Two-step deswelling in the Volume Phase Transition of thermoresponsive microgels

Abstract

Thermoresponsive microgels are one of the most investigated class of soft colloids, thanks to their ability to undergo a Volume Phase Transition (VPT) close to ambient temperature. However, this fundamental phenomenon still lacks a detailed microscopic understanding, particularly regarding the presence and the role of charges in the deswelling process. Here we fill this gap by combining experiments and 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 several microgels with different cross-linker concentrations, charge contents and charge distributions, we build a unifying master-curve able to predict the two-step deswelling. Our results have direct relevance on fundamental soft condensed matter science and on microgel applications ranging from materials to biomedical technologies.

Microgels as Smart Polymer Colloids for Sensing and Environmental Remediation

“…208,209 In general, several interactions such as hydrogen bonding, hydrophobic interaction, electrostatic interaction, and coordination bonding with metals simultaneously contribute in the heavy metal ions and dye adsorption process. 210,211 Therefore, the adsorption capacity or elimination efficiency of PNIPAM microgel can be influenced by the two factors, (i) the consequence of various interaction forces between pollutants and microgels and (ii) volume phase transition temperature (VPTT).…”