Showing papers on "Miscibility published in 2003"

Controlling the aqueous miscibility of ionic liquids: aqueous biphasic systems of water-miscible ionic liquids and water-structuring salts for recycle, metathesis, and separations.

Abstract: Hydrophilic ionic liquids can be salted-out and concentrated from aqueous solution upon addition of kosmotropic salts forming aqueous biphasic systems as illustrated by the phase behavior of mixtures of 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) and K3PO4.

Poly (l-Lactic Acid)/Layered Silicate Nanocomposite: Fabrication, Characterization, and Properties

Abstract: The possibility of making rigid polymer layered nanocomposites from biocompatible/biodegradable matrixes was explored. Three types of commercially available organophilic clay were employed to concurrently study the effects of organic modifier miscibility with the matrix and of the extent of clay modification on overall nanocomposite formation. The nanocomposites were fabricated via the exfoliation−adsorption technique with the matrix polymer poly (l-lactic acid), PLLA, a widely used, biodegradable, synthetic polyester. X-ray diffraction (XRD) data reveal that increasing the miscibility of the surfactant/polymer matrix increases the tendency of the system to exfoliate and randomly distribute the silicate layers. Transmission electron microscopy (TEM) data show that the ordering of silicate platelets is consistent with d spacings obtained from XRD. Because of the nanometer-range dispersion of silicate layers, all the nanocomposites retain their optical clarity. Mechanical properties of the fabricated nanoco...

ABC Triblock Copolymers/Epoxy−Diamine Blends. 2. Parameters Controlling the Morphologies and Properties

Abstract: The effect of composition and concentration of polystyrene-block-polybutadiene-block-poly(methyl methacrylate) (SBM) copolymer triblock on final morphologies and properties of modified epoxy networks has been investigated. The DGEBA−MCDEA epoxy system, which ensures the miscibility of most of the PMMA blocks until the end of the reaction and thus the generation of a nanostructurated material, has been chosen. For low copolymer concentration (10 wt %), the network structure is found to be independent of the composition and micelles of PS and PB blocks can be undifferently observed. However, increasing copolymer amounts from 10 to 50 wt % induces a morphology change to either “spheres on spheres” or “core−shell” structure depending on the PB content in the triblock. For copolymer concentration higher than 50 wt %, the morphology strongly depends on the processing technique used, and only films prepared by solvent casting show an organization with long-range order similar to the neat block copolymer. The tou...

Miscibility and Hydrogen Bonding in Blends of Poly(ethylene oxide) and Kraft Lignin

Abstract: Polymer blending is a convenient method to develop products with desirable properties. Through specific intermolecular interactions favorable polymer blending can occur, and composite materials with desirable properties can be produced. In this study we have prepared poly(ethylene oxide)−lignin blends using thermal mixing. Miscible blends were observed over the entire blend ratio. A melting point depression, comparable to results obtained from phenoxy/PEO blends, and a negative deviation of Tg from the weight-average values was observed. The effect of the binary interaction parameter, χ, on Tg was analyzed. Satisfactory prediction of the Tg−composition curve was obtained, in which specific intermolecular interactions exist. FT-IR analyses revealed a strong hydrogen bond between the aromatic hydroxyl proton and the ether oxygen in PEO.

Miscibility and phase structure of binary blends of polylactide and poly(methyl methacrylate)

Abstract: Blends of amorphous poly(DL-lactide) (DL-PLA) and crystalline poly(L-lactide) (PLLA) with poly(methyl methacrylate) (PMMA) were prepared by both solution/precipitation and solution-casting film methods. The miscibility, crystallization behavior, and component interaction of these blends were examined by differential scanning calorimetry. Only one glass-transition temperature (Tg) was found in the DL-PLA/PMMA solution/precipitation blends, indicating miscibility in this system. Two isolated Tg's appeared in the DL-PLA/PMMA solution-casting film blends, suggesting two segregated phases in the blend system, but evidence showed that two components were partially miscible. In the PLLA/PMMA blend, the crystallization of PLLA was greatly restricted by amorphous PMMA. Once the thermal history of the blend was destroyed, PLLA and PMMA were miscible. The Tg composition relationship for both DL-PLA/PMMA and PLLA/PMMA miscible systems obeyed the Gordon–Taylor equation. Experiment results indicated that there is no more favorable trend of DL-PLA to form miscible blends with PMMA than PLLA when PLLA is in the amorphous state. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 23–30, 2003

Pressure, Isotope, and Water Co-solvent Effects in Liquid−Liquid Equilibria of (Ionic Liquid + Alcohol) Systems

Abstract: Liquid-liquid phase splitting in ternary mixtures that contain a room-temperature ionic liquid and an alcohol aqueous solution-namely, [bmim] [PF6] + ethanol + water and [bmim] [NTf2] + 2-methylpropanol + water-is studied. Experimental cloud-point temperatures were obtained up to pressures of 400 bar, using a He-Ne laser light-scattering technique. Although pressurization favors mutual miscibility in the presence of high concentrations of alcohols, the contrary occurs in water-rich solutions. Both ternary mixtures exhibit a very pronounced water-alcohol co-solvent effect. Solvent isotope effects are also investigated. Phase diagrams are discussed using a phenomenological approach based on a "polymer-like" G(E) model coupled with the statistical-mechanical theory of isotope effects. The combined effect of a red shift of -15 cm(-1) for the O-H deformation mode of ethanol with a blue shift of +35 cm(-1) for the O-H stretching mode, both of which occurring after liquid infinite dilution in the ionic liquid, rationalizes the observed isotope effect in the phase diagram. Predicted excess enthalpy (H-E) values are inferred from the model parameters. Furthermore, using the Prigogine-Defay equation, an estimation of the excess volumes (V-E) is obtained.

Determination of gas-oil miscibility conditions by interfacial tension measurements.

Abstract: Processes that inject gases such as carbon dioxide and natural gas have long been and still continue to be used for recovering crude oil from petroleum reservoirs. It is well known that the interfacial tension between the injected gas and the crude oil has a major influence on the efficiency of displacement of oil by gas. When the injected gas becomes miscible with the crude oil, which means that there is no interface between the injected and displaced phases or the interfacial tension between them is zero, the oil is displaced with maximum efficiency, resulting in high recoveries. This paper presents experimental measurements of interfacial tension between crude oil and natural gases (using a computerized drop shape analysis technique) as a function of pressure and gas composition at the temperature of the reservoir from which the crude oil was obtained. The point of zero interfacial tension was then identified from these measurements by extrapolation of data to determine minimum miscibility pressure (MMP) and minimum miscibility composition (MMC). The gas–oil miscibility conditions thus obtained from interfacial tension measurements have been compared with the more conventional techniques using slim-tube tests and rising-bubble apparatus as well as predictive correlations and visual observations. The miscibility pressures obtained from the new VIT technique were 3–5% higher than those from visual observations and agreed well with the slim-tube results as well as with the correlations at enrichment levels greater than 30 mol% C2+ in the injected gas stream. The rising bubble apparatus yielded significantly higher MMPs. This study demonstrates that the VIT technique is rapid, reproducible, and quantitative, in addition to providing visual evidence of gas–oil miscibility.

Effect of Grafted Lewis Base Groups on the Phase Behavior of Model Poly(dimethyl siloxanes) in CO2

Abstract: The impact of various Lewis bases on the miscibility of siloxane polymers in CO2 was investigated using both ab initio calculations and experimental phase behavior studies. A series of side-chain functional silicones were synthesized containing various Lewis bases in the side chain, and their phase behavior was compared in CO2 at 295 K. Calculations showed that interactions between CO2 and ethers (either a dialkyl ether or the ether oxygen in an ester group) should be as favorable as interactions between CO2 and a carbonyl oxygen. Indeed, phase behavior results seemed to support this, as ether-functional silicones exhibited miscibility pressures as low or lower than acetate-functional analogues. Further, a keto-functional material was not nearly as CO2-philic as the acetate functional analogue. In general, the location of the phase boundary in CO2 is governed by a balance between forces working to increase miscibility pressures, such as increased cohesive energy density of the polymer or factors suppressi...

Effect of various additives on pore size of polysulfone membrane by phase-inversion process

Abstract: The phase-inversion process was used to prepare integrally skinned asymmetric polysulfone (PSf) membranes with different pore sizes. Membranes were prepared from a casting solution of PSf; N-methyl-2-pyrrolidone (NMP) as solvent; and 1,4-dioxane, diethylene glycol dimethyl ether (DGDE), acetone, and γ-butyrolactone (GBL) as additives by immersing them in water as a coagulant. The effect of the additives on membrane performance and structure was investigated. The low miscibility of 1,4-dioxane, DGDE, and acetone with the coagulant resulted in reduced membrane pore size. However, by using GBL as additive pore size of the membrane was slightly increased because of its higher miscibility with the coagulant than NMP. Changing the amount of additives in the casting solution could control the molecular-weight cutoff values of asymmetric membranes. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2562–2566, 2003

Mechanical and barrier properties of edible starch–protein-based films

Abstract: The present investigation dealt with the mechanical properties, water-vapor transmission behavior at different relative humidity conditions, and DSC thermograms of edible films formulated using various proteins (casein, gelatin, albumin) in combination with starch and nonthermal as well as intense thermal blending. Nonthermal blended film showed in the DSC thermogram a double Tg, indicating poor miscibility of the components and, hence, a poor film-forming property. However, the DSC thermogram of all the films based on intense thermal blending showed a single Tg, indicating the complete molecular miscibility of the components. Casein-based film showed a lower water-vapor transmission rate, water gain at different relative humidity conditions, and higher tensile strength compared to its counterparts containing gelatin and albumin. Since the casein–starch blend gave better film properties, a blend of hydrophobic carnauba wax and casein was prepared to compare the properties of hydrophilic–hydrophilic and hydrophobic–hydrophilic blends. Both these blends compared well with respect to the water-vapor transmission rate. Wax-based film showed multiphased behavior in the DSC thermograms and the percent elongation was lower as compared to the casein–starch blend. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 64–71, 2003

Poly(para-dioxanone) and poly(l-lactic acid) blends: Thermal, mechanical, and morphological properties

Abstract: Blends of two semicrystalline polymers, poly(L-lactic acid) (PLLA) and poly-p-dioxanone (PPD) have been prepared by solvent casting in different compositions. Thermal, morphological, and mechanical properties of the blends were studied using modulated differential scanning calorimetry, wide-angle X-ray diffractometry, scanning electron microscopy (SEM), polarizing light microscopy (PLM), and tensile tests. Thermal analysis showed two glass transition temperatures nearly constant and equal to the values of the homopolymers and constant values of melting temperature (T-m) for all blend compositions, suggesting that both polymers are immiscible. The PLM and SEM observations validated these results, and showed the different morphology obtained by changing the composition of the blend. The blends 40/60, 50/50, and 60/40 presented a clearly macroseparated system, while the 20/80 and 80/20 blends presented better homogeneity, probably due to the low amount of one component in the other. It was found by PLM that PPD is able to crystallize according to a spherulitic morphology when its content is above 40%. Under this content, the crystallization of PPD is hardly observed. The blend 20/80 is more flexible, and tough material and neck formation during elongation is also observed, due to PPD, which may act as a plasticizer. (C) 2003 Wiley Periodicals, Inc.

Effect of Metal Oxides on Thermal Degradation of Poly(vinyl acetate) and Poly(vinyl chloride) and Their Blends

Abstract: The role of metal oxides on the thermal decomposition of poly(vinyl chloride) (PVC) and poly(vinyl acetate) (PVAC) and their blends was investigated by thermogravimetry (TGA). While the degradation of PVAC was mildly affected by the presence of metal oxides, the degradation of PVC was greatly influenced by metal oxides. Both polymers followed a two-step degradation mechanism involving chlorine or acetate radical removal followed by polyolefinic backbone breakage. The isokinetic temperatures and rate determined from the compensation plots indicated that the mode of olefinic backbone breakage is the same for both the polymers. FTIR studies after the first stage showed the disappearance of the C-Cl of PVC and C=O and C-O groups of PVAC, suggesting the formation of a polyolefinic chain. Blends of PVC-PVAC were obtained by solution blending by dissolving the polymers in tetrahydrofuran. Scanning electron microscopy and TGA showed complete miscibility of polymers in the blend. The first-stage degradation of the blend was greatly influenced by the presence of PVC and metal oxides, suggesting that hydrogen chloride liberated from PVC influenced the decomposition behavior of PVAC. The second-stage degradation (olefinic breakage) of the blends was mildly affected by the metal oxides and the breakage was similar to that of pure polymers.

Miscibility and phase structure of binary blends of polylactide and poly(vinylpyrrolidone)

Abstract: The miscibility, crystallization behavior, and component interactions of two binary blends, poly(L-lactide) (L-PLA)/poly(vinylpyrrolidone) (PVP) and poly(D,L-lactide) (DL-PLA)/PVP, were studied with differential scanning calorimetry and Fourier transform infrared (FTIR) spectroscopy. The composition-dependent changes of the glass-transition temperature (Tg) and degree of crystallinity (Xc) of the L-PLA phase indicated that L-PLA and PVP were immiscible over the composition range investigated. However, the sharp decrease of Xc with increasing PVP content in the second heating run demonstrated that the cold crystallization process of L-PLA was remarkably restricted by PVP. In DL-PLA/PVP blends, the existence of two series of isolated Tg's indicated that DL-PLA and PVP were phase-separated, but evidence showed that there was some degree of interaction at the interface of the two phase, especially for the blends with low DL-PLA contents. FTIR measurements showed that there was no appreciable change in the spectra of L-PLA/PVP with respect to the coaddition of each component spectrum, implying the immiscibility of the two polymers. In contrast to L-PLA, the intermolecular interaction between DL-PLA and PVP was detected by FTIR; this was evidenced by the observation of a high-frequency shift of the CO stretching vibration band of PVP with increasing DL-PLA content, which suggested some degree of miscibility. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 973–979, 2003

The Role of Elasticity in the Anomalous Swelling of Polymer Thin Films in Density Fluctuating Supercritical Fluids

Abstract: In situ neutron reflectivity was used to investigate the effects of density fluctuations on the solubility of supercritical carbon dioxide (scCO2) in polymer thin films. Deuterated polystyrene, deuterated polybutadiene, and the corresponding random copolymer, deuterated styrene-random- butadiene copolymer, as well as deuterated poly(methyl methacrylate) were investigated. Data were obtained as a function of pressure under two isothermal conditions (T ) 36 and 50 °C). All the polymer films used showed anomalous swelling and CO2 sorption on the density fluctuation ridge in the P-T phase diagram of CO2. We found that the magnitude of the swelling was a function of the elasticity of the films rather than the bulk solubility of CO2. The enhanced miscibility of the rubber/CO2 systems, which are very poor in bulk, was found to be almost identical to that of the silicon rubber/CO2 mixture, which is one of the highly miscible polymeric materials under moderate CO2 conditions.

Material Characterisation Characterisation of beta-chitin/poly(vinyl alcohol) blend films

Abstract: Blend films of β-chitin (derived from squid pens) and poly(vinyl alcohol) (PVA) were prepared by a solution casting technique from corresponding solutions of β-chitin and PVA in concentrated formic acid. Upon evaporation of the solvent, films prepared from pure β-chitin and pure PVA were found to be transparent, while the film having 50/50 composition was found to be cloudy. Miscibility of the polymers in the amorphous phase of the films at various compositions was assessed using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) techniques. The glass transition temperature of the blend films was found to increase slightly with an increase in the β-chitin content. The effect of blend compositions on apparent degree of crystallinity, mechanical properties, and swelling behavior of the as-prepared blend films was also investigated.  2002 Elsevier Science Ltd. All rights reserved.