Organo-Bentonite-Coated Interfaces: Interfacial Properties and Cyclic Response

The accumulation of amphiphilic molecules, nanoparticles, or microorganisms at interfaces has important implications for multiphase flow in porous media. We optimize the composition of stable organo-bentonite suspensions to enhance particle adsorption onto the oil-water interface. Then, we use the pendant drop method to explore time-dependent effects on surface tension and the consequences of contraction-expansion cycles. Brownian motion brings organo-bentonite particles to the oil-water interface where they adsorb and accumulate to reduce the apparent interfacial tension in time. The adsorption energy of platy organo-bentonite particles is significantly higher than the adsorption energy of spherical nanoparticles of the same volume. Then, a shell-like interface develops after particle jamming during droplet contraction, and further contraction leads to shell buckling and wrinkle formation (rather than desorption). The shell-like interface experiences an anisotropic stress field and cannot be described by the Young-Laplace equation. The evolution of interfacial tension during contraction and expansion shows strong hysteresis; furthermore, the results suggest that the number of adsorbed particles at the interface increases with the number of cycles. Natural clay nanoparticles can facilitate the development of cost-effective and environmentally friendly alternatives for field-scale applications.