Electrostatic interactions reshape the internal architecture of ionic microgels

Incorporating ionic co-monomers into polymer microgels can alter their swelling behavior and introduce pH-responsiveness; however, their effect on the internal microgel structure remains poorly understood. Here we present a comprehensive study of poly(N-isopropylacrylamide-co-acrylic acid) microgels, revealing that the incorporation of ionic groups significantly alters their internal architecture. Using dynamic and static light scattering combined with small-angle X-ray scattering, we observe pronounced differences in form factors and swelling behavior between neutral and ionic microgels. These findings can be rationalized by monomer-resolved simulations, which reproduce the experimental form factors only when charge-induced alterations to the network architecture are explicitly accounted for during in silico synthesis. Our results demonstrate that electrostatic interactions modulate not only the swelling behavior but also the internal monomer density profile, highlighting the need to integrate and extend current modeling approaches for charged microgels.