Depleted depletion drives polymer swelling in poor solvent mixtures

• Published in: Nature communications Vol. 8; no. 1; pp. 1374 - 7
• Main Authors: Mukherji, Debashish, Marques, Carlos M., Stuehn, Torsten, Kremer, Kurt
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 09.11.2017; Nature Publishing Group; Nature Portfolio
• Subjects: 639/301/923/1028; 639/301/923/916; 639/766/94; Alcohols; Collapse; Conformation; Depletion; Humanities and Social Sciences; Macromolecules; multidisciplinary; Particle interactions; Physics; Polymer physics; Polymers; Polymethyl methacrylate; Polymethylmethacrylate; Science; Science (multidisciplinary); Solvation; Solvents; Swelling
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-017-01520-5

Establishing a link between macromolecular conformation and microscopic interaction is a key to understand properties of polymer solutions and for designing technologically relevant “smart” polymers. Here, polymer solvation in solvent mixtures strike as paradoxical phenomena. For example, when adding polymers to a solvent, such that all particle interactions are repulsive, polymer chains can collapse due to increased monomer–solvent repulsion. This depletion induced monomer–monomer attraction is well known from colloidal stability. A typical example is poly(methyl methacrylate) (PMMA) in water or small alcohols. While polymer collapse in a single poor solvent is well understood, the observed polymer swelling in mixtures of two repulsive solvents is surprising. By combining simulations and theoretical concepts known from polymer physics and colloidal science, we unveil the microscopic, generic origin of this collapse–swelling–collapse behavior. We show that this phenomenon naturally emerges at constant pressure when an appropriate balance of entropically driven depletion interactions is achieved. Whilst polymer collapse in a single poor solvent is well understood, polymer swelling in mixtures of two repulsive solvents is surprising. Here, the authors unveil the microscopic origin of collapse-swelling-collapse behaviour, showing how it emerges at constant pressure when a balance of depletion interactions is achieved.