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

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