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.

Molecular dynamics simulations are employed to investigate the crystallization of pentadecane-containing systems. Reference crystalline and rotator phase constructed from crystallographic data benchmark the structures formed upon cooling. Phase identification is achieved through global and local structural descriptors, with the fraction of gauche conformations and angular P₂ profiles outlined as the most sensitive indicators.
Pentadecane exhibits a markedly more stable rotator phase than hexadecane. This is confirmed by simulations spanning more than 30 K for the reference rotator phase. In this temperature range, a model regular rotator phase of pentadecane remains stable without undergoing significant structural changes, showing high reproducibility across independent trajectories. This contrasts hexadecane, for which a rotator phase rapidly transforms toward a triclinic structure [Iliev et al. 2023]. The presence of a surfactant in the system promotes heterogeneous nucleation, shifts crystallization to higher temperatures, and stabilizes the rotator phase, in agreement with experiments.
A computationally efficient protocol for simulating SAXS spectra from MD trajectories is proposed. The simulated spectra align very well with experimental data for both crystalline and rotator phases. Crystallographic lattice parameters can be extracted from the most intense SAXS peaks, even for experimentally unknown structures, demonstrating the general applicability of the approach to solid-state phase analysis.

Phase behavior of lipids is of primary importance for the manufacturing and applications of foods, cosmetics and pharmaceuticals, as well as for the functions of biological membranes. Upon cooling, the molten bulk lipids crystallize into ordered domains which determine their rheological properties. While storage and loss moduli are typically used to describe these properties, their direct connection to the underlying molecular rearrangement remains poorly understood. In the current study, we performed a detailed rheological characterization of the rotator phases (intermediate phases between fully ordered crystalline and completely disordered liquid phases) formed in bulk linear alkanes. Large series of stress-relaxation and creep-recovery experiments were performed and interpreted, using generalized Kelvin-Voigt model with one spring, connected in series with three combined elements of a spring and a dashpot. We determined the elasticities and viscosities of all these rheological elements, along with the respective three relaxation times of the combined elements. These relaxation times are governed by different molecular processes in the sheared samples and differ by three orders of magnitude: t1 ≈ 0.45 s and t2 ≈ 8–9 s are related to local molecular rearrangements at the domain boundaries, while t3 ≈ 140–200 s most probably describes the rearrangement of disordered lipid molecules entrapped between the ordered domains. The storage and loss moduli, calculated from the constants of the generalized Kelvin-Voigt model, were in a very good agreement with those measured directly in amplitude sweep and temperature ramps oscillatory tests, thus supporting the self-consistency of data interpretation. The methodology presented here is applicable to other polycrystalline lipid materials with 2D or 3D domain structures, providing a valuable framework for interpreting their rheological behavior.

Sugar esters, a class of surfactants derived from renewable resources, have attracted significant attention due to their biodegradability, low toxicity, and broad applications in food, cosmetic, and pharmaceutical formulations. Despite their widespread use, the phase behavior of these compounds in aqueous systems remains incompletely understood. In this study, we investigate the self-assembly of a nonionic sucrose ester of lauric acid in 1–40 wt% concentration range using rheological measurements, dynamic light scattering, X-ray scattering, DOSY NMR, and molecular dynamics simulations. Formation of spherical micelles with a diameter of 5.4 nm is observed at low surfactant concentrations, driven by hydrophobic interactions between the alkyl tails. These solutions exhibit Newtonian flow behavior with viscosities close to that of pure water. However, the viscosity increases from 5 mPa.s at 16 wt% to 640 mPa.s at 40 wt%, while the Newtonian character persists even at 40 wt%. This behavior is explained with the formation of interconnected, thread-like micellar structures of (almost) spherical micelles that largely preserve their distinctiveness, resembling the “pearl necklace” arrangement known for polymer systems. The main driving force for this supramolecular organization was found to be the hydrogen bonding between sucrose headgroups. The addition of 6 M urea, a known hydrogen bond disruptor, significantly reduces micelle clustering and the viscosity decreases to 150 mPa.s at 40 wt% concentration, supporting the proposed aggregation mechanism. These findings contribute to a deeper understanding of the self-assembly behavior of sucrose esters in aqueous environment and highlight their potential for controlled aggregation in practical formulations.

Small emulsion droplets typically adopt spherical shapes under positive interfacial tension, minimizing unfavorable oil-water contact. This shape, along with the initial drop size, are generally preserved upon drop freezing or melting. However, in a series of studies, we demonstrated that simple temperature fluctuations near the melting point of the dispersed oil phase can spontaneously induce a wide range of dynamic behaviors in droplets. These activities include morphogenesis into various non-spherical shapes such as hexagonal, triangular, and tetragonal platelets, rods and fibers; the formation of complex composite micrometer-sized structures in the presence of adsorbed latex particles on initially spherical droplets; spontaneous desorption of the initially adsorbed particles; the generation of synthetic microswimmers capable of self-propulsion through the continuous phase, driven by the rapidly growing elastic filaments; spontaneous drop fragmentation and bursting into smaller particles (with sizes down to 20 nm) without any mechanical energy input; and the engulfment of the surrounding media spontaneously producing double water-in-oil-in-water droplets. All these phenomena were found to be intricately related to surface and polymorphic phase transitions proceeding within the droplets. The underlying mechanisms and control parameters were systematically investigated and published in a series of papers. The present review aims to summarize the key discoveries, present them within a unified conceptual framework, and compare them with other processes reported in the literature to lead to similar outcomes. Furthermore, the practical implications of these phenomena are discussed, and potential future research directions in this emerging area at the intersection of emulsion science and phase transition phenomena are outlined.