Gelled lyotropic liquid crystals (G-LLCs) and gelled micellar solutions (G-MS) are promising soft materials for biomedical applications, combining mechanical stability with functional nanostructures capable of encapsulation and delivery. In such systems, the interactions between the gel network and the self-assembled surfactant structures significantly influence their properties. We investigated the simultaneous self-assembly of the biosurfactant di-rhamnolipid (Rha2C10C10) and the low molecular weight gelator 12-hydroxyoctadecanoic acid (12HOA). We showed the dual role of 12-HOA as both gelator and co-surfactant at two different pH-values. Rheological measurements confirmed successful gelation, with enhanced elastic properties observed in both isotropic and liquid crystalline phases. SAXS and FFEM analyses reveal the coexistence of the gel network and the respective surfactant structure (LLCs or micelles). Furthermore, pH-dependent variations in fibre morphology suggest interactions between protonated rhamnolipid molecules and growing gel fibres, leading to structural defects and altered chirality. These findings highlight the complex interplay between surfactant self-assembly and gelation, providing design principles for tunable hybrid soft materials.

Biological surfactants are amphiphilic molecules obtained from biobased resources, like plants, sugars and oils, using a variety of physical, chemical, biochemical or biotechnological methods. More specifically, the word biosurfactant, or microbial biosurfactants, is classically used for those molecules, like sophorolipids, rhamnolipids or surfactin, produced by fermentation. Historically developed by microbiologists and originally used as natural emulsifiers, recent trends in fundamental and applied research depict a set of molecules with a rich, and somewhat unexpected, physicochemical behavior making it difficult to introduce them as such in existing formulations. A broad research activity is then developing worldwide both in academia and industry with the goal of better understanding this class of amphiphiles with the ultimate perspective of introducing them to the market in fields as varied as detergency, cosmetics, pest control, medicine.

New surfactants are not necessarily better than established surfactants; new surfactants need to be better, cheaper or have a lower environmental impact to have an advantage over existing products. Attributes like aquatoxicity, mildness, sourcing from renewable carbon and emissions of greenhouse gases during production and use of surfactants had become more and more important. Biosurfactants (BS) which are not really new to the world but which have been so far only produced at low concentrations by microorganisms or plants have attained attention in academical research and interest of industry in the last 25 years resulting in the commercial availability of Sophorolipids and Rhamnolipids by several companies. BS are dedicated to applications in PersonalCare and HouseHold Care due to their consumer-recognizable mildness; BS can, however, not simply replace established components in formulations due to their different performance profile, which makes comparison to traditional surfactants rather complicated.

The microstructure of the aqueous solutions of purified acidic Sophorolipid (SL) has previously been studied using highly sophisticated methods such as SANS and Cryo-TEM. We were interested in whether (a) the main findings also apply to commercially available SL (which is a mixture of acidic and lactonic SL) and (b) more readily available methods such as DLS can be used to gain insight into the molecular aggregation of SL. Our work was motivated by the increasing interest in biosurfactants for applications in personal and household care. Moreover, the origin behind the more or less lack of rheological response to changes in pH is of practical relevance, as it is somewhat unusual for a carboxylate-group containing surfactant. By using DLS microrheology, we could elucidate the aggregation structure and dynamics of the surfactant on a microscopic scale. Surprisingly, the different degrees of protonation only impacted the microscopic properties such as exchange kinetics and the plateau values of the storage moduli.

We report new dirhamnolipid ester forming reverse wormlike micelles in nonpolar solvents without the addition of any primer. Therefore, these compounds represent a rare case of a binary system showing this gel-like behavior. In this study, the influence of the concentration of the rhamnolipid ester and the ester alkyl chain length on the rheological properties of the reverse wormlike micelles in toluene was investigated in detail. Highly viscoelastic solutions were obtained even at a relatively low concentration of less than 1 wt %. The phase transition temperatures indicate that the formation of reverse wormlike micelles is favored for dirhamnolipid esters with shorter alkyl chain lengths. Oscillatory shear measurements for the viscoelastic samples reveal that the storage modulus (G') and the loss modulus (G'') cross each other and fit the Maxwell model very well in the low-ω region. As is typical for wormlike micelle systems, the normalized Cole–Cole plot of G''/G''max against G'/G''max was obtained as a semicircle centered at G'/G''max = 1. The formation of network structures was also verified by polarized light microscopy. The sample was birefringent at ambient temperature and anisotropic at an elevated temperature. Differential scanning calorimetry analysis yielded a transition enthalpy of about ΔHSG/GS = ±7.2 kJ/mol. This value corresponds to a strong dispersion energy and explains the formation of the highly viscous gels by the entanglement of wormlike micelles through the interaction of the alkyl chains.

Vesicles have recently found widespread use in applications such as conditioning of textiles, paper and hair, as well as transdermal drug delivery. The mode of treatment in several such cases involves the application of droplets of aqueous dispersions of vesicles onto dry porous substrates like paper and textiles. One of the factors which affects the performance of such treatments is the rate at which the droplets spread and imbibe on the porous substrate. Depending upon the specific purpose of the treatment either a fast or slow droplet spreading kinetics could be desired. Therefore, it is important to have a good understanding of the droplet spreading process and the factors which influence it. In this work, an experimental investigation of the simultaneous spreading and imbibition of vesicle dispersion droplets on cellulose filter papers is carried out. Two different types of vesicles which are composed of similar lipid molecules but exhibit contrasting lipid bilayer phase behavior are used. Two different grades of filter papers with comparable porosities but different thicknesses are used as porous substrate. It is found that the droplet spreading behavior is of the “complete wetting” type on the thicker porous substrate, whereas it is of the “partial wetting” type on the thinner substrate. Furthermore, it is observed that the spreading of droplets containing vesicles with liquid-crystalline phase bilayers occurs faster than that of vesicles with solid-gel phase bilayers. The secondary radial penetration which commences after the initial droplet spreading is complete is also investigated and discussed.

Organomodified silicones (OMS), which conventionally find use in textile finishing processes, have recently become a very interesting prospect in the field of fabric softeners. Here, we present OMS-based fabric softener formulations in the form of classical emulsion (droplet size ≈0.1 μm – 10 μm) and microemulsions (droplet size ≈5 nm–50 nm) using nonionic surfactants (NIS) as emulsifier. Streaming potential measurements are used to obtain a measure of droplet surface charge, and it was found to be related to the ratio of masses of OMS and NIS present in the formulations. In this work, it is investigated how the performance of these formulations is influenced by properties such as droplet size and streaming potential. Panel tests were carried out to evaluate the sensory properties of fabric treated by these formulations, and they reveal that the classical emulsion performs better than the microemulsions. For the microemulsions, it is found that softening performance increases with streaming potential. The observed trends in softening performance are explained by considering the difference in location or penetration of softening actives on or into fabric. Two different experimental approaches are implemented to gain insights into the underlying phenomena. In the first approach, batch deposition experiments are carried out to characterize OMS deposition on fabric. In the second approach, a chromatographic technique is used to compare the deposition kinetics of different formulations. The findings of the experiments provide insights into the reasons underlying the contrasting softening performance. The final results are discussed with respect to existing literature.

Rheology-controlling agents are of importance for numerous products in a variety of industries. Replacement of synthetic chemicals with natural additives is desired in light of current environmental awareness and limited fossil resources. This study investigates the rheological features of Paenan, an exopolysaccharide produced by Paenibacillus polymyxa. Paenan exhibits highly shear-thinning flow behavior at concentrations ≥0.1% in 0.5% NaCl. Because of its pronounced intermolecular network, it forms stable, weak gels, thereby delivering elasticity as well as thixotropy. Application-relevant flow behavior is obtained with 60-65% less polymer as compared to the benchmark commercial products Xanthan and Gellan. In mixtures with surfactants (sodium lauryl ether sulfate, cetrimonium chloride, cocamidopropyl betaine, or lauryl glucoside), Paenan displays outstanding compatibility with every class of surfactant, making it superior to the partially incompatible Xanthan and Gellan. The weak-gel character of Paenan/surfactant systems is retained with three out of four surfactants, rendering Paenan highly interesting for various applications.

An analytical approach is presented to describe pressure-driven streaming current (Istr) and streaming potential (Ustr) generation in geometrically complex samples, for which the classical Helmholtz-Smoluchowski (H-S) equation is known to be inaccurate. The new approach is valid under the same prerequisite conditions that are used for the development of the H-S equation, that is, the electrical double layers (EDLs) are sufficiently thin and surface conductivity and electroviscous effects are negligible. The analytical methodology is developed using linear velocity profiles to describe liquid flow inside of EDLs and using simplifying approximations to describe macroscopic flow. At first, a general expression is obtained to describe the Istr generated in different cross sections of an arbitrarily shaped sample. Thereafter, assuming that the generated Ustr varies only along the pressure-gradient direction, an expression describing the variation of generated Ustr along the sample length is obtained. These expressions describing Istr and Ustr generation constitute the theoretical foundation of this work, which is first applied to a set of three nonuniform cross-sectional capillaries and thereafter to a square array of cylindrical fibers (model porous media) for both parallel and transverse fiber orientation cases. Although analytical solutions cannot be obtained for real porous substrates because of their random structure, the new theory provides useful insights into the effect of important factors such as fiber orientation, sample porosity, and sample dimensions. The solutions obtained for the model porous media are used to device strategies for more accurate zeta potential determination of porous fiber plugs. The new approach could be thus useful in resolving the long-standing problem of sample geometry dependence of zeta potential measurements.

Hypothesis: Colloidal deposition on porous substrates is a complex process influenced by both, (i) characteristics of colloidal permeation into porous substrates, and (ii) mechanism of colloidal deposition on solid surfaces. Such processes are quintessential to action of products such as hair conditioners and fabric softeners where the substrates to be treated are porous. The performance of these formulations is linked with the distribution of deposited colloids across porous substrates i.e. whether deposition is localized near substrate periphery, or deposition is homogeneously distributed. Experiments: In this work, we investigate the deposition of cationic vesicles, commonly used in fabric softeners, on anionic porous cotton yarns via spectrophotometric measurement of adsorption density of vesicles on yarns and electrokinetic measurement of cotton yarn apparent zeta potentials. Under the employed conditions, cotton yarn apparent zeta potentials are sensitive predominantly to external yarn surfaces. Therefore, these measurements can distinguish between deposition on external and internal yarn surfaces. Findings: The phase behavior of lipid bilayers constituting the vesicles is identified as an important governing factor with solid-gel vesicles depositing more near yarn periphery, and liquid-crystalline vesicles depositing more uniformly throughout the yarns. Bulk electrical conductivity also influences the distribution of deposited vesicles. The results are explained with the help of a newly proposed theory. (C) 2017 Elsevier Inc. All rights reserved.

Deposition of vesicles on solid surfaces can in some cases result in the formation of assemblies of intact surface-bound vesicles known as supported vesicular layers (SVLs). Understanding the mechanism of SVL formation is thus important for effective utilization of vesicles in applications involving vesicle-substrate interactions such as drug delivery and fabric softening. In this work, we investigate SVL formation of two different types of cationic vesicles made up of lipid bilayers existing in the solid-gel and liquid crystalline phases, respectively, on both smooth and rough anionic cellulose fibers. Deposition is studied quantitatively via spectrophotometric determination of bulk lipid concentrations, and characterization of fiber apparent zeta, potentials via streaming potential measurements. Equilibrium deposition results, and profiles of variation of substrate apparent zeta potentials with deposition reveal that the deposition mechanisms of the two vesicle types are similar on rough surfaces (cotton) but significantly different on smooth surfaces (viscose). It is concluded that vesicle deposition mechanism is governed by the surface mobility of deposited vesicles which is dependent on substrate roughness and lipid bilayer phase behavior controlled vesicle properties. Results indicate that while both the vesicle types are immobile on rough surfaces, on smooth surfaces liquid-crystalline vesicles are preferentially mobile over solid-gel vesicles. Possible reasons underlying the vesicle surface mobility characteristics are discussed. (C) 2016 Elsevier B.V. All rights reserved.

Lichens, mosses and ferns have previously received little attention in cosmetics. Because they do not have flowers, these original plants do not easily capture the imagination of the general public. However, these woodland plants have exceptional natural properties and a mental association with moisture and freshness. This makes them interesting base materials, whether for anti-ageing and moisturising care in general, or for foot care in particular. The anti-ageing moisturiser HYDRACTIN®-LMF combines the extract of the Cetraria lichen (Icelandic moss), Sphagnum moss (peat moss) and the Polypodium fern (Polypody). By providing the skin with adequate moisture, the active ingredient turns the epidermal clock back by approximately 20 years in just 4 weeks. This article focuses on foot care properties: stressed, calloused and cracked feet become noticeably and visibly softer and more supple. Moisture: a simple but all the more important anti-ageing strategy The many sophisticated cosmetic actives developed in recent years, such as peptides or stem cell protectants, all focused on combating wrinkles and preventing skin ageing. The natural elixir of water and the simple mechanism of skin hydration have been largely forgotten. Moisture may sound mundane, but it is a very important and probably underestimated anti-aging strategy [1]. Dry skin is more prone to premature ageing and reduced turgor, resulting in reduced elasticity and firmness in ageing skin. In other words, dry skin is an ideal breeding ground for changes in skin physiology. [2]. Thus, the skin loses its elasticity, leading to the development of lines and wrinkles. Regardless of how many active ingredients are applied that have an immediate effect against the signs of ageing, moisture content is crucial and keeps the skin fresh and young. Against this backdrop, it becomes obvious that intelligent moisturisers not only solve the problem of dry skin, but also improve the elasticity, firmness and unevenness of the skin and prevent the formation of wrinkles. [1]. Moisturisers should both provide the skin with additional moisture and store and preserve this as long as possible. The anti-ageing moisturiser presented here—HYDRACTIN®-LMF—has precisely this dual function and is both moisturising and moisturepreserving.

Surfactant formulations are often based on an anionic primary surfactant combined with an amphoteric secondary surfactant. One popular option is the combination of lauryl ether sulfate and cocamidopropyl betaine, because such formulations are not only mild but also easy to thicken. Changes in the molecular structure of the betaine in terms of alkyl chain length distribution and headgroup structure do have dramatic effects on the viscosity of these formulations, as can be explained in terms of properties of rod-like micelles and exchange kinetics by oscillatory rheological measurements. The root cause of the effect of the different betaine derivatives on the micellar structure, however, remains unclear when considering rheology only. Although the streaming potential of colloidal objects is typically determined to forecast the stability of dispersions, we have used the streaming potential to characterize micellar solutions of different betaine surfactant structures. It could be shown that (a) the hydrophilicity of the surfactants can be nicely probed by this method and (b) there is a good correlation of these values with the rheological properties of binary mixtures of the betaines with anionic surfactant. Also, the chemical structure of the headgroups has a significant influence on both the isoelectric point and the magnitude of the streaming potential of the zwitterionic surfactants. These effects have again a dramatic influence on the interaction with anionic surfactants, as becomes obvious when looking at the rheology of such mixtures. Therefore, the findings obtained can be utilized to better understand and design surfactant formulations of a desired viscosity profile.

Hypothesis: Understanding the mechanism of intact vesicle deposition on solid surfaces is important for effective utilization of vesicles as active ingredient carriers in applications such as drug delivery and fabric softening. In this study, the deposition of large (d(avg) = 12 mu m) and small (d(avg) = 0.27 mu m) cationic vesicles of ditallowethylester dimethylammonium chloride (DEEDMAC) on smooth and rough anionic cellulose fibers is investigated.Experiments: The deposition process is studied quantitatively using streaming potential measurements and spectrophotometric determination of DEEDMAC concentrations. Natural and regenerated cellulose fibers, namely cotton and viscose, having rough and smooth surfaces, respectively, are used as adsorbents. Equilibrium deposition data and profiles of substrate streaming potential variation with deposition are used to gain insights into the fate of vesicles upon deposition and the deposition mechanism.Findings: Intact deposition of DEEDMAC vesicles is ascertained based on streaming potential variation with deposition in the form of characteristic saturating profiles which symbolize particle-like deposition. The same is also confirmed by confocal fluorescence microscopy. Substrate roughness is found to considerably influence the deposition mechanism which, in a novel application of electrokinetic methods, is elucidated via streaming potential measurements. (C) 2016. Elsevier Inc. All rights reserved.