Effects of nanoparticles on immiscible polymer blends

Modified layered silicates and silica nanoparticles were introduced as compatibilizing agents for immiscible blends of polystyrene and poly(methyl methacrylate). The nanoparticle location in the blend depends on the relative interaction between the nanoparticle and the blend components. Experimental results demonstrate that while the layered silicates modified with alkyl chains locate at the interface between droplets of PS and the matrix of PMMA, silica nanoparticles grafted with short PS chains reside at the interface between PS and PMMA irrespective of the blend morphology.;Within the studied range of particle loading, the layered silicates do not affect the melt-state theological behavior of the blends when residing in the discrete phase. However, when residing at the interface between PS droplets and PMMA matrix, the linear dynamic rheological response of these samples shows a significant increase in the low-frequency elastic modulus. The size of the PS-rich domains decreases sharply at low concentrations of added layered silicate and becomes independent of silicate concentration beyond 0.5 wt.%. Mechanical properties such as yield stress, strain at break and toughness show significant increases with added silicate. The most significant property improvements occur at relatively modest silicate loadings which correspond to an uncompleted coverage of interface by the silicate sheets. Silica grafted PS particles segregating at PS droplets-PMMA matrix interface exhibit similar effects as those of layered silicates: decreasing PS domain size and increasing of low frequency elastic modulus.;The viscoelastic models of Palierne and Park-Lee were used to relate the interfacial properties of the nanoparticles to the measured viscoelastic characteristics. Both models indicate a significant increase of interfacial modulus with increasing amount of nanoparticles. The results agree with theoretical predictions and suggest that the interfacial particles not only change the interfacial modulus but also affect the dynamic behavior of polymer chains on both sides of the interface. This effect depends on the size as well as the shape of the particles. This work demonstrates that the stabilizing mechanism for such nanoparticle compatiblized polymer blends is through the reducing of contact area between two immiscible phases and not through a change in the interfacial tension caused by the nanoparticle.