Evolution of structure in a comb copolymer-surfactant coacervate

The interaction between a double-hydrophilic comb copolymer with the polyanionic backbone poly[methacrylic acid-stat-poly(ethylene glycol) methyl ether methacrylate] (PMAA-PEGMA) and the cationic surfactant N-dodecylpyridinium chloride (DPCl) was studied in alkaline aqueous solutions by using a combination of light and X-ray scattering techniques, covering 5 orders of magnitude in space (the q vector range from 10-5 to 5 nm-1) and time (from milliseconds to several hours). The results showed that the polyelectrolyte-surfactant (PE-S) complex of PMAA-PEGMA and DPCl forms micrometer-sized coacervate particles containing collapsed PMAA-PEGMA chains with attached and densely packed DPCl micelles. Time-resolved SAXS measurements coupled with a stopped-flow apparatus revealed that the phase separation of the PE-S complex into a coacervate phase occurred in <25 ms after mixing the polyelectrolyte and the surfactant. Thus, microphase separation was faster than the self-assembly of DPCl into densely packed micelles. The terminal stages of polyelectrolyte-surfactant coacervation were dictated by the Ostwald ripening of the droplets in the time range of hours.