Two-step deswelling in the Volume Phase Transition of thermoresponsive microgels
Giovanni Del Monte, Domenico Truzzolillo, Fabrizio Camerin, Andrea Ninarello, Edouard Chauveau, Letizia Tavagnacco, Nicoletta Gnan, Lorenzo Rovigatti, Simona Sennato, Emanuela Zaccarelli
Abstract
-isopropylacrylamide)-based microgels, where the constituent monomers are neutral but charged groups arise due to the initiator molecules used in the synthesis. Here, we address this point combining experiments with state-of-the-art simulations to show that the microgel collapse does not happen in a homogeneous fashion, but through a two-step mechanism, entirely attributable to electrostatic effects. The signature of this phenomenon is the emergence of a minimum in the ratio between gyration and hydrodynamic radii at the VPT. Thanks to simulations of microgels with different cross-linker concentrations, charge contents, and charge distributions, we provide evidence that peripheral charges arising from the synthesis are responsible for this behavior and we further build a universal master curve able to predict the two-step deswelling. Our results have direct relevance on fundamental soft condensed matter science and on applications where microgels are involved, ranging from materials to biomedical technologies.