Effect of organically modified layered silicates on the morphology of symmetrical blends of polystyrene and poly(methyl methacrylate)

The changes in morphology caused by the addition of organically modified layered silicate on equal volume fraction blends of polystyrene and poly(methyl methacrylate) are investigated. In thin films supported on silicon, without layered silicates, the PMMA forms a layer on the silicon, while the PS tend to minimize contact with both the hydrophilic silicon substrate and the PMMA phase, and tend to form discrete domains on top of the PMMA layer. With the introduction of layered silicates, the characteristic length scale of the structure decreases. On the other hand, in bulk samples, without the layered silicates, the equal volume fraction blend has the PS domains in a PMMA matrix. At 0.6 wt% of added silicate, in both thin film and bulk, the blend morphology converts from discrete to co-continuous. Electron micrographs reveal well dispersed silicate sheets locating at the interface between small PS domains in the PMMA phase. The change in morphology is conjectured to be the result of the interfacial location of the layered silicates rather than the change in viscosity ratio between the two phases.