| Addition of particulate fillers into polymeric materials is a common route to enhance physical, chemical and environmental properties of the host polymers. Recent studies have shown that when the size of filler materials reduces from micron to nano length scales, totally new, unique flow behavior emerges. In this work, we systematically studied the role of polystyrene nanospheres PS(nano) on blending behavior by using a variety of techniques. The PS(nano) is essentially a dense, star-like, hyperbranched polystyrene molecule with about 50 unentangled arms. In systems with similar monomer chemistry i.e., PS(nano)/L-PS (linear polystyrene) blends, we showed that effect of PS(nano) on blending behavior strongly depends on R g of linear polystyrene, half inter-particle distance between two nanospheres (h) and finally, the radius of the PS(nano) itself. Using DSC and rheology measurements we showed that PS(nano) in high molecular weight, high viscosity L-PS act as a solvent molecule; whereas, it acts a filler when added to low molecular weight, low viscosity L-PS. In systems with different monomer chemistry i.e., PS/PVME blends, our preliminary results suggest that the length scale of miscibility is affected by changing L-PS to PS(nano). L-PS/PVME blend is miscible on a segmental level whereas PS(nano) is molecularly dispersed in PVME matrix in case of PS(nano)/PVME blends. This is also reflected in the flow behavior analysis of these blends. Rheology data of these blends suggests that the relaxation time of each component is significantly altered upon blending. However, filler effect was observed in case of PS(nano)/PVME blends. Further, flow birefringence measurements helped us to extract component dynamics in PS/PVME as well as PS(nano )/PVME blends. Phase-separation phenomenon was found not be sensitive to changes in molecular architecture. In addition, experimental data on rheology of phase-separated blends indicates that the morphology of phase-separated blend and hence mechanical properties, which depend strongly on morphological changes, are strong but complex functions of the architecture of the polystyrene molecule. Weaker interfacial adhesion and chain connectivity was manifested in case of PS(nano)/PVME blends when compared to L-PS/PVME blends. |
