Dr. Debashish Mukherji, Max-Planck Institut für Polymerforschung, Ackermannweg 10, 55128 Mainz Germany

Biography: Debashish Mukherji is a Computational Soft Matter Physicist. He studied Physics at the Banaras Hindu University, India, completing a Masters degree. For his doctoral studies he moved to the University of Western Ontario, Canada. He was then appointed as a research associate within the Army Material Center of Excellence at Drexel University, USA. In September 2010, he joined the theory group of the Max Planck Institute for Polymer Research in Mainz, Germany, where he is currently working as a scientist.
His research is concerned with the large-scale molecular dynamics Simulations of soft matter properties. Within this field, he is involved in the development of the scale-bridging (grand canonical) multiscale methods and coarse-grained models for bio-inspired complex systems. He applies these methods to systems, which include understanding macromolecular solvation, polymer friction under strong geometric confinements and structure-function relationship of nano-composites. [More details about his research can be found on his personal website at http://www2.mpip-mainz.mpg.de/~mukherji/

Speech Title: The puzzle of polymer solvation in mixed good and mixed poor solvent mixtures
Abstract: Smart polymers are a modern class of soft materials that show drastic changes in their structure, function, and stability by a slight change in external stimuli. This talk will address two opposite (yet related) paradoxical phenomena of polymers in mixed solvent environment, specifically the cases of PNIPAM and PMMA in water alcohol mixtures. The first system reveals an interesting coil-globule-coil transition, also known as co-non-solvency. Co-non-solvency occurs when a polymer is added in two (perfectly) miscible and competing good solvents. As a result, the same polymer collapses into a globule within intermediate mixing ratios [1]. More interestingly, polymer collapses when the solvent quality remains good or even gets increasingly better by the addition of the better cosolvent [2]. This puzzling phenomenon, where the solvent quality is completely decoupled from the polymer conformation, is driven by strong local preferential adsorption of better cosolvent with the polymer [1-3]. Because a polymer collapses in good solvent, depletion forces, that are responsible for standard poor solvent collapse, do not play any role in describing co-non-solvency [4]. However, a case where depletion forces do play a significant role is when a polymer swells in a mixture of two competing poor solvents [5]. This swelling can be explained by the reduction of depletion induced attraction resulting from a delicate interplay between the local depletion effects and the bulk solution density. Furthermore, it will be presented that both these phenomena can be understood within universal (generic) concepts. Therefore, the specific chemical details do not play any role in understanding these complex conformational behaviors and thus a broad range of polymers is expected to exhibit these phenomena [6].

References:
[1]D. Mukherji and K. Kremer, Macromolecules 46, 9158 (2013).
[2]D. Mukherji, C. M. Marques, and K. Kremer, Nature Communications 5, 4882 (2014).
[3]D. Mukherji, M. Wagner, M. D. Watson, S. Winzen, T. E. de Oliveira, C. M. Marques, and K. Kremer, Soft Matter 12 7995 (2016).
[4]T. E. de Oliviera, P. A. Netz, D. Mukherji, and K. Kremer, Soft Matter 11 8599 (2015).
[5]D. Mukherji, C. M. Marques, T. Stuehn and K. Kremer, submitted (https://arxiv.org/abs/1609.09839).
[6] D. Mukherji, C. M. Marques, T. Stuehn and K. Kremer, Journal of Chemical Physics 142, 114903 (2015)