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When oppositely-charged polymers are mixed in water they self-assemble into polyelectrolyte complexes (PECs). These complexes have numerous technological applications that require control over their shape. To this end, we show how PEC geometry can be tailored through photodirected assembly. A commonly-used weak polycation, poly(allylamine) (PAH), was co-dissolved in a basic solution (significantly above its effective pKa) with a commonly-used polyanion, poly(styrene sulfonate) (PSS), and a photoacid generator (diphenyliodonium nitrate). The solution was then irradiated with UV light through photomasks to spatially control the protonation (and therefore the ionization) of PAH. The ionization resulted in the formation of insoluble PECs, whose shapes were predictably tuned by varying the photoirradiation pattern. Also analyzed were the phase behavior of PAH/PSS/diphenyliodonium nitrate mixtures, and the kinetics and spatial resolution limits of their photodirected assembly. This revealed that pH-mediated photodirected assembly works well for macroscopic structures (i.e., larger than about a millimeter in size), but is impeded by ion diffusion when smaller irradiation sites are used. [ABSTRACT FROM AUTHOR]

Template polymerization (i.e., polymerization of monomers along a macromolecular template) provides a scalable method for preparing colloidal polyelectrolyte complexes (PECs) with narrow size distributions. To our knowledge, however, the formation of sub-50-nm PECs through template polymerization has generally required the use of block copolymers or involved covalent crosslinking. Here, we report a one-step synthesis of such PEC nanoparticles through a simple free-radical polymerization of an anionic monomer (acrylic acid) on a polycationic poly(allylamine) (PAH) template. The self-assembly of the resulting poly(acrylic acid) (PAA) with the PAH generated narrowly dispersed particles with average sizes ranging between roughly 20 and 400 nm, which could be readily tuned by adjusting the parent solution concentration. At particle-forming compositions, most of the PAH became incorporated into the PECs, thus indicating high particle yields. Once assembled, these particles remained stably dispersed throughout a monthlong stability experiment when stored at low ionic strengths. When stored in ≥ 40 mM NaCl solutions, however (unless the particles were prepared in an excess of PAH), the dispersions underwent at least partial agglomeration. Collectively, these findings show template polymerization to be an effective technique for generating nanoparticles (including those with sub-50-nm dimensions) with tunable, narrowly dispersed sizes and high yields. [ABSTRACT FROM AUTHOR]