Effect of multiwall carbon nanotubes on the phase separation of concentrated blends of poly[(α-methyl styrene)-co-acrylonitrile] and poly(methyl methacrylate) as studied by melt rheology and conductivity spectroscopy

Thermally induced phase separation in concentrated lower critical solution temperature (LCST) blends of poly[(α-methyl styrene)-co-acrylonitrile]/poly(methyl methacrylate) (PαMSAN/PMMA) in presence of multiwall carbon nanotubes (MWNTs) with different surface characteristics (∼NH2 functionalized and polyethylene modified) was monitored by modulated differential scanning calorimetry, melt rheology, conductivity spectroscopy and microscopic techniques. At a concentration of 2 wt%, the MWNTs clearly reduce the macromolecular mobility of the blend components and induce phase separation at lower temperatures as compared to the neat blends. Electron microscopic images revealed that phase separation resulted in a selective thermodynamically driven localization of both types of MWNTs in the PαMSAN phase whereas they were randomly distributed in the mono-phasic materials. Hence, a percolative MWNT network was formed at much lower concentrations as compared to those needed for percolation in the blend components. However, the significant changes in viscosity and elasticity of the blend components, brought about by the MWNTs, can also affect morphology development. This way, effective percolation in the blends can be hindered, as was observed for the 60/40 blend with polyethylene coated MWNTs (PE-MWNTs). Finally, a dramatic transition from an insulating one-phasic material at room temperature to a highly conductive material in the melt was induced by the phase separation.