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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 46: Poster II

CPP 46.56: Poster

Donnerstag, 12. März 2026, 09:30–11:30, P5

Demystifying the decoupling of conformation and phase behavior in PNIPAM cononsolvency — •Ved Mahajan and Nico F. A. van der Vegt — Department of Chemistry, Technical University of Darmstadt

Cononsolvency describes the situation in which a polymer becomes insoluble in a mixture of two individually good solvents. PNIPAM, a widely studied thermoresponsive polymer, exhibits a strong coupling between its temperature-driven coil-globule transition and its phase behavior at low methanol concentrations; however, these two responses decouple as the methanol content increases. In this work, we use a minimal physical model, a hydrophobic polymer in water-methanol mixtures, that reproduces these key experimental observations. Despite its simplicity, the model captures both the emergence of cononsolvency and the crossover from coupled to decoupled thermal responses. At low methanol concentration, the polymer conformation remains temperature dependent, whereas at high methanol concentration, it becomes insensitive to temperature. In contrast, hydrophobic aggregation consistently strengthens with increasing temperature. Together, these results reveal a simple mechanism for the observed decoupling: the differing temperature sensitivities of polymer collapse and hydrophobic aggregation, both rooted in the hydrophobic effect.

Keywords: Cononsolvency; PNIPAM; Coil-Globule transition; Phase separation; Hydrophobic effect