The formation of gold nanoparticles in photopolymerized networks

Photopolymer networks containing a phosphonium polyelectrolyte were used as scaffolds for the synthesis of gold nanoparticles (AuNPs). Chloride anions electrostatically bound to the phosphonium salt were exchanged with AuCl4− and then reduced with NaBH4 to form AuNPs. The stiffness of the photopolymer matrix had a pronounced effect on the concentration of AuNPs formed within the material, where softer, more swellable networks provided greater anion-exchange sites and therefore more AuNP formation. Numerous loading/reduction cycles with AuCl4− and NaBH4 increased the concentration of AuNPs upon each cycling step without significantly changing AuNP size, thus providing a means to control AuNP concentration within the material. SEM and TEM analysis revealed particles sizes ranging from 10 to 30 nm with significant microscale heterogeneity likely arising from phase separation of the phosphonium polyelectrolyte from the photopolymer matrix followed by AuNP synthesis within those regions. We also demonstrate how this methodology can be applied to patterned photopolymer networks, providing the means to explore this approach for photolithographic applications.