Can Oppositely Charged Polyelectrolyte Stars Form a Gel? A Simulational Study

Abstract

We present a Langevin molecular dynamics study of an equimolar mixture of<br>monodispersed oppositely charged di-block four-armed polyelectrolyte stars. We use<br>an implicit solvent coarse-grained representation of the polyelectrolyte stars and varied<br>the length of the terminal charged blocks that reside on each arm. By varying the<br>polymer concentration we computed P-V diagrams and determined the free-swelling<br>equilibrium concentration with respect to a pure water reservoir as a function of the<br>charged block length. We investigate various structural properties of the resulting<br>equilibrium structures, like the number of ionic bonds, dangling arms, isolated stars,<br>and cluster sizes. The ionic bonds feature a broad distribution of the number of arms<br>involved and also display a distribution of net charges peaked around the neutral ionic<br>bond. Our main result is that for charged block length equal to 4 and 5 ionized beads<br>the resulting macro-aggregate spans the box and forms a network phase. Furthermore,<br>we investigated the dynamics of ionic bonds, and computed their lifetimes and turing dynamics. The bonds are weak enough to allow a network restructuring under<br>thermal fluctuations but are still strong enough to yield a stable gel phase.<br>