Shear-induced fractal morphology of immiscible reactive polymer blends

The origin of shear-induced morphology of two-component immiscible reactive polymer blends is studied by the example of grafting and crosslinking multilayer systems of statistic terpolymer of ethylene, butyl acrylate, and maleic anhydride and statistic copolymers including polyamide and acid groups terminated by acid and/or amine groups. It is found that in contrast to the non-reactive system, the reactive polymer blends display pronounced hydrodynamic instabilities followed by the formation of branched fingers. The observed morphologies are shown to evolve towards the fractal structures. Their fractal dimensions depend on the type of chemical interactions between the blend components resulting either in grafted or crosslinked interfaces. It is shown that the obtained morphologies resemble the Laplacian growth patterns. A simple model of the interface chemical modifications is discussed to explain a physical origin of the observed shear-induced finger instability.     

Effects of polymer matrix and processing on the conductivity of polymer blends

The influence of different hosts, processing conditions and conducting fillers on the percolation threshold (Φ_c) of the resulting conducting blends was investigated. Results indicate that microscopic properties, such as the dipole moments of the side‐groups, and distribution of these groups on the host polymer backbone govern the strength of host–filler interactions, and to a large extent, the value of Φ_c, rather than macroscopic properties such as surface tension. The grade of carbon black used in this experiment was found to be polar in nature and it resulted in lower values of Φ_c with the polar hosts, contrary to published literature. In general, melt blending has been shown to result in higher values of Φ_c when compared to hot pressing alone. In the latter method the conductive filler was found to be isolated at the grain boundaries of the polymer host, resulting in the formation of continuous conducting pathways at low filler concentration. © 2001 Society of Chemical Industry     

Elongational viscosity for miscible and immiscible polymer blends. I. PMMA and AS with similar elongational viscosity

The effects of miscibility and blend ratio on uniaxial elongational viscosity of polymer blends were studied by preparing miscible and immiscible samples at the same composition by using poly(methyl methacrylate) (PMMA) and poly(acrylonitrile-co-styrene) (AS). Miscible polymer blend samples for the elongational viscosity measurement were prepared by using three steps: solvent blends, cast film, and hot press. A phase diagram of blend samples was made by visual observation of cloudiness. Immiscible blend samples were prepared by maintaining the prepared miscible samples at 200°C, which is higher than cloud points using a LCST (lower critical solution temperature) phase diagram. The phase structure of immiscible blends was observed by an optical microscope. The elongational viscosity of all samples was measured at 145°C, which is lower than the cloud-point temperature at all blend ratios. The elongational viscosity of PMMA and AS was similar to each other. The strain-hardening property of miscible blends in the elongational viscosity was only slightly influenced by the blend ratio, and this was also the case with immiscible blends. The strain-hardening property was only slightly influenced, whether it was miscible or immiscible at each blend ratio. Polydispersity in molecular weight for blend samples was not changed by GPC (gel permeation chromatography) analysis. Almost no change in the polydispersity of the molecular weight for blends and the similarity of elongational viscosity between PMMA and AS resulted in little influence of the blend ratio and miscibility on the strain-hardening property. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 757–766, 1999     

Carbon black‐filled PET/HDPE blends: Effect of the CB structure on rheological and electric properties

The rheological and electric properties of blends of poly(ethylene terephthalate) (PET) and high‐density polyethylene (HDPE) filled with various types of carbon black (CB) were analyzed in detail in this project. Four types of CB samples with available values of surface area, particle size, porosity, density, and maximum packing fraction were considered. Blends were prepared using an internal mixing chamber at two different rotational speeds, prior to mold compression of the samples. The rheological properties of the blends with varying polymer composition and a constant amount of CB were recorded in terms of torque variation with time for two shear rates (in terms of rotational speed). Rheological data were related to the resistivity of blends. Results show that the CB structure (porosity, surface area, apparent bulk density, and particle size) largely determine the resulting equilibrium torque and electrical properties. Furthermore, since CB is preferentially located in the HDPE phase, higher conductivity is observed as the PET content decreases, since the relative CB content in this phase increases. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 562–569, 2001     

The viscosity of immiscible polymer blends: influences of the interphase and deformability

The viscosity of immiscible polymer blends has been studied via application of certain aspects of rheology. A symmetric mixture rule was derived, and the deviations from the ‘additivity rule’ have been associated, essentially, with the properties of the interphase, with its influence on the effective volumes of the two polymers constituting the blend and with the deformability of both the interphase and the disperse phase. The rule predicts a positive deviation for a mixture with a disperse-phase viscosity (η_d) greater than that (η_m) of the continuous medium, and a much higher-viscosity interphase, i.e. η_i å η_d ≥ η_m. Negative deviation is to be expected when the interphase has a much lower viscosity than those of the two pure polymers (η_d, η_m å η_i) in the blend. The viscosity and strength of the interphase depend mostly on the specific thermodynamic interactions that led to its creation.     

Phase morphology control of immiscible polymer blends under vibration force field

The formulas of polymer melt velocity, shearing rate, and shearing stress under vibration force field are established through simplifying coaxial cylinder circular flow into plane motional flow. On the basis of the concept of energy ratio model, the rate of energy dissipation and the energy ratio about blending systems are expressed, and the affected factors on phase morphology are studied theoretically. The calculated and analytical results of dynamic flow field and energy ratio show that with the increasing of vibration strength, the fluctuating shearing force field exerted on polymer melt and the negative pressure diffusion behavior of instantaneous impulse strengthen. The energy consumption for phase inversion of immiscible polymer blends under vibration force field is less than that of steady state. The parameter controllability of vibration force field provides a more effective method for realizing phase inversion of immiscible polymer blends. The analysis of transmission electron microcopy micrographs of ethylene–propylene–diene terpolymer/polypropylene blends verifies that the energy ratio model and its phase morphology controlling theory have a good coincidence in comparison with experimental results. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2299–2307, 2006     

Chemical sensing materials. I. Electrically conductive SEBS copolymer systems

Chemical sensing materials based on conductive carbon black (CB) filled [styrene‐ethylene butylene‐styrene] triblock‐copolymers (SEBS) were investigated. Several types of SEBS copolymers were studied, differing in composition and melt viscosity. The sensing is based on electrical conductivity changes upon solvent sorption/desorption. Compression molding SEBS composites containing various amounts of CB were prepared. Their electrical conductivity was measured and samples containing CB, preferentially located in the continuous ethylene/butylene (EB) phase, at a level near the corresponding percolation threshold were used for the sensing experiments. The conductivity was measured during several exposure/drying cycles. Structure characterization included scanning electron microscopy (SEM), dynamic mechanical analysis (DMA), and calorimetry (DSC). The SEBS composites exhibit large reversible changes in conductivity upon exposure to a limited number of solvents, e.g., acetone, n‐heptane, and air drying cycles. This behavior was related to the sorption kinetics, affected by the solvent characteristics (solubility parameter, polarity, molecular volume and vapor pressure). The samples' resistance tended to return to their initial value upon short drying of acetone, and longer drying of other studied solvents. The nature of the SEBS, the CB content, and mixing temperature are all significant parameters, determining the sample's structure and the resultant sensing property. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Carbon black self-networking induced co-continuity of immiscible polymer blends

This work aims to clarify the mechanism of nanoparticle-induced co-continuity in immiscible polymer blends. An industrially relevant system, carbon black (CB)-filled acrylonitrile-butadiene-styrene (ABS)/polyamide 6 (PA6) blends, is investigated via scanning electron microscopy, selective extraction tests, dynamic mechanical analysis, and electrical conductivity measurements. The CB particles are found to be preferentially localized in the PA6 phase, and with an increase in CB loading (Φ_CB), the critical volume fraction of PA6 (Φ_PA6) that is essential for building the co-continuous structure decreases. The product of Φ_PA6 and Φ_CB, n, remains constant for the given system, suggesting that there exists an intrinsic cooperative effect between the CB and the CB-localized polymer phase. A further decrease in Φ_PA6 is achieved either by loading CB with a higher self-networking capability or by isothermal post-treatments for sufficient self-agglomeration of the CB clusters. It is demonstrated that, under the direction of CB self-networking, the CB-localized polymer domains tend to fuse together into co-continuous organization with little phase coarsening. Therefore, CB self-assembly not only plays a key role in extending phase co-continuity over a much larger composition range but also acts on stabilizing the co-continuous polymer domains during the melt processing.     

Elongational viscosity for miscible and immiscible polymer blends. II. Blends with a small amount of UHMW polymer

The effect of miscibility on elongational viscosity of polymer blends was investigated in homogeneous, miscible, and immiscible states by the blend of 1.5 wt % of ultrahigh‐molecular‐weight (UHMW) polymer. The matrix polymer was either poly(methyl methacrylate) (PMMA), or poly(acrylonitrile‐co‐styrene) (AS) that has a comparable elongational viscosity value. The homogeneous blend consisted of 98.5 wt % of PMMA and 1.5 wt % of UHMW–PMMA. The miscible blend was composed of AS and UHMW–PMMA at the same ratio. The immiscible blend was a combination of AS and UHMW–polystyrene (PS) at the same ratio. The strain‐hardening behavior of the different blends were compared with that of pure PMMA. It was demonstrated that 1.5 wt % of UHMW induces a strong strain‐hardening property in the homogeneous and miscible blends but was hardly changed in the immiscible blend. The optical microscope observation of the immiscible blend suggested that the UHMW domains were stretched, but that the degree of domain deformation was less than a given elongational strain. It was concluded that the strain‐hardening property is strongly affected by the miscibility of UHMW chain and matrix. The strong strain‐hardening property is caused by the deformation of the UHMW polymer. UHMW chains are stretched when they are entangled with surrounding polymers. However, UHMW chains in an immiscible state are not so deformed because of viscosity difference and no entanglements between domain and matrix. A smaller degree of UHMW chain deformation in immiscible state results in weaker strain‐hardening property. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 961–969, 1999     

Effect of filler treatment on temperature dependence of resistivity of carbon-black-filled polymer blends

Polyblends prove to be able to provide more possibilities for tailoring conductive polymer composites in comparison with individual polymer systems. Accordingly, ethylene–vinyl acetate—low-density polyethylene (EVA–LDPE) filled with carbon black (CB) was prepared in this study as a candidate for positive temperature coefficient (PTC) material. In consideration of the fact that CB distribution plays the leading role in controlling a composite's conduction behavior, chemical treatment of CB was applied to reveal its influence on percolation and the PTC effect. It was found that titanate coupling agent treatment facilitated sufficient distribution of CB in LDPE phase, leading to lower resistivity and a squarer PTC curve. Composites filled with nitric-acid-treated CB exhibited specific temperature dependence of resistivity as a result of the heterogeneous dispersion of CB at the interface of EVA–LDPE, which might provide the materials with a new function. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 489–494, 1999     

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     

The effect of the embedded interface dynamics on mass transport in immiscible polymer blends

Mass transport of solvents into immiscible blends may exhibit a non-Fickian behavior due to the deformation of the embedded interface that couples with diffusion. We introduce an interface area covariant tensor N as a structural state variable and derive a set of thermodynamically-consistent PDEs and ODEs transport equations for the bulk and time-dependent boundaries. The proposed model, which is a reformulation of that derived by El Afif (2008) and El Afif et al. (2003), improves both mathematically and numerically the investigation of the diffusion-interface coupling and provides reasonable predictions of the sorption-permeation one dimensional treatment affording good agreement with experimental data. The tensor N englobes, into a single morphological quantity, all information regarding diffusion-induced changes in the size and shape anisotropy of the interface area. Predicted results include concentration, components of N , residual stresses, mass-uptake, and swelling. Scaling leads to three relevant dimensionless parameters: a mixing-interface coupling constant and bulk and boundary diffusion Deborah numbers.     

Effect of confinement on glass dynamics and free volume in immiscible polystyrene/high‐density polyethylene blends

The effect of confinement on glass dynamics combined with the corresponding free volume changes of amorphous polystyrene (PS) in blends with semi‐crystalline high‐density polyethylene (HDPE) have been investigated using thermal analyses and positron annihilation lifetime spectroscopy (PALS). Two different glass transition temperatures (T_g) were observed in a PS/HDPE blend due to the dissimilarity in the chemical structure, consistent with an immiscible blend. However, T_g of PS in the incompatible PS/HDPE blend showed an upward trend with increasing PS content resulting from the confinement effect, while T_g of the semi‐crystalline HDPE component became lower than that of neat HDPE. Moreover, the elevation of T_g of PS was enhanced with a decrease of free volume radius by comparing annealed and unannealed PS/HDPE blends. Positron results showed that the free volume radius clearly decreased with annealing for all compositions, although the free volume hole size agreed well with linear additivity, indicating that there was only a weak interaction between the two components. Combining PALS with thermal analysis results, the confinement effect on the glass dynamics and free volume of PS phase in PS/HDPE blends could be attributed to the shrinkage of HDPE during crystallization when HDPE acted as the continuous phase. © 2015 Society of Chemical Industry     

Compatibilizing efficiency of copolymer precursors for immiscible polymer blends

An anhydride‐terminated polystyrene (PS‐b‐Anh) as a block copolymer precursor and a copolymer (PS‐co‐TMI) of styrene (St) and 3‐isopropenyl‐α,α‐dimethylbenzene isocyanate (TMI) as a graft copolymer precursor are chosen to investigate the effect of the type of the copolymer precursor on its compatibilizing and stabilizing efficiency for polymer blends. Results show that during the melt blending of the PS and PA6, the addition of PS‐b‐Anh dramatically decreases the size of the dispersed phase domains, irrespective of its molecular weight. This indicates that a diblock copolymer PS‐block‐PA6 (PS‐b‐PA6) is formed by a reaction between the terminal anhydride moiety of the PS‐b‐Anh and the terminal amine group of the PA6. When PS/PA6 (30/70) blends are annealed at 230°C for 15 min, their morphologies are much more stable in the presence of the PS‐b‐Anh block copolymer precursor than in the presence of the PS‐co‐TMI graft copolymer precursor. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

高分子基气敏导电复合材料

综述了高分子基气敏导电复合材料的制备方法，导电机理和近年来的研究状况。     

Tuning gradient microstructures in immiscible polymer blends by viscosity ratio

Bioinspired gradient microstructures provide an attractive template for functional materials with tailored properties. In this study, filaments with gradient microstructures are developed by melt-spinning of immiscible polymer blends. The distribution of the gradient morphology is shown to be controlled by the viscosity ratio of polymers as well as the geometry of the capillary die. Distinct microstructure gradients with long thin fibrils near the surface region and short large droplets near the center region of the filament, as well as the inverse pattern, are formed in systems with different viscosity ratios. The shear flow field in the capillary can elucidate the formation mechanisms of gradient morphologies during processing. The results demonstrate how the features of a gradient microstructure can be tailored by the design of capillary geometry and processing conditions. The viscosity ratio is then introduced as an adjusting tool to control the gradient morphology in a given processing setup. In consequence, this study provides novel design routes for achieving gradient morphologies in immiscible polymers. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48165.     

Prediction of average droplet size in flowing immiscible polymer blends

The paper is focused on calculation of the average droplet size in immiscible blends during their steady flow. Available theoretical and experimental results of studies of the droplet breakup and coalescence are utilized to derive the equations describing dynamic equilibrium between the droplet breakup and coalescence. New expression for the coalescence efficiency, reliably reflecting recent theoretical results, is proposed. The equation for the average steady droplet size, controlled by the stepwise breakup mechanism and coalescence of droplets with not very different sizes, is derived for blends containing up to 10–20 vol % of the droplets. For blends with above approximate 20 vol % of the droplets, the breakup by the Tomotika mechanism and coalescence in highly polydisperse system is modeled. Results of the derived equations are compared with experimental data; qualitative agreement is found for the dependence of the droplet size on the amount of the dispersed phase. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45250.     

Electrical behavior and structure of polypropylene/ultrahigh molecular weight polyethylene/carbon black immiscible blends

This study investigates the electrical behavior, which is the positive temperature coefficient/negative temperature coefficient (PTC/NTC), and structure of polypropylene (PP)/ultrahigh molecular weight polyethylene (UHMWPE)/carbon black (CB) and PP/γ irradiated UHMWPE (XL‐UHMWPE)/CB blends. As‐received UHMWPE or XL‐UHMWPE particles are chosen as the dispersed phase because of their unusual structural and rheological properties (extremely high viscosity), which practically prevent CB particles penetration. Because of their stronger affinity to PE, CB particles initially form conductive networks in the UHMWPE phase, followed by distribution in the PP matrix, thus interconnecting the CB‐covered UHMWPE particles. This unusual CB distribution results in a reduced electrical percolation threshold and also a double‐PTC effect. The blends are also investigated as filaments for the effect of shear rate and processing temperature on their electrical properties using a capillary rheometer. Because of the different morphologies of the as‐received and XL‐UHMWPE particles in the filaments, the UHMWPE containing blends exhibit unpredictable resistivities with increasing shear rates, while their XL‐UHMWPE containing counterparts depict more stable trends. The different electrical properties of the produced filaments are also related to differences in the rheological behavior of PP/UHMWPE/CB and PP/XL‐UHMWPE/CB blends. Although the flow mechanism of the former blend is attributed to polymer viscous flow, the latter is attributed to particle slippage effects. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 104–115, 2001     

Electrically conductive sensors for liquids based on quaternary ethylene vinyl acetate (EVA)/copolyamide/maleated‐EVA/polyaniline blends

Electrically conductive blends, containing two immiscible polymers (ethylene vinyl acetate copolymer, EVA‐19, and copolyamide 6/6.9, CoPA), polyaniline (PANI), and maleated EVA compatibilizer were studied as sensing materials for a homologous series of alcohols (methanol, ethanol, and 1‐propanol). Recent results have shown that the corresponding uncompatiblized blends exhibited a preferred localization of PANI in the CoPA phase, leading to a cocontinuous morphology (i.e., both the CoPA phase and the PANI component located in it are continuous). The concept of the compatibilizer addition was to improve compatibility between the EVA‐19 and the CoPA, modifying the morphology of the PANI‐containing blend and altering its sensing properties. Extruded EVA‐19/CoPA/maleated‐EVA/PANI filaments produced by a capillary rheometer process at various shear rate levels were used for the sensing experiments. The filaments displayed high sensitivity levels upon exposure to the various alcohols as well as improved sensing stability and reproducibility at low compatibilizer contents. The sensing properties vary with compatibilizer concentration and are of inferior quality beyond a certain content. The sensing behavior of the compatibilized filaments is compared to the previously reported results for the corresponding uncompatibilized filaments. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 110–117, 2006