The surface diffusivity of nanoparticles physically adsorbed at a solid-liquid interface.

This work proposes an analytical model considering the effects of hydrodynamic drag and kinetic barriers induced by liquid solvation forces to predict the translational diffusivity of a nanoparticle on an adsorbing surface. Small nanoparticles physically adsorbed to a well-wetted surface can retain significant in-plane mobility through thermally activated stick-slip motion, which can result in surface diffusivities comparable to the bulk diffusivity due to free-space Brownian motion. Theoretical analysis and molecular dynamics simulations in this work show that the surface diffusivity is enhanced when (i) the Hamaker constant is smaller than a critical value prescribed by the interfacial surface energy and particle dimensions, and (ii) the nanoparticle is adsorbed at specific metastable separations of molecular dimensions away from the wall.

Kinetic trapping of nanoparticles by solvent-induced interactions.

Theoretical analysis based on mean field theory indicates that solvent-induced interactions ( structural forces due to the rearrangement of wetting solvent molecules) not considered in DLVO theory can induce the kinetic trapping of nanoparticles at finite nanoscale separations from a well-wetted surface, under a range of ubiquitous physicochemical conditions for inorganic nanoparticles of common materials (, metal oxides) in water or simple molecular solvents. This work proposes a simple analytical model that is applicable to arbitrary materials and simple solvents to determine the conditions for direct particle-surface contact or kinetic trapping at finite separations, by using experimentally measurable properties (, Hamaker constants, interfacial free energies, and nanoparticle size) as input parameters. Analytical predictions of the proposed model are verified by molecular dynamics simulations and numerical solution of the Smoluchowski diffusion equation.

Toward controlling wetting hysteresis with nanostructured surfaces derived from block copolymer self-assembly.

The synthesis of nanostructured surfaces via block copolymer (BCP) self-assembly enables a precise control of the surface feature shape within a range of dimensions of the order of tens of nanometers. This work studies how to exploit this ability to control the wetting hysteresis and liquid adhesion forces as the substrate undergoes chemical aging and changes in its intrinsic wettability. Via BCP self-assembly we fabricate nanostructured surfaces on silicon substrates with a hexagonal array of regular conical pillars having a fixed period (52 nm) and two different heights (60 and 200 nm), which results in substantially different lateral and top surface areas of the nanostructure.

The effects of surface hydration on capillary adhesion under nanoscale confinement.

Nanoscale phenomena such as surface hydration and the molecular layering of liquids under strong nanoscale confinement play a critical role in liquid-mediated surface adhesion that is not accounted for by available models, which assume a uniform liquid density with or without considering surface forces and associated disjoining pressure effects. This work introduces an alternative theoretical description that the potential of mean force (PMF) considers the strong spatial variation of the liquid number density under nanoscale confinement. This alternative description based on the PMF predicts a dual effect of surface hydration by producing: (i) strong spatial oscillations of the local liquid density and pressure and, more importantly, (ii) a configuration-dependent liquid-solid surface energy under nanoscale confinement.