Study On Phase Behavior And Conductivity Of LCST - Type Styrene Acrylonitrile Copolymer / Polymethyl Methacrylate Blends Filled With Graphite

Conductive polymer composites (CPC) have been widely used in antistatic, electromagnetic shielding, self-regulation heater and so on, due to their advantages, such as light weight, low cost, easy processing, corrosion resistance, adjustable electrical and mechanical performance in a large range. It is difficult to achieve the optimal balance among electrical conductivity, processability and mechanical properties only by controlling the loading of conductive fillers. If the conductive fillers are introduced into polymer blends, especially into partial miscible blends, CPC materials with desired ultimate properties can be obtained by controlling the annealing conditions to change the morphology of blend matrix and further realize the efficient distribution of conductive fillers in the blend. The sufficient understanding to the effect of filler on the phase behavior of blend matrix and the aggregation of conductive fillers due to the morphology evolution of matrix may provide a theoretical guidance for the preparation of lower loading, high performance conductive polymer nanocomposites.In this thesis, poly (methyl methacrylate)/poly (styrene-co-acrylonitrile) (PMMA/SAN) blend was selected as a polymer matrix, and the effect of chemically reduced graphene oxide (CRGO) on phase behavior was studied by small angle laser light scattering (SALLS) and dynamic rheology. The contribution of phase separation of blend matrix and CRGO aggregation to the viscoelastic and conductive properties for the nanocomposites was investigated through simultaneous measurement of conductive and rheological behaviors. Moreover, the variation of dispersion state of CRGO with the morphology evolution of blend matrix was detected by transmission electron microscopy (TEM) and phase contrast microscopy (PCM).With the evolution of phase separation, the well-dispersed CRGO gradually migrates to SAN-rich phase due to the interfacial tension. The existence of CRGO causes the delay of spinodal decomposition (SD) phase separation for the blend matrix, and decreases their phase separation rate at different stages of SD, which indicates that CRGO could increase the stability of phase structure for the nanocomposites. On the other hand, the influence of CRGO on the cloud point Tc of the nanocomposites is dependent on the composition of blend matrix, and the incorporation of CRGO results in the obvious decrease of Tb, and the increase of Ts, indicating the expansion of their metastable regime. Moreover, the existence of CRGO may lead to some characteristic phenomenon corresponding to thermally induced phase separation shifting to the lower frequency region. Hence, in the metastable regime, CRGO may act as a nucleating agent inducing the nuclear and grown (NG) phase separation; while in the unstable regime, CRGO may retard the concentration fluctuation of SD for PMMA/SAN blend matrix.Simultaneous measurements of rheological and conductive behaviors show that thermal-induced dynamic resistivity (DR) and moduli (DM) percolation is observed in the nanocomposites, and the percolation time is in advance with the phase separation of blend matrix. The resistivity evolution is ascribed to the agglomeration of CRGO in SAN-rich phase, while the modulus evolution is attributed to the coaction of phase separation and CRGO’s agglomeration.