The effects of nanoscopic fillers on the viscoelastic response of polymers

We have used a technique developed by Brochard (Macromolecules, 2004, 37, 1470) using free standing thin films to study the viscoelastic response of filled-polymer films. Transmission Electron Microscopy (TEM) experiments reported that fillers were well distributed within the films, and therefore no clustering and interracial segregation occurred. Results from Shear Modulation Force Microscopy (SMFM) measurements revealed that the glass transition temperature of the polymer (T_g) was depressed by 10°C relative to the bulk for Au (10 nm), and bulk like for Au (3 nm). The effects of colloidal fillers on the tracer diffusion coefficient (D) were studied using secondary ion mass spectrometry (SIMS), and results found that D was increased significantly for the Au 10 nm, and constant for the Au 3 nm. Values for zero shear rate viscosity extracted from the diffusion coefficient were compared to the shear strain calculated from the hole growth measurements, and theoretical predictions. Results were attributed to an increase in excluded volume when large particles were introduced into the matrix.