This study investigates composition-microstructure-rheology-performance relationships in Carbopol-based emulgels and bigels containing different oils. Optical microscopy revealed polydisperse droplets in liquid paraffin, isopropyl myristate, and almond oil formulations, whereas cetyl alcohol systems exhibited larger, irregular birefringent particles with Maltese cross-like patterns. All formulations showed shear-thinning behavior and predominantly elastic responses (G′ > G″). Cetyl alcohol-based emulgels exhibited higher elastic moduli and viscosity than those containing other oils. Increasing Carbopol concentration from 0.5% to 1% enhanced elasticity and viscosity, while reducing viscosity losses during heating from 10 to 40 °C from 35 to 40% to 11–26%. Bigels containing 20% and 30% oleogel exhibited elastic moduli approximately 20% and 80% higher than the hydrogel, respectively, suggesting possible synergistic mechanical reinforcement. Correlation analysis revealed relationships between rheological parameters, drug release, and spreadability. Viscosities above approximately 150 Pa·s were associated with reduced drug release, while moderate viscosity favored a balance between structural integrity, spreadability, and release performance. The absence of visible changes after 12 months of storage was consistent with temperature-ramp rheology results, suggesting potential use as a preliminary screening tool for formulation stability. Overall, oil phase selection, phase structuring, and Carbopol concentration enable tailoring stable and functional emulgel and bigel formulations for pharmaceutical and cosmetic applications.

Commercial nonionic sucrose ester surfactants (SEs) contain varying ratios of monoesters and polyesters. In our previous study, we found that when the mono-to-polyester (MP) ratio is close to 1, SE dispersions can form hydrogels at very low surfactant and electrolyte concentrations. In the current study, we systematically investigate how the MP ratio and particle size affect the salt-induced gelation process. We reveal that SE dispersions form hydrogels only within a certain MP range. At low MP ratios (<0.4), micrometer-sized particles form and sediment, preventing gel formation, whereas at high MP ratios (≳3), particle concentration decreases, confining gelation to a very narrow electrolyte region. Sonication significantly reduces particle size across all dispersions, expanding the gelation domain down to MP ≈ 0.3. The critical salt concentration required for hydrogel formation exhibits a maximum as a function of MP ratio at MP ≈ 0.43, which is explained with the highest measured zeta potential for these particles. The obtained results support the hypothesis that increasing the monoester content enhances surface mobility, suppresses hydroxide ion adsorption, and reduces particle charge, thereby lowering the threshold electrolyte concentration. Finally, particle size reduction enhances overall gel strength and lowers the minimum surfactant concentration required for gelation. These findings enable the rational design of simple, biodegradable hydrogels with tunable properties for future applications in food, pharmaceutical, and cosmetic formulations.

Essential oils are a key ingredient in foods, beverages, and personal- and home-care products due to their flavors, scents, and various biological activities. This study investigates the capacity of polysorbate 60 (PS60) micelles to solubilize eight essential oils classified into two groups based on their composition. The first group (tea tree, rose, lavender, and melissa oils) contains more than 40% polar aliphatic or alicyclic alcohols or aldehydes, whereas the oils from the second group (chamomile, yarrow, lemon, and orange oils) contain less than 20% of these compounds. The efficient solubilization of the studied essential oils within PS60 micelles is proposed to occur via a mechanism involving two steps: (1) the formation of mixed micelles between PS60 molecules and the polar alcohol or aldehyde constituents of the essential oils, and (2) the dehydration of PS60 ethoxy groups in the presence of highly water-soluble additives (such as citric acid and sodium citrate), which is suggested to decrease the hydrophilic barrier of the micellar corona, thereby facilitating the mass transfer of hydrophobic oil molecules into the micellar core. Stable, transparent microemulsions form only with the first group of essential oils in a certain concentration range. The second step in the proposed mechanism leads to the unexpected finding that reducing the concentration of water-soluble additives, such as citric acid and sodium citrate, impairs solubilization by allowing the micellar corona to rehydrate.

This work presents results, aimed at identifying the crystallization mechanism of surfactant-stabilized hexadecane-in-water droplet with 15 nm diameter at the molecular level. The question is addressed by atomistic molecular dynamics simulations of models consisting of ca. 2 million atoms. To represent as closely as possible real-world systems, a procedure for constructing droplets of different sizes is developed, allowing control of the surfactant surface coverage. Two crystallization protocols are applied: slow freezing, in which the surface solidifies first, followed by relaxation and subsequent cooling to induce crystallization in the bulk, and fast freezing, in which the droplet is directly cooled to the final temperature, leading to simultaneous surface and core crystallization. A few key results may be outlined. The droplet surface always freezes first. Nucleation occurs stochastically at multiple independent sites, gradually propagating over the surface. Both shell and core undergo heterogeneous nucleation initiated by surfactant molecules. The nuclei in the core typically form close to the surface. The cooling procedure affects the spatial freezing pathway and molecular ordering in the drop core. The preferred orientation of bulk crystallites relative to the originating surface is nearly perpendicular. Once solidified, the surface alone is sufficient to induce droplet deformation to a triangular prism-like shape, additionally stabilized by the bulk crystallites. The deformation is a clear indication of a rotator phase, stable over hundreds of nanoseconds, further confirmed by the fraction of gauche conformations, P2 order parameters, and radial distribution functions. These findings agree with and complement experimental data and provide molecular-level verification of the experimentally observed fundamental difference in the stability of hexadecane rotator phase: transient in bulk and stable under micro- and nanoconfinement. This is the fundamental knowledge on microscopic freezing mechanisms of hexadecane and similar even-parity alkane-based materials at interfaces.

Introduction: The use of intravenous fat emulsions for treatment of drug intoxication still follows
a trial-and-error approach, due to insufficient understanding of the mechanisms of the process
and lack of predictive in vitro tools.