Abitaev, K., Atanasova, P., Bill, J., Preisig, N., Kuzmenko, I., Ilavsky, J., Liu, Y., Sottmann, T.: In Situ Ultra-Small- and Small-Angle X-ray Scattering Study of ZnO Nanoparticle Formation and Growth through Chemical Bath Deposition in the Presence of Polyvinylpyrrolidone. Nanomaterials. 13, 2180(1–19) (2023).
https://doi.org/10.3390/nano13152180.
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.Benedix, R.R., Botsch, S., Preisig, N., Kovalchuk, V., Jessop, P.G., Stubenrauch, C.: Influence of a CO2-switchable additive on the surface and foaming properties of a cationic non-switchable surfactant. Soft Matter. 19, 2941–2948 (2023).
https://doi.org/10.1039/D3SM00273J.
Abstract
Switchable materials in general and CO2-switchable materials in particular are of great interest in environmental research. The replacement of common non-switchable materials (solutions, solvents, surfactants, etc.) with their switchable counterparts has a great potential to make processes more environmentally friendly by enhancing reusability and circularity and thus reducing energy costs and material consumption. Inspired by this, the present work deals with the surface and foaming properties of aqueous solutions of a non-switchable surfactant in presence of a CO2-switchable additive. A 1 : 1 and a 1 : 5 (molar ratios) mixture of the non-switchable surfactant C14TAB (tetradecyltrimethylammonium bromide) and the CO2-switchable additive TMBDA (N,N,N,N-tetramethyl-1,4-butanediamine) were investigated. It was found that surface properties, foamability, and foam stability can be changed by switching the additive with CO2 as a trigger. This observation can be explained by the fact that TMBDA is surface active in its unprotonated, i.e. neutral form, which disturbs the tight packing of the surfactant molecules on the surface. As a consequence, foams generated with surfactant solutions containing the neutral TMBDA are less stable than their TMBDA-free counterparts. On the other hand, the switched diprotonated additive is a 2 : 1 electrolyte with hardly any surface activity and thus does not affect surface and foam properties.Benedix, R.R., Poole, H., Zauser, D., Preisig, N., Jessop, P.G., Stubenrauch, C.: Surface and foaming properties of an anionic CO2-switchable tail surfactant. Tenside Surfactants Detergents. 60, 269–276 (2023).
https://doi.org/doi:10.1515/tsd-2023-2524.
Abstract
CO2-switchable materials in general and CO2-switchable surfactants in particular are of great interest in environmental research. There is a great potential to make processes more environmentally friendly by enhancing reusability and circularity and thus reducing material costs and energy consumption by replacing common non-switchable surfactants with their switchable counterparts. Inspired by this, the present work deals with the surface and foaming properties of aqueous solutions of the novel anionic CO2-switchable tail surfactant sodium 4-(methyl(octyl)amino)butane-1-sulfonate. In the presence of N2, the unprotonated surfactant is able to stabilize foams. By switching, i.e. by protonating the CO2-responsive trialkyl amine group in the surfactants hydrocarbon chain, the amphiphilic nature of the surfactant is reduced which is indicated by an increase of the plateau surface tension and a higher CMC compared to the non-protonated surfactant. Furthermore, the ability of the protonated surfactant to stabilize foams is reduced.Herbst, M., Dombrowski, M.O., Preisig, N., Dieterich, S., Giesselmann, F., Mésini, P., Stubenrauch, C.: Gelled lyotropic nematic liquid crystals. Liquid Crystals. 50, 1090–1100 (2023).
https://doi.org/10.1080/02678292.2023.2201583.
Abstract
ABSTRACTLyotropic liquid crystal gels (LLC gels) are versatile materials which combine the anisotropy of a liquid crystal with the mechanical stability of a gel. We succeeded in gelling the rare calamitic nematic NC phase of two different micellar LLC systems with the low molecular weight gelator (LMWG) 3,5-bis-(5-hexylcarbamoyl-pentoxy)-benzoic acid hexyl ester (BHPB-6). The systems of choice are: (1) a binary LLC system with the surfactant N,N-dimethyl-N-ethyl-1-hexadecylammonium bromide (CDEAB) and water; (2) a ternary LLC system with the surfactant N,N,N-trimethyl-N-tetradecylammonium bromide (C14TAB), n-decanol, and water. The obtained gels show optical birefringence and no macroscopic flow. Freeze fracture electron microscopy (FFEM) images show ribbon-like gel fibres that form the gel network and can stack into thicker bundles, while small-angle X-ray scattering (SAXS) confirms the coexistence of the nematic NC phase and the gel network. The growth of the gel network was monitored with time-resolved SAXS measurements. Additionally, significant gel ageing effects were observed in rheology measurements, showing that the gel strengthens with time. With this study, we considerably broaden the pool of available surfactant-based LLC gels and pave a way to macroscopically aligned LLC gels with the goal to apply them as stimuli-responsive actuators and sensors.Menold, P., Strey, R., Roitsch, S., Preisig, N., Stubenrauch, C.: Transition from a foam-like to an onion-like nanostructure in water-rich L3 phases. Tenside Surfactants Detergents. (2023).
https://doi.org/doi:10.1515/tsd-2023-2559.
Abstract
In dilute water-surfactant systems L3 phases are found in which bilayers interconnect to form a sample-spanning sponge-like structure. From our previous study of the system water/NaCl-AOT (sodium bis(2-ethylhexyl) sulfosuccinate) we know that a transition of this sponge-like structure to an oil-continuous foam-like structure occurs upon addition of minute amounts of oil (about 3 wt%, α = 0.03) in the L3 channel at a constant surfactant mass fraction of γ = 0.15 and T = 25 °C. The aim of the present study was to verify if the same transition occurs at γ = 0.25. To achieve this goal, we determined the relevant part of the phase diagram and studied the electrical conductivities and viscosities within the narrow one-phase L3 channel. Although the electrical conductivities and viscosities change qualitatively like those observed at γ = 0.15 we did not observe a sponge-like structure at γ = 0.25 in the oil-free system (α = 0) with freeze-fracture electron microscopy (FFEM) and freeze fracture direct imaging (FFDI). Together with the FFEM/FFDI images and SANS/SAXS curves we provide experimental evidence for a structural transition with decreasing oil content from a thermodynamically stable foam-like to a thermodynamically stable onion-like nanostructure at γ = 0.25 rather than to a sponge-like structure as is the case at γ = 0.15.Steck, K., Dijoux, J., Preisig, N., Bouylout, V., Stubenrauch, C., Drenckhan, W.: Fluorocarbon vapors slow down coalescence in foams: influence of surfactant concentration. Colloid and Polymer Science. 301, 685–695 (2023).
https://doi.org/10.1007/s00396-023-05129-7.
Abstract
Even though it has been known for a long time that traces of perfluorinated vapors suppress gas exchange (coarsening) between the bubbles of aqueous foams, its stabilizing impact on foam coalescence has been evidenced only recently. While previous work has demonstrated this effect for different surfactant types, we investigate here the influence of the surfactant concentration. We compared the foam properties of aqueous solutions of the non-ionic surfactant dodecyldimethylphospine oxide (C12DMPO) in the absence and presence of perfluorohexane (PFH) in the gas phase. In order to decouple foam coarsening and coalescence, we accompany the foam stability experiments with (a) lifetime statistics of individual, vertical foam films pulled from the same solutions and (b) surface tension measurements in controlled gas environments. All measurements show a clear increase of foam and film stability in the presence of PFH, its effect being most pronounced above the cmc of the surfactant. The surface tension measurements show a clear co-adsorption of the PFH up to the formation of macroscopic films at saturation. We complete the analysis by showing that alkane vapors also have a stabilizing effect for the same surfactant solutions, yet much less pronounced than that of PFH. The precise origin of the stabilizing action of these hydrophobic vapors remains to be elucidated.
