Viscoelastic phase separation (VPS) can produce a network structure of the minor phase, which needs to be stabilized for designing a heterogeneous structure with desired mechanical and electrical functions. In this work, we investigate the stabilization of the VPS-induced network structure in a dynamically asymmetric PS/PVME blend by incorporation of a SEBS-g-MA block copolymer or dimethyldichlorosilane modified nanosilica. The addition of SEBS-g-MA retards the volume shrinking process and slows down the kinetics of phase separation due to its localization at the PS/PVME interfaces. Consequently, in the later stage of VPS, phase inversion occurs at longer times with respect to the neat blend due to the decreased interfacial tension. In contrast, hydrophobic nanoparticles self-assemble in the bulk of PS-rich phase and restrain the dynamics of polymer chains enhancing the dynamic asymmetry of the system. The efficiency of nanoparticles in controlling the kinetics of phase separation is found to be superior compared to block copolymer-based compatibilizers indicating the significance of chain dynamics. Moreover, beyond a critical nanoparticle volume fraction, phase separation is pinned due to particle percolation within the PS-rich phase, yielding a kinetically trapped VPS-induced network structure.

The presented research reports a successful preparation of a super toughened poly(lactic acid)/poly(ethylene vinyl acetate) (PLA/EVA) blend using simultaneous dicumyl peroxide (DCP)‐induced dynamic vulcanization and addition of hydrophobic spherical silica nanoparticles (NPs). The torque evolution during melt mixing of the samples was assessed to track the dynamic vulcanization process. NPs were localized mainly in the EVA droplets and at the interface where a layer of particles was formed with a small amount dispersed in the PLA matrix. The incorporation of NPs or DCP induced compatibilization, causing a drastic decline in the size of EVA droplets in addition to improving the interfacial adhesion. On the other hand, simultaneous dynamic vulcanization and NPs incorporation synergistically affected the compatibilization of EVA and PLA phases. Differential scanning calorimetry (DSC) was employed to analyze the thermal transition and crystallization behavior of the samples. Simultaneous incorporation of silica nanoparticles and DCP at an optimum content significantly improved the tensile toughness, elongation at break, and impact strength, giving rise to super toughened PLA/EVA blend. The elongation at break and impact strength of the dynamically vulcanized PLA/EVA blend containing 5% nanosilica showed an increase from 7% to 175% and 5.1 to more than 77 kJ/m2, respectively as compared to the neat sample. Based on SEM analysis of the fractured surface of the tensile samples, cavitation in combination with intensive shear yielding of the matrix were dominating toughening mechanisms. Finally, the effect of DCP and NPs on the microstructural properties of the sample was investigated through rheological evaluations.

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We investigated the correlation between the time evolution of the different phase-separating morphologies and corresponding linear and transient rheological behaviors for the dynamically asymmetric PS/PVME blend in which there is a large difference between glass transitions of the pure components (about 125 °C). The phase diagram was obtained from dynamic temperature sweep experiments. Phase contrast optical microscopy was employed to investigate morphological evolution of PS/PVME blends at various regions of obtained phase diagram at a constant temperature of 105 °C. At this temperature depending on sample composition, the viscoelastic phase separation (VPS) was observed besides the usual phase separation mechanisms (nucleation and growth (NG) and spinodal decomposition (SD)), indicating the interplay between thermodynamics and viscoelasticity in phase-separation behavior of PS/PVME blends. The linear viscoelastic behavior for different phase separating mechanisms (NG, SD, and VPS) was measured to investigate the kinetics of phase separation. It was found that the linear viscoelastic behavior can be described by Palierne’s emulsion model, if the self-generated stresses induced during the phase separation in the matrix phase are taken into account. Furthermore, the stress growth behavior of different phase-separating morphologies was investigated by transient start-up of shear flow.