Interactions between colloids induced by a soft cross-linked polymer substrate

TL;DR

This study reveals how soft cross-linked polymer substrates induce tunable, short-range equilibrium attractions between colloids, leading to aggregation, with potential control via substrate stiffness and surface coatings.

Contribution

It demonstrates the existence of tunable colloid-colloid interactions mediated by soft polymer gels and correlates these with colloid-surface attractions.

Findings

Colloids exhibit short-range equilibrium attraction on soft gels.

Interaction strength can be tuned by gel stiffness and coatings.

Soft substrates induce large-scale colloidal aggregation.

Abstract

Using video-microscopy imaging we demonstrate the existence of a short-ranged equilibrium attraction between heavy silica colloids diffusing on soft surfaces of cross-linked polymer gels. The inter-colloid potential can be tuned by changing the gel stiffness or by coating the colloids with a polymer layer. On sufficiently soft substrates, the interaction induced by the polymer matrix leads to large-scale colloidal aggregation. We correlate the in-plane interaction with a colloid-surface attraction.