Glassy Dynamics Of Two-dimensional Model Chains

The study of dynamics of polymer chains has been a hot topic in recent years. However, most studies consider chains in three dimensions. The topological interaction in two dimensions is completely different compared to the three dimensions case, thus the dynamic behavior of 2D chains could be totally different and interesting, but there has not been much work on it. In this paper, we use molecular dynamics simulation together with granular system experiment to investigate the dynamics of two-dimensional packing model chains.First, we investigated the dynamics of 2D polymer melts by means of molecular dynamics simulation. The glass transition was induced by increasing the packing fraction. As the glass transition approaches, the mean squared displacements of particles decrease and the plateau regime emerge. Also, the decay of the function Fs(q, t) slows down and the relaxation time dramatically increases and diverges. All the results show that the motions of particles are hold up at high densities, when the particles are trapped temporarily by their neighbors(the cage effect). Meanwhile the peak values of non-Gaussian parameter and four-point susceptibility become larger, which demonstrates the increment of dynamical heterogeneity and there is more particles take part in rearrangement. At last, we carefully studied the fast particles in the system and found that chain connectivity is not necessary for dynamical heterogeneity.Then, we used the air-fluidized granular bed system to study the dynamic of 2D granular chains experimentally. At the very beginning, we tested the relationship between mean squared end to end distance and chain length. The result conforms to the prediction of scaling law, which ensures the high reliability of the model system. As the density increases, the dynamics slow down and the relaxation time increases dramatically when approaching the glass transition point. Besides, we analyzed the four-point susceptibility of the system and found that the cooperative rearrangement strengthened close to the glass transition. The dynamic behavior of granular chains agrees well with the results obtained from the computer simulation. In conclusion, the two-dimensional model chains show great glassy dynamics as the system is approaching the glass transition point.