Showing papers on "Polymer blend published in 2005"

Device annealing effect in organic solar cells with blends of regioregular poly(3-hexylthiophene) and soluble fullerene

Abstract: Here we report enhanced efficiency bulk heterojunction organic solar cells using blend films of regioregular poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM) that are subjected to a thermal annealing process. Blend films (P3HT:PCBM=1:1 by weight) were prepared using chlorobenzene and 1,2-dichlorobenzene in order to investigate the role of the solvent. Irrespective of the chosen solvent, the optimal device annealing temperature was found to be 140 °C. The highest power conversion efficiency, 3% under air mass 1.5 simulated solar illumination (100mW∕cm2), was achieved by device annealing at 140 °C for 15 min using blend films prepared from chlorobenzene (2.3% for 1,2-dichlorobenzene).

Tuning of Metal Work Functions with Self‐Assembled Monolayers

Abstract: Work functions of gold and silver are varied by over 1.4 and 1.7 eV, respectively, by using self-assembled monolayers. Using these modified electrodes, the hole current in a poly(2-methoxy-5-(2'-ethylhexyloxy)- 1,4-phenylene vinylene) light-emitting diode is tuned by more than six orders of magnitude (see Figure). Suppression of the hole current enables measurement of the electron current in a polymer/polymer blend photovoltaic cell.

An interfacial instability in a transient wetting layer leads to lateral phase separation in thin spin-cast polymer-blend films

Abstract: Spin-coating is a very widely used technique for making uniform thin polymer films. For example, the active layers in most experimental semiconducting polymer-based devices, such as light-emitting diodes and photovoltaics, are made this way. The efficiency of such devices can be improved by using blends of polymers; these phase separate during the spin-coating process, creating the complex morphology that leads to performance improvements. We have used time-resolved small-angle light scattering and light reflectivity during the spin-coating process to study the development of structure directly. Our results provide evidence that a blend of two polymers first undergoes vertical stratification; the interface between the stratified layers then becomes unstable, leading to the final phase-separated thin film. This has given us the basis for establishing a full mechanistic understanding of the development of morphology in thin mixed polymer films, allowing a route to the rational design of processing conditions so as to achieve desirable morphologies by self-assembly.

The effect of silica nano particles and rubber particles on the toughness of multiphase thermosetting epoxy polymers

Abstract: The substantial increase in toughness achieved when nano-SiO2 particles were dispersed in a hot-cured single-part epoxy polymer was investigated. The synergistic effect of having a multiphase structure is based upon both nano-SiO2 and rubbery particles. The modulus, of the rubber-particulate epoxy polymer increases steadily as the wt.% of the silica nanophase was increased. The results suggested that the volume fraction of the rubbery-particulate phase which was formed was independent of the concentration of the nano-silicate phase present.

Electrospun Nanofibers of Blends of Conjugated Polymers: Morphology, Optical Properties, and Field-Effect Transistors

Abstract: Electrospun nanofibers of two series of binary blends of poly[2-methoxy-5-(2-ethylhexoxy)-1,4-phenylenevinylene] (MEH−PPV) with regioregular poly(3-hexylthiophene) (PHT) and with poly(9,9-dioctylfluorene) (PFO) were prepared, and their morphology and optical and electrical properties were characterized. Morphological and photophysical studies showed that the phase-separated domains in MEH−PPV/PHT nanofibers (30−50 nm) are much smaller as compared to blend thin films (100−150 nm), and efficient energy transfer was observed in these blend nanofibers. The MEH−PPV/PFO blend nanofibers had cocontinuous or core−shell structures, and significant energy transfer was absent in these blend nanofibers as compared to bulk thin films. Field-effect transistors based on MEH−PPV/PHT blend nanofibers showed exponential dependence of hole mobility on blend composition. The hole mobility decreased from 1 × 10-4 cm2/(V s) in 20 wt % MEH−PPV blend nanofibers to 5 × 10-6 cm2/(V s) at 70 wt %. If corrected for the reduced chann...

Influence of Nanoparticles on Miscibility of Polymer Blends. A Simple Theory

Abstract: We propose a simple theory describing the influence of nanoparticles on thermodynamics of binary polymer mixture. In particular, we consider the case in which nanoparticles preferentially segregate into one of the polymeric components. Depending on the particle radius Rp and the polymer degree of polymerization N, addition of nanoparticles can either promote or hinder mixing of the polymers. We calculate how the addition of nanoparticles shifts the spinodal of the polymer blend. These results help to improve understanding of recent simulations on the dynamics of polymer/particle mixtures.

Efficient Polymer Solar Cells Based on M3EH−PPV

Abstract: We report on polymer blend solar cells with an external quantum efficiency of more than 30% and a high overall energy conversion efficiency (ECE) under white light illumination (100 mW/cm2) of up to 1.7% using a blend of M3EH−PPV (poly[2,5-dimethoxy-1,4-phenylene-1,2-ethenylene-2-methoxy-5-(2-ethylhexyloxy)−(1,4-phenylene-1,2-ethenylene)]) and CN−ether−PPV (poly[oxa-1,4-phenylene-1,2-(1-cyano)ethenylene-2,5-dioctyloxy-1,4-phenylene-1,2-(2-cyano)ethenylene-1,4-phenylene]). We attribute these high efficiencies to the formation of a vertically composition graded structure during spin coating. Photoluminescence measurements performed on the blend layers indicated the formation of exciplexes between both types of polymers, which we propose to be one factor preventing even higher efficiencies.

Elastomeric Flexible Free-Standing Hydrogen-Bonded Nanoscale Assemblies

Abstract: Poly(ethylene oxide) (PEO) is a key material in solid polymer electrolytes, biomaterials, drug delivery devices, and sensors. Through the use of hydrogen bonds, layer-by-layer (LBL) assemblies allow for the incorporation of PEO in a controllable tunable thin film, but little is known about the bulk properties of LBL thin films because they are often tightly bound to the substrate of assembly. The construction technique involves alternately exposing a substrate to a hydrogen-bond-donating polymer (poly(acrylic acid)) and a hydrogen-bond-accepting polymer (PEO) in solution, producing mechanically stable interdigitated layers of PEO and poly(acrylic acid) (PAA). Here, we introduce a new method of LBL film isolation using low-energy surfaces that facilitate the removal of substantial mass and area of the film, allowing, for the first time, the thermal and mechanical characterization that was previously difficult or impossible to perform. To further understand the morphology of the nanoscale blend, the glass transition is measured as a function of assembly pH via differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The resulting trends give clues as to how the morphology and composition of a hydrogen-bonded composite film evolve as a function of pH. We also demonstrate that LBL films of PEO and PAA behave as flexible elastomeric blends at ambient conditions and allow for nanoscale control of thickness and film composition. Furthermore, we show that the crystallization of PEO is fully suppressed in these composite assemblies, a fact that proves advantageous for applications such as ultrathin hydrogels, membranes, and solid-state polymer electrolytes.

Flash welding of conducting polymer nanofibers

Abstract: The welding of certain polymeric nanofibers can be accomplished by exposure to an intense short burst of light, such as is provided by a camera flash, resulting in an instantaneous melting of the exposed fibers and a welding of the fibers where they are in contact. The preferred nanofibers are composed of conjugated, conducting polymers, and derivatives and polymer blends including such materials. Alternatively, the nanofibers can be composed of colored thermoplastic polymeric fibers or opaque polymers by proper selection of the frequency or frequency range and intensity (power) of the light source. The flash welding process can also be used to weld nanofibers which comprise a blend of polymeric materials where at least one of the materials in the blend used to form the nanofiber is a conductive, conjugated polymer or a suitable colored thermoplastic. Alternatively the material blend used to form the nanofibers may comprise a polymeric material containing a colored additive, which is not necessarily a polymer, for example carbon black, or a colored nano-particulate organic or inorganic material, dye or pigment.

Effect of Organic Modification on the Compatibilization Efficiency of Clay in an Immiscible Polymer Blend

Abstract: This communication describes the effect of organic modifier miscibility with the matrices, and the effect of the initial interlayer spacing of the organoclay, on the overall morphology and properties of an immiscible polycarbonate/poly(methyl methacrylate) blend. By varying the organic-modifier-specific interactions with the blend matrices at the same time as changing the initial interlayer spacing of the organoclay, different levels of compatibilization were revealed. The evidence for the interfacial compatibilization of the organoclay was assessed by scanning electron microscopy observations and was supported by differential scanning calorimetry analyses. The effect on the level of clay exfoliation was also examined.

Co-continuous Polyamide 6 (PA6)/Acrylonitrile-Butadiene-Styrene (ABS) Nanocomposites

Abstract: Polyamide 6 (PA6)/acrylonitrile-butadiene-styrene (ABS) (40/60 w/w) nanocomposites with a novel morphology were prepared by the melt mixing of PA6, ABS and organoclay. The blend nanocomposites had a co-continuous structure, in which both PA6 and styrene-acrylonitrile (SAN) were continuous phases. It was found that the toughening rubber particles were only located in the SAN phase and the strengthening clay platelets were selectively dispersed in the PA6 phase. The co-continuous nanocomposites showed greatly improved mechanical properties over the whole temperature range when compared with the same blend sample without clay.

Kraft lignin/poly(ethylene oxide) blends: Effect of lignin structure on miscibility and hydrogen bonding

Abstract: Blends of poly(ethylene oxide) (PEO) with softwood kraft lignin (SKL) were prepared by thermal blending. The miscibility behavior and hydrogen bonding of the blends were investigated by differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy. The experimental results indicate that PEO was miscible with SKL, as shown by the existence of a single glass-transition temperature over the entire composition range by DSC. In addition, a negative polymer–polymer interaction energy density was calculated on the basis of the melting point depression of PEO. The formation of strong intermolecular hydrogen bonding was detected by FTIR analysis. A comparison of the results obtained for the SKL/PEO blend system with those previously observed for a hardwood kraft lignin/PEO system revealed the existence of stronger hydrogen bonding within the SKL/PEO blends but weaker overall intermolecular interactions between components; this suggested that more than just hydrogen bonding was involved in the determination of the blend behavior in the kraft lignin/PEO blends. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1437–1444, 2005

Precision synthesis of a fluorinated polyhedral oligomeric silsesquioxane-terminated polymer and surface characterization of its blend film with poly(methyl methacrylate)

Abstract: Incompletely condensed, fluorinated polyhedral oligomeric silsesquioxane with the highly reactive group of trisodium silanolate was used for the synthesis of an initiator for atom transfer radical polymerization The initiator was applied to solution polymerization of methyl methacrylate (MMA) in the presence of a copper complex The polymerization proceeded in a living fashion, providing tadpole-shaped polymers with an “inorganic head” of polyhedral oligomeric silsesquioxane (POSS) and an “organic tail” of well-defined PMMA A blend film composed of the tadpole-shaped polymer and a matrix PMMA was annealed at 180 °C for 5 days and then analyzed by neutron reflectometry, X-ray photoelectron spectroscopy, and contact angle measurement These analyses revealed that the tadpole-shaped polymer was preferentially populated at the air/polymer interface, and the outermost layer of the film was almost completely covered by the POSS heads This was mainly due to the low surface free energy of the fluorinated POSS

Exciplex dynamics in a blend of π-conjugated polymers with electron donating and accepting properties : MDMO-PPV and PCNEPV

Abstract: The photophysical properties of a solution processed blend of two semiconducting polymers with electron donating and electron accepting properties, respectively, as used in polymer photovoltaic devices have been investigated. We show that in the binary mixture of poly[2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) and poly[oxa-1,4-phenylene-(1-cyano-1,2-vinylene)-(2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylene)-1,2-(2-cyanovinylene)-1,4-phenylene] (PCNEPV) photoexcitation of either one of the polymers results in formation of a luminescent exciplex at the interface of the two materials. Photoinduced absorption spectroscopy shows that this exciplex can decay to the lowest triplet state $({T}_{1})$ of MDMO-PPV. Application of an electric field results in dissociation of the marginally stable exciplex into charge carriers, which provides the basis for the photovoltaic effect of this combination of materials. Spin allowed recombination of the charge carriers to the MDMO-PPV ${T}_{1}$ state is invoked to explain the field-enhanced quantum yield for triplet formation observed by photoinduced reflection measurements on photovoltaic devices made from the composite films. The field enhanced triplet yield is identified as loss mechanism for the photovoltaic performance of this combination of materials.

Influence of composition and heat-treatment on the charge transport properties of poly(3-hexylthiophene) and [6,6]-phenyl C61-butyric acid methyl ester blends

Abstract: Poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) blends have been demonstrated to form highly efficient polymer photovoltaic devices. In this letter, the time-of-flight technique is used to investigate the influence of composition and heat treatment on charge transport properties of P3HT and PCBM blends. The transport of electrons and holes both display a transition from dispersive to nondispersive and return to dispersive again as the percentage of PCBM increases. A balanced mobility of both electron and hole is obtained at a composition of 1:1 weight ratio, and it is nearly independent of the electrical field in the range of our test. The increase in carrier mobility is attributed to the formation of a more-ordered structure in the blend. This structural ordering is further enhanced by slowly evaporating the solvent during film formation which results in additional increase in carrier mobility. However, no such effect is observed in thick films (∼200nm), indicating the...

Compatibilization Efficiency of Organoclay in an Immiscible Polycarbonate/Poly(methyl methacrylate) Blend

Abstract: Summary: This communication describes the compatibilization efficiency of organically modified montmorillonite (OMMT) in immiscible polycarbonate (PC)/poly(methyl methacrylate) (PMMA) blends for the first time. The size of the dispersed PC particles was reduced significantly upon the addition of OMMT (6 wt.-%) to the blend. The compatibilization effect of the OMMT was also assessed by differential scanning calorimetry, mechanical properties and thermal stability analysis of the modified blend. SEM images of the fracture surfaces.

Highly efficient polymer light-emitting devices using ambipolar phosphorescent polymers

Abstract: We report on highly efficient polymer light-emitting devices (PLEDs) achieved using a phosphorescent polymer, which is a copolymer that has bis(2-phenylpyridine)iridium (acetylacetonate) [Ir(ppy)2(acac)], N,N′-diphenyl-N,N′-bis(3-methylphenyl)-[1,1′-biphenyl]-4,4′-diamine (TPD) and 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) as a side group. The phosphorescent polymer has an ambipolar charge-transport ability. An increase in PBD unit concentration allows an improvement in the efficiency of the PLEDs. Ba and Cs were used for electron-injection layers as well as Ca, to improve the electron injection. An external quantum efficiency of 11.8% and a power efficiency of 38.6lm∕W were obtained by using Cs. The results indicate that this can be attributed to an improvement in the charge balance of electrons and holes.