We present a numerical study of the slip link model introduced by Likhtman for describing the dy- namics of dense polymer melts. After reviewing the technical aspects associated with the implemen- tation of the model, we extend previous work in sever
al directions. The dependence of the relaxation modulus with the slip link density and the slip link stiffness is reported. Then the nonlinear rheolog- ical properties of the model, for a particular set of parameters, are explored. Finally, we introduce excluded volume interactions in a mean field such as manner in order to describe inhomogeneous systems, and we apply this description to a simple nanocomposite model. With this extension, the slip link model appears as a simple and generic model of a polymer melt, that can be used as an alternative to molecular dynamics for coarse grained simulations of complex polymeric systems.
We investigate the problem of heat conduction across a molecular junction connecting two nanoparticles, both in vacuum and in a liquid environment, using classical molecular dynamics simulations. In vacuum, the well-known result of a length independe
nt conductance is recovered; its precise value, however, is found to depend sensitively on the overlap between the vibrational spectrum of the junction and the density of states of the nanoparticles that act as thermal contacts. In a liquid environment, the conductance is constant up to a crossover length, above which a standard Fourier regime is recovered.
We investigate various possible definitions of an effective temperature for a particularly simple nonequilibrium stationary system, namely a heated Brownian particle suspended in a fluid. The effective temperature based on the fluctuation dissipation
ratio depends on the time scale under consideration, so that a simple Langevin description of the heated particle is impossible. The short and long time limits of this effective temperature are shown to be consistent with the temperatures estimated from the kinetic energy and Einstein relation, respectively. The fluctuation theorem provides still another definition of the temperature, which is shown to coincide with the short time value of the fluctuation dissipation ratio.
