Diverse Spreading Behavior of Binary Polymer Nanodroplets

TL;DR

This study uses molecular dynamics simulations to explore how binary polymer nanodroplets spread on surfaces, revealing how differences in surface interaction and chain length influence wetting behavior and spreading dynamics.

Contribution

It provides new insights into the spreading behavior of binary polymer nanodroplets, highlighting the effects of chain length and surface interaction strength on wetting and film formation.

Findings

More strongly wetting component forms a monolayer film.

Short and long chains coexist in the precursor foot.

Dilution of wetting component slows spreading rate.

Abstract

Molecular dynamics simulations are used to study the spreading of binary polymer nanodroplets in a cylindrical geometry. The polymers, described by the bead-spring model, spread on a flat surface with a surface-coupled Langevin thermostat to mimic the effects of a corrugated surface. Each droplet consists of chains of length 10 or 100 monomers with ~350,000 monomers total. The qualitative features of the spreading dynamics are presented for differences in chain length, surface interaction strength, and composition. When the components of the droplet differ only in surface interaction strength, the more strongly wetting component forms a monolayer film on the surface even when both materials are above or below the wetting transition. In the case where the only difference is the polymer chain length, the monolayer film beneath the droplet is composed of an equal amount of short chain and long chain monomers even when one component (the shorter chain length) is above the wetting transition and the other is not. The fraction of short and long chains in the precursor foot depends on whether or not both the short and long chains are in the wetting regime. Diluting the concentration of the strongly wetting component in a mixture with a weakly wetting component decreases the rate of diffusion of the wetting material to the surface and limits the spreading rate of the precursor foot, but the bulk spreading rate is not affected until the more strongly wetting component is removed completely.