Hierarchical development of equilibrium structures in polyelectrolyte-micelle coacervates
Par Paul Dubin
Dept of Chemistry, Univ Massachusetts
Complex coacervates are dense, viscous and optically clear aqueous fluids, arising from 20-50 nm complexes that interact in solution through short-range attraction and long-range repulsion.
Their association and aggregation, driven by ion-pairing and counterion release and opposed by charge accumulation, may be viewed as reductions in surface free energy. A similar balance of forces that accompanies coacervation leads to creation of regions of charge neutrality which serve as viscoelastic transient crosslinks. The low heterogeneity and temperature sensitivity of a polyelectrolyte-micelle system facilitates comparisons of the coacervate phase with its precursors.
Analogous disproportionation processes appear to lead to transfer among soluble complexes of excess polycations, and in coacervates to their expulsion (with counterions) into 50-300 nm dilute domains. Structural similarities between soluble aggregates and coacervate mesodomains thus arise from similar balances of enthalpic and entropic forces.