Dynamic Properties of a Model Polymer/Metal Nanocomposite:  Gold Particles in Poly(tert-butyl acrylate)

A combination of methods has been used to study the dynamic properties of a nanocomposite consisting of evaporated gold particles embedded in poly(tert-butyl acrylate). Rutherford backscattering spectrometry was used to measure the diffusion coefficients of the gold particles and of the polymer molecules; dewetting experiments were used to probe the viscosity of thin films with and without gold particles. The gold particles diffused with a temperature dependence similar to the temperature dependence of the polymer viscosity, but with hydrodynamic radii that greatly exceeded the actual radii of the gold particles. The gold particles also increased the viscosity of a low molecular weight polymer film by a factor of 4. Our interpretation of these results is that long-lived polymer bridges between individual gold particles stabilize clusters with dimensions of approximately 50 nm. A geometrical model of the bridging process was also developed. Results from this model can readily be applied to homogeneous nanoparticle dispersions in polymeric matrixes.