(290a) Semi-Grand Canonical Monte Carlo (Sgmc) Simulations to Interpret Non-Equilibrium Polymer Melt Experiments

Application of the Semi-Grand Canonical Monte Carlo (SGMC) method is described for the atomistic scale interpretation of experimental data taken from polymer melts under non-equilibrium conditions. Closure of this inverse problem is achieved by selecting the lowest-free-energy ensemble of configurations that reproduces the experimental data. This free energy of this ensemble is calculated using a new thermodynamic potential defined by the specific semi-grand (SG) ensemble used to incorporate the experimental data. We apply the method to the case of uniaxially oriented polymer melts, which we simulate in the re-weighted [NPT] ensemble for systems of average chain length C₂₄ and C₇₈. We show how the method can be applied to birefringence or Small Angle Neutron Scattering (SANS) measurements to characterize features of the system not explicitly measured by those methods. Such features include, for example, the density, torsion distributions, mesoscale orientation and work of deformation. This allows us to understand more fully the underlying features of these non-equilibrium states and to assess quantitatively the differences between particular models and experimental data.