Conducting transition analysis of thin films composed of long flexible macromolecules: Percolation study

TL;DR

This study investigates the percolation and critical phenomena in films of long flexible macromolecules, revealing that dynamic network structures exhibit similar universality and thresholds regardless of topological constraints.

Contribution

It introduces a molecular Monte Carlo simulation of freely moving macromolecules, demonstrating that dynamic networks share percolation properties with constrained systems.

Findings

Percolation phenomena occur in dynamic, freely diffusing macromolecular networks.

Universality class and percolation threshold are unaffected by topological constraints.

Dynamic network structures exhibit critical phenomena similar to fixed systems.

Abstract

Simulating percolation and critical phenomena of labelled species inside films composed of single-component linear homogeneous macromolecules using molecular Monte Carlo method in 3 dimensions, we study dependence of these conducting transition and critical phenomena upon both thermal movement, i.e. spontaneous mobility, and extra-molecular topological constraints of the molecules. Systems containing topological constraints and/or composed of immobile particles, e.g. lattice models and chemical gelation, were studied in conventional works on percolation. Coordinates of the randomly distributed particles in the conventional lattice models are limited to discrete lattice points. Moreover, each particle is spatially fixed at the distributed position, which results in a temporally unchanged network structure. Although each polymer in the chemical gels can spontaneously move in the continuous space, the network structure is fixed when cross-linking reaction ends. By contrast to these conventional systems, all the molecules in the present system freely move and spontaneously diffuse in the continuous space. The network structure of the present molecules continues changing dynamically. The percolation and critical phenomena of such dynamic network structures are examined here. We reveal that these phenomena also occur in the present system, and that both the universality class and percolation threshold are independent from the extra-molecular topological constraints.