Molecular dynamics polymer configuration

Molecular dynamics, in contrast to MC simulations, is a typical model in which hydrodynamic effects are incorporated in the behavior of polymer solutions and may be properly accounted for. In the so-called nonequilibrium molecular dynamics method [54], Newton s equations of a (classical) many-particle problem are iteratively solved whereby quantities of both macroscopic and microscopic interest are expressed in terms of the configurational quantities such as the space coordinates or velocities of all particles. In addition, shear flow may be imposed by the homogeneous shear flow algorithm of Evans [56]. 

Fig. 14.10 Chain configurations from a nonisothermal deformation simulation. From top to bottom, the images were taken at 374, 368, 364, 360 K, and 290K, corresponding to 7.6, 8.2, 8.6, 9.0, and 16.0 ns. [Reprinted by permission from M. C. Levine, N. Waheed, and G. C. Rutledge, Molecular Dynamics Simulation of Orientation and Crystallization of Polyethylene during Uniaxial Extension, Polymer, 44, 1771-1779, (2003).]...

Clarke and co-workers studied the effect of chain configurational properties on the stress—strain behavior of glassy linear polymers. They examined the relationship between chain structure and strain hardening by employing controlled stress molecular dynamics on a polyethylenelike chain. Variation of the sample preparation history produces chemically identical materials with vastly different responses to applied stress. 

A good example of results from a molecular dynamics simulation of entangled polymers is shown in Fig. 9.29. The 40 configurations of the chain shown are equally spaced in time up to the Rouse time of the chain. The chain is clearly confined to a tube-like region, with only the ends of the chain beginning to explore the rest of the volume. 

Molecular dynamics simulation of a chain with N = 400 monomers in an entangled polymer melt. Forty configurations of the chain are shown at equally spaced time intervals up to the Rouse time of the chain. Picture---------... 

Here, we consider a molecular dynamics method to sample configurations of the above isomorphic polymers. First, we define the following classical Hamiltonian ... 

Potential impact of rotator phase on crystallization. Molecular dynamics simulations have been carried out to study the conformational defects in the orientationally ordered structures of short-chain molecules and polymer chains. The simulation showed the creation of orientationally ordered structures from a random coil configuration by cooling from the melt. The longer chains exhibit folding with double gauche defects with the same sign ( tg( + )g( + )t. . . ) predominantly located at the chain ends and the kink... 

A major challenge in polymer simulations is to produce a large number of uncorrelated configurations, to sample various chain conformations. In molecular dynamics, each time step involves small changes in the monomer positions. Significantly changing the chain conformation involves large... 

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