Issue 7, 2008

Complex coacervate core micro-emulsions


Complex coacervate core micelles form in aqueous solutions from poly(acrylic acid)-block-poly(acrylamide) (PAAxPAAmy, x and y denote degree of polymerization) and poly(N,N-dimethyl aminoethyl methacrylate) (PDMAEMA150) around the stoichiometric charge ratio of the two components. The hydrodynamic radius, Rh, can be increased by adding oppositely charged homopolyelectrolytes, PAA140 and PDMAEMA150, at the stoichiometric charge ratio. Mixing the components in NaNO3 gives particles in highly aggregated metastable states, whose Rh remain unchanged (less than 5% deviation) for at least 1 month. The Rh 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-μEs) whose Rh 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 Rh 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 (PAA26PAAm405 and PAA39PAAm381) the ζ-potential is nearly zero. For shorter neutral blocks the ζ-potential is around −10 mV. This shows that the C3-μEs have excess charge, which can be almost completely screened by long enough neutral blocks.

Graphical abstract: Complex coacervate core micro-emulsions

Supplementary files

Article information

Article type
06 Feb 2008
09 Apr 2008
First published
06 May 2008

Soft Matter, 2008,4, 1473-1482

Complex coacervate core micro-emulsions

B. Hofs, A. de Keizer, S. van der Burgh, F. A. M. Leermakers, M. A. Cohen Stuart, P.-E. Millard and A. H. E. Müller, Soft Matter, 2008, 4, 1473 DOI: 10.1039/B802148A

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