Polymeric Solvents Control Swelling-Induced Surface Creasing

TL;DR

This study demonstrates that the polymerization degree of solvents can independently control surface creasing in swollen polymer gels, revealing a new thermodynamic-mechanical regulation mechanism.

Contribution

It introduces the role of solvent polymerization degree as an independent parameter influencing surface creasing in swollen gels, supported by a coupled thermodynamic-mechanical theory.

Findings

Increasing solvent polymerization degree suppresses surface creasing.

Theoretical model accurately predicts the stability boundary for creasing.

Polymeric solvents modify osmotic pressure, affecting surface stability.

Abstract

Surface creasing in swelling polymer gels is commonly attributed to compressive strain or interlayer mismatch, yet its general control remains unclear. Here we show that solvent polymerization degree $N_{\rm s}$ provides an independent control parameter for crease onset in surface-bound polydimethylsiloxane gels swollen by silicone oils. Despite nearly identical swelling kinetics and through-thickness solvent concentration profiles, we observe a transition from creased to stable surfaces with increasing $N_{\rm s}$. A theory coupling swelling thermodynamics and mechanical stability reveals that polymeric solvents reduce the mixing entropy and thereby modify the osmotic pressure, allowing $N_{\rm s}$ to tune separately the equilibrium swelling and the crease threshold. This framework captures the stability boundary across solvent polymerization degree and network elasticity. These results identify polymeric solvents as active thermodynamic-mechanical regulators of swelling-induced surface.