# A new look at effective interactions between microgel particles

## TL;DR

This study investigates the temperature-dependent effective interactions between microgel particles in suspensions, revealing complex behaviors influenced by internal architecture and proposing a multi-Hertzian model to unify their phase diagram behavior.

## Contribution

It introduces a multi-Hertzian interaction model that captures the complex, temperature-dependent behavior of microgel suspensions, surpassing simple Hertzian models.

## Key findings

- Microgel interactions are strongly temperature dependent.
- Mixtures of microgels show enhanced stability over hard colloids.
- The multi-Hertzian model accurately reproduces experimental results.

## Abstract

Thermoresponsive microgels find widespread use as colloidal model systems, because their temperature-dependent size allows facile tuning of their volume fraction "in situ". However, an interaction potential unifying their behavior across the entire phase diagram is sorely lacking. Here we investigate microgel suspensions in the fluid regime at different volume fractions and temperatures, and in the presence of another population of small microgels, combining confocal microscopy experiments and numerical simulations. We find that effective interactions between microgels are clearly temperature dependent. In addition, microgel mixtures possess an enhanced stability compared to hard colloid mixtures - a property not predicted by a simple Hertzian model. Based on numerical calculations we propose a multi-Hertzian model, which reproduces the experimental behaviour for all studied conditions. Our findings highlight that effective interactions between microgels are much more complex than usually assumed, displaying a crucial dependence on temperature and the internal core-corona architecture of the particles.