Poly(N-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 (T < 32 °C) and a reswelling when T > 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 T, this is not a standard upper critical solution behavior.

中文翻译：

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酒精中毒下的聚（N-异丙基丙烯酰胺）微凝胶：当 LCST 聚合物随着温度升高而膨胀时

聚 ( N-异丙基丙烯酰胺) (PNIPAM) 微凝胶是一种智能聚合物，在水溶液中的体积相变温度 (VPTT) 约为 32 °C，高于此温度就会塌陷。在这项工作中，结合实验和分子模拟，表明 PNIPAM 微凝胶在 VPTT 上方并不总是表现出塌陷结构。相反，水性醇混合物中的 PNIPAM 显示出两步构象转变，即在低温 ( T < 32 °C) 下塌陷和在T > 50 °C 时再膨胀。目前的分析表明，精细的微观相互作用细节以及整体溶液特性在决定再膨胀行为中起关键作用。即使 PNIPAM 微凝胶随着T的增加而膨胀，这不是标准的上临界解决方案行为。