Molecular dynamics simulation of polymer liquid and glass. I. Glass transition

Abstract

Molecular dynamics simulation of bulk liquid and glass oflong-chain molecules has been performed. The system consists of linear chains of up to 50 spherical segments, each subject to forces due to bond stretching, bending, and torsion, and to nonbonded interaction, according to a truncated Lennard-Jones potential, between segments in neighboring chains and between segments separated by more than three bonds along the chain. The parameters are chosen to mimic polymethylene, the segment representing a CH 2 unit. Behaviors suggestive of liquid-toglass transition were exhibited by (i) cessation of trans-gauche conformational transitions, (ii) changes in the temperature coefficients of the density and internal energy, and (iii) effective vanishing of the segmental self-diffusion coefficient. The "freezing in" of these properties occurs at decreasing temperatures in the order given above, indicating the decreasing size of domains of cooperative motion required. The dependence of the transition temperature on the chain length and on the flexibility of the chain (effected by switching of the torsional potential off) obtained is in accord with experimental observations. Below the transition temperature the system behavior depends on the path through which the state was reached, suggesting that simulation of relaxation effects could be achieved in longer runs.

Dynamics and rheology of a supercooled polymer melt in shear flow

“…Long time simulations of order 10 2 τ R , which corresponds to 10 9 MD steps for T = 0.2, were performed. In the previous simulations, 20,[23][24][25][28][29][30] however, the integrated times did not much exceed τ R in supercooled states.…”

“…[16][17][18][19] While the predictive power of analytic theories in polymer science is still poor, computer simulations [20][21][22] can provide us a useful tool to investigate the microscopic origins of experimentally observed macroscopic phenomena. In quiescent states, diffusive motions in supercooled melts have been extensively studied using molecular dynamics (MD) [23][24][25][26][27] and Monte Carlo 28-30 simulations. In another application, nonequilibrium molecular dynamics (NEMD) simulations have been useful to investigate chain deformations and rheology in flow.…”

Free energy calculations of small molecules in dense amorphous polymers. Effect of the initial guess configuration in molecular dynamics studies

“…21 A serious disadvantage of this method is the long time in which the dihedral angles relax towards their equilibrium values.…”

Polymer chain generation for coarse-grained models using radical-like polymerization

“…The objective of our contribution is to propose an innovative method for polymer chain generation, (i) based on a realistic approach close to radical polymerisation [3,4]; (ii) particularly adapted to generate non linear architec- * Email: fabien.leonforte@insa-lyon.fr tures (branched polymers, star polymers, copolymers,...) and/or polydisperse chains; (iii) providing equilibrated melts.…”