Linear and nonlinear viscoelastic properties under dynamic oscillatory shear flow were used to investigate the effects of compatibilization on polypropylene (PP)/ polystyrene (PS) blends. Two different nanoparticles (organo-modified clay and fumed silica) were used at various concentrations. To analyze nonlinear stress under large amplitude oscillatory shear (LAOS) flow, nonlinearity (I 3/1 ) was calculated from FT-rheology. To quantify the degree of dispersion of different particles at various concentrations, a new parameter, nonlinear−linear viscoelastic ratio (NLR ≡ normalized nonlinear viscoelasticity/normalized linear viscoelasticity), was used. The relationship was determined between NLR value and PS droplet size in the PP matrix. From the TEM images, clay was located mostly at the interface or partially inside the PS drops, thereby reinforcing the compatibilization effect. Therefore, clay increased the dispersion morphologies of the PP/PS blends. In contrast, fumed silica was located mostly inside the PS droplets, which means the morphologies of PP/PS blends were not improved. Linear viscoelasticities of both PP/ PS/clay and PP/PS/silica showed improvements at elevated particle concentrations. NLR values for the PP/PS/Clay blends were larger than 1 (NLR > 1), whereas NLR values for the PP/PS/silica blends were less than 1 (NLR < 1). Therefore, NLR could be classified into two categories depending on morphology. Based on these results, NLR can be used to distinguish between the effects of two different types of nanoparticles on the morphologies of PP/PS blends.

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Effects of silica nanoparticles with different natures (hydrophilicity and hydrophobicity) on (80/20) PP/PS blends were investigated via linear and nonlinear rheological properties. The hydrophilic silica nanoparticle was fumed silica OX50 while the two hydrophobic ones were precipitated silica D17 and fumed silica R202. SEM images revealed that hydrophilic OX50 could not improve morphological properties of the blends. On the other hand, the two hydrophobic silica nanoparticles (R202 and D17) improved morphological properties. TEM examination showed that OX50 silica nanoparticles aggregated inside PS droplets, thereby making breakup of PS (dispersed) phase into smaller sizes more difficult. D17 and R202 improved morphological properties regardless of the different droplet size reduction mechanisms, and rheological properties improved as a result. Both linear rheological properties from SAOS (small-amplitude oscillatory shear) tests and nonlinear rheological properties from LAOS (large-amplitude oscillatory shear) tests were obtained. The nonlinear−linear viscoelastic ratio (NLR ≡ normalized nonlinear rheological properties/normalized linear rheological properties) was used to quantify the degree of droplet dispersion and distinguish the effects of silica particles on the morphology of PP/PS blends. Previous research has observed an inverse correlation between NLR and droplet size. PP/PS/OX50 blends with no alteration of droplet size showed constant NLR values (≅1) with increasing concentration of OX50 (hydrophilic silica). However, NLR values of PP/PS blends with hydrophobic silica nanoparticles (D17 and R202) were much larger than 1 (NLR > 1) and increased with silica concentration, which is consistent with morphological evolution, i.e., reducing droplet size. However, NLR values of PP/PS/R202 blends were relatively larger than those of PP/PS/D17 blends despite smaller droplet sizes. This can be attributed to a different morphology microstructure, i.e., R202 located in PP matrix phase and D17 at interface between PP and PS. Therefore, the NLR value of PP/PS/silica blend could be due to the combined effects of the interface between droplets (PP/PS blend) and particle−polymer interactions (PP/silica nanocomposites). Especially, R202 showed larger NLR values due to PP/R202 nanocomposites. Based on these findings, relative NLR (= NLR PP/PS/silica /NLR PP/silica ) is proposed as an effective measurement of droplet size information in PP/PS blends by eliminating the effects of PP/silica nanocomposites. Relative NLR matched well with droplet size evolution from the SEM results.

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This study illustrates the effects of the kinetic parameters [processing time, polyvinylidene fluoride (PVDF) viscosity, carbon nanotube (CNT) aspect ratio, and processing method] on the CNT migration and consequently the viscoelastic properties, electromagnetic interference shielding effectiveness (SE), dielectric properties, and electrical conductivities of the corresponding polylactide (PLA)/PVDF/CNT (70/30/0.25 w/w/w) nanocomposites. In the internal mixer, CNTs are premixed with either PLA or PVDF, whereas in the extruder, CNTs are only predispersed in PVDF because the migration route is from PVDF to PLA. The morphology development and CNT migration exhibit time-dependent mechanisms where the properties of the nanocomposites prepared in the internal mixer are relatively higher than those of nanocomposites prepared via the extruder. The viscosity ratio also plays an important role, and more CNTs are found at the interface and PLA when low-viscosity PVDF is employed. The highest SE (7.86 dB), dielectric permittivity (935.23εp ′), and electrical conductivity (1.06 × 10–4 S·cm–1 at 0.1 Hz) values are attained when high aspect ratio (L)-CNTs are predispersed with low-viscosity (L)-PVDF, whereas the lowest properties belong to the blends prepared in the extruder when small aspect ratio (S)-CNTs are predispersed with high-viscosity (H)-PVDF (4.5 dB, 6.00 εp ′, and 2.16 × 10–14 S·cm–1 at 0.1 Hz).

This article critically reviews the detailed fundamental understanding of the influence of conductive nanoparticle migration on the localization, and hence, electrical conductivity of immiscible polymer blend nanocomposites. Three types of conductive nanoparticles, namely, spherical, tubular, and platelet, are discussed with respect to their migration and electrical conductivity of obtained nanocomposites. A complete migration process consists of bulk migration within one component, contact with the interface, and penetration to the other component. During processing, the wetting coefficient parameter is the main thermodynamically controlling factor for nanoparticle localization. However, kinetic effects, such as mixing sequence and intensity, viscosity ratio, size and shape of the nanoparticles, and mixing time, can play a substantial role in determining the final locations of nanoparticles. Moreover, the rate of migration varies with the surface chemistry of the nanoparticles. It has been reported that nanoparticles in a more viscous phase move slower compared with a low viscous phase. Furthermore, nanoparticles having high aspect ratios and surface polarities compatible with the other component migrating faster. It is established that immiscible polymer blend nanocomposites with a “double percolation” structure having higher conductivity with nanoparticles are localized at the interface of the co‐continuous blends.

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