Kinetics of phase separation in systems exhibiting simple coacervation

The kinetics of phase separation of a homogeneous polyelectrolytic solution into a dense polymer-rich coacervate and the dilute supernatant phase is discussed through statistical thermodynamics. It has been shown that the coacervate phase is associated with higher internal pressure, consequently giving rise to syneresis. Physical conditions for phase separations has been deduced explicitly which reveals that σ²∕√I0.2em0ex constant (where σ is polyelectrolyte charge density and I is solution ionic strength), consistent with experimental observations. In the lattice model, r is the number of sites occupied by the polymer having a volume critical fraction φ2c, it was found that phase separation would ensue when σ³r(64∕9α²)[φ2c∕(1-φ2c)²], which reduces to (σ³r∕φ2c)(64∕9α²)≈0.45 at 20 ^∘{}C for φ2c⪡1. The separation kinetics mimics a spinodal decomposition process. Rate of release of supernatant due to syneresis was found to be independent of the initial coacervate mass. Syneresis results are discussed in the context of temporal evolution of self-organization in polymer melts through Avrami model.