Anisotropic domain growth and complex coacervation in nanoclay-polyelectrolyte solutions

In this review, the generalized domain growth in a coacervating solution is discussed. Associative electrostatic interaction between nanoclay (Laponite) and gelatin-A (a polyelectrolyte) is shown to drive complex coacervation at room temperature (25°C). Phase separation kinetics, leading to spontaneous coacervation transition occurring below spinodal temperature (315K) was studied by depolarized dynamic light scattering. Depolarization and axial ratio data clearly revealed that the domains formed of soluble complexes undergo time-dependent anisotropic growth during the initial period of phase separation (t<500s). The equatorial axis of these domains was observed to grow following a power-law behavior: a(t)~t(β) and β=0.25 ± 0.04 independent of quench depth that was not deep. In contrast, the polar axis shrunk with time following: b(t)~t(-δ) and δ=0.15 ± 0.05 independent of quench depth. These domains preferentially grew as oblate ellipsoids during this time. Effect of gravity on domain growth was not observed in our experiments. These results answer the basic issue of binding between discotic colloidal particles and polyelectrolytes in dispersion phase and the resultant phase separation kinetics.