Elastocapillary interactions of thermoresponsive microgels across the volume phase transition temperatures

Effective interactions of thermoresponsive microgels are known to be influenced by their volume phase transition. These soft colloids behave as repulsive spheres in the swollen state but show strong attraction in the collapsed state. We hypothesize that this transition in microgel interactions is governed by the interplay between surface tension and bulk elasticity.

Using dissipative particle dynamics, we modeled the interactions between two coarse-grained microgel particles having a lower critical solution temperature around 32 °C, which are suspended in an explicit solvent. The potentials of mean force between microgels with different crosslinking densities were systematically characterized in the temperature range of 12-58 °C across the volume phase transition from steered molecular dynamics simulation trajectories.

The detailed dynamics of interaction is uncovered for microgels in different states. The simulations reveal the formation of capillary bridges between collapsed microgels at high temperatures, which contributes to strong attraction at contact. An elastocapillary model based on interface thermodynamics is proposed to describe microgel interactions and accurately predicts simulation data in a wide range of temperatures and overlapping distances. The results provide important physical insights into effective interactions between soft colloids that underpin broad applications of stimuli-responsive microgels.