Complex coacervate core micro-emulsions

Complex coacervate core micelles form in aqueous solutions from poly( acrylic acid)-blockpoly(acrylamide) (PAA(x)PAAm(y), x and y denote degree of polymerization) and poly(N,N-dimethyl aminoethyl methacrylate) (PDMAEMA(150)) around the stoichiometric charge ratio of the two components. The hydrodynamic radius, R-h, can be increased by adding oppositely charged homopolyelectrolytes, PAA(140) and PDMAEMA(150), at the stoichiometric charge ratio. Mixing the components in NaNO3 gives particles in highly aggregated metastable states, whose R-h remain unchanged ( less than 5% deviation) for at least 1 month. The R-h increases more strongly with increasing addition of oppositely charged homopolyelectrolytes than is predicted by a geometrical packing model, which relates surface and volume of the particles. Preparation in a phosphate buffer-known to weaken the electrostatic interactions between PAA and PDMAEMA-yields swollen particles called complex coacervate core micro-emulsions (C3-mu Es) whose R-h increase is close to that predicted by the model. These are believed to be in the stable state (lowest free energy). A two-regime increase in R-h is observed, which is attributed to a transition from more star-like to crew-cut-like, as shown by self-consistent field calculations. Varying the length of the neutral and polyelectrolyte block in electrophoretic mobility measurements shows that for long neutral blocks (PAA(26)PAAm(405) and PAA(39)PAAm(381)) the zeta-potential is nearly zero. For shorter neutral blocks the zeta z-potential is around -10 mV. This shows that the C3-mu Es have excess charge, which can be almost completely screened by long enough neutral blocks.