The Puzzle of Smart Polymers in Miscible Solvent Mixtures

Smart, stimuli responsive polymers pose challenges for our theoretical understanding. In this context the response to changes in relative solvent co-solvent concentration in solvent mixtures is of special interest. Polymers in perfectly miscible good solvents can collapse, while in mixed poor solvents they can expand. Specific relations between atomistic structure, architecture, molecular weight and material properties are of basic concern and the validity of generic models has been questioned. To shed more light on this, computer simulations on different levels of resolution play an increasingly important role. Typical examples of polymer solvation in mixed solvents are PNIPAM and PMMA in water alcohol mixtures. The first shows an interesting coil-globule-coil transition. This conformational transition cannot be explained within the classical Flory-Huggins picture, which is the standard mean field theory for polymer solutions and mixtures. The results point towards a general design concept of 'smart stimuli responsive polymers'. The second displays a weak swelling in a mixture of two miscible poor solvents. This swelling couples in a delicate way to the mixing properties of the solvents.
This work has been performed in a fruitful collaboration with mainly D. Mukherji (Mainz) and C. Marques (Strasbourg).
D. Mukherji, C. M. Marques, K. Kremer, Nat. Comm. 5, 4882 (2014)
D. Mukherji, M. Wagner, M. D. Watson, S. Winzen, T. E. de Oliveira, C. M. Marques, K. Kremer, Soft Matter 12, 7995—8003 (2016)
D. Mukherji, C. M. Marques, T. Stuehn, K. Kremer, Nat. Comm. (2017)