Co-non-solvency: Mean-field polymer theory does not describe polymer collapse transition in a mixture of two competing good solvents

摘要

Smart polymers are a modern class of polymeric materials that often exhibitunpredictable behavior in mixtures of solvents. One such phenomenon isco-non-solvency. Co-non-solvency occurs when two (perfectly) miscible andcompeting good solvents, for a given polymer, are mixed together. As a result,the same polymer collapses into a compact globule within intermediate mixingratios. More interestingly, polymer collapses when the solvent quality remainsgood and even gets increasingly better by the addition of the better cosolvent.This is a puzzling phenomenon that is driven by strong local concentrationfluctuations. Because of the discrete particle based nature of theinteractions, Flory-Huggins type mean field arguments become unsuitable. Inthis work, we extend the analysis of the co-non-solvency effect presentedearlier [Nature Communications 5, 4882 (2014)]. We explain why co-non-solvencyis a generic phenomenon that can be understood by the thermodynamic treatmentof the competitive displacement of (co)solvent components. This competition canresult in a polymer collapse upon improvement of the solvent quality. Specificchemical details are not required to understand these complex conformationaltransitions. Therefore, a broad range of polymers are expected to exhibitsimilar reentrant coil-globule-coil transitions in competing good solvents.