Solvent-Mediated Forces between Ellipsoidal Nanoparticles Adsorbed at Liquid–Vapor Interfaces

Abstract

Classical capillary theory predicts that a non-neutrally wetting ellipsoidal particle adsorbed at a liquid–vapor interface will deform the interface. The deformation gives rise to anisotropic capillary forces of a quadrupolar nature that induce strong directionality in the particle interactions. Here, we investigate the interactions between nanoparticles with characteristic lengths of 1–5 nm. We show that the near-field interactions are dominated by solvent-mediated forces, which arise from the fluid packing between the nanoparticles and direct nanoparticle–nanoparticle interactions. The solvent-mediated forces are two orders of magnitude larger than the estimated capillary force. We find that interacting ellipsoidal nanoparticles adsorbed at the liquid–vapor interface have a larger repulsion in the depletion region than the nanoparticles submerged in a dense bulk phase and argue that this is because of a negative line tension associated with the three-phase line.

Legendre-Fenchel transforms capture layering transitions in porous media

“…Similarly, we observed that the grand potential of a fluid in a slit pore is a non-convex function of the distance between the parallel plates at constant chemical potential and temperature [3]. Also, the Helmholtz energy of solid colloids in solution is non-convex as a function of the controlled distance between the colloids, keeping the temperature, volume, and the number of particles constant [18]. Both cases can be explained by a disjoining pressure (also known as the solvation pressure) [19], which is the excess normal pressure relative to the bulk pressure due to the packing of fluid particles between the solids.…”

Legendre-Fenchel transforms capture layering transitions in porous media

“… 3 Also, the Helmholtz energy of solid colloids in solution is non-convex as a function of the controlled distance between the colloids, keeping the temperature, volume, and the number of particles constant. 18 Both cases can be explained by a disjoining pressure (also known as the solvation pressure), 19 which is the excess normal pressure relative to the bulk pressure due to the packing of fluid particles between the solids. The observations mentioned all stem from size effects.…”

Nanothermodynamic Description and Molecular Simulation of a Single-Phase Fluid in a Slit Pore

“…The thermodynamic state of a fluid in confinement is important for the understanding of adsorption to walls, chemical reactions, film formation and transport in porous media [ 1 , 2 , 3 , 4 , 5 , 6 ]. The molecular structuring at the walls and the forces between particles and walls are central.…”

“…Confinement is considered to be important, for instance, in the context of CO separation and sequestration by metal-organic frameworks [ 2 ] or for adsorption in zeolites [ 3 ]. The disjoining pressure is of interest when studying aggregation of colloidal particles, suspended or adsorbed [ 4 , 5 , 6 ]. It is likely to be important also for film flow on the macroscale [ 8 ].…”