Entropic Trapping of Particles at Polymer Surfaces and Interfaces

TL;DR

This paper explores how Gaussian random walk statistics can explain the entropic trapping of nanoscopic particles at polymer surfaces and interfaces, highlighting the roles of enthalpic and entropic surface energy contributions in particle positioning.

Contribution

It introduces a model based on Gaussian random walk statistics to describe particle trapping at polymer surfaces, emphasizing the balance of enthalpic and entropic surface energy effects.

Findings

Entropic effects relax when particles reach the surface.

The model predicts the equilibrium wetting angle based on surface energies.

Experimental measurement of the wetting angle can separate enthalpic and entropic contributions.

Abstract

I consider the possibility that Gaussian random walk statistics are sufficient to trap nanoscopic additives at either a polymer interface or surface. When an additive particle goes to the free surface, two portions of the polymer surface energy behave quite differently. The purely enthalpic contribution increases the overall free energy when the additive protrudes above the level of the polymer matrix. The entropic part of the surface energy arising from constraints that segments near a surface can't cross it, is partly relaxed when the additive moves to the free surface. These two portions of the polymer surface energy determine the equilibrium wetting angle formed between the additive and the polymer matrix, the measurement of which in an experiment would allow an independent determination of each piece of the polymer surface energy.