Morphological study on water‐borne conducting polyaniline‐poly(ethylene oxide) blends

Conducting polyaniline‐poly(ethylene oxide) blends were prepared from their aqueous solutions. The blends displayed an electrical conductivity percolation threshold as low as 1.83 wt % of polyaniline loading. As demonstrated by scanning electron microscopy, polarized optical microscopy, and wide‐angle X‐ray diffraction studies, the conducting polyaniline took a fibrillar morphology in the blend, and it existed only in the amorphous phase of poly(ethylene oxide). A three‐phase model combining morphological factors instead of a two‐phase model was proposed to explain the low‐conductivity percolation threshold. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 605–612, 2002; DOI 10.1002/polb.10114     

Stability of the co‐continuous morphology during melt mixing for poly(ε‐caprolactone)/polystyrene blends

Over the last 10 years, research into co‐continuous polymer blends has been intense. Despite these efforts, there are very few detailed studies on the stability of this complex morphology. In this work, blends of poly(ε‐caprolactone) and polystyrene were melt‐mixed in an internal mixer for time intervals of 0.5–120 min at set temperatures of 140 and 170 °C, and the effect of the mixing time on the co‐continuous morphology was studied. This blend system was chosen because each component could be selectively dissolved and this allowed for a complete study of the co‐continuous region. The phase continuity was measured with a solvent‐extraction gravimetric technique, and the concentration range for co‐continuity was determined. The phase size and phase size distribution were obtained with the mercury intrusion porosimetry technique. The results indicate that the co‐continuous morphology forms very early in the mixing process and achieves a stable morphology within the first 5 min of mixing for virtually all the co‐continuous compositions. For all cases studied, the co‐continuous morphology remains unchanged over mixing times as long as 1–2 h. These results support the notion of a stable steady‐state formation of co‐continuous morphologies during melt mixing similar to that observed for matrix/dispersed phase type blends. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 864–872, 2007     

Direct observation of morphological development during the spin‐coating of polystyrene–poly(methyl methacrylate) polymer blends

We present results of the direct observation, in real‐space, of the phase separation of high molecular weight polystyrene and poly(methyl methacrylate) from ortho‐xylene using our newly developed technique of high speed stroboscopic interference microscopy. Taking a fixed concentration (3 wt % in o‐xylene) at a fixed composition (1:4 by weight) and by varying the rotational rate during the spin‐coating process, we are able to observe the formation of a range of phase separated bicontinuous morphologies of differing length‐scales. Importantly, we are able to show that the mechanism by which the final phase separated structure is formed is through domain coarsening when rich in solvent, before vitrification occurs and fixes the phase separated structure. The ability to directly observe morphological development offers a route toward controlling the length‐scale of the final morphology through process control and in situ feedback, from a single stock solution. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B Polym. Phys. 2013, 51, 875–881     

Morphological development and rheological changes of phenoxy/SAN blends during in‐situ polymerization

This article reports the results of an investigation into the time‐dependent morphological and rheological changes that accompany the in‐situ polymerization of blends composed of poly(hydroxyether of bisphenol A) (phenoxy) and poly(styrene‐co‐acrylonitrile) (SAN). The rheological behavior was monitored continuously during the in‐situ polymerization, whereas the miscibility and phase structure of blends formed in situ were examined at discrete stages of polymerization by differential scanning calorimetry and transmission electron microscopy. In the blend with 30 wt % SAN, a co‐continuous blend morphology was associated with gradual changes in the dynamic moduli, suggesting that phase separation proceeded by spinodal decomposition (SD). In contrast, phenoxy‐rich dispersions were uniformly dispersed in a continuous SAN‐rich matrix in the blend with 50 wt % SAN, and the corresponding rheological signature revealed a sharp initial increase in the dynamic moduli, followed by slower growth after long times, indicative of phase separation via nucleation and growth (NG). The rheological property changes are closely related to morphology development and mechanisms of phase separation induced duringin‐situ polymerization. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2614–2619, 2007     

Temperature‐dependent polymer–polymer interactions in polystyrene–polyethylene blends

The effect of the temperature on the interaction between the components of an immiscible polystyrene–polyethylene blend has been analyzed with different techniques. Lap‐shear‐strength data and morphological observations indicate an enhanced interaction between the polymeric phases at elevated temperatures, at which dispersive forces are known to predominate. This raises the degree of compatibility of the polymeric components. Rheological measurements also justify the concept of increased adhesion between the components of the blend when it is processed at very high temperatures. Differential scanning calorimetry analysis lends support to an improved homogeneity of the blend at an elevated temperature; this is again consistent with an improved interaction between the blend phases. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2545–2557, 2004     

Poly‐(ε‐caprolactone) (PCL) and poly(hydroxy‐butyrate) (PHB) blends containing seaweed fibers: Morphology and thermal‐mechanical properties

Massive quantities of marine seaweed, Ulva armoricana are washed onto shores of many European countries and accumulates as waste. Attempts were made to utilize this renewable resource in hybrid composites by blending the algal biomass with biodegradable polymers such as poly(hydroxy‐butyrate) and poly‐(ε‐caprolactone). Compression‐molded films were developed and examined for their morphological, thermal and mechanical property. The Ulva fibers were well dispersed throughout the continous matrix exhibiting considerable cohesion with both polymers. Occasionally, regions with exposed fibres or aggregates were visible. About 50% algal content seemed to be an ideal concentration, thereafter, thermal stability was impacted. A progressive decrease in melting heat (ΔH_m) was observed with increased algal content as well as a decrease in the crystallinity of the polymer matrix due to the presence of the organic filler. The addition of algal fibres improved the Young modulus of the blends, creating a concomitant loss in percent elongation (El) and ultimate tensile strength. Fiber content above 40% impacted tensile property negatively and composites with over 70% fiber contents composites were too fragile. Data suggest that macro algae are compatible with both polymers and processable as fillers in hybrid blends. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Well‐defined PE‐b‐PDMS diblock copolymers via the combination of thiol‐ene click and esterification reactions: Facile synthesis and compatibilization for HDPE/silicone oil blends

Well‐defined diblock copolymers of linear polyethylene (PE) and poly(dimethylsiloxane) (PDMS) have been synthesized through a facile route combining the thiol‐ene click chemistry of vinyl‐terminated polyethylene (PE‐ene) and the sequential esterification reaction. The resulting diblock copolymers are characterized by ¹H NMR, FT‐IR, DSC, TGA, and TEM. In addition, the PE‐b‐PDMS diblock copolymers have been evaluated as compatibilizers in the blends of high‐density polyethylene (HDPE) and silicone oil. The morphological analysis and mechanical properties demonstrate that the compatibilized blends with low loading concentration of PE‐b‐PDMS display significant improvements in modulus of elasticity and elongation at break as compared to the uncompatibilized binary blends. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3205–3212     

Erosion‐dependant continuity development in high viscosity ratio blends of very low interfacial tension

This work studies continuity development and cocontinuity in high viscosity ratio EPDM/PP blends. A very low interfacial tension (0.3 mN/m) between the blend components together with high viscosity ratios (11 and 17) result in a variety of unusual morphological features, including isolated nanometer diameter fibers, very large particles, partially coalesced particles, and numerous particles interconnected by fibers. This unique combination of morphologies leads the blend to a novel and stable cocontinuous structure of partially coalesced particles and particles interconnected by fibers. Compared with low to medium viscosity ratio EPDM/PP blends, these cocontinuous networks demonstrate early percolation thresholds, rapid continuity development, and attain cocontinuity at lower compositions of minor phase. The slow surface erosion of the high viscosity EPDM phase during melt blending is shown to be responsible for the generation of these unusual morphological structures. Typically the timescale for erosion phenomena are so small that they have defied study in the mixing environment itself and typical blend morphology studies almost always examine the final steady‐state morphology obtained after several minutes of mixing. The combination of very low interfacial tension and very high viscosity ratios of these EPDM/PP systems provide a unique opportunity to examine erosion phenomena persisting over longer time scales during melt mixing. We propose a new concentration‐dependant erosion mechanism that is based on particle collision–coalescence–separation dynamics. The proposed conceptual mechanism is shown to dramatically accelerate the erosion process and maintain cocontinuity over prolonged periods of mixing. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1919–1929, 2006     

Multifunctional mesoporous silica nanoparticles in poly(ethylene‐co‐vinyl acetate) for transparent heat retention films

Transparent inorganic‐polymer nanocomposite films are of tremendous current interest inemerging solar coverings including photovoltaic encapsulants and commercial greenhouse plastics, but suffer from significant radiative heat loss. This work provides a new and simple approach for controlling this heat loss by using mesoporous silica/quantum dot nanoparticles in poly(ethylene‐co‐vinyl acetate) (EVA) films. Mesoporous silica shells were grown on CdS‐ZnS quantum dot (QDs) cores using a reverse microemulsion technique, controlling the shell thickness. These mesoporous silica nanoparticles (MSNs) were then melt‐mixed with EVA pellets using a mini twin‐screw extruder and pressed into thin films of concentration variable controlled thickness. The results demonstrate that the experimental MSNs showed improved infrared and thermal wavebands retention in the EVA transparent films compared to commercial silica additives, even at lower concentrations. It was also found MSNs enhanced the quantum yield and photostability of the QDs, providing high visible light transmission and blocking of UV transmission of interest for next generation solar coatings. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 851–859     

Sulfonated dendrimer‐ and hyperbranched polyglycerol‐PBIOO® blend membranes for fuel cells

A new sulfonated dendrimer with an arylene ether sulfone backbone has been synthesized, fully characterized, and blended with PBIOO^® to prepare acid‐base proton‐conducting membranes under different conditions and with different composition ratios. Water‐soluble sulfonated hyperbranched polyglycerols of different molecular weights were also used as the acidic components. Membrane properties such as ion‐exchange capacity, water uptake, thermal stability, proton conductivity, and morphology have been studied and discussed. The nature of the acidic component and the morphology of the membranes had a marked influence on the final properties. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 69–80     

A SAXS and swelling study of cured natural rubber/styrene–butadiene rubber blends

A small‐angle X‐ray scattering (SAXS) and swelling study of natural rubber and styrene–butadiene rubber blends (NR/SBR) is presented. To this aim, specimens of NR and SBR and blends with 75/25, 50/50, and 25/75 NR/SBR ratios (in phr) were prepared at a cure temperature of 433 K and the optimum cure time (t₁₀₀). This time was obtained from rheometer torque curves. The system of cure used in the samples was sulfur/n‐t‐butyl‐2‐benzothiazole sulfenamide. From swelling tests of the cured samples, information about the molecular weight of the network chain between chemical crosslinks was obtained. For all cured compounds, in the Lorentz plots built from SAXS scattering curves, a maximum of the scattering vector q around 0.14 Å^?1 was observed. However, the q position shows a linear‐like shift toward lower values when the SBR content in the SBR/NR blend increases. In pure NR or SBR the q values show a different tendency. The results obtained are discussed in terms of the existence of different levels of vulcanization for each single phase forming the blend and the existence of a third level of vulcanization located in the interfacial NR/SBR layer. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2320–2327, 2009     

Phase separation of off‐critical polymer blends of poly(styrene‐co‐maleic anhydride) and poly(methyl methacrylate). II. Morphology and mechanical properties

The effects of the phase‐separation temperature and time on the mechanical properties and morphology of poly(methyl methacrylate)/poly(styrene‐co‐maleic anhydride with 10 wt% ethyl acrylate) (SMA) blends were studied. Two compositions (20/80 and 40/60 w/w SMA/PMMAe) were prepared with a miniature twin‐screw extruder. Compared with those of the miscible blends, the Young's modulus values of the blends increased after the phase separation of the 40/60 SMA/PMMAe blend and within the early stage of spinodal decomposition of the 20/80 SMA/PMMAe blend. The mechanical properties, in terms of the tensile strength at break and the elongation, were better for the miscible blends than for the phase‐separation blends. This was believed to be the result of changes in the composition and molecular reorganization. The changes in the phase‐separating domains of both compositions, as observed by transmission electron microscopy, had no significant influence on the tensile moduli. Detailed studies of the morphology revealed a cocontinuous structure, indicating that the blends underwent spinodal decomposition. A morphological comparison of the two compositions illustrated the validity of the level rule. The growth rate of the droplet size was determined by approximation from the light scattering data and by direct measurements with transmission electron microscopy. The discrepancies observed in the droplet size growth rate were attributed to heat variations induced by the different sample thicknesses and heat transfer during the investigation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 886–897, 2004     

The role of segregation in the polarized emission from polyfluorene embedded in a liquid crystal

Polyfluorene (PFO) embedded in a nematic liquid crystal (LC) matrix is investigated. For low PFO weight contents, a homogeneous dispersion is obtained which displays a strong fluorescence anisotropy along the LC director, indicating a significant alignment of the polymeric chains along this direction. Besides, for relatively high PFO weight contents, phase separation takes place. Under these conditions, the sample is composed of micrometer‐sized domains, where the two species are in solution, enclosed by segregated polymeric boundaries. By polarized‐photoluminescence imaging and spectroscopy, it is found that most of the light emission originates from these boundaries and gets strongly pinned along their orientation. Since boundaries are mainly oriented orthogonal to the LC chains, this morphological alignment results in a system in which the orientation of the polarization emission can be predicted and possibly controlled. Conversely, in the homogeneous sample one can obtain a homogeneous emission polarization by controlling the alignment of the LC. These features are potentially relevant for the development of flexible polarization‐sensitive optoelectronic devices. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1558–1563     

Crew‐cut aggregates from self‐assembly of blends of polystyrene‐b‐poly(acrylic acid) block copolymers and homopolystyrene in solution

The formation and morphological characteristics of crew‐cut aggregates from blends of polystyrene‐b‐poly(acrylic acid) diblock copolymer and polystyrene homopolymer in solution were studied by static light scattering, transmission electron microscopy and size exclusion chromatography. The crew‐cut aggregates, consisting of a polystyrene core and a poly(acrylic acid) corona, were prepared by direct dissolution of the polymer blends in a selective solvent mixture consisting of 93 wt % dimethylformamide and 7 wt % water. It is found that the aggregation behavior depends strongly on the relative volume fractions of the block copolymer and homopolymer in the blends. This is a result of the difference in solubility between the copolymer and the homopolymer in solution which, in turn, influences their miscibility and mutual solubility and consequently the morphology of the formed crew‐cut aggregates. Specifically, when the homopolymer fraction is low, it is mainly dissolved in the cores of the crew‐cut aggregates formed by the block copolymer. When the homopolymer fraction exceeds its solubility limit in the copolymer micelles, aggregates of another type are formed which contain a major fraction of the homopolymer. These aggregates are usually much larger than the primary micelles and have an internal structure due to the formation of reverse micelles from the dissolved block copolymer chains. The importance of thermodynamic vs. kinetic aspects during the formation of the crew‐cut aggregates is also discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1469–1484, 1999     

Interfacial tension and acid‐base approaches to polymer interactions

A significant correlation has been shown to exist between the interfacial tension of polymer pairs and their acid‐base pair interaction. The relationship is inverse, with interfacial tensions decreasing as acid‐base interactions increase. Interfacial tensions, frequently used as an indicator of polymer compatibility, were measured by the breaking thread method at temperatures in the vicinity of 200 °C. Acid‐base pair interaction values were measured by inverse gas chromatography over wide temperature ranges. The observed correlation confirms the important contribution made by short‐range, acid‐base interactions to the observed value of interfacial tension and supports the prediction of equations based on fundamental definitions of surface forces. A collateral finding of this work is the decrease of acid‐base functionality with rising temperature for all polymers studied. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2096–2104, 2000     

Reactivity of functional SAN toward coreactive EPR‐g‐MA at planar interface

The grafting kinetics of reactive poly(styrene‐co‐acrylonitrile) (SAN) onto EPR‐g‐MA was studied under isothermal conditions, at the planar interface of an SAN/ethylene‐propylene rubber (EPR) bilayer film in relation to the type of reactive groups, NH₂ versus carbamate (which is an amine precursor), attached to SAN. The amount of SAN chemically bound to EPR chains at the interface was estimated by selectively washing off the unreacted SAN chains before X‐ray photon spectroscopic analysis of the released surface. It is clear that the mutual reactivity of the reactive groups, i.e., the NH₂–MA pair versus the carbamate–MA pair, has a decisive effect on the amount of SAN that reacts with EPR‐g‐MA at the interface. In case of SAN‐carb, the grafting reaction is controlled by the thermolysis of the carbamate groups into primary amines. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3682–3689, 2000     

Processing and morphological development of carbon black filled conducting blends using a binary host of poly(styrene co‐acrylonitrile) and poly(styrene)

The effects of host/filler interactions, processing, and morphological development of low percolation threshold (Φ_c) conducting blends were investigated. It was found that the value of Φ_c was dramatically reduced by the isolation of the carbon black (CB) conducting filler at the cocontinuous interface of a binary poly(styrene) (PS) and poly(styrene co‐acrylonitrile) (SAN) insulating host, resulting in a multiple percolation effect. Accumulation of the filler at the interface was possible due to the incompatibility of the CB filler with the PS phase and partial compatibility with the SAN phase. The best results were obtained by initially dispersing the CB in the PS phase during melt‐ blending, followed by the addition of the SAN phase. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3106–3119, 2000     

Solid‐state NMR as a tool to describe and quantify the morphology of photoactive layers used in plastic solar cells

The optimization and control of the nanomorphology of thin films used as active layer in bulk heterojunction (BHJ) plastic solar cells is of key importance for a better understanding of the photovoltaic mechanisms and for increasing the device performances. Hereto, solid‐state NMR relaxation experiments have been evaluated to describe the film morphology of one of the “work‐horse” systems poly(2‐methoxy‐5‐(3′,7′‐dimethyloctyloxy)‐1,4‐phenylene‐vinylene)/[6, 6]‐phenyl‐C₆₁butyric acid methyl ester (MDMO‐PPV/PCBM) in a quantitative way. Attention is focused on the influence of the processing solvent (toluene vs. chlorobenzene), the blend composition, and the casting technique, that is, spin coating versus doctor blading. It is demonstrated that independently of the solvent and casting technique, part of the PCBM becomes phase separated from the mixed phase. Whereas casting from toluene results in the development of well‐defined PCBM crystallites, casting from chlorobenzene leads to the formation of PCBM‐rich domains that contain substructures of weakly organized PCBM nanoclusters. The amount and physico‐chemical state of the phase separated PCBM is quantified by solid‐state NMR relaxation times experiments. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Morphological changes during heating in poly(L‐lactic acid)/poly(butylene succinate) blend systems as studied by synchrotron X‐ray scattering

Blends of poly(L ‐lactic acid) (PLA) and poly(butylene succinate) (PBS) were prepared in various compositions via melt mixing, and the morphological changes were investigated with differential scanning calorimetry and synchrotron wide‐angle and small‐angle X‐ray scattering techniques at a heating rate of 10 °C/min. Differential scanning calorimetry thermograms of PLA/PBS blends showed two distinct melting peaks over the entire composition range. The exothermal peak for PLA shifted significantly to a lower temperature and overlapped with that of PBS around 100 °C. A depression of the melting point of the PLA component via blending was observed. The synchrotron wide‐angle X‐ray scattering during heating revealed that there was no cocrystallization or crystal modification via blending. The synchrotron small‐angle X‐ray scattering data showed that well‐defined double‐scattering peaks (or peaks with a clear scattering shoulder) appeared during crystallization, indicating that this system possessed dual lamellar stacks. These peaks were deconvoluted into two components with a peak separation computer program, and then the morphological parameters of each component were obtained by means of the correlation function. The long period and average lamellar thickness of the two components before melting decreased with an increasing content of the other polymer component. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1931–1939, 2002     

Effects of the copolymer microstructure on the morphology of polyethylene–poly(ethylene‐co‐α‐olefin) blends

The effects of the copolymer microstructure on the morphology evolution in polyethylene/poly(ethylene‐co‐α‐olefin) blends were investigated. Microscopy revealed that the melt‐phase morphology, inferred from the solid‐state morphologies of annealed and quenched samples, was strongly affected by the copolymer structure, that is, the branch content and branch length. Higher molecular weight α‐olefin comonomer residues and residue contents in the copolymers led to faster coarsening of the morphology. The molecular weight of the polyethylene and the copolymers affected the coarsening rates of the morphology, principally through its influence on the melt viscosity. The effects of the molecular weight were largely explained by the normalization of the coarsening rate data with respect to the thermal energy and zero‐shear‐rate viscosity. Thus, the effect of the molecular weight on the compatibility of the blends was much smaller than the effects of the branch length and branch number. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 965–973, 2004