A systematic study on the mechanisms of cleansing artificial skin by solutions of widely used in personal care surfactants disodium laureth sulfosuccinate (DSLSS), sodium laureth sulfate (SLES), sodium dodecyl sulfate (SDS), dodecyl trimethyl ammonium bromide (DTAB), and coco glucoside (CG), is presented. The systematic characterization of soil removal from artificial skin revealed two primary cleansing mechanisms: emulsification and roll-up. Emulsification occurs in systems with very low interfacial tension, such as sebum in SLES solutions, while dimethicone soil was only removed by roll-up. The roll-up effectiveness depends on the surfactant’s interfacial activity and its adsorption on the soiled surface. Thus, the strong adsorption of DTAB on the skin leads to dimethicone roll-up at a relatively high interfacial tension of 11 mN/m. The anionic and nonionic surfactants adsorbed less at the artificial skin surface, and the oil/water interfacial tension value lowering below 5 mN/m is necessary for the roll-up to occur. Nonionic CG removed dimethicone at a lower concentration than ionic surfactants. Combining CG with ionic surfactants improved cleaning at lower total concentrations. Surfactant mixtures are used to formulate simple cleansing formulations, whose performance is also investigated by the developed in vitro approach. The results obtained allow for a good rating of the formulations, which correlates well with the performance of the surfactant mixtures and their interfacial activity.

The class of volatiles, which possess low saturated vapor pressures, appreciable solubilities in water, and well pronounced surface activities, have gained wide applications in diverse areas of industry, cosmetics, and medicine. One way to qualitatively characterize their mass transfer between vapor and aqueous solutions is to measure the relaxation of the interfacial tension, σ, with time, t, under different nonequilibrium initial conditions. This approach is applied in the present work for geraniol and menthol. By means of combining σ(t) data with the respective equilibrium surface tension isotherms, the instantaneous values of the fragrance adsorption, Γ(t), have been determined. Quantitative characterization of the geraniol and menthol mass transfers in the case of adsorption from vapor to aqueous drops is achieved by using a mixed barrier-diffusion model. The obtained values of the rates of adsorption and desorption are compared with those reported in the literature for benzyl acetate, linalool, and citronellol. In the case of evaporation of the volatiles from their saturated aqueous solutions to the ambient atmosphere, the mass transfer is found to be driven both by mixed barrier-diffusion and by convection-enhanced mechanisms – depending on the air humidity. The quantitative description of the evaporation of volatile molecules is modelled theoretically by adsorption rate constants. In order to achieve the reported model representations, complex numerical calculations are implemented. On the other hand, having in mind the cases when one wishes to avoid extensive computational work, we developed a simple semiempirical model suitable for all five studied fragrances. This simplified approach is convenient for the express comparison and characterization of the evaporation rates. The obtained physicochemical parameters related to the evaporation and condensation of volatiles are important for the rigorous modeling of their complex mixed solutions of practical interest. The semiempirical model could be used for the quantitative classification of volatile molecules with respect to their ability to evaporate.

Spontaneous bubble growths in liquids are usually triggered by rapid changes in pressure or temperature that can lead to liquid gas supersaturation. Here, we report alternative scenarios of the spontaneous growths of bubbles inside a high-saturation-vapor-pressure and high-air-solubility perfluorocarbon liquid (PP1) that were observed under ambient quiescent conditions. First, we investigate spontaneous bubble growth inside the single PP1 phase, which was left to evaporate freely. The bubble growth is explained by the difference in the PP1 vapor pressure inside the bubble and that above the freely evaporating PP1 interface. Next, we study the bubble growth inside the liquid PP1 covered with a layer of a second air-saturated immiscible liquid: low-air-solubility water or higher-air-solubility ethanol. In both cases, the bubble growth rates were accelerated, indicating mass transfer of air from the water or ethanol phases to the PP1 phase. The bubble growth rates significantly increase for bubbles trapped at the PP1–water or PP1–ethanol interfaces due to faster air diffusion through the thin PP1 liquid films separating the bubbles from the upper phases. Finally, we consider the case of bubbles inside millimeter-sized PP1 emulsion droplets in water or ethanol. The bubble growth inside the droplet leads to an increase in the PP1 droplet’s effective buoyancy and to the detachment of the droplets from the substrate. The observed bubble growth rate in the case of emulsion droplets was much faster for PP1 droplets in ethanol than for PP1 droplets in water (minutes vs hours). The underlying physical mechanism of the increase of bubble volumes is the spontaneous mass transfer of both air and PP1 vapor to the bubbles produced by a colloidal diffusion pump effect.

Hypothesis
Polyglycerol esters of fatty acids are generated via the esterification of a polydisperse mixture of polyglycerol with naturally derived fatty acids. The polymerization process of polyglycerol results in the production of various oligomers, ranging from di-, tri-, and higher-order forms, which contribute to the complexity of final products. The combination of complementary experimental techniques and adequate theoretical interpretations can reveal the wide variety of their physicochemical properties.

Experiments
The colloid and interface properties of polyglyceryl mono-laurate, mono-stearate, mono-oleate, and a mixture of mono-caprylate and mono-caprate esters solutions were characterized by measurements of the electrolytic conductivity, static and dynamic surface tension, aggregate and micelle sizes and distributions, thin liquid film stability and stratification, and solubility in aqueous and in oil phases. The formation, stability, and bubble size distribution of foams generated from polyglycerol esters aqueous solutions were systematically investigated.

Findings
The low concentrations of double-tail molecules and fatty acids in polyglycerol esters affect considerably their micellar, aggregation, and vesicle formations in aqueous solutions. The theoretical data interpretation of polyglycerol esters isotherms and thin liquid films data provide information on the adsorption energies, excluded areas per molecule, interaction parameters of molecules at interfaces, surface electrostatic potential, and the size of micelles. Polyglyceryl mono-oleate exhibits spontaneous emulsification properties. Short chain length polyglycerol esters have excellent foaming ability but relatively low foam stability. The optimal weight fractions of the short-chain polyglyceryl esters and polyglyceryl mono-stearate mixtures with respect to good foaminess and foam stability upon Ostwald ripening are obtained. The reported physicochemical characterization of the water-soluble polyglycerol esters could be of interest to increase the range of their applicability in practice.

Hypothesis: Methyl ester sulfonates (MES) show limited water solubility at lower temperatures (Krafft point). One way to increase their solubility below their Krafft points is to incorporate them in anionic surfactant micelles. The electrostatic interactions between the ionic surfactant molecules and charged micelles play an important role for the degree of MES solubility. Experiments: The solubility and electrolytic conductivity for binary and ternary surfactant mixtures of MES with anionic sodium alpha olefin sulfonate (AOS) and sodium lauryl ether sulfate with two ethylene oxide groups (SLES-2EO) at 5 °C during long-term storage were measured. Phase diagrams were established; a general phase separation theoretical model for their explanation was developed and checked experimentally. Findings: The binary and ternary phase diagrams for studied surfactant mixtures include phase domains: mixed micelles; micelles + crystallites; crystallites, and molecular solution. The proposed general phase separation model for ionic surfactant mixtures is convenient for construction of such complex phase diagrams and provides information on the concentrations of all components of the complex solution and on the micellar electrostatic potential. The obtained maximal MES mole fraction of transparent micellar solutions could be of interest to increase the range of applicability of MES–surfactants.