Poly(<i>N</i>‑isopropylacrylamide) Microgels under Alcoholic Intoxication: When a LCST Polymer Shows Swelling with Increasing Temperature

Poly­(<i>N</i>-isopropylacrylamide) (PNIPAM) microgel is a smart polymer that shows a volume phase transition temperature (VPTT) at around 32 °C in aqueous solutions, above which it collapses. In this work, combining experiments and molecular simulations, it is shown that PNIPAM microgels do not always exhibit a collapsed structure above the VPTT. Instead, PNIPAM in aqueous alcohol mixtures shows a two-step conformational transition, i.e., a collapse at low temperatures (<i>T</i> < 32 °C) and a reswelling when <i>T</i> > 50 °C. The present analysis indicates that delicate microscopic interaction details, together with the bulk solution properties, play a key role in dictating the reswelling behavior. Even when PNIPAM microgels swell with increasing <i>T</i>, this is not a standard upper critical solution behavior.