The research paper explores the adsorption properties of cationic surfactants on silicon wafers through imaging ellipsometry. The objective of this research is to shed light on the layer structures formed by cationic surfactants, specifically those based on dimethyl ammonium chloride, on silicon wafers. The study involved the deposition of three distinct cationic surfactants on the wafer’s surface, followed by the measurement of the adsorption layers formed. The findings reveal the creation of thin, smooth, and irregular adsorption layers. Interestingly, no correlation was found between the thickness of the adsorption layer and the surfactant tail’s chain length. The research underlines the significant role which the imaging ellipsometry can have for studying surfactants’ adsorption properties on surfaces, contributing to their optimal usage in various fields.

Hypothesis: The critical micelle concentration, aggregation number, shape and length of spherocylindrical micelles in solutions of zwitterionic surfactants can be predicted by knowing the molecular parameters and surfactant concentrations. This can be achieved by upgrading the quantitative molecular thermodynamic model with expressions for the electrostatic interaction energy between the zwitterionic dipoles and micellar hydrophobic cores of spherical and cylindrical shapes. Theory: The correct prediction of the mean micellar aggregation numbers requires precise calculations of the free energy per molecule in the micelles. New analytical expressions for the dipole electrostatic interaction energy are derived based on the exact solutions of the electrostatic problem for a single charge close to a boundary of spherical and cylindrical dielectric media. The obtained general theory is valid for arbitrary ratios between dielectric constants, radii of spheres and cylinders, positions, and orientations of dipoles. Findings: The detailed numerical results show quantitatively the effects of the micelle curvature and dielectric properties of the continuum media on the decrease of the dipole electrostatic interaction energy. Excellent agreement was achieved between the theoretical predictions and experimental data for the critical micelle concentration, size and aggregation number of zwitterionic surfactant micelles. This study can be extended to mixed micelles of zwitterionic and ionic surfactants in the presence of salt to interpret and predict the synergistic effect on the rheology of solutions.

The subject of this work is to investigate the rheological behavior of mixed micellar solutions (sodium laurylethersulfate and cocamidopropyl betaine) in the presence of Mg2+ divalent counterions. With the rise of salt concentration, the viscosity of micellar solutions increases to a high maximum followed by a steep decrease because of the initial growth and entanglement of wormlike micelles and a subsequent transition to branched micelles forming of a saturated micellar network. The proposed systematic rheological measurements show considerable variations in the rheological responses of the solutions when increasing the salt concentration. Rheological behavior and data are used to distinguish the micellar phases and to study the relation to micellar structures. The wormlike micellar solutions have a typical shear thinning behavior with a well-defined zero-shear viscosity, η0, described by the Cates reptation-reaction model or the augmented Maxwell model. Our data show that the power law dependence of η0 on the surfactant concentration is stronger than that reported in the literature and it is influenced of the added electrolytes. The branched micellar structures are characterized by the lower viscosities and larger elasticities, which follow the Maxwell model up to the intermediate values of the frequency of oscillations, however peculiar deviations from the Cole-Cole plot at large frequencies are detected. The isolated bicontinuous micellar phases are Newtonian fluids with viscosity 0.4–0.7 Pa.s independent on the salt concentration up to high shear rates. The threshold salt concentration ensuring the onset of the bicontinuous micellar phase is described by a simple empirical rule. These phases are characterized by large elasticities and not negligible yield stresses. The property of the bicontinuous micellar phases to form spontaneously oil-in-water nanoemulsions could find applications in drug delivery, extraction and separation processes, pharmaceutics production, etc.

Here, we present results from a systematic study on cleaning of oily deposits from solid surfaces (porcelain and stainless steel) by solutions of fatty acid sulfonated methyl esters (SME), sodium salts. The zwitterionic dodecyldimethylamine oxide (DDAO) has been used as a cosurfactant. As representatives of the vegetable and mineral oils, sunflower seed oil and light mineral oil have been used. The process of oil drop detachment from the solid substrates (roll-up mechanism) has been monitored. In the case of porcelain, excellent cleaning of oil is achieved by mixed solutions of SME and DDAO. In the case of stainless steel, excellent cleaning (superior than that by linear alkylbenzene sulfonate and sodium lauryl ether sulfate) is provided by binary and ternary mixtures of SME, which may contain also DDAO. For the studied systems, the good cleaning correlates neither with the oil/water interfacial tension, nor with the surfactant chainlength and headgroup type. The data imply that governing factors might be the thickness and morphology of admicelle layers formed on the solid/water interface. The results indicate that the SME mixtures represent a promising system for formulations in house-hold detergency, having in mind also other useful properties of SME, such as biodegradability, skin compatibility, and hard water tolerance.

Colloidosomes provide a possibility to encapsulate oily substances in water in the form of core-in-shell structures. In this study, we produced microcapsules with shell from colloidal particles, where the interparticle openings are blocked by mixed layers from polymer and surfactant that prevent the leakage of cargo molecules. In other words, the particles and polymer play the role of bricks and mortar. For this goal, we used hydrophilic silica particles, which were partially hydrophobized by the adsorption of potassium oleate to enable them to stabilize Pickering emulsions. Various polymers were tested to select the most appropriate one. The procedure of encapsulation is simple and includes single homogenization by ultrasound. The produced capsules are pH responsive. They are stable in aqueous phase of pH in the range 3–6, but at pH > 6 they are destabilized and their cargo is released. With the optimized formulation of silica particles, polymer, oleate and NaCl, we were able to encapsulate various oils and fragrances, such as tetradecane, limonene, benzyl salicylate and citronellol. All of them have a limited and not too high solubility in water. In contrast, no stable microcapsules were obtained with oils that either have zero water solubility (mineral and silicone oil) or higher water solubility (phenoxyethanol and benzyl alcohol). By analysis of results from additional interfacial-tension and thin-film experiments, we concluded that a key factor for obtaining stable capsules is the irreversible adsorption of the polymer at the oil/water interface. The hydrophobization of the particles by surfactant adsorption (instead of silanization) plays an important role for the pH responsiveness of the produced capsules. The obtained information about the role of various factors for the stabilization of microcapsules, which are based on the brick-and-mortar concept, can be further used to achieve better stability; selection of polymers that are appropriate for different classes of oils, as well as for the production of smaller capsules stabilized by nanoparticles.