Self-assembled nanoparticle-coated interfaces: Capillary pressure, shell formation and buckling

Hypothesis: Particle accumulation at liquid-liquid or liquid-gas interfaces can significantly alter capillary behavior and give rise to unusual interfacial phenomena including the asymmetric macroscopic mechanical response of the interface. Experiments: This study explores the accumulation of cetyltrimethylammonium bromide-modified nanoparticles at fluid interfaces and the subsequent mechanical response of nanoparticle-coated droplets during contraction and expansion. Droplet tests involve the simultaneous recording of the droplet shape and the capillary pressure. Complementary single-pore experiments examine the response of particle-coated interfaces as they traverse a pore constriction. Findings: Interfaces promote order. The time-dependent nanoparticle accumulation at the interface is diffusion-controlled. The nanoparticle coated droplets can sustain negative capillary pressure before they buckle. Buckling patterns strongly depend on the boundary conditions: non-slip boundary conditions lead to crumples while slip boundary conditions result in just a few depressions. The particle-coated interface exhibits asymmetric behavior in response to particle-level capillary forces: an oil droplet in a nanofluid bath withstands a significantly higher capillary pressure difference than a nanofluid droplet in an oil bath. A first-order equilibrium analysis of interaction forces explains the asymmetric response. Single-constriction experiments show that the formation of particle-coated interfaces has a pronounced effect on fluid displacement in porous media. (C) 2020 The Author(s). Published by Elsevier Inc.

Automated summary

This study investigates the impact of nanoparticle accumulation at fluid interfaces on capillary behavior and interfacial phenomena, revealing asymmetric responses of particle-coated droplets under different conditions.