Mean-Square Displacements of Polymers in Simulated Blend Melts

We apply numerical analysis to interpret reported simulations of polymer blend melts, in particular simulational determinations of mean-square displacements g(t) of polymer beads and polymer centers of mass. Our interest is a quantitative comparison of g(t) with theoretical models that predict g(t). Many models predict that g(t) can be described as a sequence of power-law regimes g(t)∼tα. In each regime, α has a model-predicted value. We find that these models are not consistent with simulations of blend melts. Instead, g(t) generally has a single power-law regime and (when those times are reached) a long-time diffusive (α≈1) regime. Outside these two regions, if one writes g(t)∼tα, then α is a smoothly-changing function of time.