Anomalous Dynamics in Macromolecular Liquids

Abstract

Macromolecular liquids display short-time anomalous behaviors in disagreement with conventional single-molecule mean-field theories. In this study, we analyze the behavior of the simplest but most realistic macromolecular system that displays anomalous dynamics, i.e., a melt of short homopolymer chains, starting from molecular dynamics simulation trajectories. Our study sheds some light on the microscopic molecular mechanisms responsible for the observed anomalous behavior. The relevance of the correlation hole, a unique property of polymer liquids, in relation to the observed subdiffusive dynamics, naturally emerges from the analysis of the van Hove distribution functions and other properties.

Cooperative Dynamics of Highly Entangled Linear Polymers within the Entanglement Tube

“…The CDGLE approach relates the anomalous diffusion to the presence of an interchain potential between sections of pairs of distinct polymer chains, which correlates with the dynamics of slowly diffusing chain molecules. CDGLE was able to quantitatively account for the NSE results . Relating to this observation, it is highly likely that the subdiffusive com diffusion within the PBO12K melt originates from the same phenomenon.…”

Activation energy and molecular weight dependence of cooperative tracer chains diffusion in highly entangled polymer melts

“…The subdiffusive dynamics of the tracers is not only cooperative but also significantly non-Gaussian. 5,6,20 Moreover, d cross is close to the entanglement distance of the host. Thus, these features of the dynamics of the tracers reflect that of the host entangled chains within the entanglement distance.…”

“…The theory is based on the generalized Langevin equation (GLE) for the correlated dynamics (CD) of multiple chains. [1][2][3][4][5][6][7] The theoretical predictions of CDGLE are applicable to both unentanged and entangled polymers. Different from the mean-field Rouse model 8 for unentangled polymers and the tube-reptation theory 9,10 for entangled polymers, CDGLE explicitly includes the forces generated by the presence of intermolecular correlation, and the motion of the interacting chains is coupled by the time-dependent potential of mean force.…”

“…The very slow increase of the MSD in the very short time regime before the onset of the subdiffusive dynamics suggests the chains are caged, in analogy to that found in the MSD of various glass-forming systems and ionic conductors at short times. 22,23 After the predicted subdiffusive dynamics of the CDGLE for short and weakly entangled chains had been verified, 7 Guenza 5,6 extended the theory to highly entangled melts. Many chain dynamics originating from interaction through a time-dependent potential of mean force result in subdiffusive dynamics of the cooperative chain fluctuations which are restricted to the entanglement volume $ d 3 .…”

“…Recently the extended CDGLE results in highly entangled polymers 5,6 have led Zamponi et al 19 in 2021 to verify these properties and the cooperativity length scale by using NSE spectroscopy. Zamponi et al made a systematic study of the MSD of short labeled (hydrogenated) polyethylene (PE) tracer chains dispersed in a highly entangled and deuterated PE host matrix.…”