Rheological Behavior Completely Wetted PDMS-Grafted Silica Nanoparticles In PDMS Melts

This aim of this work is to elucidate the impact of the graft polymer layer on the dispersion of sterically stabilized nanoparticles in homopolymer melts. Specifically, we have investigated the rheological behavior of well-characterized dispersions of poly(dimethylsiloxane) (PDMS)-grafted silica nanoparticles in PDMS melts. It is well understood that the graft layer must be completely wet by the matrix polymer to achieve uniform colloidal dispersion; however, to date, there is a little fundamental research that systematically investigates the effect of system parameters, such as graft density, matrix chain length, and particle size, on the bulk properties of polymer nanocomposites. By formulating dispersions of decreasing matrix chain length, we enhanced the stretching of the brush as detected through capillary viscometry measurements. The conformation (i.e. wetability) of the graft polymer has a strong impact on bulk flow behavior as measured with steady-state and oscillatory rheological measurements. We have studied a range of particle sizes and core volume fractions to probe both particle softness and interparticle separation distance. These measurements suggest that the onset of interparticle interactions occurs at lower core volume fractions for softer particles. Ultimately, a better understanding of the role of the graft layer on nanoparticles dispersed in polymer melts will aid in optimization of material properties of polymer nanocomposites in applications in biotechnology, optics, catalysis, and plastics.