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Surfactant crystals can stabilize liquid foams. The crystals are adsorbed at bubble surfaces, slowing down coarsening and coalescence. Excess crystals in the liquid channels between bubbles arrest drainage, leading to ultrastable foams. The melting of crystals upon raising the temperature allows thermoresponsive foams to be designed. In the case of oil foams, the stabilization by crystals received substantial renewed interest in the last 5 years due to their potential applications, particularly in the food industry. For aqueous foams, several reports exist on foams stabilized by crystals. However, these two kinds of liquid foams possess similarities in terms of stabilization mechanisms and the design of surfactant crystal systems. This field will certainly grow in the coming years, and it will contribute to the engineering of new soft materials not only for food but also for cosmetics, pharmaceuticals, and biomedical applications.

The crucial roles of the ionization state and counterion presence on the phase behavior of fatty acid in aqueous solutions are well-established. However, the effects of counterions on the adsorption and morphological state of fatty acid on nanoparticle surfaces are largely unknown. This knowledge gap exists due to the high complexity of the interactions between nanoparticles, counterions, and fatty acid molecules in aqueous solution. In this study, we use adsorption isotherms, small angle neutron scattering, and all-atom molecular dynamic simulations to investigate the effect of addition of ethanolamine as a counterion on the adsorption and self-assembly of decanoic acid onto aminopropyl-modified silica nanoparticles. We show that the morphology of the fatty acid assemblies on silica nanoparticles changes from discrete surface patches to a continuous bilayer by increasing concentration of the counterion. This morphological behavior of fatty acid on the oppositely charged nanoparticle surface alters the interfacial activity of the fatty acid–nanoparticle complex and thus governs the stability of the foam formed by the mixture. Our study provides new insights into the structure–property relationship of fatty acid–nanoparticle complexes and outlines a framework to program the stability of foams formed by mixtures of nanoparticles and amphiphiles.

Recently, we described that the weight ratio (

In the food industry, the surfaces of processing equipment are considered to be major factors in the risk of food contamination. The cleaning process of solid surfaces is essential, but it requires a significant amount of water and chemicals. Herein, we report the use of foam flows based on alkyl polyglucosides (APGs) to remove spores of Bacillus subtilis on stainless-steel surfaces as the model-contaminated surface. Sodium dodecyl sulfate (SDS) was also studied as an anionic surfactant. Foams were characterized during flows by measuring the foam stability and the bubble size. The efficiency of spores’ removal was assessed by enumerations. We showed that foams based on APGs could remove efficiently the spores from the surfaces, but slightly less than foams based on SDS due to an effect of SDS itself on spores removal. The destabilization of the foams at the end of the process and the recovery of surfactant solutions were also evaluated by using filtration. Following a life cycle assessment (LCA) approach, we evaluated the impact of the foam flow on the global environmental footprint of the process. We showed significant environmental impact benefits with a reduction in water and energy consumption for foam cleaning. APGs are a good choice as surfactants as they decrease further the environmental impacts.

Hypothesis In oleogel food systems (based on the mixture between stearic acid and stearyl alcohol) the strong effect of the weight ratio (R) between these two components on the textural and structural properties is well described. The effect of R for other fatty acids and fatty alcohols is less explored. Moreover, they do not show an enhancement of the oleogel properties for specific R. The effect of R on the oleogel properties, for a mixture of fatty acid and fatty alcohol with longer alkyl chains (behenyl alcohol and behenic acid) in sunflower and soybean oils, which are raw materials widely used in cosmetic and pharmaceutical industries, was investigated. Experiments We characterized the oleogel properties as a function of R in terms of structuring potential: hardness, oil loss and gel stability. This information was correlated with microstructural data obtained at different length scales by coupling optical microscopy, DSC, SFC, SAXS and WAXS experiments. Findings Our results highlight that R tunes the oleogel properties in a comparable manner to previous results obtained for stearic acid and stearyl alcohol-based oleogels. Two specific R (8:2 and 7:3) close to the 3:1 molecular ratio gave oleogels with both the highest hardness and stability. The morphology and size of the mixed crystals obtained for these R cannot solely explain why they are stronger gels with low oil loss in comparison to the other R. The almost complete crystallization for these two R is one of the key parameters controlling the oleogel properties. As described in the literature, we also suggest that the differences in oleogel properties come from the spatial distribution of the crystalline mass. In this study, we confirm that the effect of the 3:1 molecular ratio in mixed surfactant systems described more than 50 years ago for foams, emulsions and Langmuir monolayers occurs also on the crystallization of mixed fatty alcohol and fatty acid in oils leading to better oleogels properties.

Oil foams could be used to create food products with reduced fat content in combination with new textures. The incorporation of air bubbles in an oily continuous phase could provide a different mouthfeel and appearance to oil products. Moreover, they could enhance flavour delivery by the inclusion of air containing odorant compounds. This chapter aims to describe how to produce edible oil foams from vegetable oils based on Ramsden-Pickering stabilization by crystal particles. When emulsions are stabilized by particles, they are commonly called Ramsden emulsions or Pickering emulsions, after the pioneering researchers in this field. Following this trend for emulsions, foams stabilized by particles are referred to as Pickering foams. To obtain edible crystalline particles, commercial mono/diglyceride surfactants, long-chain alcohols, long-chain carboxylic acids, triglycerides, sucrose esters and sunflower lecithin can be used. The presence of the crystalline particles both at the interface and in the continuous phase stabilizes the oil foam.

Oil foams that are based on oleogels are stabilized by the presence of crystalline particles at the air bubble surface and in bulk. The size of crystalline particles is an important parameter in oil foam stabilization. The creation process (cooling and shear rate) can tune its properties. The aim of this study was to determine the effect of altering the weight ratio (R) between long chain fatty acids and fatty alcohols on the oil foam. Two optimal weight ratios R = 7:3 and R = 8:2, for which mixed crystals were present, produced the best foams in terms of overrun, foam firmness and foam stability. R not only affected the crystal size, but also the number of crystalline particles present in the oleogel. Mixed crystals help to produce and stabilize the foams. We highlighted that there is a link between the oleogel stability and hardness with their resulting oleofoam properties.

International audience; Themost common types of liquid foams are aqueous ones, and correspond to gas bubbles dispersed in an aqueousliquid phase. Non-aqueous foams are also composed of gas bubbles, but dispersed in a non-aqueous solvent. In theliterature, articles on such non-aqueous foams are scarce; however, the study of these foams has recently emerged,especially because of their potential use as low calories food products and of their increasing importance in variousother industries (such as, for instance, the petroleum industry).Non-aqueous foams can be based on three differentfoam stabilizers categories: specialty surfactants, solid particles and crystalline particles. In this review, we onlyfocus on recent advances explaining how solid and crystalline particles can lead to the formation of non-aqueousfoams, and stabilize them. In fact, as discussed here, the foaming is both driven by the physical properties of theliquid phase and by the interactions between the foam stabilizer and this liquid phase. Therefore, for a given stabilizer,different foaming and stability behavior can be found when the solvent is varied. This is different fromaqueoussystems forwhich the foaming properties are only set by the foam stabilizer.We also highlight how these nonaqueousfoams systems can easily become responsive to temperature changes or by the application of light.

The development of shampoo and cleansing formulations in cosmetics is at a crossroads due to consumer demands for better performing, more natural products and also the strong commitment of cosmetic companies to improve the sustainability of cosmetic products. In order to go beyond traditional formulations, it is of great importance to clearly establish the science behind cleansing technologies and appreciate the specificity of cleansing biological surfaces such as hair and skin. In this review, we present recent advances in our knowledge of the physicochemical properties of the hair surface from both an experimental and a theoretical point of view. We discuss the opportunities and challenges that newer, sustainable formulations bring compared to petroleum-based ingredients. The inevitable evolution towards more bio-based, eco-friendly ingredients and sustainable formulations requires a complete rethink of many well-known physicochemical principles. The pivotal role of digital sciences and modelling in the understanding and conception of new ingredients and formulations is discussed. We describe recent numerical approaches that take into account the specificities of the hair surface in terms of structuration, different methods that study the adsorption of formulation ingredients and finally the success of new data-driven approaches. We conclude with practical examples on current formulation efforts incorporating bio-surfactants, controlling foaming and searching for new rheological properties.

Stimuli-responsive liquid foams and bubbles are systems for which the stability, structure, shape, and movement can be controlled by the application of stimuli. The foam stability can be modified by a stimulus which can change solution condition (pH, temperature, and ionic strength) or with the application of an external field (light and magnetic). Different foam stabilizers have been described in the literature to design these responsive foams systems ranging from surfactants, peptides, polymers, soft polymer particles, surfactants self-assembly, crystalline particles, emulsion droplets, and solid particles. This review aims to cover the recent advances of the design of stimuli-responsive liquid foams and their applications. Responsive liquid foams are attractive in textile coloring process, biomedical application, washing, and material recovery processes.

The most common types of foams are aqueous foams. Non-aqueous foams are composed of gas bubbles dispersed in a non-aqueous phase. The physical properties of the non-aqueous liquid phase drive the foaming properties. Contrary to aqueous foams, the foaming properties are not only related to the foaming capacity of the foam stabilizer, but are linked to the nature of the non-aqueous phase and to the interactions between this liquid phase and the foam stabilizer. In the literature, non-aqueous foams are scarcely studied. However, this topic is important for various industries, such as the petroleum industry. New interest in these systems has emerged recently owing to their potential use in low-calorie food products. The non-aqueous foams can be produced based on three different foam stabilizer categories: surfactants, solid particles and crystalline particles. The crystalline particles are also well known in the literature to be involved in the formation of oleogels. Therefore, edible oil foams can be obtained based on oleogels. In this book chapter, the more recent advances in the non-aqueous foams field are described. The mechanisms leading to the formation and stabilization of these non-aqueous foams are described with a focus on oil foams based on oleogel systems.

International audience; Fatty acids are natural, pH-responsive surfactants. Their properties can be tuned by adding CO2 or by applying light which modify solution pH. We investigated photoresponsive systems based on fatty acids with different chain lengths in the presence of a photoacid generator (PAG). Under UV irradiation, photolysis of the PAG in aqueous solution resulted in a decrease in pH, triggering a change in fatty acid assembly. Using a multi-scale approach before and after UV irradiation, we characterized the effect of this pH decrease on the nature of the fatty acid self-assemblies. At the molecular scale, pH and infrared spectroscopy measurements were used to determine the fatty acid ionization state. At the microscopic scale, the self-assembled structure was characterized using small-angle neutron scattering and microscopy. We showed that UV irradiation tuned the ionization state of the fatty acid molecules which in turn triggered a transition from spherical micelles to vesicles or lamellar phases, depending on fatty acid chain length. We studied the foaming properties of these systems before and after UV irradiation. We showed that after uv irradiation, foam stability was drastically enhanced as a result of a change in self-assembly. Our approach can be easily extended to various pH-responsive surfactants.

NSF Research Triangle MRSEC on Programmable Soft Matter DMR-1121107; International audience; The directed assembly of colloidal particles into linear chains and clusters is of fundamental and practical importance. In this study we characterize and analyse the mechanism of the magnetic field driven assembly of lipid-coated iron oxide nanoparticles into flexible microfilaments. Recently we showed that nanocapillary lipid binding can form a new class of magnetic nanoparticle-lipid microfilaments with unprecedented flexibility and self-healing properties. In the presence of a uniform magnetic field, the magnetophoretic attraction of the particles combined with interparticle dipole-dipole attraction drives the microfilament assembly. The fluid like lipid layer on the particles leads to stickiness on the surface of the filaments and the magnetic field concentration overcomes the potential electrostatic repulsion in the water phase. The lipid capillary bridges formed between the particles facilitate their permanent binding and sustain the flexible microfilament structure. We demonstrate that this surface stickiness combined with the magnetic response of the filaments can be used further to twist, bend and bundle the microfilaments into unusual structures.

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich. This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively. Photoresponsive surfactant system based on fatty acids has been developed by the introduction in aqueous solution of a photoacid generator (PAG). Self-assembly transitions are triggered by UV irradiation due to a pH change induced by the presence of PAG.

International audience; In this article, we show that stimuli-induced microscopic transformations of self-assembled surfactant structures can be used to tune the macroscopic bulk and interfacial rheological properties. Previously, we had described the formation of micron-sized 12-hydroxystearic acid tubes having a temperaturetunable diameter in the bulk, and also adsorbing at the air-water interface. We report now a detailed study of the bulk and interfacial rheological properties of this solution of thermoresponsive tubes as a function of temperature. In the bulk, the structural modifications of tubes with temperature lead to sharp and non-monotonous changes of rheological behavior. As well, at the air-water interface, the interfacial layer is shifted several times from rigid-like to fluid-like as the temperature is increased, due to morphological changes of the adsorbed interfacial layer. The temperature-induced variations in the fatty acid supramolecular organization and the richness in structural transitions at this microscopic level lead to unique rheological responses in comparison with conventional surfactant systems. Also, this study provides new insights into the required packing conditions for the jamming of anisotropic soft objects and highlights the fact that this system becomes glassy under heating. Due to these unique macroscopic properties both in the bulk and at the interface, this simple system with stimuli-responsive viscoelasticity is of interest for their potential applications in pharmacology or cosmetic formulations.

Resume : Les tensioactifs sont largement utilises du fait de leurs proprietes moussantes. Dans les mousses, ils se placent a l'interface entre l'eau et l'air et stabilisent les films d'eau autour des bulles d'air. Beaucoup de tensioactifs utilises actuellement sont issus de derives petroliers, leur remplacement par des biomolecules est un enjeu majeur pour la chimie verte. Par exemple, l'acide gras 12-hydroxystearique issu de l'huile de ricin a des proprietes moussantes tres avantageuses et originales. Abstract: Surfactants are used in many products because of their foaming properties. In foams, they spread at the interface between air and water which stabilizes the water films surrounding air bubbles. Currently, since most of the surfactants commercially used are derivatives of petroleum-based products, their replacement by biomolecules is a major issue for the green chemistry. For example, the 12-hydroxy stearic acid coming from the castor oil has very advantageous and original foaming properties. Mots-cles : tensioactif, mousse, interface, thermosensible, acide gras, assemblage supramoleculaire Keywords: surfactant, foam, interface, thermoresponsive, fatty acid, supramolecular assembly Points cles Domaine : Sciences fondamentales, physico-chimie, matiere molle Degre de diffusion de la technologie : Emergence / Croissance / Maturite Technologies impliquees : Mousses thermosensibles, acides gras, tensioactifs Domaines d'application : Cosmetique, detergent Principaux acteurs francais : Limite au domaine academique

The ethanolamine salt of 12-hydroxy stearic acid is known to form tubes having a temperature tunable diameter. Here, we study the behavior of those tubes at the air/water interface by using Neutron Reflectivity. We observed that tubes indeed adsorbed at this interface below a fatty acid monolayer and exhibit the same temperature behavior as in bulk. There is however a peculiar behavior at around 50 °C for which the increase of the diameter of the tubes at the interface yields an unfolding of those tubes into a multilamellar layer. Upon further heating, the tubes re-fold and their diameter re-decreases after which they melt into micelles as observed in the bulk. All structural transitions at the interface are nevertheless reversible. This provides to the system a high interest for its interfacial properties because the structure at the air/water interface can be tuned easily by the temperature.

9 pages; International audience; Unsaturated fatty acids may be extracted from various agricultural resources and are widely used as soaps in the industry. However, there also exist a large variety of saturated and hydroxy fatty acids in nature, but their metal salts crystallize at room temperature in water, hampering their use in biological and chemical studies or for industrial applications. Addition of guanidine hydrochloride (GuHCl) to sodium salt of myristic acid has been shown to prevent its crystallization in water, forming stable flat bilayers at room temperature. Herein, we extend this finding to two other saturated fatty acids (palmitic and stearic acids) and two hydroxyl fatty acids (juniperic and 12 hydroxy stearic acids) and study more deeply (by using small angle neutron scattering) the supramolecular assemblies formed in both saturated and hydroxyl fatty acid systems. In addition, we take the advantage that crystallization no longer occurs at room temperature in the presence of GuHCl to study the foaming and emulsifying properties of those fatty acid dispersions. Briefly, our results show that all fatty acids, even juniperic acid, which is a bola lipid, are arranged in a bilayer structure that may be interdigitated. Depending on the nature of the fatty acid, the systems exhibit good foamability and foam stability (except for juniperic acid), and emulsion stability was good. Those findings should be of interest for using saturated long chain (and hydroxyl) fatty acids as surfactants for detergency or even materials chemistry.

International audience; A mixture between 1% sodium myristate and guanidine hydrochloride at a molar ratio of 1 in water forms a gel of membranes below a phase transition of ca. 21°C and a viscous limpid and isotropic solution above. As observed by both TEM and AFM, we report the formation of interconnected superstructures in that latter phase. Those assemblies exhibit a size of ca. 4-40nm width and several tens of [mu]m length with unexpected disconnections and reconnections between them having the appearance of an anastomosis-like superstructure.