Phase morphology evolution and thermally conductive networks of immiscible polymer blends

The selective distribution of fillers in multi-phase polymer blends was dramatically studied to deal with thermal management fields issues. Concerning thermodynamic and kinetic effects of fillers on immiscible polymer blends, the compatibilization of fillers on phase morphology evolution and final construction of thermal conductive pathways were rarely discussed. In this work, BN fillers and polar dispersed phase were introduced into PE through various processing methods. The result showed that filler-coated shell was formed around the larger-sized dispersed phase, thereby forming more thermal conductivity network with other fillers in the two-step processing composites. When the BN content was 20 phr, the thermal conductivity was 0.8271 W/(m·K) for PE/PA6/BN-two steps composites, which was 95.48% higher than that of PE/PA6 composites. From the perspective of the regulation of the morphological structure of the dispersed phase, this study can provide methods and basic data for improving the thermal conductivity of incompatible polymer blends.     

Effects of periodic and non‐periodic chaotic mixing on morphology development of immiscible polymer blends

The effects of periodic and non‐periodic chaotic mixing on the morphology development in the blending of polypropylene as dispersed phase and polyamide 6 as continuous phase in a 2D batch chaotic mixer were investigated with experimental and computational fluid dynamic (CFD) methods. The rotor motions were delivered in steady, periodic (sine waveform and square waveform), and non‐periodic (recursive protocol (RP) and restricted random sequence (RRS)) manners. The mixing efficiency was evaluated with flow number, Poincare map, morphology, droplet size and its distribution. Compared with the sine waveform, RP waveform could eliminate the island structures which existed in the flow domains and its corresponding spatial stretching distribution was more uniform. The recursively generated flow using RP lead to higher mixing efficiency and smaller droplet size with narrow distribution. However, the performance of RRS was ordinary even worse due to its random sequence.© 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

A preliminary investigation of conductive immiscible polymer blends as sensor materials

This paper discusses the feasibility of the application of conductive immiscible polymer blends as sensor materials for detection of organic liquid solvents. Immiscible polymer blends of polypropylene (PP), nylon 6 (Ny6) and carbon black (CB) have been used to produce a series of electrically conductive filaments by a capillary rheometer process. In these immiscible blends, PP serves as a semi‐crystalline matrix and Ny6 as the semi‐crystalline dispersed phase. The enhancement of conductivity in these blends is due to the attraction of CB to Ny6 and localization of CB particles at the PP/Ny6 interface, giving rise to conductive networks. The dc electrical resistivity of extruded filaments, produced at different shear levels, is found to be sensitive to various organic liquid solvents. The shear rate at which the filaments are produced has an important effect on the PP/Ny6/CB filament's sensitivity. The compositions studied were close to the double‐percolation structure believed to perform best as sensor materials. In addition, it seems that the PP/Ny6 interface plays a major role in the sensing process. Liquid contact/drying cycling of the filaments indicates stabilization of the sensitivity change making the sensing process reversible.     

Morphology development in polymer blends produced by chaotic mixing at various compositions

Whereas blending devices commonly entail complex flow fields and internal geometries, chaotic mixing can be instilled by simple periodic motion of bounding surfaces in simple devices. Breakup and coalescence of spatially expansive structures in components can give blends with a wide variety of morphologies. In this study, polystyrene and low density polyethylene were used as model components to study the effect of composition and processing time on gradual morphology development in immiscible binary blends. Inspections of samples disclosed attainable morphologies and also how transitions between morphologies occurred. Novel findings included blends with encapsulated fibers, abundant platelets, and two distinct morphologies having single phase continuity. Additionally, interpenetrating blends formed over a broad compositional range. Results suggest that chaotic mixing is a useful tool for studying relationships among processing conditions, morphology development, and blend properties and may serve as a means to more deliberately obtain target morphologies.     

Chemical sensing materials based on electrically‐conductive immiscible polymer blends

Two families of electrically‐conductive immiscible polymer blends were studied as liquid sensing materials for an homologous series of alcohols. The systems studied include: multiphase matrices [containing carbon black (CB)] consisting of either polypropylene or high‐impact polystyrene as the major phase and thermoplastic polyurethane as the minor dispersed phase; and polyaniline (PANI) dispersed within a polystyrene matrix. Extruded filaments, produced by a capillary rheometer at various shear‐rate levels were used in the sensing experiments. The electrical resistance of these filaments was selectively sensitive to the various alcohols. Moreover, the responses displayed by these filaments are reproducible and reversible. The sensing behaviour of these blends is determined by the nature of the blend components, the blend composition and the processing conditions. An attempt is made to identify the dominant mechanisms controlling the sensing process in CB‐containing immiscible polymer blends and PANI‐containing blends. In addition, the sensing performances of these blends are compared in the light of their sensing mechanisms. Copyright © 2005 Society of Chemical Industry     

The effect of mixing time on the morphology of immiscible polymer blends

The effect of mixing time on the morphology, with the viscosity ratio and composition as parameters in the mixing process, was studied for two immiscible binary polyblend systems, polyamide/polyethersulfone (PA/PES) and poly(butylene terephthalate)/polystyrene (PBT/PS), by selective dissolution followed by macroscopic and microscopic observations. At a short mixing time, the morphology of each phase depends not only on the composition, but also on the viscosity difference of two phases, shown by the results of PA/PES blends with a viscosity ratio of 0.03. The lower viscous phase (PA) forms particles, fibrils, and layers successively with its increasing content and becomes a continuous one at low concentrations as the minor phase, while the high viscous phase (PES) appears mainly in the form of particles and directly becomes a continuous one at high concentrations. With increasing mixing time, the effect of the viscosity ratio becomes less and the morphology is determined mainly by the volume fraction of each phase. Particles are the final morphology of the minor phase. Only at a viscosity ratio of unity is the morphological development of two phases (PBT and PS) with mixing time the same, and any one of these two components is in the form of particles when it is the minor phase. At the composition near 50/50, fibrillar or continuous structure may coexist for both phases. The composition range of co-phase continuity is decided not only by the viscosity ratio but also by the mixing time. With increasing mixing time, this range becomes narrower and finally occurs at volume fraction of 50/50, no longer affected by the viscosity ratio. © 1996 John Wiley & Sons, Inc.     

The effect of mixing history on the morphology of immiscible polymer blends

A laboratory prototype tester was used to systematically study the effects of geometrical and operational variables on the mixing of two immiscible polymer melts. Results verify that the number of passages is a dominant variable in dispersive mixing. The development of micromorphology in a controlled fashion was studied extensively and backed up with a finite element simulation of the flow in the tester geometry. Complex deformational fields in the laboratory mixer are evident from the highly deformed dispersed phase morphologies.     

Morphology development in immiscible polymer blends

This paper presents the results obtained using a new method for analyzing polymer blend morphologies. The method is based on the selective solubilization of the matrix followed by a separation of the dispersed phase in suspension by filtering. A suspension of the nodular part going through the filter is obtained and can be analyzed with a particle counter. The other part of the dispersed phase retained by the filter is constituted of fibers. The average droplet diameters were compared with those obtained using a Scanning Electron Microscope on fracture surfaces for different compositions and flow conditions. The average diameter obtained with the counter technique increases with the dispersed phase content up to an optimum where simultaneously a decrease in the mean diameter and an increase of the fibrillar part are observed, which means that there is a concentration range where these two types of morphologies are present in the blends. The results indicates that the stability of the fibrillar part seems to determine whether the blend morphology will evolve into nodules by the Rayleigh mechanism or into phase inversion by coalescence of stable fibers.     

Thermodynamically induced self‐assembled electrically conductive networks in carbon‐black‐filled ternary polymer blends

By calculating the surface tensions of the components, composites with innovative thermodynamically induced self‐assembled electrically conductive networks were designed, prepared and investigated. Carbon black (CB) was added into a ternary blend system comprised of poly(methyl methacrylate) (PMMA), ethylene–acrylic acid copolymer (EAA) and polypropylene (PP). Scanning electron microscopy images show that the PMMA/EAA/PP ternary blend forms a tri‐continuous phase structure like a sandwich, in which PMMA and PP form a co‐continuous phase while EAA spreads at the interface of the PMMA and PP phases as a sheath. The micrographs and resistivity–temperature characteristic curve results indicate that CB fillers are selectively located at the interface of the PMMA and PP phases, namely the EAA phase. The percolation threshold of PMMA/EAA‐CB/PP composites is 0.2 vol%, which is only one‐fifth of that of PP/CB composites. Copyright © 2011 Society of Chemical Industry     

Co-phase continuity in immiscible binary polymer blends

Methods of microscopic observation and macroscopic characterization have been developed for determining the co-phase continuity in immiscible binary blends. After selective dissolution of the component polymers, the morphologies of microscopic observation are consistent with the results of macroscopic observation and weight percentage determination. By using these methods, the relationship between co-phase continuity, composition and blending time has been explored for two immiscible binary polyblends with different viscosity ratios (λ), polyamide 6/polyethersulfone (PA/PES, λ = 0.03) and poly(butylene terephthalate)/polystyrene (PBT/PS, λ = 1). Both blend systems show a similar dependence of co-phase continuity on the composition and mixing time. That is at short mixing time (for example, 2 minutes), the co-phase continuity takes place in a wide composition range. With increasing blending time, the composition range of co-phase continuity becomes narrow, and finally shrinks to one point. After a long enough mixing time the co-phase continuity region will occur only at a volume fraction of

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, no matter what the viscosity ratio of the blend is. © 1997 Elsevier Science Ltd.     

Orientation of miscible and immiscible polymer blends

Polystyrene (PS) and poly(vinylmethylether) (PVME) were used to study the orientation of miscible and immiscible polymer blends. A miscible blend containing 60 wt% PS was prepared by casting the sample from a benzene solution. The immiscible blend was made by annealing the initially miscible mixture above its lower critical solution temperature for different times and temperatures. Fourier transform infrared spectroscopy and birefringence were used to measure the orientation of PS and PVME, before and after phase separation. Stress-strain curves were also measured for the two types of systems. It was found that the two polymers orient differently and that phase separation induces an increase in the overall orientation of the mixture, in the modulus and in PS orientation. The differences observed between pure PS and PS in the blend were attributed to changes in specific interactions and density of entanglements. The variations with phase separation were attributed to a change in the morphology of the system.     

Investigation of interfacial slip in immiscible polymer blends

In this study, we investigated an interfacial slip phenomenon occurring in immiscible polymer blends. We chose a binary polymer blend in which the interaction parameter, χ, between the component polymers is high, and thus the interface is thin and entanglement is weak. It was observed that the negative viscosity deviation (NVD) of the blends is large, which might be attributable to interfacial slippage between the interfaces. It was also observed that incorporation of a compatibilizer in the blends significantly reduced the NVD, via suppression of interfacial slip due to increased interfacial strength. We carried out a specially designed experiment to verify that interfacial slip is indeed responsible for the NVD. We prepared several blend samples having different phase sizes ranging from 50 ∼ 5 μm, and evaluated the shear stress vs. shear rate relationships of the samples using a capillary rheometer. We observed that the viscosities of the samples decreased as the phase sizes decreased, which is strong evidence of the occurrence of interfacial slip.     

Nonuniformity of phase structure in immiscible polymer blends

This article is focused on the phase structure development in immiscible polymer blends during melt mixing. Nonuniformity of the phase structure, i.e., the coexistence of areas containing particles with markedly different size distribution, was detected in quenched and compression molded samples of a number of various blends prepared by long and intensive mixing in the chamber of a Plasticorder. The same effect was found also for polystyrene/polyamide blends prepared in a twin‐screw extruder. It was shown that neglecting nonuniformity of the phase structure can lead to considerable error in evaluation of the effect of system parameters on the blend morphology. The reasons for the effect were discussed and it was found that inhomogeneous flow field in mixers is a plausible explanation of the nonuniform phase structure. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Processable intrinsically conductive polymer blends

Blends of intrinsically conductive polymers (ICPs) with conventional thermo-plastics exhibit conductivities approaching those of neat ICPs and can be processed using conventional thermoplastic processing equipment. They display good environmental stability and mechanical properties suitable for commercial applications.     

Electrically conductive polymer blends comprising polyaniline

Summary Electroactive polymer blends comprising polyaniline (PANI) as conductive constituent and poly(methyl methacrylate) (PMMA), polystyrene (PS) and methyl methacrylate-butadiene-styrene (MBS) copolymer as a thermoplastic constituent (TC) were prepared by using various techniques:in situ by oxidative polymerization of aniline in aqueous dispersions of the TC; by, coagulating of latex of TC in the acidic dispersions wherein PANI has been preliminary obtained; and by dry blending. It was shown that highest conductivity values revealedin situ prepared PANI/PMMA blends, where the intermolecular interactions between the constituents were suggested to be stronger than in the other systems studied.     

Electrically conductive polymer composites and blends

Increasing utilization of the electrical properties of polymeric blends and composites has prompted our renewed interest in developing a general working relationship which can explain the electrical properties of polymer composites and blends in terms of processing characteristics, morphology, and compositions. Here, we restrict our attention to the following two-component systems: (1) two component systems with conductive particulate inclusions (e.g. carbon black) embedded in a continuous polymeric matrix, and (2) two component polymer blend systems with one conductive polymer (e.g., polyether copolymer) dispersed in another continuous polymeric matrix. The following processing aspects related to the electrical property of particulate filled composites are discussed: (1) critical concentration of rigid conductive fillers, ?_c, and (2) redistribution of conductive fillers upon processing. An equation based on the crowding factor of concentrated suspension rheology and Janzen's particle contacts percolation is proposed to describe the relationship between ?_c, and the maximum packing fraction of conductive fillers. The relationship is used to explain the influence of particle morphology on conductivity, and the conductivity difference in the high shear and the low shear region of a processed polymer composite part. Furthermore, some qualitative guidelines for blending a low conductivity polyether copolymer to achieve an overall balance of antistatic and mechanical properties of polymer blends are also discussed.     

Double emulsions of immiscible polymer blends stabilized by interfacially active nanoparticles

The stability of particle‐stabilized double emulsions under flow is of great scientific and technical interest in many fields. In this work, a two‐step mixing procedure was adopted to produce double emulsions based on viscous polyisobutylene (PIB)/polydimethylsiloxane (PDMS) blends and a small amount of interfacially active hydrophobic silica nanoparticles were used to stabilize the morphology. The structures of nanoparticle‐stabilized double emulsions with varying blend ratios and nanoparticle concentrations were investigated via optical microscopy and rheology technique. It was found that increasing the nanoparticle content effectively facilitated the formation of double emulsion droplets under shear flow and improved their stabilities. Rheology results suggested that these nanoparticle‐stabilized double emulsions displayed a slower relaxation dynamics. Decreasing the concentration of dispersed phase was in favor of the generation of more stable double emulsions, possibly due to the higher particle coverage at the interface between two phases. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4373–4382, 2013     

Fabrication of alumina based electrically conductive polymer composites

Novel electrically conductive composites were synthesized by incorporating Cu coated alumina (Cu‐Al₂O₃) powder prepared via electroless plating technique as filler (0–21wt %) into polystyrene‐b‐methylmethacrylate (PS‐b‐PMMA) and polystyrene (PS) matrices. XRD analysis depicted maximum Cu crystallite growth (26.116 nm～ plating time 30 min) onto Al₂O₃ along with a significant change in XRD patterns of composites with Cu‐Al₂O₃ inclusion. SEM–EDX analyses exhibited uniform Cu growth onto Al₂O₃ and confirmed presence of Cu, Al, Pd in Cu‐Al₂O₃, and C, O, Al, Cu, and Pd in PS‐b‐PMMA and PS composites. Increasing filler loadings exhibited increased electrical conductivity (5.55 × 10^?5S/cm for PS‐b‐PMMA; 5.0 × 10^?6S/cm for PS) with increased Young's modulus (1122MPa for PS‐b‐PMMA; 1053.9MPa for PS) and tensile strength (27.998MPa for PS‐b‐PMMA; 30.585MPa for PS) and decreased % elongation. TGA demonstrated increased thermal stability and DTG revealed two‐step degradation in composites while DSC depicted pronounced increment in T_g of Cu‐Al₂O₃/PS‐b‐PMMA with increased filler loading. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42939.     

Production of electrically conducting plastic composites by three‐dimensional chaotic mixing of melts and powder additives

Extended micron‐scale structures were produced in thermoplastic melts from initially large clusters of conducting carbon black particles transported by three‐dimensional chaotic mixing. The structures formed extensive networks that were captured by solidification and rendered the materials electrically conducting. In essence, percolating structures were constructed in situ in lieu of being the result of chance associations among particles. A systematic study was carried out to assess the influence of key parameters and to relate the electrical properties to the microstructures. Micrographs showed complex structures exhibiting patterns characteristic of chaotic advection. Electrical measurements indicated that conductivity was achieved at carbon black concentrations significantly lower than those achievable by common mixing methods and lower than those reported recently for two‐dimensional chaotic mixing.