Influence of stimulus-responsive swelling on suspension properties of ionic microgels*

Microgels can swell in response to environmental changes, enabling precise control over particle traits. Despite various models attempting to explain microgel swelling and its effects on bulk properties, a comprehensive theory linking microscopic behaviors to suspension properties remains a challenge.

In this work, we study theoretically the effects of swelling of weakly-crosslinked ionic microgels on bulk properties. By combining Poisson-Boltzmann theory for the electrostatic interactions with Flory theory for modeling polymer degrees of freedom, we present a theoretical model for swelling of stimulus-responsive microgels in dependence of concentrations, charge and pH. Our mean-field type calculations are corroborated with particle-based coarse-grained simulations in order to assess their accuracy and scope. Furthermore, we analyse the influence of different microgel architectures on swelling. With the help of density functional theory, we derive expressions for the microgel-microgel effective interactions for different architectures. We use the resulting mean-field effective pair potentials for analysing the impact of swelling on thermodynamic- and structural properties as well as on the phase behaviour. Our results are also compared with experimental results. This work provides a first-principle theoretical description that allows for an accurate characterisation of microgel suspensions, useful for an optimal synthesis and a trustworthy result interpretation.