Effect of nanoscopic fillers on dewetting dynamics

We synthesized C-18-functionalized gold and palladium nanoparticles with average diameter size of 10 and 3 nm, respectively, and carried out a systematic study of the effect of nanoscale metallic fillers on the dewetting dynamics of PS/PMMA bilayer substrates. Optical and atomic force microscopies were used to study the hole growth and determine the viscosity of the films as a function of PS molecular weight, particle radius, and concentration. Neutron reflectivity was used to measure the effects of the nanoparticles on the tracer diffusion coefficient. X-ray reflectivity and TEM microscopy were used to study the distribution of the particles within the film and ensure that no segregation or clustering occurred. The results indicated that the dynamics are a sensitive function of the ratio between the filler radius, R-particle, and the polymer radius of gyration, R-g. The data were found to collapse on a universal curve where the relative velocity of the filled system was faster than that for the unfilled system when R-g/R-particle > 4 and slower when R-g/R-particle < 4. Shear modulation force microscopy method (SMFM) measurements were performed as a function of temperature and indicated that T-g was depressed by 12 degrees C relative to the bulk when R-g/R-particle > 4 and unchanged when Rg/R-particle < 4. The results were interpreted in terms of an increase in the local excluded volume and possible elastic distortions of the polymer matrix.