# Reversible Formation of Thermoresponsive Binary Particle Gels with Tunable Structural and Mechanical Properties

## TL;DR

This study explores how binary microgel gels can be reversibly formed with tunable structures and mechanics by controlling heating profiles, revealing new insights into their formation, aging, and property modulation.

## Contribution

It introduces a method to control the structure and mechanical properties of binary microgel gels through temperature-dependent gelation and aging processes.

## Key findings

- Slow heating produces core-shell networks
- Fast heating results in random binary networks
- Aging influences final gel properties

## Abstract

We investigate the collective behavior of suspended thermoresponsive microgels, that expel solvent and subsequently decrease in size upon heating. Using a binary mixture of differently thermoresponsive microgels, we demonstrate how distinctly different gel structures form, depending on the heating profile used. Confocal laser scanning microscopy (CLSM) imaging shows that slow heating ramps yield a core-shell network through sequential gelation, while fast heating ramps yield a random binary network through homo-gelation. Here, secondary particles are shown to aggregate in a monolayer fashion upon the first gel, which can be qualitatively reproduced through Brownian dynamics simulations using a model based on a temperature-dependent interaction potential incorporating steric repulsion and van der Waals attraction. Through oscillatory rheology it is shown that secondary microgel deposition enhances the structural integrity of the previously formed single species gel, and the final structure exhibits higher elastic and loss moduli than its compositionally identical homo-gelled counterpart. Furthermore, we demonstrate that aging processes in the scaffold before secondary microgel deposition govern the final structural properties of the bigel, which allows a detailed control over these properties. Our results thus demonstrate how the temperature profile can be used to finely control the structural and mechanical properties of these highly tunable materials.