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 (t ₁) and gold salt solution soak time (t ₂). Combinatorial infusion is accomplished by creating orthogonal gradients in t ₁ and t ₂ 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.