Molecular dynamics simulation of a two-dimensional polymer melt

A melt of two-dimensional polymer chains was simulated by molecular dynamics. A chain consisting of particles linked by elastic strings (bonds) was used as a model. The interaction of the particles was described by the modified Lennard-Jones potential, which accounts only for the repulsion of particles. Melts of chains consisting of N=20-60 units were modeled. The chains in a melt are collapsed and segregated. The average square sizes of chains are proportional to N and the distribution function of the end-to-end distances of chains is close to Gaussian. In the range of displacements smaller than the gyration radius, the time dependences of the average square displacements of monomers are characterized by a slope slightly larger, 1/2, than that typical of the Rouse model. As in the case of the Rouse model, the relaxation time of the kth normal mode of chains is proportional to (N + 1)(2)/k(2). However, the diffusion of a chain as a whole is slightly faster than that predicted by the Rouse model. The characteristics of the local and global orientational mobilities of chains were also calculated.