Polymer-specific effects of bulk relaxation and stringlike correlated motion in the dynamics of a supercooled polymer melt

Abstract

We analyze dynamical heterogeneities in a simulated ''bead-spring'' model of a nonentangled, supercooled polymer melt. We explore the importance of chain connectivity on the spatially heterogeneous motion of the monomers. We find that when monomers move, they tend to follow each other in one-dimensional paths, forming strings as previously reported in atomic liquids and colloidal suspensions. The mean string length is largest at a time close to the peak time of the mean cluster size of mobile monomers. This maximum string length increases, roughly in an exponential fashion, on cooling toward the critical temperature T MCT of the mode-coupling theory, but generally remains small, although large strings involving ten or more monomers are observed. An important contribution to this replacement comes from directly bonded neighbors in the chain. However, mobility is not concentrated along the backbone of the chains. Thus, a relaxation mechanism in which neighboring mobile monomers along the chain move predominantly along the backbone of the chains, seems unlikely for the system studied.

Interfacial mobility scale determines the scale of collective motion and relaxation rate in polymer films

“…Glass-forming liquids generally exhibit dynamical heterogeneity, typically manifested by spatial correlations of particle mobility. In particular, those monomers with the greatest mobility tend to cluster and subsets within these clusters move collectively in a string-like manner, observed both in computer simulations 23,26,[37][38][39][40][41][42][43] and colloidal experiments [44][45][46][47] . Significantly, several publications [25][26][27]48 indicate that the string size may offer a molecular realization of CRR.…”

A unifying framework to quantify the effects of substrate interactions, stiffness, and roughness on the dynamics of thin supported polymer films

“…64,66 Among these highly mobile monomers, we consider two monomers to be in the same string if, over an interval t, one monomer has replaced the other within a radius δ = 0. 55,65 which is smaller than monomer diameter. As has been noted previously, 65 this string-like collective motion is not strongly correlated with chain connectivity and should not be confused with reptation-like motion.…”

“…55,65 which is smaller than monomer diameter. As has been noted previously, 65 this string-like collective motion is not strongly correlated with chain connectivity and should not be confused with reptation-like motion. The variation of L(T ) with h g , ε, and k mimics that of τ(T ) shown in Figure 5.…”

“…We next evaluate L(T) following the approach described in previous works 35,64,65 to see if we can also describe the dynamics of thin polymer films within the same formalism. Specifically, to identify the monomers that are involved in the string-like cooperative motion, we first identify the top 6.5% most mobile monomers.…”

The study of diffusion mechanism in network-forming liquid: Silica liquid

“…Through MD simulation the DH can be identified on the basis of multi-point correlation function 18,19 or by the cluster analysis and visualization of atom trajectory. [20][21][22][23][24][25][26][27] Recently many simulations focus on the organization of TO x and O y of the network structure. Here T is the cationic atom (Si, Ge, Al ...); y is the number of T atom connected to the bridging oxygen.…”