Natalie Preisig

Abstract

We developed a new, innovative foam-based cleaning method with which the amount of detergent can be reduced by up to 90%. In addition, foams generate physical cleaning mechanisms, namely imbibition and wiping. The combination of imbibition and wiping is so efficient that it is sufficient to simply let the foam sit on the surface for a while before removing it by vacuuming. No additional mechanical action is needed! This publication describes how we managed to clean the historic carriages of kings and emperors of past centuries in the “Marstallmuseum” in Nymphenburg Palace in cooperation with the “Bavarian Administration of State-Owned Palaces, Gardens and Lakes”.

Abstract

Abstract Liquid foams of intermediate stability have been shown to be very efficient in the cleaning of sensitive surfaces because of the synergy between imbibition and foam decay. While we quantified these mechanisms for contaminations with liquid oils in our previous work, we show here their extension to oils containing soot particles in an effort to simulate increasingly realistic contaminations. Using foams with a wide range of liquid fractions and with different stabilities, we show that the main cleaning mechanisms remain very similar, with the oil entraining the soot particles. However, we find much less efficient soot removal when the liquid channels of the foams are small enough to hinder efficient transport of the soot particles.

Abstract

Hypothesis The micrometer-sized gas bubbles of a liquid foam with a dispersed gas phase of > 74 vol% are polyhedral and surrounded by a continuous aqueous phase. The structure of a water-rich microemulsion with a water phase of > 74 vol% normally consists of oil droplets in water or is bicontinuous. We hypothesize that at these high water contents polyhedral water droplets in oil can also exist. Experiments We (a) carried out phase studies on the water-rich side of the phase diagram of the quaternary system water/NaCl – hexyl methacrylate – AOT, because AOT is known for its propensity to form water-in-oil structures and hexyl methacrylate can be polymerized, (b) measured the electrical conductivities and viscosities, and (c) visualized the nanostructure with freeze-fracture electron microscopy (FFEM). Findings We found narrow 1-phase regions emanating from the L3 phase of the oil-free water/NaCl – AOT system by adding small amounts of oil. In these regions the conductivities become extremely low and the viscosities are extremely high. In addition, FFEM images clearly show the foam-like nanostructure.

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

Abstract Lyotropic liquid crystal (LLC) gels are a new class of liquid crystal (LC) networks that combine the anisotropy of micellar LLCs with the mechanical stability of a gel. However, so far, only micellar LLC gels with lamellar and hexagonal structures have been obtained by the addition of gelators to LLCs. Here, the first examples of lyotropic nematic gels are presented. The key to obtain these nematic gels is the use of gelators that have a non-amphiphilic molecular structure and thus leave the size and shape of the micellar aggregates essentially unchanged. By adding these gelators to lyotropic nematic phases, an easy and reproducible way to obtain large amounts of lyotropic nematic gels is established. These nematic gels preserve the long-range orientational order and optical birefringence of a lyotropic nematic phase but have the mechanical stability of a gel. LLC nematic gels are promising new materials for elastic and anisotropic hydrogels to be applied as water-based stimuli-responsive actuators and sensors.

Abstract

Hypothesis Foamed surfactant solutions can clean surfaces! We hypothesise that the cleaning efficiency depends on the liquid fraction and on the stability of the foam. We also hypothesise that the cleaning efficiency is the better the smaller the average bubble size is. Experiments The double syringe technique was used to generate foams with varying liquid fractions but the same, very small bubble sizes with and without perfluorohexane in the gas phase. We performed cleaning tests in which the foams were applied to glass substrates contaminated with a fluorescent oil. Findings We found that unstable foams clean better than stable foams. Three cleaning mechanisms were identified: (1) imbibition at low liquid fractions, (2) wiping, i.e., shifting of the contact line between oil, foam and glass, at all liquid fractions, and (3) drainage at high liquid fractions. The change of the liquid fraction and of the foam stability lead to different combinations of these mechanisms and thus to different cleaning results.

Abstract

The saponin β-aescin from the seed extract of the horse chestnut tree Aesculus hippocastanum has demonstrated a beneficial role in clinical therapy which is in part related to its strong interaction with biological membranes. In this context the present work investigates the self-assembly of nm-sized discoidal lipid nanoparticles composed of β-aescin and the phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC). The discoidal lipid nanoparticles reassemble from small discs into larger discs, ribbons and finally stacks of sheets upon heating from gel-phase to fluid phase DMPC. The morphological transition of the lipid nano-particles is mainly triggered by the phospholipid phase state change. The final morphology depends on the phospholipid-to-saponin ratio and the actual temperature. The study is conducted by small-angle X-ray scattering (SAXS) and transmission (TEM) and freeze fracture electron microscopy (FFEM) are used to cover larger length scales. Two different models, representing a disc and ribbon-like shape are applied to the SAXS data, evaluating possible geometries and molecular mixing of the nano-particles. The stacked sheets are analysed by the Caillé theory.