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.

•Core-shell (CS) nanoparticles with crosslinked PMMA shell were fabricated.•The remarkable depression of Tg induced by SiO2 and CS was both observed at low loadings.•The formation of RAF layer around SiO2 leaded to the adjacent molecular packing frustration.•The “lubrication” effect of nonwetting interface around CS caused the segmental acceleration.Core-shell (CS) nanocomposite particles with 53.4 wt% cross-linked poly (methyl methacrylate) (PMMA) shell of 11.6 nm in thickness were fabricated via miniemulsion polymerization of methyl methacrylate in the presence of modified nanosilica. The influence of nanosilica and CS nanoparticles on glass transition and segmental dynamics of PMMA in the nanocomposites prepared via solution casting was compared. The remarkable depression (≥10 °C) of glass transition temperature (Tg) induced by the incorporation of SiO2 and CS was both observed at low loadings. Here, different mechanisms were responsible for the effect of SiO2 and CS on the segmental acceleration of PMMA matrix. The formation of rigid amorphous fraction (RAF) layer around SiO2 with the thickness of 16.4 nm led to the adjacent molecular packing frustration, while the “lubrication” effect of nonwetting interface between the grafted crosslinked chains and matrix chains resulted in the segmental acceleration and the reduction of dynamic fragility.The formation ofRAF layer around SiO2 leaded to the adjacent molecular packing frustration, while the “lubrication” effect of nonwetting interface around CS caused the segmental acceleration.Download high-res image (129KB)Download full-size image

•Novel core–shell TiO2-g-PMMA nanoparticles with crosslinked PMMA shell were prepared via seeded emulsion polymerization.•The TiO2-g-PMMA nanoparticles demonstrated excellent dispersion stability in the composites subjected to melt annealing.•The TiO2-g-PMMA nanoparticles scarcely affected molecular dynamics of the PVDF/PMMA (70/30) blend.•The TiO2-g-PMMA nanoparticles provided a general and effective strategy to fabricate composites with morphology stability.Titania (TiO2) or poly (methyl methacrylate) (PMMA)-grafted titania (TiO2-g-PMMA) were incorporated into miscible poly (vinylidene fluoride) (PVDF)/PMMA (70/30 by weight) blend by melt mixing. TiO2 particles exhibited aggregation in the composites as displayed by scanning electron microscopy observations and the storage modulus (G′) plateau in the low frequency (ω) region. This is accompanied with the restriction of molecular mobility and the elevation of glass transition temperature (Tg). Conversely, TiO2-g-PMMA nanoparticles with well-defined cross-linked PMMA shells of 5 nm in thickness are well-distributed in the matrix, without the influence on Tg and the appearance of low-ω plateau. The dispersion of TiO2 is not stable during the thermal annealing of the composite in the melt while the TiO2-g-PMMA nanoparticles demonstrate excellent dispersion stability. Broadband dielectric spectroscopies indicate that TiO2 influenced the molecular relaxations of αa and αc, while the effect of TiO2-g-PMMA was negligible. Furthermore, the core–shell structured TiO2-g-PMMA nanoparticles produced considerable smaller interfacial polarization than TiO2 in the composites.

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.

The molecular relaxations in melt-extruded poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) blends with less than 40 wt% PMMA were investigated using dynamic rheological measurement and broadband dielectric spectroscopy. According to dynamic rheology, the total chain entanglement density of the blend melts increased with adding PMMA, and the dissimilar chains were more likely to entangle with each other than similar ones. Furthermore, PMMA facilitated the relaxation process. The dielectric temperature spectra revealed strong structural heterogeneity in the semicrystalline blends whose αa and αc relaxations were accelerated by increasing PMMA content. The αa and αc relaxations were shown to follow the Vogel–Fulcher–Tamman and Arrhenius equations, which allows assigning their molecular origins clearly to amorphous PVDF interphase and the amorphous portions within the crystalline PVDF phase, respectively. However, there exist structural heterogeneities in amorphous PVDF/PMMA mixture phase associated to intermolecular entanglement between dissimilar chains, giving rise to one or two αm relaxations in the dielectric temperature spectra depending on the PMMA content.

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 = Alnk + 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.

The effect of chemically reduced graphene oxide (CRGO) on the phase separation behavior of poly(methyl methacrylate)/poly(styrene-co-acrylonitrile) (PMMA/SAN) blends and the simultaneous response of rheological and conductive behavior of PMMA/SAN/CRGO nanocomposites upon annealing above the phase-separation temperatures were investigated. The introduction of CRGO causes the decrease of binodal temperature and the increase of spinodal temperature for PMMA/SAN blends and then enlarges their metastable regime. During annealing, the well-dispersed CRGO in the homogeneous blend matrix tends to be selectively located in the SAN-rich phase with the evolution of phase separation and then the CRGO further agglomerates effectively in the SAN-rich phase to form the conductive pathway. Thermal-induced dynamic percolation is observed for both the resistivity ρ and dynamic storage modulus G′ as a function of annealing time. The resistivity variation is ascribed to the agglomeration of CRGO in the SAN-rich phase, while the modulus evolution is attributed to the combined contribution of phase separation for blend matrix and the agglomeration of CRGO in the SAN-rich phase.

The effect of nanoclay on the phase-separation behavior of poly(methyl methacrylate)/poly(vinyl acetate) (PMMA/PVAc) blends has been mainly investigated by small-angle laser light scattering. It is found that the effect of clay on the thermodynamics and kinetics of phase-separation for PMMA/PVAc blends seems inconsistent. The kinetics phase-separation rate decreases, while the thermodynamics parameters, cloud points Tc and delay time tD of isothermal phase-separation also decrease, and the variation amplitude depends on the matrix composition. The affinity of clay to PMMA results in the composition difference between the border layer and the polymer matrix and further causes the concentration fluctuation at the early stage of phase separation to reduce Tc and tD. On the other hand, the decrease of phase-separation rate is caused by the mechanical barrier effect of clay on the macromolecular diffusion of blend matrix. Hence, such seemingly counterintuitive results on the thermodynamics and kinetics of phase-separation are attributed to different dominant factors.

•The phase separation behavior of PMMA/SAN/SiO2 was investigated.•The effect of SiO2 on phase separation of PMMA/SAN depends on matrix composition.•The phase separation rate is indubitably retarded by SiO2.•The matrix composition is different from that of boundary layer.•A surface-directed NG occurs in metastable region for filled 30/70 PMMA/SAN system.The phase separation behaviors of poly (methyl methacrylate) (PMMA)/ poly (styrene-co-acrylonitrile) (SAN) blends with and without fumed silica (SiO2) have been investigated using time-resolved small-angle light scattering and dynamic rheological measurements. It is found that the effect of SiO2 on the phase separation behavior of PMMA/SAN blend obviously depends on the composition of the blend matrix. The addition of SiO2 causes the cloud point (Tc) and binodal temperature (Tb) to slightly increase for 60/40 PMMA/SAN, and sharply decrease for 30/70 PMMA/SAN. However, the introduction of SiO2 just causes a small increase of the spinodal temperatures (Ts) for PMMA/SAN with all compositions. Hence, the metastable region of 30/70 PMMA/SAN filled with 5 wt% SiO2 is expanded in large amplitude by the fillers, while the same region of 60/40 filled PMMA/SAN hardly changes. The selective absorption of PMMA on the surface of SiO2 results in the difference between the composition of surface layer and that of polymer matrix, especially for 30/70 PMMA/SAN filled with 5 wt% SiO2. For such system, the phase separation of the surface layer occurs according to an SD mechanism at relatively low annealing temperatures. The SiO2 particles then act as nuclei, inducing the phase separation of the matrix according to NG mechanism.Graphical abstract

The effect of clay on the morphology and phase-separation behavior of poly(methyl methacrylate)/poly(styreneco-acrylonitrile) (PMMA/SAN) blends and the variation of clay dispersion have been investigated. With the evolution of phase separation in PMMA/SAN, most of the clays are first located at the boundaries between PMMA and SAN, and then gradually move to the PMMA-rich domain, owing to the affinity of clay to PMMA. The introduction of clay causes the increase of binodal and spinodal temperatures of PMMA/SAN and enlarges their metastable region, indicating the phase stabilizing effect of clay on the matrix. But the influence of clay on the cloud points obviously depends on the composition of PMMA/SAN. The selective adsorption of PMMA on the clay results in the difference between the composition of surface layer and that of polymer matrix. Hence, the clay plays the role of an agent changing the conditions of phase structure formation.