Image analysis for interfacial area and cocontinuity detection in polymer blends

A novel image processing method was developed to extract interfacial area concentration measurements from 2D micrographs of immiscible polymer blends. Although this method can be used for analyzing different types of 2D micrographs such as optical or transmission electron microscopy images, it was designed for analyzing scanning electron microscopy (SEM) images. The method operates by detecting edges within the images and using standard image processing operations to selectively eliminate false edges. SEM images of polyethylene oxide/polystyrene (PEO/PS) blends were analyzed using this image processing method to measure the amount of interfacial area in the samples. Interfacial area per unit volume exhibits maxima for blend compositions at the boundary between droplet and cocontinuous morphologies. In addition to the detection of cocontinuity, the interfacial area measurements facilitated by this method may be used in future investigations of blend dynamics, including coalescence, drop deformation, and blend rheology studies. These measurements may also be used to quantify the effects of compatibilizers on blend morphology.     

Continuity development in polymer blends of very low interfacial tension

Phase continuity development and co-continuous morphologies are highly influenced by the nature of the interface in immiscible polymer blends. Blends of ethylene-propylene-diene terpolymer (EPDM) and polypropylene (PP) possess an interfacial tension of about 0.3 mN/m and provide an interesting model system to study the detailed morphology development in a very low interfacial tension binary system. A variety of blends with viscosity ratios of 0.2-5.0 and shear stresses of 11.7-231.4 kPa were considered. Using a variety of sophisticated morphology protocols it is shown that at low blend compositions, the dispersed phase actually exists as stable fibers of extremely small diameter of 50-200 nm and the continuity develops by fiber-fiber coalescence. An analysis using break-up times from Tomotika theory also supports the notion of highly stable dispersed fiber formation. These results challenge the current view of the dispersed phase as small spherical droplets. It is shown, under these conditions, that a seven-fold variation in the viscosity ratio has virtually no influence on % continuity or morphology, while a large change in the matrix shear stress from 11.7 to 90.9 kPa has an important effect on pore diameter. Both sides of the continuity diagram are studied and highly symmetrical continuity behavior is observed with composition. In fact a single master continuity curve is observed for these blends varying in viscosity ratio from 0.7-5.0 and with shear stresses from 11.7-90.9 kPa. Although the glass transition temperatures indicate that these materials are completely immiscible after melt mixing and cooling, it is shown that the blends demonstrate the morphological features of a partially miscible system. These results support a concept that the blend was partially miscible during melt blending, at which time the gross morphological features of the blend were developed, but becomes fully phase separated upon cooling. It appears that the quenching of the EPDM/PP blend from the melt is rapid enough to preserve the imprint of that partial miscibility on the gross blend morphology.     

Effect of multiblock copolymers in polymer blends

The use of multiblock copolymers for the compatibilization of immiscible polymer blends is controversially discussed in the literature. Investigations have been carried out to estimate the effect of multiblock copolymers containing segments of a liquid crystalline polyester (LCP) and polysulfone (PSU) segments in blends of the based homopolymers. One goal was to determine whether multiblock copolymers provide an opportunity for compatibilizing PSU/LCP blends. By using PSU/LCP multiblock copolymers with different molecular weights of the blocks in the appropriate binary, solution-casted blends, it was shown that the interpenetration of the polysulfone phase of the block copolymer and the PSU matrix leads to an improved miscibility of the blend. This effect is retained in ternary blends of PSU, LCP, and the multiblock copolymer, assuming a certain critical molecular weight of the multiblock copolymer segments. In addition, some mechanical characteristics of PSU/LCP melt blends such as the E-modulus and fracture strength are improved by adding long-segmented multiblock copolymers. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2293–2309, 1997     

Sub-micron dispersed-phase particle size in polymer blends: overcoming the Taylor limit via solid-state shear pulverization

A comparison was made of the fineness of dispersion in immiscible polymer blends achieved by a continuous mechanical alloying technique, solid-state shear pulverization, relative to that achieved by melt mixing. Two polymer blend systems were investigated. A polystyrene (PS)/polyethylene (PE) wax blend was studied because, based on a classic analysis by G.I. Taylor, melt mixing was expected to yield a number-average dispersed-phase domain size, D_n, well above 1 μm. A PS/high density polyethylene (HDPE) blend was also studied because it was known to produce a sub-micron number-average dispersed-phase particle size when mixed by twin-screw extrusion. In the case of the PS/PE wax blend at compositions ranging from 1 to 15 wt% polyethylene wax, pulverization resulted in nearly identical D_n values (typical value of 0.7 μm) independent of minor-phase content; these D_n values were an order of magnitude smaller than the anticipated Taylor limit for melt-mixed blends. In contrast, PS/PE wax blends made by batch, intensive melt mixing yielded D_n values between ∼3 μm at both 1 and 5 wt% minor-phase content and 17.5 μm at 15 wt% minor-phase content. The increase in D_n with increasing dispersed-phase content in the melt-mixed blend is a consequence of coalescence present during melt processing; such effects are disallowed in the pulverization process occurring in the solid state. Scanning electron microscopy of a 95/5 wt% PS/HDPE blend provided D_n values of 500 and 270 nm in the twin-screw extruded and pulverized samples, respectively. Fractionated crystallization studies further corroborated the ability of pulverization to result in a finer, nanoscopic dispersion of the minor phase as compared to extrusion.     

Morphology development and size control of PA6 nanofibers from PA6/CAB polymer blends

Polyamide 6 (PA6) nanofibers were prepared by the melt blending extrusion process of PA6/cellulose acetate butyrate (CAB) immiscible polymer blends. The average diameter of obtained PA6 nanofibers was 95–190 nm which could be controlled by varying the process conditions, such as blend ratio was 10/90‐40/60, shear rate was 10 and 80 s^?1and two different blending equipments, and the effect of adding graphene for the diameters was also discussed. In addition, and the formation mechanism of nanofibers was studied by viscoelastic analysis and collecting samples at four different sites along the extruder. The morphology of PA6 dispersed phase in CAB matrix included three stages: PA6 pellets changed into sheets or ribbons, the formation of microfibers and size reduction, the size of microfibers continued refinement to nanofibers. The morphology development of dispersed phase may be postponed by blend ratio. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42184.     

Electroactive polymer blends

The rapid development of two new classes of electrically active polymer materials, electronically conducting and electroactive polymers and ion-conducting polymers respectively, offers new possibilities for application of both classes of material, especially in combination with each other. While some of these combinations have been attempted before, they all met serious problems due to poor interpenetration of the two polymers. The recent availability of solubilized and soluble electroactive and conductive polymers has greatly advanced the possibilities of reducing the interpenetration problem. Some experimental studies using the combination of solubilized electroactive polypyrrole with poly(ethylene oxide) in an electroactive polymer blend electrode for solid-state polymer batteries are discussed. The opportunities for using polymer blends for solid-state electrochemical polymeric devices, and avenues for the development of materials for such devices, are also reviewed.     

聚合物共混相容性研究进展

介绍了聚合物共混相容性的热力学理论，讨论了相容性的实验表征方法，包括共混物形态和物性表征等，提出了改善聚合物相容性的重要途径及其进展。     

Efficiency of graft copolymers as compatibilizers for immiscible polymer blends

This work was aimed at studying the emulsification efficiency of graft copolymers and the effect of feeding mode on the emulsification efficiency using the emulsification curve approach. The blends were composed of polystyrene (PS) and polyamide 6 (PA6). PS was always the matrix and PA6 the dispersed phase. A series of graft copolymers of PS and PA6, denoted as PS-g-PA6, with different molecular structures were used as emulsifiers. Feeding mode had a very significant effect on the size of the dispersed phase domains at short mixing time and its effect decreased or became negligible at long mixing time. This indicates that feeding mode affected mostly the time necessary for the PS-g-PA6 emulsifier to reach and emulsify the PS/PA6 interfaces. The molecular structure of the PS-g-PA6 graft copolymer also had a profound effect on its emulsification efficiency. The longer the PA6 grafts (from 1.7 to 5.1 kg/mol), the higher the emulsification efficiency. On the other hand, the number of PA6 grafts had little effect on the emulsification efficiency when the PA6 grafts were short (1.6-1.7 kg/mol). The effect of the blend composition was also investigated.     

A rheological model for polymer blends based on the concentric multilayer approach. I. Homogeneous polymer blends

The melt rheological behavior of polymer blends was investigated by means of a capillary rheometer. The systems chosen for study were blends of polystyrene (PS) with different molecular weights and blends of polymethylmethacrylate (PMMA) with different molecular weights. A modified concentric multilayer model was proposed to correlate the rheological properties of the polymer blends with the composition and shear rate. The agreement between the calculated values and the measured ones is satisfactory.     

Compatibilization and morphology development of immiscible ternary polymer blends

We report a novel and effective strategy that compatibilizes three immiscible polymers, polyolefins, styrene polymers, and engineering plastics, achieved by using a polyolefin-based multi-phase compatibilizer. Compatibilizing effect and morphology development are investigated in a model ternary immiscible polymer blends consisting of polypropylene (PP)/polystyrene(PS)/polyamide(PA6) and a multi-phase compatibilizer (PP-g-(MAH-co-St) as prepared by maleic anhydride (MAH) and styrene (St) dual monomers melt grafting PP. Scanning electron microscopy (SEM) results indicate that, as a multi-phase compatibilizer, PP-g-(MAH-co-St) shows effective compatibilization in the PP/PS/PA6 blends. The particle size of both PS and PA6 is greatly decreased due to the addition of multi-phase compatibilizer, while the interfacial adhesion in immiscible pairs is increased. This good compatibilizing effect is promising for developing a new, technologically attractive method for achieving compatibilization of immiscible multi-component polymer blends as well as for recycling and reusing of such blends. For phase morphology development, the morphology of PP/PS/PA6 (70/15/15) uncompatibilized blend reveals that the blend is constituted from PP matrix in which are dispersed composite droplets of PA6 core encapsulated by PS phase. Whereas, the compatibilized blend shows the three components strongly interact with each other, i.e. multi-phase compatibilizer has good compatibilization between the various immiscible pairs. For the 40/30/30 blend, the morphology changed from a three-phase co-continuous morphology (uncompatibilized) to the dispersed droplets of PA6 and PS in the PP matrix (compatibilized).     

Light emission in phase separated conjugated and non-conjugated polymer blends

Phase separations in conjugated polymer (MEH-PPV) and non-conjugated polymer (PMMA) blended films are studied by photoluminescent (PL) near-field scanning optical microscope and spectrometer. The morphologies of blended films changed from stripe patterns to isolated islands as PMMA concentrations increased. The PL spectra in isolated micron dots are the same as MEH-PPV. Nevertheless, we found new PL spectra, peaked at 500 nm wavelength, in the PMMA matrix. Since, PMMA does not emit light, the new spectra indicate some MEH-PPV diluted in the PMMA rich regions. The excitons of MEH-PPV in the PMMA matrix are localized and emit light as PPV oligomers.     

Highly efficient polymer blends from a polyfluorene derivative and PVK for LEDs

The photophysical and electroluminescent properties of blends of a polyfluorene derivative of the PPV type, poly[(9,9-dihexyl-9H-fluorene-2,7-diyl)-1,2-ethenediyl-1,4-phenylene-1,2-ethenediyl] (labeled as LaPPS16) and poly(vinylcarbazole) - PVK are presented and discussed in terms of the operating light emission mechanisms. Static and dynamic fluorescence measurements and morphology data showed a powerful exciton migration from the host (PVK) to the guest (LaPPS16) resulting in emission coming from solely LaPPS16, even when in concentrations small as 1%. Electroluminescence was greatly enhanced with the blending; increases of 18 times in efficiency and 20 times in luminance were achieved in the blend containing 20% LaPPS16, with 3 V applied voltage.     

Block copolymer compatibilization of cocontinuous polymer blends

The effect of block copolymers on the cocontinuous morphology of 50/50 (w/w) polystyrene (PS)/high density polyethylene (HDPE) blends was investigated using symmetric polystyrene-polyethylene block copolymers (PS-PE) with molecular weights varying from 6 to 200 kg/mol. The coarsening rate during annealing was compared to the Doi-Ohta theory. An intermediate molecular weight PS-PE, 40 kg/mol, showed remarkable results in reducing the phase size and stabilizing the blend morphology during annealing. Mixing small amounts of 6, 100 or 200 kg/mol PS-PE in the blend did not reduce the phase size significantly, but did decrease the coarsening rate during annealing. In stabilizing the morphology, 6 kg/mol PS-PE was inferior to 100 and 200 kg/mol. The existence of an optimal molecular weight block copolymer is due to a balance between the ability of the block copolymer to reach the interface and its relative stabilization effect at the interface.     

Morphology study of immiscible polymer blends in a vane extruder

This study reports the morphology development of polymer blends in a novel vane extruder in which polymer mainly suffers from elongational deformation field. Rapidly cooled samples of polypropylene/polystyrene (PP/PS) are collected in the vane extruder after stable extrusion. Furthermore, the shape and size of the dispersed phase from initial to final stages are analyzed. In addition, in order to compare the final size of the dispersed phase, different immiscible blends, including polypropylene/polyamide and PP/PS, are prepared by vane extruder and twin‐screw extruder, respectively. The results show that the dispersed phase is made to change rapidly from stretched striations to droplets under the strong elongational deformation field in the vane extruder. Furthermore, the droplet size of dispersed phase of blends prepared by vane extruder is much smaller than that prepared by twin‐screw extruder, indicating that the vane extruder is more efficient in mixing for immiscible polymer blends. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Interface morphology snapshots of vertically segregated thin films of semiconducting polymer/polystyrene blends

We present atomic force microscopic images of the interphase morphology of vertically segregated thin films spin coated from two-component mixtures of poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene-vinylene] (MEH-PPV) and polystyrene (PS). We investigate the mechanism leading to the formation of wetting layers and lateral structures during spin coating using different PS molecular weights, solvents and blend compositions. Spinodal decomposition competes with the formation of surface enrichment layers. The spinodal wavelength as a function of PS molecular weight follows a power-law similar to bulk-like spinodal decomposition. Our experimental results indicate that length scales of interface topographical features can be adjusted from the nanometer to micrometer range. The importance of controlled arrangement of semiconducting polymers in thin film geometries for organic optoelectronic device applications is discussed.     

Effect of shear flow on multi-component polymer mixtures

The effect of shear flow on the structure of multi-component polymer blends and solutions is reviewed. The techniques of small-angle light and neutron scattering, optical microscopy, and fluorescence microscopy are used to directly assess the influence of an externally applied shear field on the phase stability and morphology of model polymer blends and solutions. The polymeric fluids of interest vary from miscible blends and pseudo-binary solutions near a critical point of unmixing to thermodynamically unstable and completely immiscible blends undergoing spinodal decomposition and coarsening in the presence of simple shear flow. We review the influence that critical concentration fluctuations, viscoelasticity, and rheological asymmetry have on the shear response of polymer blends and solutions individually, and we discuss the practically important interplay of these three separate effects. We conclude our review by discussing the need for more computational and theoretical efforts focused on shear-induced structure in polymer blends.     

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.     

Electric force microscopy of dielectric heterogeneous polymer blends

We report the applicability of Electric Force Microscopy (EFM) for the analysis of thin films of dielectric heterogeneous polymer blends constituted of polymers with both close and significantly different dielectric constants and offer a simple model that enables quantitative analysis of EFM images of such blends.     

Hydrogen-bonding in polymer blends

Hydrogen bonding in polymer blends is a topic of great interest to polymer scientists because such systems have many potential applications. Introducing functional groups to one component to make it capable of forming hydrogen bonds to another, thereby enhancing the miscibility of otherwise immiscible blends, is one of the major achievements during the past 20 years of polymer science. The Painter–Coleman association model generally describes these interactions accurately. This Review discusses in detail the effects of hydrogen bonding on the miscibility and thermal properties of polymer blend systems.     

Relaxation behavior of polymer blends with complex morphologies: Palierne emulsion model for uncompatibilized and compatibilized PP/PA6 blends

This paper deals with the dynamic rheological behavior of polypropylene/polyamide6 (PP/PA6) uncompatibilized blends and those compatibilized with a maleic anhydride grafted PP (PP/PP-g-MAH/PA6). The terminal relaxation times of the blends predicted by the Palierne emulsion model were compared with those obtained from experimental relaxation time spectra. The Palierne model succeeded well in describing PP/PA6 uncompatibilized blends with relatively low dispersed phase contents (10 wt%) and failed doing so for those of which the dispersed contents were high (30 wt%). It also failed for the compatibilized ones, irrespective of the dispersed phase content (10 or 30 wt%) and whether or not interface relaxation was taken into consideration. In the case of the uncompatibilized blend with high dispersed-phase content, interconnections among inclusions of the dispersed phase were responsible for the failure of the Palierne model. As for the compatiblized blends, in addition to particle interconnections, the existence of emulsion-in-emulsion (EE) structures was another factor responsible for the failure of Palierne model. A methodology was developed to use Palierne emulsion model upon taking into account the effects of the EE structure on the viscosity of the continuous phase and the effective volume fraction of the dispersed phase.