Study On Phase Behavior And Conductivity Of Carbon Nanotubes Filled With LCST Polymethyl Methacrylate / Styrene Acrylonitrile Copolymer

More concern has been paied to conductive polymer composites (CPC) meterials due to their advantages of continuous adjustable electric properties and processability. In general, CPCs are multiphase or multicomponent systems, their performances are strongly dependent on the morphology of polymer matrix and conductive fillers. If the conductive fillers are incorporated into the partially miscible polymer blends, CPC materials with excellent conductive property and low filler loading could be obtained by simply changing the processing conditions. It will reduce the percolation value of the composites by controlling the fillers dispersed at the continuous phase or at the continuous interface phase during phase separation. Carbon nanotube (CNT) is a kind of one-dimension conductive filler with high aspect ratio and the performances of CNT filled polymer is strongly related with the dispersion state of fillers, the aggregation and network of CNT particles.In this work, CNT and poly (methyl methacrylate)/poly (styrene-co-acrylonitrile) (PMMA/SAN) blend and CNT were selected to prepare ternary CPC materials. Small Angle laser light scattering (SALLS) and dynamic rheological tests were carried out to determine the effect of CNT on the phase behavior of blend matrix. Combined with the simultaneous measurement of rheological and conductive behaviors as well as the transmission electron microscope characterization, the aggregation of CNTs, the morphology evolution of blend matrix and their respective contribution on dynamic moludus (G’) during isothermal annealing above the phase separation temperature were investigated.With the phase separation of polymer blends, CNTs well dispersed in homogeneous polymer blend gradually migrate and aggregate in the SAN-rich phase with more thermodynamics affinity. The existence of CNTs reduces the phase separation rate at different stage of spinodal decomposition (SD), indicating CNTs may retard the concentration fluctuation and domain coarsening of PMMA/SAN blend matrices. However, the effect of CNTs on the phase separation temperatures of PMMA/SAN blend was found to depend on the composition of blend matrix and the filler loading, as a result of the composition difference between surface layer of CNTs and polymer matrix induced by the selective absorption of SAN on the surface of CNTs. Furthermore, the time-temperature superposition (TTS) principle and Williams-Landel-Ferry (WLF) equation are applicable to describe the temperature dependence of SD phase separation behavior at the early stage and late stage for both unfilled and filled systems, indicating that the introduction of CNTs hardly changes the viscous diffusion essence of macromolecular chains during phase separation.Synchronous evolution of G’and resistivity p for PMMA/SAN/CNT nanocomposites upon isothermal annealing well above the phase separation temperature shows the more remarkable DM and DC percolation behaviors. DC percolation origins from the aggregation of CNTs in SAN-rich phase, while the origin of DM percolation is more complicated than that of DC percolation, which is a combined effect of morphology evolution of polymer matrix and the aggregation of CNTs. The apparent activation energies of PMMA/SAN(57/43)/CNT nanocomposites for conductive path formation are found filler loading independent and close to that of viscous flow for SAN.