SMP & Maths Seminar: Chi parameters from simulations

Professor Scott Milner, the Joyce Chair and Professor of Chemical Engineering, Penn State University, USA, will be presenting his research at an open seminar.

The Flory–Huggins χ parameter describes the excess free energy of mixing and governs phase behaviour for polymer blends and block copolymers. For chemically distinct nonpolar polymers, χ is dominated by mismatch in cohesive energy density. For chemically similar polymers, the entropic part of χ arising from non-ideal packing can be significant. To investigate this, we perform molecular dynamic (MD) simulations for bead-spring chains differing only in stiffness. Using thermodynamic integration, we extract χ as low as 10^-4 per monomer, in good agreement with field-theory based predictions of Fredrickson et al. We also obtain χ for the archetypical coarse-grained model of enthalpic polymer blends: flexible bead-spring chains with different LJ interactions between A and B monomers. Using this χ and self-consistent field theory (SCFT), we predict the interfacial profile for phase-separated binary blends, in good agreement with MD simulations for immiscible blends. Extended to atomistic simulations, our method can predict χ for polymer blends from chemical structures.

For more information please contact Dr Mamatha Nagaraj or Dr Daniel Read.