Joachim P. Wittmer | Searcharxiv

arXiv2017

Marginally compact fractal trees with semiflexibility

We study marginally compact macromolecular trees that are created by means of two different fractal generators. In doing so, we assume Gaussian statistics for the vectors connecting nodes of the trees. Moreover, we introduce bond-bond correlations that make the trees locally semiflexible. The symmetry of the structures allows an iterative construction of full sets of eigenmodes (notwithstanding the additional interactions that are present due to semiflexibility constraints), enabling us to get physical insights about the trees' behavior and to consider larger structures. Due to the local stiffness the self-contact density gets drastically reduced.

cond-mat.soft↗

arXiv2011

Scale-free center-of-mass displacement correlations in dense polymer solutions and melts without topological constraints and momentum conservation: A bond-fluctuation model study

By Monte Carlo simulations of a variant of the bond-fluctuation model without topological constraints we examine the center-of-mass (COM) dynamics of polymer melts in $d=3$ dimensions. Our analysis focuses on the COM displacement correlation function $\CN(t) \approx \partial_t^2 \MSDcmN(t)/2$, measuring the curvature of the COM mean-square displacement $\MSDcmN(t)$. We demonstrate that $\CN(t) \approx -(\RN/\TN)^2 (\rhostar/ρ) \ f(x=t/\TN)$ with $N$ being the chain length ($16 \le N \le 8192$), $\RN\sim N^{1/2}$ the typical chain size, $\TN\sim N^2$ the longest chain relaxation time, $ρ$ the monomer density, $\rhostar \approx N/\RN^d$ the self-density and $f(x)$ a universal function decaying asymptotically as $f(x) \sim x^{-ω}$ with $ω= (d+2) \times α$ where $α= 1/4$ for $x \ll 1$ and $α= 1/2$ for $x \gg 1$. We argue that the algebraic decay $N \CN(t) \sim - t^{-5/4}$ for $t \ll \TN$ results from an interplay of chain connectivity and melt incompressibility giving rise to the correlated motion of chains and subchains.

cond-mat.soft↗