Quantifying Interfacial Tensions of Surface Nanobubbles: How Far Can Young’s Equation Explain?

Nanobubbles at solid-liquid interfaces play a key role in various physicochemical phenomena and it is crucial to understand their unique properties. However, little is known about their interfacial tensions due...

Endocytic proteins with prion-like domains form viscoelastic condensates that enable membrane remodeling

Membrane invagination and vesicle formation are key steps in endocytosis and cellular trafficking. Here, we show that endocytic coat proteins with prion-like domains (PLDs) form hemispherical puncta in the budding yeast, Saccharomyces cerevisiae. These puncta have the hallmarks of biomolecular condensates and organize proteins at the membrane for actin-dependent endocytosis. They also enable membrane remodeling to drive actin-independent endocytosis. The puncta, which we refer to as endocytic condensates, form and dissolve reversibly in response to changes in temperature and solution conditions. We find that endocytic condensates are organized around dynamic protein–protein interaction networks, which involve interactions among PLDs with high glutamine contents. The endocytic coat protein Sla1 is at the hub of the protein–protein interaction network. Using active rheology, we inferred the material properties of endocytic condensates. These experiments show that endocytic condensates are akin to viscoelastic materials. We use these characterizations to estimate the interfacial tension between endocytic condensates and their surroundings. We then adapt the physics of contact mechanics, specifically modifications of Hertz theory, to develop a quantitative framework for describing how interfacial tensions among condensates, the membrane, and the cytosol can deform the plasma membrane to enable actin-independent endocytosis.

Shear relaxation governs fusion dynamics of biomolecular condensates

Phase-separated biomolecular condensates must respond agilely to biochemical and environmental cues in performing their wide-ranging cellular functions, but our understanding of condensate dynamics is lagging. Ample evidence now indicates biomolecular condensates as viscoelastic fluids, where shear stress relaxes at a finite rate, not instantaneously as in viscous liquids. Yet the fusion dynamics of condensate droplets has only been modeled based on viscous liquids, with fusion time given by the viscocapillary ratio (viscosity over interfacial tension). Here we used optically trapped polystyrene beads to measure the viscous and elastic moduli and the interfacial tensions of four types of droplets. Our results challenge the viscocapillary model, and reveal that the relaxation of shear stress governs fusion dynamics. These findings likely have implications for other dynamic processes such as multiphase organization, assembly and disassembly, and aging.

Effects of Surfactant and Hydrophobic Nanoparticles on the Crude Oil-Water Interfacial Tension

Surfactants and nanoparticles play crucial roles in controlling the oil-water interfacial phenomenon. The natural oil-wet mineral nanoparticles that exist in crude oil could remarkably affect water-oil interfacial characteristics. Most of recent studies focus on the effect of hydrophilic nanoparticles dispersed in water on the oil-water interfacial phenomenon for the nanoparticle enhanced oil recovery. However, studies of the impact of the oil-wet nanoparticles existed in crude oil on interfacial behaviour are rare. In this study, the impacts of Span 80 surfactant and hydrophobic SiO2 nanoparticles on the crude oil-water interfacial characteristics were studied by measuring the dynamic and equilibrium crude oil-water interfacial tensions. The results show the existence of nanoparticles leading to higher crude oil-water interfacial tensions than those without nanoparticles at low surfactant concentrations below 2000 ppm. At a Span 80 surfactant concentration of 1000 ppm, the increase of interfacial tension caused by nanoparticles is largest, which is around 8.6 mN/m. For high Span 80 surfactant concentrations, the less significant impact of nanoparticles on the crude oil-water interfacial tension is obtained. The effect of nanoparticle concentration on the crude oil-water interfacial tension was also investigated in the existence of surfactant. The data indicates the less significant influence of nanoparticles on the crude oil-water interfacial tension at high nanoparticle concentration in the presence of Span 80 surfactant. This study confirms the influences of nanoparticle-surfactant interaction and competitive surfactant molecule adsorption on the nanoparticles surfaces and the crude oil-water interface.

Computational simulation a system of waterborne polyurethane matrix by β-C induction with ZnO and CaCO3 particles

This work includes the search for the development of a composite of a WPU (waterborne polyurethane), β-CD (β-Cyclodextrin), PZnO (zinc oxide particles), and the presence of CaCO3, to obtain new properties such as adhesion to multiple substrates of organic and inorganic origin. Therefore, a development sequence was proposed: Computational development: conformation of the polymeric matrix (with the intermediary polymers) and simulation of the interaction between β-CD and PZnO and Ca+2 and CO3-2 ions, as well as insertions in β-CD, computational simulations were carried out with the help of ACD LABS™ (free version) software and by molecular dynamics with GROMACS™. With the above, we were able to determine properties such as interfacial tensions, surface tensions, and contact angles, and degrees of solvation and stability in waterborne emulsions. Therefore, it is important to point out that one of the main contributions of this research proposal is that there are no studies that combine these materials.