Showing papers on "Polymer blend published in 2012"

Morphology of all-polymer solar cells

Abstract: The blending of two semiconducting polymers with offset energy levels enables efficient charge generation in thin-film ‘all-polymer’ solar cells. A key requirement for efficient charge separation and collection is the formation of interconnected phase-separated domains structured on the sub-20 nm length-scale. This review provides an overview of recent advances in the characterisation of conjugated polymer blend nanostructure and developments in the linking of blend structure and device performance. This review also provides a general introduction to the polymer physics behind phase separation, experimental techniques used for characterising blend structure and novel ways to control nanomorphology.

Solution-processed small molecule-polymer blend organic thin-film transistors with hole mobility greater than 5 cm2/Vs.

Abstract: Using phase-separated organic semiconducting blends containing a small molecule, as the hole transporting material, and a conjugated amorphous polymer, as the binder material, we demonstrate solution-processed organic thin-film transistors with superior performance characteristics that include; hole mobility >5 cm(2) /Vs, current on/off ratio ≥10(6) and narrow transistor parameter spread. These exceptional characteristics are attributed to the electronic properties of the binder polymer and the advantageous nanomorphology of the blend film.

Design of electrical conductive composites: tuning the morphology to improve the electrical properties of graphene filled immiscible polymer blends.

Abstract: Polystyrene (PS) and poly(methyl methacrylate) (PMMA) blends filled with octadecylamine-functionalized graphene (GE-ODA) have been fabricated to obtain conductive composites with a lower electrical percolation threshold according to the concept of double percolation. The dependence of the electrical properties of the composites on the morphology is examined by changing the proportion of PS and PMMA. Our results reveal that the electrical conductivity of the composites can be optimal when PS and PMMA phases form a cocontinuous structure and GE-ODA nanosheets are selectively located and percolated in the PS phase. For the PS/PMMA blend (50w/50w), the composites exhibit an extremely low electrical percolation threshold (0.5 wt %) because of the formation of a perfect double percolated structure. Moreover, the rheological properties of the composites are also measured to gain a fundamental understanding of the relationship between microstructure and electrical properties.

Rheology of Ring Polymer Melts: From Linear Contaminants to Ring-Linear Blends

Abstract: Ring polymers remain a challenge to our understanding of polymer dynamics. Experiments are difficult to interpret because of the uncertainty in the purity and dispersity of the sample. Using both equilibrium and nonequilibrium molecular dynamics simulations we have investigated the structure, dynamics, and rheology of perfectly controlled ring-linear polymer blends of chains of up to about 14 entanglements per chain, comparable to experimental systems. Linear contaminants increase the zero-shear viscosity of a ring polymer melt by about 10% around one-fifth of their overlap concentration. For equal concentrations of linear and ring polymers, the blend viscosity is about twice that of the pure linear melt. The diffusion coefficient of the rings decreases dramatically, while the linear polymers are mostly unaffected. Our results are supported by a primitive path analysis.

Correlating the efficiency and nanomorphology of polymer blend solar cells utilizing resonant soft x-ray scattering

Abstract: Enhanced scattering contrast afforded by resonant soft X-ray scattering (R-SoXS) is used to probe the nanomorphology of all-polymer solar cells based on blends of the donor polymer poly(3-hexylthiophene) (P3HT) with either the acceptor polymer poly((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(3-hexylthien-5-yl)-2,1,3-benzothiadiazole]-2′,2″-diyl) (F8TBT) or poly([N,N′-bis(2-octyldodecyl)-11-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-12-bithiophene)) (P(NDI2OD-T2)). Both P3HT:F8TBT and P3HT:P(NDI2OD-T2) blends processed from chloroform with subsequent annealing exhibit complicated morphologies with a hierarchy of phase separation. A bimodal distribution of domain sizes is observed for P3HT:P(NDI2OD-T2) blends with small domains of size ∼5–10 nm that evolve with annealing and larger domains of size ∼100 nm that are insensitive to annealing. P3HT:F8TBT blends in contrast show a broader distribution of domain size but with the majority of this blend structured on the 10 nm length scale. Fo...

Correlating the efficiency and nanomorphology of polymer blend solar cells utilizing resonant soft X-ray scattering.

Abstract: Enhanced scattering contrast afforded by resonant soft X-ray scattering (R-SoXS) is used to probe the nanomorphology of all-polymer solar cells based on blends of the donor polymer poly(3-hexylthiophene) (P3HT) with either the acceptor polymer poly((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(3-hexylthien-5-yl)-2,1,3-benzothiadiazole]-2′,2″-diyl) (F8TBT) or poly([N,N′-bis(2-octyldodecyl)-11-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-12-bithiophene)) (P(NDI2OD-T2)). Both P3HT:F8TBT and P3HT:P(NDI2OD-T2) blends processed from chloroform with subsequent annealing exhibit complicated morphologies with a hierarchy of phase separation. A bimodal distribution of domain sizes is observed for P3HT:P(NDI2OD-T2) blends with small domains of size ∼5–10 nm that evolve with annealing and larger domains of size ∼100 nm that are insensitive to annealing. P3HT:F8TBT blends in contrast show a broader distribution of domain size but with the majority of this blend structured on the 10 nm length scale. Fo...

Polymer/polymer blend solar cells improved by using high-molecular-weight fluorene-based copolymer as electron acceptor.

Abstract: The highest power conversion efficiency (PCE) of 2.7% has been achieved for all-polymer solar cells made with a blend of poly(3-hexylthiophene) (P3HT, electron donor) and poly[2,7-(9,9-didodecylfluorene)-alt-5,5-(4′,7′-bis(2-thienyl)-2′,1′,3′-benzothiadiazole)] (PF12TBT, electron acceptor). The PCE of the P3HT/PF12TBT solar cells increases from 1.9% to 2.7% with an increase in the molecular weight (Mw) of PF12TBT from 8500 to 78 000 g mol–1. In a device with high-molecular-weight PF12TBT, efficient charge generation is maintained even at high annealing temperatures because of the small phase separation on the length scale of exciton diffusion due to an increase in the glass transition temperature (Tg) and a reduced diffusional mobility of the PF12TBT chains above Tg. On the other hand, efficient charge transport is also achieved through the formation of interconnected networks of PF12TBT-rich domains, which is facilitated by the high molecular weight of PF12TBT, and the ordering of P3HT chains in P3HT-ric...

Water Soluble Polymers as Proton Exchange Membranes for Fuel Cells

Abstract: The relentless increase in the demand for useable power from energy-hungry economies continues to drive energy-material related research. Fuel cells, as a future potential power source that provide clean-at-the-point-of-use power offer many advantages such as high efficiency, high energy density, quiet operation, and environmental friendliness. Critical to the operation of the fuel cell is the proton exchange membrane (polymer electrolyte membrane) responsible for internal proton transport from the anode to the cathode. PEMs have the following requirements: high protonic conductivity, low electronic conductivity, impermeability to fuel gas or liquid, good mechanical toughness in both the dry and hydrated states, and high oxidative and hydrolytic stability in the actual fuel cell environment. Water soluble polymers represent an immensely diverse class of polymers. In this comprehensive review the initial focus is on those members of this group that have attracted publication interest, principally: chitosan, poly (ethylene glycol), poly (vinyl alcohol), poly (vinylpyrrolidone), poly (2-acrylamido-2-methyl-1-propanesulfonic acid) and poly (styrene sulfonic acid). The paper then considers in detail the relationship of structure to functionality in the context of polymer blends and polymer based networks together with the effects of membrane crosslinking on IPN and semi IPN architectures. This is followed by a review of pore-filling and other impregnation approaches. Throughout the paper detailed numerical results are given for comparison to today’s state-of-the-art Nafion® based materials.

Role of specific interfacial area in controlling properties of immiscible blends of biodegradable polylactide and poly[(butylene succinate)-co-adipate].

Abstract: Binary blends of two biodegradable polymers: polylactide (PLA), which has high modulus and strength but is brittle, and poly[(butylene succinate)-co-adipate] (PBSA), which is flexible and tough, were prepared through batch melt mixing. The PLA/PBSA compositions were 100/0, 90/10, 70/30, 60/40, 50/50, 40/60, 30/70, 10/90, and 0/100. Fourier-transform infrared measurements revealed the absence of any chemical interaction between the two polymers, resulting in a phase-separated morphology as shown by scanning electron microscopy (SEM). SEM micrographs showed that PLA-rich blends had smaller droplet sizes when compared to the PBSA-rich blends, which got smaller with the reduction in PBSA content due to the differences in their melt viscosities. The interfacial area of PBSA droplets per unit volume of the blend reached a maximum in the 70PLA/30PBSA blend. Thermal stability and mechanical properties were not only affected by the composition of the blend, but also by the interfacial area between the two polymers...

Electrical conduction mechanism in NaCl complexed PEO/PVP polymer blend electrolytes

Abstract: Sodium ion‐conducting polymer blend electrolytes were prepared by dissolving NaCl salt in a polyethylene oxide–polyvinyl pyrrolidone (PEO–PVP) blend using solution cast technique. XRD and FTIR studies confirmed the complexation of the salt with polymer host which leads the reduction of its crystalline nature. FTIR spectra indicate the miscibility between PEO and PVP. Electrical conduction mechanism in the blend polymer complexes has been revealed by employing the complex impedance spectroscopy in the frequency range 1 Hz–1 MHz within the temperature range 303 K–343 K. The total conductivity, dielectric constant and electric modulus of the blend electrolytes are analyzed in order to explore the long range and short‐range dynamics of ions. Ionic conductivity increased with the increase of salt concentration as well as temperature. The dielectric constant showed large value at lower frequencies and increased with temperature indicating polar nature of PEO and PVP of the blend. The electric modulus formalism reveals the non‐Debye nature of the samples. The activation energies responsible for relaxation process measured from modulus spectra are found to be in good agreement with those obtained from dc conductivity studies.

Biphasic Polymer Blends Containing Carbon Nanotubes: Heterogeneous Nanotube Distribution and Its Influence on the Dielectric Properties

Abstract: Electrically percolative composites with high dielectric permittivity are currently finding increasing interest in academic and industrial research. They are essential for designing new energy-storage capacitors and electromagnetic interference shielding devices. Herein, we report a percolative multiwalled carbon nanotube (MWNT) filled low density polyethylene (LDPE)/poly(vinylidene fluoride) (PVDF) composite. As compared to the MWNT-filled single LDPE composites, this biphasic polymer composite displays a significantly reduced percolation threshold (9.6 → 5.7 vol %) but still maintains a high permittivity level to reach (∼500). This can be attributed to a double percolated structure observed on the basis of morphological evidence. MWNTs are selectively localized in LDPE phase during melt-mixing. This is contrary to the wetting coefficient evaluation yet still possible when the colossal difference in viscosity of two polymers is taken into account. The effect of double percolation on the dielectric proper...

Solvent and polymer matrix effects on TIPS-pentacene/polymer blend organic field-effect transistors

Abstract: We report on a systematic study of solvent and polymer matrix effects on the phase segregation behavior of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) blends incorporated into two different amorphous polymer matrices, poly (α-methyl styrene) and poly (triarylamine), and using two solvents, chlorobenzene and tetralin. Optical microscopy, X-ray diffraction analyses, and optical absorption measurements are used to evaluate the film morphology, crystallinity, and optical density, respectively. These analyses are correlated with the extent of vertical segregation of TIPS-pentacene, as observed for the blended films by depth-profile XPS analyses. The microstructure and vertical phase segregation of TIPS-pentacene in blend films are found to be strongly influenced by the choice of solvent. Tetralin, a solvent with a high boiling temperature, was found to be more desirable for achieving distinct phase segregation/crystallization of TIPS-pentacene in blend films and best performance in OFETs with a dual-gate geometry. The electrical properties of top and bottom channels were consistent with the morphological characterization and OFETs processed from tetralin showed higher mobility values than those from chlorobenzene. Further modification of the annealing conditions in the TIPS-pentacene/PTAA/tetralin ternary system led to top-gate OFETs with mobility values up to 2.82 cm2/Vs.

Mechanical Properties of Polypropylene Blended with Esterified and Alkylated Lignin

Abstract: Lignin does not show miscibility with com- mercial polyolefins. Therefore, industrial waste lignin was modified in two different ways and subsequently blended with commercial polypropylene (PP) up to 25 wt %. A Brabender electronic plasticorder was used for melt mix- ing at 190 � C. The influence of different modifications on the mechanical properties and processing stability was studied for both polymer blends. The blends of PP and lig- nin modified (esterified) with maleic anhydride showed less deterioration in the mechanical properties compared to blends of PP and alkylated lignin with dichloroethane. Intermolecular interactions between the PP matrix and modified lignin were concluded on the basis of indicative values derived from various relevant theoretical models to

Effect of glycidyl methacrylate-grafted natural rubber on physical properties of polylactic acid and natural rubber blends

Abstract: Natural rubber (NR) was melt blended with polylactic acid (PLA) at various ratios using an internal mixer. The impact strength and elongation at break of PLA/NR blend dramatically increased with increasing NR content up to 10% (w/w). Glycidyl methacrylate-grafted natural rubber (NR-g-GMA) was used as a compatibilizer for PLA/NR blend. The effects of content and %grafting of NR-g-GMA on mechanical properties of PLA/NR blend were studied. The experimental result showed that the addition of NR-g-GMA in PLA/NR blend significantly improved impact strength and elongation at break of PLA/NR blend when compared with that of neat PLA and PLA/NR blend without NR-g-GMA. The impact strength and elongation at break of PLA/NR blend increased with increasing NR-g-GMA content up to 1% (w/w). Moreover, with increasing % grafting of NR-g-GMA in PLA/NR blend up to 4.35, the impact strength and elongation at break of the blend increased. Morphological and thermal property of PLA, PLA/NR, and PLA/NR/NR-g-GMA were elucidated as well. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Polypropylene-grafted graphene oxide sheets as multifunctional compatibilizers for polyolefin-based polymer blends

Abstract: As amphiphilic substances, graphene oxide sheets (GOSs) can be used as surfactants in numerous technological fields. Wherein, utilizing GOSs to compatibilize immiscible polymer blends constitutes a promising direction because it not only harnesses their amphiphilic character but also exploits their extraordinary properties. Here, we show that polymer functionalization of GOSs can greatly expand their compatibilizing range. For example, commercially important polyolefin-based polymer blends, which are beyond the compatibilizing scope of unmodified GOSs, can be compatibilized by polypropylene-grafted GOSs (PP-g-GOSs). With the incorporation of 0.5 wt% of PP-g-GOSs into immiscible PP/polyphenylene oxide (PP/PPO, 90/10) blends, the dispersion of the minor phase (PPO) is remarkably improved without visible agglomerates. The compatibilizing effect of PP-g-GOSs should be due to the fact that they can adsorb PPO on their basal planes while exhibit intermolecular interactions with PP through their grafted PP chains. Moreover, PP-g-GOSs also act as multifunctional fillers for PP/PPO blends, thus enhancing their flame retardancy, thermal stability, mechanical strength and nucleation ability. The PP-g-GOS-compatibilized PP/PPO blends achieve an excellent combination of good melt processability and low cost of PP with multifunctional performances of PPO and GOSs, thereby holding enormous potential in many fields.

The Influence of the Solvent Evaporation Rate on the Phase Separation and Electrical Performances of Soluble Acene‐Polymer Blend Semiconductors

Abstract: The phase-separation characteristics of spin-cast difluorinated-triethylsilylethynyl anthradithiophene (F-TESADT)/poly(methyl methacrylate) (PMMA) blends are investigated with the aim of fabricating transistors with a high field-effect mobility and stability. It is found that the presence of PMMA in the F-TESADT/PMMA blends prevents dewetting of F-TESADT from the substrate and provides a platform for F-TESADT molecules to segregate and crystallize at the air–film interface. By controlling the solvent evaporation rate of the spin-cast blend solution, it is possible to regulate the phase separation of the two components, which in turn determines the structural development of the F-TESADT crystals on PMMA. At a low solvent evaporation rate, a bilayer structure consisting of highly ordered F-TESAT crystals on the top and low-trap PMMA dielectric on the bottom can be fabricated by a one-step spin-casting process. The use of F-TESADT/PMMA blend films in bottom gate transistors produces much higher field-effect mobilities and greater stability than homo F-TESADT films because the phase-separated interface provides an efficient pathway for charge transport.

Studies on electrical conductivity and dielectric behaviour of PVdF–HFP–PMMA–NaI polymer blend electrolyte

Abstract: Polymer blend electrolytes composed of poly(vinylidene fluoride-co-hexafluoro-propylene), poly(methyl methacrylate) and 1·0 M NaI as salt have been synthesized using solution caste technique by varying the PVdF(HFP)–PMMA blend concentration ratio systematically. A.c. impedance studies were performed to evaluate the ionic conductivity of the polymer electrolyte films. The highest ionic conductivity at room temperature for [PVdF(HFP)–PMMA(4:1)](20 wt%) – [NaI(1·0 M)](80 wt%) system is found to be 1·67 × 10 − 2 S cm − 1. XRD studies reveal complete complexation of the salt in the polymeric blend systems. The temperature dependence conductivity has been performed in the range of 303–373 K and it is observed that it obeys the Arrhenius behaviour. It has been observed that the dielectric constant, e r and dielectric loss, e i, increases with temperature in the lower frequency region and is almost negligible in the higher frequency region. This behaviour can be explained on the basis of electrode polarization effects. Plot of real part, M r and imaginary part, M i vs frequency indicates that the systems are predominantly ionic conductors. The phenomenon suggests a plurality of relaxation mechanism.

Proton Exchange Membrane Developed from Novel Blends of Polybenzimidazole and Poly(vinyl-1,2,4-triazole)

Abstract: In continuation (J. Phys. Chem. B2008, 112, 5305; J. Colloid Interface Sci. 2010, 351, 374) of our quest for proton exchange membrane (PEM) developed from polybenzimidazole (PBI) blends, novel polymer blend membranes of PBI and poly(1-vinyl-1,2,4-triazole) (PVT) were prepared using a solution blending method. The aim of the work was to investigate the effect of the blend composition on the properties, e.g., thermo-mechanical stability, swelling, and proton conductivity of the blend membranes. The presence of specific interactions between the two polymers in the blends were observed by studying the samples using varieties of spectroscopic techniques. Blends prepared in all possible compositions were studied using a differential scanning calorimetry (DSC) and exhibited a single Tg value, which lies between the Tg value of the neat polymers. The presence of a single composition-dependent Tg value indicated that the blend is a miscible blend. The N–H···N interactions between the two polymers were found to be ...

Improvement in toughness and heat resistance of poly(lactic acid)/polycarbonate blend through twin-screw blending: Influence of compatibilizer type

Abstract: The thermal mechanical properties and morphological changes of modified poly(lactic acid) (PLA) and polycarbonate (PC) polymer blends based on the equal weight fraction of each component were investigated. Several blend samples were prepared by melt processing with a twin screw extruder using both poly(butylene succinate-co-lactate) (PBSL) and epoxy (EP) as compatibilizers for the PLA/PC binary system. Differential scanning calorimetry (DSC) of PLA/PBSL and PC/PBSL binary blends showed that individual components were immiscible. Scanning electron microscopy (SEM) analysis of these blends revealed the domain size of PBSL was ∼ 0.5–1 μm in PLA/PBSL blend, and reduced to around 0.1 μm in PC/PBSL blend. The notched Izod impact strength (IS) of PLA/PC/PBSL ternary blends increased with PBSL content up to 10 phr PBSL due to enhanced interfacial interaction and proper domain size of the dispersed phase on the basis of DMA, DSC, and SEM analysis. The heat deflection temperature (HDT) showed a maximum at 5 phr PBSL, and it dropped with increasing PBSL content which is a ductile polymer. However, the HDT of PLA/PC/EP ternary blends increased considerably with 10 phr EP due to rigid interphase formation, and it increased further with 1 phr quaternary amine catalyst, however, the IS dropped nearly the same as that of unmodified PLA/PC blend. To take advantage of the two compatibilizers, PBSL and EP were added to the PLA/PC blend at 10 phr each plus 1 phr catalyst and both IS and HDT were improved significantly over unmodified PLA/PC pair. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012