Home About us Contact
|
Home About us Contact | ||
|
|
||
Copolymer Blends (copolymer + blend)
Terms modified by Copolymer Blends Selected AbstractsPhotophysics and Photocurrent Generation in Polythiophene/Polyfluorene Copolymer BlendsADVANCED FUNCTIONAL MATERIALS, Issue 19 2009Christopher R. McNeill Abstract Here, studies on the evolution of photophysics and device performance with annealing of blends of poly(3-hexylthiophene) with the two polyfluorene copolymers poly((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(3-hexylthien-5-yl)-2,1,3-benzothiadiazole]-2,,2,,-diyl) (F8TBT) and poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) are reported. In blends with F8TBT, P3HT is found to reorganize at low annealing temperatures (100,°C or below), evidenced by a redshift of both absorption and photoluminescence (PL), and by a decrease in PL lifetime. Annealing to 140,°C, however, is found to optimize device performance, accompanied by an increase in PL efficiency and lifetime. Grazing-incidence small-angle X-ray scattering is also performed to study the evolution in film nanomorphology with annealing, with the 140,°C-annealed film showing enhanced phase separation. It is concluded that reorganization of P3HT alone is not sufficient to optimize device performance but must also be accompanied by a coarsening of the morphology to promote charge separation. The shape of the photocurrent action spectra of P3HT:F8TBT devices is also studied, aided by optical modeling of the absorption spectrum of the blend in a device structure. Changes in the shape of the photocurrent action spectra with annealing are observed, and these are attributed to changes in the relative contribution of each polymer to photocurrent as morphology and polymer conformation evolve. In particular, in as-spun films from xylene, photocurrent is preferentially generated from ordered P3HT segments attributed to the increased charge separation efficiency in ordered P3HT compared to disordered P3HT. For optimized devices, photocurrent is efficiently generated from both P3HT and F8TBT. In contrast to blends with F8TBT, P3HT is only found to reorganize in blends with F8BT at annealing temperatures of over 200,°C. The low efficiency of the P3HT:F8BT system can then be attributed to poor charge generation and separation efficiencies that result from the failure of P3HT to reorganize. [source] Study on the Phase Behavior of High Density Polyethylene , Ethylene Octene Copolymer BlendsMACROMOLECULAR MATERIALS & ENGINEERING, Issue 3 2007Daniela Mileva Abstract The processes of melting and crystallization of blends based on HDPE and EOC were investigated. DSC thermograms showed that a separate crystallization and co-crystallization occurred in the blends studied. Avrami approach was used to analyze the kinetics of crystallization in the blends. It is shown that the Avrami exponent depends on the EOC concentration of the samples studied. The difference in the Avrami parameters for HDPE, EOC and the blends indicated that the nucleation mechanism and dimension of the spherulite growth of the blends were different from that of HDPE to some extent. The crystal growth was examined in the context of the Lauritzen-Hoffman theory. DSC traces obtained at different cooling rates were used for analyzing the non-isothermal crystallization. It was found that the Ozawa model was rather inapplicable for the materials studied. In contrast, the Avrami equation modified by Jeziorny can be used more efficiently to describe the non-isothermal crystallization behavior of HDPE-EOC blends. [source] Time-Temperature Creep Behaviour of Poly(propylene) and Polar Ethylene Copolymer BlendsMACROMOLECULAR MATERIALS & ENGINEERING, Issue 2 2007Antonietta Genovese Abstract Polymers commonly undergo deformation under an applied stress over their lifetime; some deformations are irrecoverable once the source of stress is removed. Therefore an understanding of the response of a polymer can be achieved by investigating the viscoelastic properties using creep experiments, where the behaviour can be monitored under small deformational loads. Poly(propylene) (PP) was blended with a polar elastic, thermoplastic, poly[ethylene- co -(methyl acrylate)] (EMA), to toughen the matrix. EMA formed a dispersed phase in PP that maintained its strength through its crystallinity rather than crosslinking. EMA can form a compatible interface with PP through inclusion of maleated-PP as a compatibiliser. The viscoelasticity of the PP,EMA blends, particularly the creep behaviour is an important factor if the properties of PP are to be maintained. The creep and recovery of PP,EMA blends with varying compositions were investigated under different loads and number of cycles. High EMA content provided an alternative deformation pathway due to its elastomeric properties. The experimental creep behaviour has been evaluated using the 4-element model with some limitations evident in the viscoelastic transitional region. [source] Polymer Photovoltaics with Alternating Copolymer/Fullerene Blends and Novel Device ArchitecturesADVANCED MATERIALS, Issue 20 2010Olle Inganäs Abstract The synthesis of novel conjugated polymers, designed for the purpose of photovoltaic energy conversion, and their properties in polymer/fullerene materials and photovoltaic devices are reviewed. Two families of main-chain polymer donors, based on fluorene or phenylene and donor,acceptor,donor comonomers in alternating copolymers, are used to absorb the high-energy parts of the solar spectrum and to give high photovoltages in combinations with fullerene acceptors in devices. These materials are used in alternative photovoltaic device geometries with enhanced light incoupling to collect larger photocurrents or to enable tandem devices and enhance photovoltage. [source] Influence of Domain Size on Toughness of Poly(styrene- block -butadiene) Star Block Copolymer/Polystyrene BlendsMACROMOLECULAR RAPID COMMUNICATIONS, Issue 24 2004Ralf Lach Abstract Summary: The toughness of poly(styrene- block -butadiene) star block copolymer/polystyrene (PS) blends have been investigated using the essential-work-of-fracture approach. The blends show a co-continuous or layer-like structure of polystyrene-rich and polybutadiene-rich domains arising from the used extrusion process. A tough-to-brittle transition at a critical domain size of polystyrene-rich domains of about 50 nm and a maximum in the non-essential work of fracture at 20,30% PS (co-continuous morphology) have been found. Non-essential work of fracture as a function of the mean thickness of polystyrene-rich domains, demonstrating a tough-to-brittle transition at a critical domain thickness about 50 nm. AFM micrograph of a star block copolymer/PS-blend containing 40% PS. [source] A study of the novel intumescent flame-retarded PP/EPDM copolymer blendsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008Shun Zhou Abstract Flammability of polypropylene/ethylene,propylene-diene copolymer (PP/EPDM) filled with melamine phosphate (MP) and pentaerythritol phosphate (PEPA) was studied by limiting oxygen index (LOI), UL 94, and cone calorimetry. The thermal degradation of the composites was investigated using thermogravimetric analysis (TG) and real-time Fourier transform infrared spectrum (RT-FTIR), and the mechanical properties of the materials were also studied. It had been found that the PP/EPDM/PEPA/MP composites (PEPM series) showed better flame retardancy than that of the PP/EPDM composites containing MP or PEPA. TG and RT-FTIR studies indicated that the interaction occurs among MP, PEPA, and PP/EPDM. The incorporation of the flame retardants deteriorated the mechanical properties of the materials. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Dynamic rheological and morphological study of the compatibility of thermoplastic polyurethane/ethylene,octene copolymer blendsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008Jin Yang Abstract Two grafted ethylene,octene copolymers [POEs; i.e., POE-g-maleic anhydried (MAH) and aminated POE (denoted by POE-g-NH2) were used as compatibilizers in immiscible blends of thermoplastic polyurethane (TPU) and POE. The effects of the compatibilizers on the dynamic rheological properties and morphologies of the TPU/POE blends were investigated. The characteristic rheological behaviors of the blends indicated that the strong interactions between the two phases were due to the compatibilization. Microstructural observation confirmed that the compatibilizers were located at the interface in the blends and formed a stable interfacial layer and smaller dispersed phase particle size. Compared with POE- g -MAH, POE- g -NH2 exhibited a better compatibilization effect in the TPU/POE blends. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Weld line characteristics of PC/ABS blend.JOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008Abstract The effects of reactive compatibilizer and processing temperature on the morphology and the mechanical properties at the weld line of 60/40 (wt/wt) poly- carbonate (PC) and acrylonitrile-butadiene-styrene (ABS) copolymer blends were investigated. Amine functionalized styrene/n -phenyl maleimide/maleic anhydride terpolymer (amine-SPMIMA) was used as the in-situ reactive compatibilizer for PC/ABS blend. Weld tensile strength increased as the content of amine-SPMIMA was increased. Weld impact strength showed maximum value for the blend containing about 3% amine-SPMIMA. The variation in the mechanical property at the weld line was correlated with the change in the morphology of the blend. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Thermal and mechanical properties of uncrosslinked and chemically crosslinked polyethylene/ethylene vinyl acetate copolymer blendsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2007H. A. Khonakdar Abstract Uncrosslinked and chemically crosslinked binary blends of low- and high-density polyethylene (PE), with ethylene vinyl acetate copolymer (EVA), were prepared by a melt-mixing process using 0,3 wt % tert -butyl cumyl peroxide (BCUP). The uncrosslinked blends revealed two distinct unchanged melting peaks corresponding to the individual components of the blends, but with a reduced overall degree of crystallinity. The crosslinking further reduced crystallinity, but enhanced compatibility between EVA and polyethylene, with LDPE being more compatible than HDPE. Blended with 20 wt % EVA, the EVA melting peak was almost disappeared after the addition of BCUP, and only the corresponding PE melting point was observed at a lowered temperature. But blended with 40% EVA, two peaks still existed with a slight shift toward lower temperatures. Changes of mechanical properties with blending ratio, crosslinking, and temperature had been dominated by the extent of crystallinity, crosslinking degree, and morphology of the blend. A good correlation was observed between elongation-at-break and morphological properties. The blends with higher level of compatibility showed less deviation from the additive rule of mixtures. The deviation became more pronounced for HDPE/EVA blends in the phase inversion region, while an opposite trend was observed for LDPE/EVA blends with co-continuous morphology. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3261,3270, 2007 [source] The Formation of Ordered Nanoholes in Binary, Chemically Similar, Symmetric Diblock Copolymer Blend Films,MACROMOLECULAR RAPID COMMUNICATIONS, Issue 12 2004Yu Xuan Abstract Summary: Binary symmetric diblock copolymer blends, that is, low-molecular-weight poly(styrene- block -methyl methacrylate) (PS- b -PMMA) and high-molecular-weight poly(styrene- block -methacrylate) (PS- b -PMA), self-assemble on silicon substrates to form structures with highly ordered nanoholes in thin films. As a result of the chemically similar structure of the PMA and the PMMA block, the PMMA chain penetrates through the large PMA block that absorbs preferentially on the polar silicon substrate. This results in the formation of nanoholes in the PS continuous matrix. An atomic force microscopy image of the thin film obtained from the blend of low-molecular-weight PS- b -PMMA and high-molecular-weight PS- b -PMA. The regular array of nanoholes in the films surface is clearly visible. [source] Processing behavior of polycarbonate/functionalized-ethylene copolymer blendsPOLYMER ENGINEERING & SCIENCE, Issue 12 2000Marcos L. Dias The melt blending of polycarbonate (PC) and ethylene-methacrylic acid copolymers (EFC) either in the acid form (EFC-H) or partially neutralized with sodium (EFC-Na) or zinc (EFC-Zn) was investigated. Torque monitoring of the blending showed that the polymers are capable of reacting generating new chemical species that increase the melt viscosity. As general behavior, the torque curves pass by a maximum that takes place before 30 min, the final torque being higher than that of the individual polymers. SEC analyses reveal that PC degradation also occurs and is stronger in the case of blends with EFC-Na that acts to catalyze PC degradation, promoting CO2 formation. FTIR studies on chloroform insoluble fractions of the PC/EFC-Zn blends showed that in addition to a very small number of carbonate groups, feature absorption bands of aromatic ester and hydroxyl groups appear in the new chemical species formed during the reactive processing. [source] Self-assembled structures in blends of disordered and lamellar block copolymers: SAXS, SANS and TEM studyPOLYMER INTERNATIONAL, Issue 1 2009Jaroslav Holoubek Abstract BACKGROUND: The phase behaviour of copolymers and their blends is of great interest due to the phase transitions, self-assembly and formation of ordered structures. Phenomena associated with the microdomain morphology of parent copolymers and phase behaviour in blends of deuterated block copolymers of polystyrene (PS) and poly(methyl methacrylate) (PMMA), i.e. (dPS- block - dPMMA)1/(dPS- block -PMMA)2, were investigated using small-angle X-ray scattering, small-angle neutron scattering and transmission electron microscopy as a function of molecular weight, concentration of added copolymers and temperature. RESULTS: Binary blends of the diblock copolymers having different molecular weights and different original micromorphology (one copolymer was in a disordered state and the others were of lamellar phase) were prepared by a solution-cast process. The blends were found to be completely miscible on the molecular level at all compositions, if their molecular weight ratio was smaller than about 5. The domain spacing D of the blends can be scaled with Mn by D , Mn2/3 as predicted by a previously published postulate (originally suggested and proved for blends of lamellar polystyrene- block -polyisoprene copolymers). CONCLUSIONS: The criterion for forming a single-domain morphology (molecularly mixed blend) taking into account the different solubilization of copolymer blocks has been applied to explain the changes in microdomain morphology during the self-assembling process in two copolymer blends. Evidently the criterion, suggested originally for blends of lamellar polystyrene- block -polyisoprene copolymers, can be employed to a much broader range of block copolymer blends. Copyright © 2008 Society of Chemical Industry [source] Reactive compatibilization of nylon copolymer/EPDM blends: experimental aspects and their comparison with theoryPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 5 2008Cibi Komalan Abstract In situ reactive compatibilization was first time applied to a low melting nylon (nylon 6 and 66 copolymer) and EPDM blend system. The effects of in situ compatibilization and concentration of compatibilizer on the morphology and mechanical properties of nylon/EPDM blends have been investigated. The influence of EPM-g-MA on the phase morphology was examined by the scanning electron microscopy (SEM) after preferential extraction of the minor phase. The SEM micrographs were quantitatively analyzed for domain size measurements. The compatibilizer concentrations used were 0, 1, 2.5, 5, and 10,wt%. The graft copolymer (nylon-g-EPM) formed at the interface showed relatively high emulsifying activity. A maximum phase size reduction was observed when 2.5,wt% of compatibilizer was added to the blend system. This was followed by a leveling-off at higher loadings indicating interfacial saturation. The conformation of the compatibilizer at the interface was deduced based on the area occupied by the compatibilizer at the blend interface. The experimental compatibilization results were compared with theoretical predictions of Noolandi and Hong. It was concluded that the molecular state of compatibilizer at interface changes with concentration. The in situ compatibilized blends showed considerable improvement in mechanical properties. Measurement of tensile properties shows increased elongation as well as enhanced modulus and strength up on compatibilization. At higher concentrations of compatibilizer, a leveling-off of the tensile properties was observed. A good correlation has been observed between the mechanical properties and morphological parameters. Copyright © 2007 John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||