Probing gels and emulsions using large-amplitude oscillatory shear and frictional studies with soft substrate skin surrogates

Green, tough, and heat-resistant: A GDL-induced strategy for starch-alginate hydrogels

Hydrogels fabricated by non-covalent interaction garnered significant attention for their eco-friendly and robust mechanical attributes, and are often used in food, medicine and other fields. Although starch-alginate hydrogels exhibit high adhesion and are environmentally sustainable, their applications are limited due to their low elasticity and hardness. Addressing this challenge, we introduce a solvent-induced strategy using glucolactone (GDL) to fabricate hydrogels with enhanced strength and thermal resilience. Utilizing corn starch with varying amylose contents, sodium alginate and calcium carbonate to prepare a double network structure. This GDL-induced hydrogel outperforms most previous starch-based hydrogels in mechanical robustness and thermal stability. Typical starch-alginate hydrogel had a homogeneous network structure and exhibited a high tensile stress of 407.57 KPa, and a high enthalpy value of 1857.67 J/g. This investigation furnishes a facile yet effective method for the synthesis of hydrogels with superior mechanical and thermal properties, thereby broadening the design landscape for starch-based hydrogels.

Tailoring 3D-printed high internal phase emulsion-rice starch gels: Role of amylose in rheology and bioactive stability

This study investigated the properties of 3D-printed high internal phase emulsion (HIPE)-rice starch gels, specially tailored for personalized nutrition by co-encapsulating resveratrol and β-carotene. We examined the influence of amylose content on various parameters, including functional groups, linear and nonlinear rheology, printed precision and microstructural stability. Additionally, we assessed the protective efficacy and release in vitro digestion of these gels on the encapsulated bioactive components. Compared to HIPE, HIPE-starch gels differently impacted by amylose content in starches. Low-level amylose weakened the network structure, attributed to amylose mainly responsible for gel formation and weak hydrogen bond interaction between the surface-active molecules and amylose due to gelatinized starch granules rupturing the protein network. Oppositely, high-level amylose led to denser, more gel-like structures with enhanced mechanical strength and reversible deformation resistance, making them suitable for 3D printing. Furthermore, 3D-printed gels with high-level amylose demonstrated well-defined structures, smooth surfaces, stable printing and less dimension deviation. They were also regarded as effective entrapping and delivery systems for resveratrol and β-carotene, protecting them against degradation from environment and damage under the erosion of digestive fluid. Overall, this research offers a straightforward strategy for creating reduced-fat HIPE gels that serve as the carrier for personalized nutraceutical foods.

Tribological and Rheological Study of Thixotropic Gels of 2D Nanoparticles

A thixotropic colloidal gel constituting an aqueous dispersion of synthetic clay Laponite with varying concentrations of salt has been studied for its rheological and tribological performance as a lubricant. We observed that the incorporation of NaCl induces notable enhancements in the colloidal gel's relaxation time, elastic modulus, and yield stress. Although an increase in NaCl concentration decreases the material's relaxation time dependence on waiting time (tw), overall, the strength of its thixotropic character has been observed to increase with an increase in salt concentration. The analysis of friction and wear indicated that the utilization of a thixotropic colloidal gel of Laponite with a higher concentration of NaCl resulted in progressively greater reductions in both the coefficient of friction and specific wear rates under various load-speed conditions. Severe abrasive wear on disc surface under dry test, gradually mitigated upon the introduction of these lubricants. Two simultaneous lubricating mechanisms, first, the smooth sliding of the friction pair, facilitated by the alignment of Laponite particles in the direction of shear forces, and second, the stable structure of Laponite, coupled with the addition of NaCl, enabling continuous replenishment of the wear track with lubricant, are attributed to lubrication effectiveness.

Glassy and compressed nanoemulsions stabilized with sodium dodecyl sulfate in the presence of poly(ethylene glycol)-diacrylate

The rheology of concentrated nanoemulsions is critical for their formulation in various applications, such as pharmaceuticals, foods, cosmetics, and templating advanced materials. The rheological properties of nanoemulsions depend on interdroplet interactions, Laplace pressure, dispersed phase volume fraction, and continuous phase properties. The interdroplet forces can be tuned by background electrolytes (i.e., charge screening), surfactant type, the excess surfactant micelle concentration, and depletant molecules such as polymer chains. In the current research, we study the effect of varying the content of poly(ethylene glycol)-diacrylate (PEGDA) on the interfacial tension of the water-oil phase and rheological properties of concentrated nanoemulsions with 50% and 60% volume fractions. Sodium dodecyl sulfate (SDS) is used as the ionic surfactant. The final concentrated nanoemulsions are repulsive according to overall interaction potentials and are in the glass and compressed states based on the effective volume fraction estimation. They contain nearly same SDS concentration on the droplet surface and also in the bulk, but a different amount of PEGDA. The scaled rheological properties of the glassy nanoemulsions show a higher dependency on the PEGDA content and the possible effect of polymer-surfactant complexations compared to those of the compressed ones. This dependency is more pronounced in small strain amplitudes but not in large strains in the non-linear regime. These results provide insights into formulating concentrated nanoemulsions with controlled rheology for expanded application areas.

Enhanced freeze-thawing stability of water-in-oil pickering emulsions stabilized by ethylcellulose nanoparticles and oleogels

This study developed water-in-oil (W/O) Pickering emulsions stabilized by ethylcellulose (EC) nanoparticles and EC oleogels, which presented significantly improved freeze-thawing (F/T) stability. Microstructural observation suggested EC nanoparticles were distributed at the interface and within the water droplets, and the EC oleogel trapped oil in the continuous phase. Freezing and melting temperatures of water in the emulsions with more EC nanoparticles were lowered and the corresponding enthalpy values were reduced. F/T led to lower water binding capacity but higher oil binding capacity of the emulsions, compared to the initial emulsions. Low field-nuclear magnetic resonance confirmed the increased mobility of water but decreased mobility of oil in the emulsions after F/T. Both linear and nonlinear rheological properties proved that emulsions exhibited higher strength and higher viscosity after F/T. The widened area of the elastic and viscous Lissajous plots with more nanoparticles suggested the viscosity and elasticity of emulsions were increased.