases by 3 orders of magnitude for a change of i from 6 to 12. Interestingly, all interfacial tension curves have a similar shape. Centering the curves around Tm and reducing the temperature scale by Tu-T1 permits determining the factors, by which the individual interfacial tension curves differ. The factors are found to be proportional, respectively, to square of the maximum length scale ζ or the inverse surfactant volume fraction Φc,i in the interface. Accordingly, plotting σab/Φc, j2 vs. 2(T-Tm)/(Tu-T1) an almost perfect superposition of all interfacial tension curves is observed.

Abstract

As triacylglycerols are the main components of natural fats and oils their solubilization in the form of emulsions or microemulsions was of great interest within the last years. However, systematic studies of their properties along the classical lines of complex fluids science are still missing. In the present paper we focus on the phase behavior, the interfacial tension and the microstructure of systems of type H2O/NaCl–triacylglycerol–alkylpolyglycolether (CiEj). The interfacial tension between water and oil σab is high in a microemulsion system containing triolein. Thus, one needs high surfactant mass fractions to formulate a single-phase microemulsion. We show that this is not only true for triolein, but also for saturated long-chained triacylglycerols. The determination of the amphiphilicity factor fa and the calculation of the bending rigidities of the amphiphilic film confirm that despite the fact that high surfactant mass fractions and high temperatures are needed to solubilize triolein in a system of type H2O/NaCl–triacylglycerol–alkylpolyglycolether (CiEj), this is still a microemulsion in the narrower sense.

Abstract

This paper describes the fabrication of paper-based plasmonic refractometric sensors through the embedding of metal nanoparticles (NPs) onto flexible papers using reversal nanoimprint lithography. The NP-embedded papers can serve as gas sensors for the detection of volatile biogenic amines (BAs) released from spoiled food. Commercial inkjet papers were employed as sensor substrates—their high reflectance (>80\%) and smooth surfaces (roughness: ca. 4.9 nm) providing significant optical signals for reflection-mode plasmonic refractometric sensing and high particle transfer efficiency, respectively; in addition, because inkjet papers have lightweight and are burnable and flexible, they are especially suitable for developing portable, disposable, cost-effective, eco-friendly sensing platforms. Solid silver NPs (SNPs), solid gold NPs (GNPs), and hollow Au–Ag alloyed NPs (HGNs) were immobilized on a solid mold and then transferred directly onto the softened paper surfaces. The particle number density and exposure height of the embedded NPs were dependent on two imprinting parameters: applied pressure and temperature. The optimal samples exhibited high particle transfer efficiency (ca. 85\%), a sufficient exposure surface area (ca. 50\% of particle surface area) presented to the target molecules, and a strong resonance reflectance dip for detection. Moreover, the HGN-embedded paper displayed a significant wavelength dip shift upon the spontaneous adsorption of BA vapors (e.g., Δλ = 33 nm for putrescine; Δλ = 24 nm for spermidine), indicating high refractometric sensitivity; in contrast, no visible spectroscopic responses were observed with respect to other possibly coexisting gases (e.g., air, N2, CO2, water vapor) during the food storage process, indicating high selectivity. Finally, the plasmonic sensing papers were used to monitor the freshness of a food product (salmon).

Abstract

Here we investigate the thermal diffusion behavior of the nonionic microemulsion water/n-decane/pentaethylene glycol monododecyl ether (C12E5). We study the dependence of the Soret coefficient on the structure and composition by infrared thermal diffusion Rayleigh scattering. The form and size of the microemulsion structure is characterized by dynamic light scattering and small angle neutron scattering. The system was examined in the one-phase region between the emulsification failure boundary and the near critical boundary, where oil swollen nanostructures stabilized by an amphiphilic surfactant film are dispersed in a continuous water phase. The size and shape of these structures as well as the interfacial properties of microemulsions can be varied by changing temperature and composition, which allows a systematic study of their influence on the thermal diffusion properties. In addition, we analyze the relationship between the Soret coefficient and the temperature dependence of the interfacial tension as proposed by A. Parola and R. Piazza (Eur. Phys. J. E2004, 15, 255–263) and find reasonable agreement for spherical microemulsion droplets.

Abstract

Aiming at a new type of salt-free CASAIL (Catanionic Surface Active IL) for electrochemical applications or emulsifiers, dispersants, and foaming or antifoaming agents, we combined mesogenic anions (carboxylate) and cations (imidazolium) of similar shape and size to synthesize a series of congruent ion pairs of 1-alkyl-3-methylimidazolium alkylcarboxylates CnmimCm−1COO (n = 10–16, m = 10–16). With particular focus on alkyl chain length varieties in both, imidazolium cations and carboxylate anions (n/m), the self-assembly in the bulk phase and in solution was investigated by differential scanning calorimetry (DSC), polarized optical microscopy (POM), X-ray diffraction (XRD) experiments and surface tension measurements. Our results revealed that the presence of long alkyl chains on both the cation n and anion m leads to improved thermal stability of the bulk material while maintaining broad lamellar (SmA) mesophases. In water, we observed a strong and linear decrease of log(cmc) for increasing both the carboxylate anion and imidazolium cation chain length due to the increasing hydrophobic effect. Surprisingly, for both thermotropic behavior and micellization, the chain length of the carboxylate anion had a stronger impact than the chain length of the imidazolium cation, indicating its greater surface activity and tendency to form micelles.

Abstract

Favorable interactions between injection gas and crude oil are crucial for successful carbon dioxide (CO2) recovery processes. The miscibility behavior and thereby the flooding scheme changes with the pressure applied. Although first contact miscibility (FCM) flooding schemes result in most efficient recovery processes, in many cases multiple contact miscibility (MCM) provides economically viable recovery rates already at lower injection pressure. Thus, the determination of the miscibility pressure is a key step in the lab evaluation for CO2 EOR. Miscibility enhancing additives are able to improve the interactions between CO2 and crude oil leading to reduced miscibility pressure. This paper illustrates an easily applicable procedure to identify the pressure required for full miscibility. Using a pressure resistant sapphire cell the phase behavior of mixtures of different crude oils and CO2 with and without additives was investigated at common reservoir conditions. The effect of the additives on the physical phase behavior of CO2/crude oil mixtures and the benefit that can be achieved by their application will be discussed. The miscibility gaps are determined by measuring the phase behavior of CO2/additive/crude oil mixtures as a function of pressure and temperature. The pressure required for full miscibility (physical minimum miscibility pressure (MMPP)), coming along with an FCM scheme, can easily be detected as the pressure above which the miscibility gap closes and a homogeneous mixture is obtained. Another important point, which was determined in this study, was the critical point of the miscibility gap. Its corresponding pressure is the maximum value of the minimum miscibility pressure (MMP) from a thermodynamical viewpoint, above which MCM schemes take place. Hence, knowledge of the critical point of the mixture is an easy to use method to estimate the maximum value of the MMP for a specific reservoir. Adding proper additives to the CO2 improves the miscibility of injection gas and crude oil. By this the miscibility gap shrinks and both the MMP and the MMPP will be reduced significantly compared to the pure CO2/crude oil system. The method presented is a proper, quick, and low-cost alternative to the time-consuming and expensive slim tube experiments commonly used in the oil industry to measure the MMP. Since at pressures above the MMP an MCM procedure is ensured by physics it is the lowest injection pressure that needs to be applied to ensure miscible CO2 EOR. Reducing the MMP and the MMPP using proper additives can lead to a more economical CO2 flood or can even make reservoirs accessible for this technology, which are naturally not.

Abstract

ZnO inverse opals combine the outstanding properties of the semiconductor ZnO with the high surface area of the open-porous framework, making them valuable photonic and catalysis support materials. One route to produce inverse opals is to mineralize the voids of close-packed polymer nanoparticle templates by chemical bath deposition (CBD) using a ZnO precursor solution, followed by template removal. To ensure synthesis control, the formation and growth of ZnO nanoparticles in a precursor solution containing the organic additive polyvinylpyrrolidone (PVP) was investigated by in situ ultra-small- and small-angle X-ray scattering (USAXS/SAXS). Before that, we studied the precursor solution by in-house SAXS at T = 25 °C, revealing the presence of a PVP network with semiflexible chain behavior. Heating the precursor solution to 58 °C or 63 °C initiates the formation of small ZnO nanoparticles that cluster together, as shown by complementary transmission electron microscopy images (TEM) taken after synthesis. The underlying kinetics of this process could be deciphered by quantitatively analyzing the USAXS/SAXS data considering the scattering contributions of particles, clusters, and the PVP network. A nearly quantitative description of both the nucleation and growth period could be achieved using the two-step Finke–Watzky model with slow, continuous nucleation followed by autocatalytic growth.

Abstract

The effect of non-saturated corner and edge sites of Pd particles on the long-term selectivity of cis-3-hexen-1-ol in the hydrogenation of 3-hexyn-1-ol was studied in this work. Non-supported Pd agglomerates were synthesized through the microemulsion synthesis route and used at nalkynol/APd ratios between 0.08 and 21 mol/m2 for the catalytic conversion of 3-hexyn-1-ol for 20 h. The selectivity of the cis-hexenol product increased by reducing the quantity of Pd catalytic sites (increasing the nalkynol/APd ratio) without introducing any modifier or doping agent to poison the nonselective sites. Then, Pd aggregates with fused primary particles and, thus, fewer corner and edge sites were produced through thermal sintering of the agglomerates at 473–723 K. By comparing the catalytic performance of the agglomerates and aggregates, it was observed that at a rather similar kinetic behavior (99.99% conversion and 85–89% selectivity to cis-hexenol), the sintered aggregates could stay selective despite a catalytic surface area about seven times larger. This emphasizes the role of low-coordinated edge and corner sites on the final selectivity of the cis product and demonstrates that thermal sintering allows the number of non-selective sites to be reduced without any need for toxic or organic doping agents or modifiers.

Abstract

In gas flooding EOR applications the injection pressure plays a significant role. It has to be higher than the minimum miscibility pressure (MMP) for a fully miscible flood to obtain the highest oil recovery, since the swelling, and consequently the efficiency of a flood, strongly depends on the miscibility of the residual oil and the recovery fluid. Poor miscibility leads to poor recovery. On the other hand the injection pressure must not be higher than the reservoir fracture pressure to avoid the creation of high thief zones in the formation. The addition of proper additives to the injection gas can reduce the MMP significantly. Using a pressure resistant sapphire cell firstly the solubility of different additives in the gas at common reservoir conditions was determined. The compatibility of the additives with CO2 is needed to be ascertained first in order to identify compounds that enable an easy co-injection of the additive within the flow of the CO2. Then the miscibility behavior of the gas and a model oil was studied and the change of the miscibility pressure in the presence of chosen additives was investigated. Phase behavior studies at typical reservoir pressures and temperatures show the miscibility behavior of the fluids and the effect of the different additives on the mutual miscibility. It was proven that the minimum miscibility pressure can be lowered significantly by the choice of an appropriate additive. Through determination of phase diagrams it is shown how the miscibility gap between crude oil and CO2 can be decreased, thereby going from immiscible or multi-contact miscible to fully miscible conditions. Adjusting the MMP broadens the pressure range of high sweep efficiency that is limited by the formation fracture pressure as the upper and the MMP as the lower limit. Thus, conditions can be created at which the reservoir pressure leads to fully miscible floods. Using an appropriate additive can lead to an improvement of the miscibility behavior at given reservoir conditions and make it more favorable for a CO2 EOR process. A former near-miscible or even immiscible application can become a miscible flood. By this the sweep efficiency is maximized and the recovery rate is highest. The parameters that define an economic reasonable gas flooding application now comprise a larger number of reservoirs due to the improved miscibility of crude oil and injection gas.

Abstract

We demonstrate a new approach to determine the bending rigidity of the amphiphile film in microemulsions and sponge phases from neutron scattering data. This method is precise enough to measure the logarithmic scale dependence of the bending rigidity and its universal prefactor for the first time. Furthermore, we show that in the mushroom regime the bending rigidity of a membrane decorated by amphiphilic block copolymers increases linearly with the polymer concentration on the membrane; the amplitude is found to be about a factor 1.5 larger than theoretical results for ideal chains.

Abstract

In ternary water−oil−nonionic alkyl polyglycol ether (CiEj) microemulsions, an increase in efficiency is always accompanied by the formation of a lamellar (Lα) phase. The addition of an amphiphilic block copolymer to the ternary base system increases the efficiency of the microemulsion drastically while suppressingat least partlythe formation of the Lα phase. However, amphiphilic block copolymers can be used not only to suppress the formation of lyotropic liquid crystals but also for the opposite effect, namely, to induce their formation. To understand to what extent the increase in efficiency is accompanied by the formation of lyotropic liquid crystals, we studied phase diagrams of water−n-alkane−n-alkyl polyglycol ethers (CiEj)−PEPX−PEOY at a constant volume fraction of oil in the water/oil mixture. Using polymers of the poly(ethylene propylene)−copoly(ethylene oxide) type, with MPEP = X kg mol-1 and MPEO = Y kg mol-1, we determined phase diagrams as a function of the polymer concentration, size, and symmetry. Moreover, the influence of a particular polymer mixture was studied, which turned out to be the best system if both a high efficiency and a low tendency to form an Lα phase are needed.

Abstract

We demonstrate how rather hydrophilic surfactants can be used for solubilizing simultaneously water and alkane. The required hydrophilic−lipophilic balance can be achieved by the addition of a medium-chain alcohol, that is, a hydrophobic cosurfactant. Specifically, the phase behavior of the quaternary water−n-octane−n-octyl β-d-glucopyranoside (C8G1)−n-octanol (C8E0) system has been investigated. Sugar surfactants, in general, are hydrophilic and, because of the comparatively large number of hydroxyl groups, much less temperature-sensitive than the well-known alkylpolyglycolether (CiEj) surfactants. Therefore, one has to resort to tuning the phase behavior by mixing with a hydrophobic cosurfactant. Once this is done, the phase behavior mimics that of water−alkane−CiEj microemulsions. To show this, the trajectory of the middle-phase is determined as the phase inversion is passed. A scaling of the trajectory onto the trajectories of conventional temperature-sensitive ternary microemulsions is possible after the composition (i.e. the fraction of n-octanol) of the mixed amphiphilic film is determined from phase behavior and density measurements.

Abstract

The effect of amphiphilic diblock copolymers of several molecular weights on the structure and phase behavior of ternary amphiphilic systems (water, oil, and nonionic surfactant) is investigated. Small amounts of amphiphilic block copolymer polyethyleneoxide–polyethylpropylene lead to a dramatic decrease of the amount of total surfactant needed to solubilize given equal volumes of water and oil in a bicontinuous microemulsion. Neutron scattering experiments employing a high-precision two-dimensional contrast variation technique demonstrate that the polymer is distributed uniformly on the surfactant membrane. Based on these observations, we propose a mechanism for the enhancement of swelling behavior, which is due to the variation of the membrane curvature elasticity by polymer mushrooms anchored to the interface.

Abstract

We studied the thermal diffusion behavior of the nonionic surfactant C8G1 (n-octyl β-d-glucopyranoside) in water for different concentrations between w = 0.25 wt\% and w = 2.0 wt\% in a temperature range from T = 15 to 60 °C using the classical and infrared thermal diffusion forced Rayleigh scattering (TDFRS) setup. The purpose of the present paper is the investigation of the thermal diffusion behavior of surfactant systems around the critical micelle concentration (cmc), which is independently determined by surface tension measurements. In the classical TDFRS, the surfactant solutions show in the presence of a light-absorbing dye a pronounced change of the thermal diffusion coefficient (DT) and the Soret coefficient (ST) at the cmc. This result agrees with a recent thermal lens study Santos et al., Phys. Rev. E 2008, 77, 011403, which also showed in the presence of dye a pronounced change of the thermal lens matter signal around the cmc. We found that this change becomes less pronounced, if the dye is absent or a light source is used, which is not absorbed by the dye. At higher concentrations, we observed a temperature-dependent sign change of ST as has also been found for solutions of hard spheres at higher concentrations.

Abstract

A clipped random wave model (CRW) with an inverse 8th-order polynomial spectral density function (SDF) is proposed for the analysis of small-angle neutron scattering intensities from isometric bicontinuous microemulsions. The spectral density function contains three basic length scales which are essential in describing mesoscopic scale structures of porous materials. The scattering intensities from ionic and non-ionic bicontinuous microemulsions were analyzed using the model to obtain the average Gaussian and square mean curvatures, the specific interfacial area and the bending rigidity constant

Abstract

The phase behavior of water/n-octane/n-octyl-β-d-glucopyranoside (C8G1)/1-octanol (C8E0) permits formulating temperature-insensitive microemulsions spanning the whole water−oil composition range. The types of microstructures formed along the trajectory of the middle-phase microemulsion are examined by NMR diffusometry, yielding the respective diffusion coefficients of all the components. The diffusion experiments provide clear evidence of the transition from oil-in-water to water-in-oil microemulsions via bicontinuous structures in a remarkably large range around phase inversion. Small-angle neutron scattering (SANS) along the same path confirm the picture. Furthermore, SANS curves on the absolute scale permit extracting the specific internal interface in the microemulsion as it passes through phase inversion. When the composition of the internal interface is known, the mean area per surfactant molecule is determined. It is found that as the interfacial film becomes increasingly rich in C8E0, that is, the phase inversion is passed, the mean area per surfactant molecule C8G1 decreases along the same progression.

Abstract

Pluronic F-127 hydrogels are highly efficient microenvironments for photochemical reactions, as demonstrated for singlet oxygen reactions of monoalkenes. Nonpolar substrates are localized in the nanosized polymer compartment, which can be visualized by neutron scattering. The efficiency of 1O2 reactions is strongly increased for tiglate derivatives and the regioselectivity of the ene reaction of trisubstituted alkenes is completely switched in comparison with solution phase and inverted in comparison with intrazeolite photo-oxygenations.

Abstract

Amphiphilic block copolymers of the type poly(ethylenepropylene)-co-poly(ethyleneoxide) dramatically enhance the solubilisation efficiency of non-ionic surfactants in microemulsions that contain equal volumes of water in oil. Consequently, the length scale of the microstructure of such bicontinuous microemulsions is dramatically increased up to the order of a few 100nm. In this paper, we show that this so-called efficiency boosting effect can also be applied to water-in-oil microemulsions with droplet microstructure. Such giant water-in-oil microemulsions would provide confined compartments in which chemical reactions of biological macromolecules can be performed on a single molecule level. With this motivation we investigated the phase behavior and the microstructure of oil-rich microemulsions containing D2O, n-decane(d22), C10E4 and the amphiphilic block copolymer PEP5-PEO5 poly(ethylenepropylene)-co-poly(ethyleneoxide), weight per block of 5000g∕mol. We found that 15wt% of water can be solubilised by 5wt% of surfactant and block copolymer when about 6wt% of surfactant is replaced by the block copolymer. Small-angle-neutron-scattering experiments were performed to determine the length scales and microstructure topologies of the oil-rich microemulsions. To analyze the scattering data, we derived a novel form factor that also takes into account the scattering contribution of the hydrophobic part of the block copolymer molecules that reside in the surfactant shell. The quantitative analysis of the scattering data with this form factor shows that the radius of the largest droplets amounts up to 30nm. The novel form factor also yielded qualitative information on the stretching of the polymer chains in dependence on the polymer surface density and the droplet radius

Abstract

Balanced scCO2-microemulsions contain equal volumes of water and CO2 and are a novel class of microemulsions of substantial interest for both fundamental research and technical applications. One existing feature of these systems is that the solvent quality of scCO2, and hence the overall microemulsion properties, is tuned simply by adjusting pressure, which is not possible with “classical” microemulsions containing oil instead of CO2. Motivated by this, we systematically investigated the phase behavior, the microstructure, and the dynamics of balanced microemulsion systems of the type H2O–CO2–Zonyl FSO 100/Zonyl FSN 100. In systematic phase behavior studies, we found that upon increasing pressure, CO2 and water are more efficiently solubilized. Small angle neutron scattering (SANS) experiments were conducted in order to determine the topology and the length scales of the underlying microstructure. The results obtained strongly suggest the existence of bicontinuously structured microemulsions with an adjustable characteristic length scale of up to 330 Å. From a quantitative analysis of the SANS data, we found that at a fixed microemulsion composition the stiffness of the surfactant membrane is increased solely by increasing the pressure, whereby the renormalization corrected (i.e. bare) bending rigidity κ0,SANS rises from κ0,SANS = 0.88 kBT at 200 bar to 0.93 kBT at 300 bar. These findings were confirmed with high pressure neutron spin echo experiments