(514e) Photodirected Assembly of Custom-Designed Polyelectrolyte Complexes

When oppositely charged polyelectrolytes are mixed in aqueous solutions they self-assemble into insoluble complexes ranging from micro- and nanoparticles, to thin films, to macroscopic fibers and capsules. This phenomenon has an electrostatic driving force and finds use in numerous applications (e.g., controlled release, separation and sensor technologies), many of which require polyelectrolyte complex (PEC) structures with well-defined geometries. To expand the range of their structural motifs, we have developed a simple strategy for directing PEC assembly between two commonly-used polyelectrolytes – poly(allylamine) (PAH) and poly(styrene sulfonate) (PSS) – using light.  Deprotonated PAH (which was neutral) was mixed with anionic PSS and a photoacid generator (diphenyliodonium nitrate), and irradiated with long-wave ultraviolet light (λ = 365 nm). The photoactivated acid generation led to the protonation of PAH amines at the photoirradiation site and (because the neutral PAH became cationic) resulted in the rapid PAH/PSS association into either colloidal or macroscopic PECs. The shape of these PECs was easily tuned using a photomask, which controlled the photoirradiation pattern, and thus the shape of the resulting PECs. The formation and structure of these PECs were characterized through phase studies, microscopy and isothermal titration calorimetry (ITC), and suggest photodirected assembly as an effective tool for preparing PECs with custom-designed, anisotropic geometries.