Combinatorial study of a gold nanoparticle infusion process in a polymer film

A novel two-step process is described for infusion of gold nanoparticles (5–20 nm typical diameter) into a polymer film. The technique is demonstrated for the first time in a thermoplastic polyurethane elastomer (TPU). An amine-functional monomer, 2-(diethylamino)ethyl methacrylate, and a free-radical photoinitiator are infused into the surface of the TPU, followed by photopolymerization. An amine-functional semi-interpenetrating network (SIPN) is created within a shallow (~100 μm) surface layer. In the second step, a gold salt, HAuCl4·3H2O, is infused into the SIPN from a ternary solvent mixture, and redox reaction with the immobilized amine functional groups produces Au0 nanoparticles. Combinatorial processing is conducted to visualize the interdependent effects of two variables, monomer soak time (t1) and gold salt solution soak time (t2). Combinatorial infusion is accomplished by creating orthogonal gradients in t1 and t2 in a square TPU plate, allowing examination of sample color, particle size, and polydispersity over a wide range of parameter space. Small angle X-ray scattering (SAXS) is employed as non-invasive means to characterize the Au0 particles at three locations in the plate. SAXS measurements are validated by TEM analysis of Au0 particle size in a reference sample. A rationale is developed for changing particle size and polydispersity through variation of simple process parameters.