Showing papers on "Polymer blend published in 1999"

Preparation of Protein-Resistant Surfaces on Poly(vinylidene fluoride) Membranes via Surface Segregation

Abstract: Self-organizing blends of an amphiphilic comb polymer having a poly(methyl methacrylate) (PMMA) backbone and poly(ethylene oxide) (PEO) side chains in poly(vinylidene fluoride) (PVDF) have been examined as a means to create foul-resistant, self-healing surfaces on polymer membranes. X-ray photoelectron spectroscopy (XPS) analysis of phase inversion membranes prepared from these blends indicates substantial surface segregation of the amphiphilic component, which occurs both during the coagulation step of the phase inversion process and in subsequent annealing of the membranes in water. With annealing, a near-surface coverage of nearly 45 vol % comb polymer is produced on a membrane with a bulk comb concentration of only 3 vol %. Surface enrichment of the hydrophilic comb polymer is shown to impart significant resistance to the adsorption of bovine serum albumin (BSA). XPS analysis of membranes treated with concentrated acid shows that hydrophilic surface layers removed by acid exposure may be regenerated b...

Charge transfer in photovoltaics consisting of interpenetrating networks of conjugated polymer and TiO2 nanoparticles

Abstract: We study the effect of blended and layered titanium dioxide (TiO2) nanoparticles on charge transfer processes in conjugated polymer photovoltaics. A two order of magnitude increase in photoconductivity and sharp saturation is observed for layered versus blended structures, independent of the cathode work function. Using electrodes with similar work functions, we observe low dark currents and open circuit voltages of 0.7 V when a TiO2 nanoparticle layer is self-assembled onto the indium–tin–oxide electrode. Our results for the layered morphologies are consistent with charge collection by exciton diffusion and dissociation at the TiO2 interface.

Fluorene copolymers and devices made therefrom

Abstract: This invention relates to: (a) fluorene copolymers comprising at least 10 percent (by residual monomeric units) of 9-substituted and/or 9,9-disubstituted fluorene moieties and at least two other monomeric units containing delocalized p-electrons, (b) polymer blends comprising at least 10 weight percent of a copolymer specified in (a), and (c) electronic devices (such as polymer light emitting diodes) containing one or more films derived from these copolymers.

Poly(vinyl alcohol)/poly(acrylic acid) hydrogels: FT-IR spectroscopic characterization of crosslinking reaction and work at transition point

Abstract: The crosslinking reaction of pure poly(acrylic acid) and its blend with poly(vinyl alcohol) was studied by FT-IR spectroscopy. It is demonstrated that also in blends the anhydride formation characteristic for pure poly(acrylic acid) is the predominant crosslinking reaction upon heating. But the ester formation between poly(vinyl alcohol) and poly(acrylic acid) is detectable due to the ester C=O vibrations and C—O—C vibrations, respectively. The degree of swelling and the Young's modulus of the crosslinked blend in deionized water depend on the time and temperature of the heat treatment. In dependence of the pH-value of the swelling agent the blends swell or shrink. The working energy at the shrinking or swelling process induced by a change of the pH-value of differently treated blends was measured. The values are in a range of technical interests and comparable with other microactuators.

Epoxy-Diamine Thermoset/Thermoplastic Blends. 1. Rates of Reactions before and after Phase Separation

Abstract: Rates of epoxy−amine reactions in thermoset/thermoplastic blends with different thermoplastic concentrations were studied. The selected thermoset system was bisphenol A diglycidyl ether cured with 4,4‘-methylenebis[3-chloro-2,6-diethylaniline] in the presence of various concentrations of polyetherimide (PEI) (10−64 wt %). As the initial systems are homogeneous, the rate constants for the epoxy−amine neat system and the rate constants of the blends are the same, the addition of PEI in the epoxy−amine system leads only to a dilution of reactive groups during this first step. But due to the epoxy−amine reaction, a liquid−liquid phase separation occurs at a given conversion (in the range 0.2−0.4). At the same time and for PEI concentrations equal or higher than 30 wt %, a sudden increase of the reaction rate is observed from experimental results. Comparison between blends based on PEI and polystyrene (PS) shows that after phase separation the reaction rate of the PS blend was higher than the PEI blend due to ...

Amphiphilic block copolymers as efficiency boosters for microemulsions

Abstract: We demonstrate that block copolymers of the poly(ethylenepropylene)-co-poly(ethylene oxide) (PEP−PEO) type dramatically enhance the solubilization capacity of medium-chain surfactants in microemulsions, for example, in the ternary system water−n-decane−C10E4. The effect exhibits itself in an enormous increase of the swelling of the middle phase with an associated increase in the structural length scale of the microemulsion, while at the same time the (already ultralow) interfacial tension between water- and oil-rich phases decreases even further. Typically, the surfactant mass fraction γ0 = 0.13 sufficient to form the balanced one-phase microemulsion in the ternary system can be replaced by γ = 0.035 of surfactant plus polymer. If δ is the polymer mass fraction in the surfactant/polymer mixture, the overall mass fraction of polymer in the microemulsion amounts only to γδ = 0.004. Accordingly, in this example the polymer is fB = 24 times more efficient than the surfactant, where we define an efficiency boo...

Solid polymer electrolytes

Abstract: A wide range of solid polymer electrolytes characterized by high ionic conductivity at room temperature, and below, are disclosed. These all-solid-state polymer electrolytes are suitable for use in electrochemical cells and batteries. A preferred polymer electrolyte is a cationic conductor which is flexible, dry, non-tacky, and lends itself to economical manufacture in very thin film form. Solid polymer electrolyte compositions which exhibit a conductivity of at least approximately 10?-3 - 10-4? S/cm at 25°C comprise a base polymer or polymer blend containing an electrically conductive polymer, a metal salt, a finely divided inorganic filler material, and a finely divided ion conductor. The new solid polymer electrolytes are combinable with various negative electrodes such as an alkali metal, alkaline earth metal, transition metal, ion-insertion polymers, ion-insertion inorganic electrodes, carbon insertion electrodes, tin oxide electrode, among others, and various positive electrodes such as ion-insertion polymers and ion-insertion inorganic electrodes to provide batteries and supercapacitors having high specific energy (Wh/kg) (gravimetric) and energy density (Wh/l) (volumetric), high cycle life, low self-discharge and providing improved safety.

Sustained release polymer blend for pharmaceutical applications

Abstract: A pharmaceutical composition has a blend of at least first and second components and a medicament in a sufficient amount to be therapeutic where the first component is hydroxypropylcellulose (HPC) and the second component is at least one other polymer selected from the group consisting of methylcellulose (MC), ethylhydroxyethylcellulose (EHEC), hydroxyethylmethylcellulose (HEMC), hydrophobically modified hydroxyethylcellulose (HMHEC), hydrophobically modified ethylhydroxyethylcellulose (HMEHEC), carboxymethylhydroxyethylcellulose (CMHEC), carboxymethyl hydrophobically modified hydroxyethylcellulose (CMHMHEC), guar, pectin, carrageenan, agar, algin, gellan gum, acacia, starch and modified starches, co-polymers of carboxyvinyl monomers, co-polymers of acrylate or methacrylate monomers, mono- and co-polymers of oxyethylene and oxypropylene and mixtures thereof and a medicament in a sufficient amount to be therapeutic, with the proviso that low-substituted hydroxypropylcellulose (L-HPC) is excluded from said first and second components. The medicament can be a variety of drugs or nutritional supplements. The pharmaceutical composition releases the medicament for a prolonged or sustained period of time and can be formulated into many dosage forms.

Microdomain Morphology of Thin ABC Triblock Copolymer Films

Abstract: We combine scanning force microscopy experiments with ex-situ swelling in different solvent vapors to investigate the microdomain structure of a thin ABC triblock copolymer film (poly(styrene-b-2-vinylpyridine-b-tert-butyl methacrylate)). We demonstrate that short treatment in a selective vapor and subsequent drying lead to characteristic changes in the surface morphology. The use of different solvents then allows to unambiguously identify the different phases present at the surface. This approach is established studying polymer blend and diblock copolymer thin films of known morphology. It is then applied to the a priori unknown morphology of the ABC triblock copolymer thin film. The results indicate a laterally microphase-separated polymer surface in agreement with recent theoretical considerations. The conclusions are corroborated by XPS measurements monitoring the average surface composition of the copolymer films.

Confinement-induced miscibility in polymer blends

Abstract: The use of polymer thin films in technology is increasingly widespread—for example, as protective or lithographic surface coatings, or as active (electronic or optical) elements in device architectures. But it is difficult to generate films of polymer mixtures with homogeneous surface properties, because of the tendency of the polymers to phase-separate1,2. Copolymer compatibilizers can induce miscibility in polymer blends, but only with chemical components that are either close to a critical point in the phase diagram3 or which have an attractive interaction between them4,5. Instead of manipulating the chemical composition of the blend, we show here that complete mixing can be obtained in polymer blends by the physical effect of confinement in thin films. The compatibilization results from entropic inhibition of phase separation into micelles, owing to confinement. The result is an intimately mixed microemulsion with a perfectly flat surface and a two-dimensional maze-like structure with columnar domains that extend through the film.

Electrical and dielectric properties of carbon black filled co-continuous two-phase polymer blends

Abstract: The electrical and dielectric properties of co-continuous polystyrene (PS)/poly(methylmethacrylate)(PMMA) blends loaded with carbon black (CB) of a special grade (BP 1000) have been studied. They strongly depend on the selective localization of the CB particles at the blend interface quite consistently with the double percolation concept. The interfacial localization of CB contributes to the stabilization of the phase morphology against thermal post treatment. Nevertheless, the sample annealing has a very favourable effect on the percolation threshold that decreases. The composition range in which phases are co-continuous is also increased by the addition of the filler. Dispersion of the conductance and the dielectric constant has been measured in the wide frequency range 10-4-108 Hz for blends containing 0-5 wt% CB. On the basis of these results, the mechanism of electrical transport (trapping, hopping, tunnelling, percolation) has been discussed in relation to the CB loading and the optimum loading has been identified for the electrical and dielectric properties to be stable and reproducible.

Phase Transitions of Polymer Blends and Block Copolymer Melts in Thin Films

Abstract: 2.1 Mean-Field Theory of Phase Separation in Thin Films. . . . . . . . 8 2.2 Block Copolymers in the Weak Segregation Limit . . . . . . . . . . 22 2.3 Block Copolymers in the Strong Segregation Limit. . . . . . . . . . 37 2.4 Survey of Results Obtained with the Self-Consistent Field Theory . . 41 2.5 Concepts on Interfaces in Confined Geometry . . . . . . . . . . . . 47 2.6 Computer Simulation of Polymer Blends in Thin Films . . . . . . . 51 2.7 Computer Simulation of Confined Block Copolymers . . . . . . . . 60 2.8 Dynamics of Phase Separation in Films: an Introduction . . . . . . 65

Structure and physical properties of silk fibroin/polyacrylamide blend films

Abstract: This article deals with the characterization of blend films obtained by mixing silk fibroin (SF) and polyacrylamide (PAAm). The DSC curves of SF/PAAm blend films showed overlapping of the main thermal transitions characteristic of the individual polymers. The exothermic peak at 218°C, assigned to the β-sheet crystallization of silk fibroin, slightly shifted to a lower temperature by blending. The weight-retention properties (TG) of the blend films were intermediate between those of the two constituents. The TMA response was indicative of a higher thermal stability of the blend films, even at low PAAm content (≤25%), the final breaking occurring at about 300°C (100°C higher than pure SF film). The peak of dynamic loss modulus of silk fibroin at 193°C gradually shifted to lower temperature in the blend films, suggesting an enhancement of the molecular motion of the fibroin chains induced by the presence of PAAm. Changes in the NH stretching region of silk fibroin were detected by FTIR analysis of blend films. These are attributable to disturbance of the hydrogen bond pattern of silk fibroin and formation of new hydrogen bonds with PAAm. The values of strength and elongation at break of blend films slightly improved at 20–25% PAAm content. A sea–island structure was observed by examining the air surface of the blend films by scanning electron microscopy. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1563–1571, 1999

A novel processing aid for polymer extrusion: Rheology and processing of polyethylene and hyperbranched polymer blends

Abstract: The use of hyperbranched polymers (HBPs) as a processing aid for linear low density polyethylene (LLDPE) was investigated. Various generation (or pseudo-generation) HBPs were used which had either 16 carbon atom alkanes or a mixture of 20/22 carbon atom alkanes on the end groups. In addition, the degree of end group substitution was studied. Blends of up to 10% HBP content were mixed via extrusion at 170 °C to produce 1 mm diameter fibers. Processability, surface appearance and the rheological properties of the blends were evaluated. It was found the power requirement for extrusion was significantly decreased as a result of reduced blend viscosity, and also, the mass flow rate for a given extruder speed was greater than virgin LLDPE for all HBP blends. Melt fracture and sharkskin of the blends was successfully eliminated, and minimal preprocessing time was required for the effect to take place. Surface analysis using x-ray photoelectron spectroscopy and transmission electron microscope techniques were performed with both showing that the HBP had a preference to accumulate at the fiber surface. Rheological experiments were similarly affected, therefore, the blend viscosity is really a composite of a HBP rich phase and a neat LLDPE phase. It is hypothesized that the HBP rich phase acted as a lubricating layer at the polymer/die wall interface. The HBP with a greater degree of end group substitution acted better as a processing/rheological property aid. Blends of LLDPE and paraffin wax were also studied. The surface appearance of HBPs/LLDPE blends was superior to those blends mixed with paraffin wax, as was the extruder performance. The results suggest that HBPs, at trace levels (≈500 ppm), may offer a number of advantages when used as a processing aid for LLDPE.

Structural changes and their effect on mechanical properties of silk fibroin/chitosan blends

Abstract: Silk fibroin/chitosan blend films were prepared by the solvent casting method. Miscibility between silk fibroin and chitosan was examined by dynamic mechanical thermal analysis. Structural changes of silk fibroin by the addition of chitosan were investigated by IR spectroscopy. The conformational transition of silk fibroin from random coil form to β-sheet structure induced by blending with chitosan resulted in the increase of crystallinity and density of the blend films. The blend film containing 30 wt % chitosan exhibited a maximum increase in crystallinity and density. It was found that the tensile strength and initial tensile modulus of blend films were greatly enhanced with increasing the chitosan content and showed a maximum value at the composition of 30 wt % chitosan. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2571–2575, 1999

Proton-conducting polymers with reduced methanol permeation

Abstract: The permeability of Nafion® 117 and some types of acid-base and covalently crosslinked blend membranes to methanol was investigated. The methanol crossover was measured as a function of time using a gas chromatograph with a flame ionization detector. In comparison to Nafion, the investigated acid-base and covalently crosslinked blend membranes show a significant lower permeation rate to methanol. Additionally, another method to reduce the methanol permeability is presented. In this concept a thin barrier layer is plasma polymerized on Nafion 117 membranes. It is shown that a plasma polymer layer with a thickness of 0.3 μm reduces the permeability to methanol by an order of magnitude.

Polymer electrolyte membranes from mixed dispersions

Abstract: A polymer electrolyte membrane is provided comprising an intimate mixture of an ionomeric polymer and a structural film-forming polymer. A method of making the polymer electrolyte membrane is also provided, comprising the step of coalescing at least one of an ionomeric polymer and a structural film-forming polymer in a mixture of the two resulting from a mixed dispersion and optionally crosslinking one or both.