Min Zuo

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

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.

Effect of Chemically Reduced Graphene Oxide on the Isothermal and Non-isothermal Phase Separation Behavior of poly (methyl methacrylate)/poly (styrene-co-acrylonitrile) Binary Polymer Blends

The effect of a small amount of chemically reduced graphene oxide (CRGO) on the isothermal and non-isothermal phase separation behavior of poly(methyl methacrylate)/poly(styrene-co-acrylonitrile) (PMMA/SAN) blends was investigated by using time-resolved small angle laser light scattering (SALLS). During the non-isothermal process, a quantitative logarithm function can be established to describe the relationship between the cloud point Tc and heating rate k as given by Tc = A ln k + T0 for the unfilled and filled CRGO-filled PMMA/SAN systems. During the isothermal process, the TTS principle and WLF function are applicable to describe the temperature dependence of nonlinear phase separation behaviors at the early and late stages of spinodal decomposition (SD) for such unfilled and filled systems, indicating that the introduction of CRGO hardly changes the viscous diffusion essence of macromolecular chains during phase separation. However, the mechanical barrier effect of CRGO on the macromolecular viscous diffusion may result in the delay of their phase separation behavior. Furthermore, the effect of CRGO on the isothermal and non-isothermal phase-separation behavior of the blend matrix is found to be dependent on the composition of the blend matrix. CRGO may act as a nucleating agent to result in the decrease of Tc for the PMMA/SAN 37/63 system, while the mechanical barrier effect of CRGO on the macromolecular segment may retard the concentration fluctuation at the early stage of SD phase separation to cause the increase of Tc for the PMMA/SAN 57/43 system. Besides, when SAN is the minority of the blend matrix (PMMA/SAN 57/43), the selective location of CRGO may result in the more obvious viscosity increment and then the more remarkable hindering effect on the SD phase separation behavior of blend matrix.

Effect of grafted graphene nanosheets on morphology evolution and conductive behavior of poly(methyl methacrylate)/poly(styrene-co-acrylonitrile) blends during isothermal annealing

A facile method was developed for directly grafting poly(methyl methacrylate) (PMMA) to graphene oxide (GO) without surface modification, with the resultant insulating PMMA-g-GO nanosheets further reduced in situ to give conductive grafted reduced graphene oxide (RGO) nanosheets. The effect of PMMA-g-RGO nanosheets on the morphological evolution and conductive behavior of partially miscible blends of poly(methyl methacrylate)/poly (styrene-co-acrylonitrile) (PMMA/SAN) upon annealing above their phase-separation temperature was investigated using phase-contrast microscopy (PCM) with a real-time online digital picoammeter. With phase separation of the blend matrix, the well-dispersed PMMA-g-RGO nanosheets in the homogeneous matrix preferentially migrated to the SAN-rich phase and showed remarkably little aggregation. Surface grafting of PMMA-g-RGO might inhibit the aggregation of nanosheets in the blend matrix and weaken the retardation effect of nanosheets on the morphology evolution of the blend matrix. Furthermore, the percolation behavior of dynamic resistivity for ternary nanocomposites was attributed to the formation of a PMMA-g-RGO conductive network in the SAN-rich phase. The activation energy of conductive pathway formation was closer to the activation energy of flow for PMMA than that of SAN.

TIME AND TEMPERATURE DEPENDENCE OF PHASE-SEPARATION BEHAVIOR FOR POLY( N -METHYL METHACRYLIMIDE)/POLY(VINYLIDENCE FLUORIDE) BLENDS: TIME AND TEMPERATURE DEPENDENCE OF PHASE-SEPARATION BEHAVIOR FOR POLY( N -METHYL METHACRYLIMIDE)/POLY(VINYLIDENCE FLUORIDE) BLENDS

The liquid-liquid phase-separation(LLPS) behavior of poly(N-methyl methacrylimide)/poly(vinylidene fluoride)(PMMI/PVDF) blends was studied by using small angle laser light scattering(SALLS),and the time-temperature dependence of phase-separation behavior was discussed.According to examining the dependence of cloud points(T_c) on heating rate for PMMI/PVDF blends,it was found that T_c decreased as the temperature droped nonlinearly.When the heating rate was higher than 1.0 K/min,only the heating rate could affect the relative intensity I(t),and the difference of relaxation rate of polymer chain was difficult to be distinguished.Contrarily,both heating rate and relaxation rate of polymer chains could affect the cloud points of PMMI/PVDF blends at lower heating rates because there was enough time for the chain relaxation,and the different relaxation rates could result in the change of T_c.The cloud point curve of PMMI/PVDF blend was obtained at the heating rate of 1 K/min~(-1).The thermal behavior of PMMI/PVDF blends was measured by differential scanning calorimetry (DSC) and dynamic mechanical analysis(DMA).It was found that PMMI/PVDF exhibited a typical low critical solution temperature(LCST) behavior.Moreover,the temperature dependence of phase-separation kinetics for PMMI/PVDF blends followed the principle of time-temperature superposition(TTS) at the early phase-separation stage and may be described with a WLF-like equation.

Molecular Dynamics and Phase Behavior of Polystyrene/Poly(vinyl methyl ether) Blend in the Presence of Nanosilica

The variation of phase morphology, critical temperature of demixing, and molecular dynamics for polystyrene/poly(vinyl methyl ether) (PS/PVME) blends induced by hydrophilic nanosilica (A200) or hydrophobic nanosilica (R974) was investigated. With the phase separation of blend matrix, A200 migrated into PVME-rich phase due to strong interaction between A200 and PVME, while R974 moved into PS-rich phase. The thermodynamic miscibility and concentration fluctuation during phase separation of blend matrix were remarkably retarded by A200 nanoparticles due to the surface adsorption of PVME on A200, verified by the correlation length ξ near the critical region from rheological measurement and the weakened increment of reversing heat capacity (ΔCp) during glass transition via modulated differential scanning calorimetry (MDSC). The restricted chain diffusion induced by nanosilica still occurred despite no influence of A200 and R974 on the segmental dynamics of homogenous blend matrix. The interactions between nanosilica and polymer components could restrict the terminal relaxation of blend matrix and further manipulate their phase behavior.