Effective Interactions and Dynamical Properties of Thermoresponsive Hollow Microgels

Hollow microgels─polymer network shells─are soft colloids whose collective behavior is governed by their intrinsic network structure, their unique topology, and solvent quality. Here, we investigate the effective interactions and the dynamics of hollow microgel suspensions at different temperatures just below the volume phase transition. Despite the particles becoming mechanically stiffer as solvent quality worsens, the extracted effective interactions appear to be softer with increasing temperature. This counterintuitive behavior results from a decrease in monomer repulsion, consistent with a Hertzian description. Bulk simulations show that an effective fluid representation is very accurate in describing the structure of monomer-resolved systems, quantified by their radial distribution function, in an extended range of packing fractions well beyond random close packing. Instead, dynamical observables, such as self-diffusion coefficient and collective relaxation times, are only qualitatively captured, with a systematically faster dynamics observed in coarse-grained models due to the absence of internal degrees of freedom. These results identify hollow microgels as ideal elastic shells, interacting as Hertzian particles, well beyond the two-body regime, as opposed to standard microgels, where such an effective description is only valid in the fluid region of the phase diagram.