Structural Evolution in Flowing Immiscible Blends in the Presence of Rough Particles:Dependence of Shear Rate and Blend Ratio

The influence of polystyrene particles with different nanoscale roughnesses on the morphology of polyisobutylene/poly-dimethylsiloxane blends was studied under shear flow by using confocal laser scanning microscopy.It was found that the surface roughness of particles strongly affected their diffusion and distribution behaviors,thereby determining the size and spatial arrangement of droplets in the blends.The roughness effect of particles was found to possess a strong dependence on both the blend ratio and the shear rate.The result suggested that the particle roughness can serve as a new parameter to control the structure-property correlation in particle-filled polymer blends,especially under slow flow.

Excellent Compatibilization Effect of a Dual Reactive Compatibilizer on the Immiscible MVQ/PP Blends

Methyl vinyl silicone rubber (MVQ)/polypropylene (PP) thermoplastic vulcanizate (TPV) combines the good melt processability, recyclability and sealing performance as well as biosafety, stain and fluid resistance, and thus it is especially suitable in bio-safety areas and wearable electronic devices, etc. Nevertheless, the compatibility between MVQ and PP phases is poor. A big challenge on the compatibilization of MVQ/PP blends is that neither MVQ nor PP contains any reactive groups. In this study, a dual reactive compatibilizer composed of ethylenemethyl acrylate-glycidyl methacrylate terpolymer (EMA-co-GMA) and maleic anhydride grafted polypropylene (PP-g-MAH) was designed for the compatibilization of MVQ/PP blends. During melt blending, a copolymer compatibilizer at the MVQ/PP interface can be formed because of the in situ reaction between EMA-co-GMA and PP-g-MAH. The thermodynamic predict of its compatibilization effect through calculating the spreading coefficient of the in situ formed copolymer indicates that it can well compatibilize MVQ/PP blends. The experimental results show that under the GMA/MAH molar ratio of 0.5/1, the interface thickness largely increase from 102 nm for non-compatibilized blend to 406 nm, and the average size of MVQ dispersed phase largely decreases from 2.3 µm to 0.36 µm, the Tg of the two phases shifts toward each other, the mixing torque and mechanical properties of the blend are increased, all indicating its good compatibilization effect. This study provides a good compatibilizing method for immiscible MVQ/PP blends with no reactive groups in both components for the preparation of high performance MVQ/PP TPVs.

Enhanced thermal conductivity and microwave dielectric properties by mesostructural design of multiphase nanocomposite

Next-generation packaging materials are expected to have higher thermal conductivity,because the heat accumulated in high-performance electronic equipment should be removed to increase the service life of the equipment.At the same time,the dielectric loss of the material needs to be reduced to lessen signal delay and attenuation,especially for the applications under high frequency.In this work,we introduce nano-silicon carbide(SiC)and carbon nanotubes(CNTs)into the polystyrene(PS)and poly(methyl methacrylate)(PMMA)blends system.The design of two-way migration at the interface of CNTs and SiC nanoparticles is realized through the masterbatch method and processing technology control.As a result,the thermal conductivity is successfully increased up to 75%.Meanwhile,compared to the CNTs single-phase migration system,it effectively reduces the dielectric loss of the nanocomposite and optimizes the electrical insulation.This work has significant practical application value in the design of electronic device substrates and packaging materials,and provides an innovative methodology for the mesostructure design of multiphase nanocomposites.

Studies on Droplet Size Distributions during Coalescence in Immiscible Polymer Blends Filled with Silica Nanoparticles

The effect of silica nanoparticles on the morphology of （10/90 wt%） PDMS/PBD blends during the shear induced coalescence of droplets of the minor phase at low shear rate was investigated systematically in situ by using an optical shear technique. Two blending procedures were used： silica nanoparticles were introduced to the blends by pre-blending silica particles first in PDMS dispersed phase （procedure 1） or in PBD matrix phase （procedure 2）. Bimodal or unimodal droplet size distributions were observed for the filled blends during coalescence, which depend not so much on the surface characteristics of silica but mainly on blending procedure. For pure （10/90 wt%） PDMS/PBD blend, the droplet size distribution exhibits bimodality during the early coalescence. When silica nanoparticles （hydrophobic and hydrophilic） were added to the blends with procedure l, bimodal droplet size distributions disappear and unimodal droplet size distributions can be maintained during coalescence; the shape of the different peaks is invariably Gaussian. Simultaneously, coalescence of the PDMS droplets was suppressed efficiently by the silica nanoparticles. It was proposed that with this blending procedure the nanoparticles should be mainly kinetically trapped at the interface or in the PDMS dispersed phase, which provides an efficient steric barrier against coalescence of the PDMS dispersed phase. However, bimodal droplet size distributions in the early stage of coalescence still occur when incorporating silica nanoparticles into the blends with procedure 2, and then coalescence of the PDMS droplets cannot be suppressed efficiently by the silica nanoparticles. It was proposed that with this blending protocol the nanoparticles should be mainly located in the PBD matrix phase, which leads to an inefficient steric barrier against coalescence of the PDMS dispersed phase; thus the morphology evolution in these filled blends is similar to that in pure blend and bimodal droplet size distributions can be observed during the early coalescence. These results imply that exploiting non-equilibrium processes by varying preparation protocol may provide an elegant route to regulate the temporal morphology of the filled blends during coalescence.

Morphology and Mechanical Properties of Immiscible Polyethylene/Polyamide12 Blends Prepared by High Shear Processing

In this work, completely immiscible polyethylene/polyamidel2 （PE/PA12） blends were prepared by high shear extruder. The morphology and mechanical properties of the blends were investigated as a function of rotation speed. It was found that the high shear processing is an effective method to improve the dispersion of the PAl2 phase in PE matrix when PA 12 contents are 5 wt% and 10 wt%, and the dispersed phase particle size is reduced with the increase of rotation speed from 100 r/min to 500 r/min. However, with further increase of PAl2 content to 20 wt%, high shear processing has no effect on the phase morphology of the blends. Accordingly, a largely increased elongation at break and impact strength are observed for PE/PAl2/95/5 and PE/PA12/90/10 blends obtained at high rotation speeds but no effect on the property of PE/PAI2/80/20. Annealing experiment demonstrated that the obtained phase morphology is not stable thus compatibilizer should be introduced in the future work. This work could provide a guideline for the application of high shear processing in the preparation of polymer blends with huge polarity difference.

Coalescence Suppression in Flowing Polymer Blends Using Silica Rods with Different Surface Chemistries

Silica rods with homogeneous(hydrophilic or hydrophobic)and amphiphilic surface properties were synthesized and their efficiencies in suppressing the flow-induced droplet coalescence of immiscible polyisobutylene(PIB)/polydimethylsiloxane(PDMS)blends were evaluated via in situ visualization technique.The flow-induced coalescence behavior of blends was found to strongly depend on the surface nature and concentration of silica rods added as well as the blend ratio.While a trace amount of rods promoted coalescence,all kinds of rods demonstrated a morphology refinement effect at high rod concentrations.Good compatibilization effects were obtained at high rod concentrations,especially for hydrophilic and amphiphilic rods.Based on confocal laser scanning microscopy results,these phenomena observed were interpreted reasonably in terms of the selective distribution and aggregation of silica rods,which were suggested to be decisive for the stabilization mechanism and efficiency of these rods.