Extent of Nonequilibrium Sets Relaxation Barriers in Dewetting Polymer Films.

Abstract

Thin polymer films are archetypal nonequilibrium systems in which chain conformations are frozen by rapid preparation. The resulting molecular recoiling stress drives the system toward equilibrium and relaxes with time and temperature. We show that the activation energy governing this relaxation depends on the magnitude of the stress, revealing that polymers farther from equilibrium must overcome higher barriers, while stress release enables relaxation through progressively easier pathways. This stress-dependent evolution of activation barriers reflects a balance between energetic and entropic contributions and departs from the behavior typically observed for segmental mobility. Our experimental trends are quantitatively captured by the collective small displacements framework, consistent with recent observations of analogous relaxation behavior in adsorption-desorption, surface crystallization, and dipole reorientation. Our findings establish a direct link between nonequilibrium induced stress and molecular mobility, uncovering a general mechanism by which molecules reorganize toward equilibrium through localized, correlated motions.