Tuning the receding contact angle on hydrogels by addition of particles

TL;DR

This study explores how adding particles to hydrogels influences contact line pinning and receding contact angles, revealing that particles increase pinning force and alter absorption dynamics.

Contribution

It introduces an experimental investigation of particle effects on hydrogel contact line behavior and develops a method to measure receding contact angles considering swelling.

Findings

Particles increase contact line pinning force.

Higher particle concentration prolongs the pinned regime.

Particles decrease total absorption time.

Abstract

Control of the swelling, chemical functionalization, and adhesivity of hydrogels are finding new applications in a wide range of material systems. We investigate experimentally the effect of adsorbed particles on hydrogels on the depinning of contact lines. In our experiments, a water drop containing polystyrene microspheres is deposited on a swelling hydrogel, which leads to the drop absorption and particle deposition. Two regimes are observed: a decreasing drop height with a pinned contact line followed by a receding contact line. We show that increasing the particles concentration increases the duration of the first regime and significantly decreases the total absorption time. The adsorbed particles increase the pinning force at the contact line. Finally, we develop a method to measure the receding contact angle with the consideration of the hydrogel swelling.