Dynamical Monte Carlo Study of Equilibrium Polymers : Static Properties

TL;DR

This study uses advanced Dynamical Monte Carlo simulations to analyze static properties of equilibrium polymers, confirming theoretical predictions about chain length scaling and distribution in various density regimes.

Contribution

Introduces a novel efficient algorithm for simulating large equilibrium polymer systems, enabling detailed static and dynamic property analysis across a wide density range.

Findings

Mean-chain length scales with density and scission energy as predicted.

Chain length distribution follows Schulz-Zimm form in dilute limit.

Accurate determination of the self-avoiding walk susceptibility exponent γ ≈ 1.165.

Abstract

We report results of extensive Dynamical Monte Carlo investigations on self-assembled Equilibrium Polymers (EP) without loops in good solvent. (This is thought to provide a good model of giant surfactant micelles.) Using a novel algorithm we are able to describe efficiently both static and dynamic properties of systems in which the mean chain length $\Lav$ is effectively comparable to that of laboratory experiments (up to 5000 monomers, even at high polymer densities). We sample up to scission energies of $E/k_BT=15$ over nearly three orders of magnitude in monomer density $\phi$, and present a detailed crossover study ranging from swollen EP chains in the dilute regime up to dense molten systems. Confirming recent theoretical predictions, the mean-chain length is found to scale as $\Lav \propto \phi^\alpha \exp(\delta E)$ where the exponents approach $\alpha_d=\delta_d=1/(1+\gamma) \approx 0.46$ and $\alpha_s = 1/2 [1+(\gamma-1)/(\nu d -1)] \approx 0.6, \delta_s=1/2$ in the dilute and semidilute limits respectively. The chain length distribution is qualitatively well described in the dilute limit by the Schulz-Zimm distribution $\cN(s)\approx s^{\gamma-1} \exp(-s)$ where the scaling variable is $s=\gamma L/\Lav$. The very large size of these simulations allows also an accurate determination of the self-avoiding walk susceptibility exponent $\gamma \approx 1.165 \pm 0.01$. ....... Finite-size effects are discussed in detail.