Effect of multi-walled carbon nanotubes on the morphology evolution, conductivity and rheological behaviors of poly(methyl methacrylate)/poly(styrene-co-acrylonitrile) blends during isothermal annealing

Abstract

The effect of multi-walled carbon nanotubes (MWNTs) on the morphological evolution and conductive and viscoelastic behavior for partially miscible blends of poly(methyl methacrylate)/poly(styrene-co-acrylonitrile) (PMMA/SAN) upon annealing above the phase-separation temperature was investigated via microscopic technology, melt rheology and simultaneous measurement of rheological and conductive properties. The well-dispersed MWNTs in the homogeneous matrix preferentially migrated into the SAN-rich phase after the occurrence of phase separation and then further agglomerated in the SAN-rich phase to form the conductive pathway. The effect of MWNTs on the phase separation temperatures of a PMMA/SAN blend was found to depend on the composition of the blend matrix, as a result of the composition difference between the surface layer of the MWNTs and the polymer matrix induced by the selective absorption of SAN on the surface of MWNTs. Thermal-induced dynamic percolation was observed for both the resistivity ρ and dynamic storage modulus G′ as a function of annealing time. The respective contribution of phase separation and MWNTs aggregation to the variation of G′ was also clearly distinguished during annealing. The influence of temperature and filler loading on the percolation time of ρ was investigated and the activation energies of dynamic conductive (DC) percolation were determined, independent of the volume content of MWNTs. The activation energies of DC percolation for the nanocomposites were found to be close to those of viscous flow for SAN.