We investigate the complexation of poly(styrenesulfonate) with micelles containing both cationic and hydrophilic blocks in their coronas. Five distinct micelles were prepared by self-assembly, using D+S, OS, OD+S, D+OS, and mixtures of D+S and OS block polymers, where the hydrophobic S blocks (poly(styrene)) form the micelle cores and the cationic D+ blocks (poly(dimethylaminoethyl methacrylate)) and hydrophilic, nonionic O blocks (poly(oligo(ethylene glycol) methyl ether methacrylate)) form the coronas. Turbidimetric titration and dynamic light scattering measurements on complexes with short poly(styrenesulfonate) chains (M ≈ 1 kg/mol) that can equilibrate quickly reveal that the intrinsic colloidal stability of the complexes is determined by the identity of the outermost block of the micelle corona and that architectures with a nonionic solvating outer block promote the formation of soluble single-micelle complexes even when the complexes are fully neutralized. Although complexes with longer poly(styrenesulfonate) chains (M ≈ 30 kg/mol) are kinetically trapped in aggregates for all cation-containing micelle architectures, studies at high ionic strength show that inclusion of the outer hydrophilic block can successfully limit the size of the complexes and inhibit overall phase separation of neutralized complexes. Finally, the molecular weight dependence of the aggregation process for complexes of the OD+S architecture demonstrates that bridging is the predominant mechanism for aggregation and that careful selection of the polymer architecture and molecular weight can provide a useful strategy for controlling the structure and colloidal stability of hierarchical complexes.
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Reporting period for MRSEC
- Period 3