  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.
