Showing papers on "Miscibility published in 2002"

Room Temperature Ionic Liquids as Replacements for Conventional Solvents - A Review

Abstract: Room temperature ionic liquids are salts that are liquids at ambient temperature. They are excellent solvents for a broad range of polar organic compounds and they show partial miscibility with aromatic hydrocarbons. Typical room temperature ionic liquids have a stable liquid range of over 300 K and have a very low vapor pressure at room temperature. Ionic liquids that are not hydrolyzed show a wide range of solubility in water. These unique properties have suggested that they might be useful as environmentally benign solvents that could replace volatile organic compounds (VOC). By varying the length and branching of the alkane chains of the cationic core and the anionic precursor, the solvent properties of ionic liquids should be able to be tailored to meet the requirements of specific applications to create an almost infinitely set of “designer solvents”. A review of recent applications of ionic liquids is presented along with some results of measurements of liquid-liquid equilibria and partition coefficients with alcohols. The results are compared with predictions based on quantum mechanic calculations.

Phase behavior and morphology in blends of poly(L‐lactic acid) and poly(butylene succinate)

Abstract: Blends of poly(L-lactic acid) (PLA) and poly(butylene succinate) (PBS) were prepared with various compositions by a melt-mixing method and the phase behavior, miscibility, and morphology were investigated using differential scanning calorimetry, wide-angle X-ray diffraction, small-angle X-ray scattering techniques, and polarized optical microscopy. The blend system exhibited a single glass transition over the entire composition range and its temperature decreased with an increasing weight fraction of the PBS component, but this depression was not significantly large. The DSC thermograms showed two distinct melting peaks over the entire composition range, indicating that these materials was classified as semicrystalline/semicrystalline blends. A depression of the equilibrium melting point of the PLA component was observed and the interaction parameter between PLA and PBS showed a negative value of −0.15, which was derived using the Flory–Huggins equation. Small-angle X-ray scattering revealed that, in the blend system, the PBS component was expelled out of the interlamellar regions of PLA, which led to a significant decrease of a long-period, amorphous layer thickness of PLA. For more than a 40% PBS content, significant crystallization-induced phase separation was observed by polarized optical microscopy. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 647–655, 2002

The nature of phase separation in binary oxide melts and glasses. I. Silicate systems

Abstract: An exhaustive review of compositional and thermal extents of miscibility gaps in 41 binary silicate systems permits identification of three groups of cations exhibiting different immiscibility behaviours. The first group comprises network-modifier cations with an ionic radius larger than about 87.2 pm. They have coordination numbers equal to, or higher than, 5 and their miscibility gap size increases linearly with increasing ionic potential. The second group involves cations with an ionic radius larger than 26 pm and smaller than about 87.2 pm (in octahedral coordination). They have at least two coordination numbers: the first one is always 4 and the other 5 (or more). For this reason they are called amphoteric. Their miscibility gap sizes do not increase linearly with an increase of the ionic potential, but follow curves. The third group includes cations with variable crystal field stabilization energies. They are characterized by larger miscibility gap sizes than expected when they are compared with cations with similar ionic radii despite the fact that some of them (e.g. Cr3+) may behave as an amphoteric element because their ionic radii in octahedral coordination are smaller than about 87.2 pm. The origin of phase separation in binary silicate systems is due to coulombic repulsions between poorly screened cations bounded by bridging oxygen strongly polarized towards the silicon, and by non-bridging oxygen.

Miscibility and Mechanical Properties of Blends of (l)-Lactide Copolymers with Atactic Poly(3-hydroxybutyrate)

Abstract: Poly(l-lactide-co-glycolide) (PLLAGA) copolymers and poly(dl-lactide) (PDLLA) were synthesized using the low toxicity compound zirconium(IV) acetylacetonate. Blends with synthetic atactic poly(3-hy...

Phase behavior of polymers containing ether groups in carbon dioxide

Abstract: Polyethers of different composition and chain length were investigated with regard to their solubility in CO2. The nature of the monomeric unit, the degree of polymerization, the endgroup effect, the composition and the temperature significantly influence the solubility and thus the CO2 pressures required for miscibility. In general, it was found that polymers of propylene oxide are more ‘CO2-philic’ than analogs of either ethylene oxide or tetrahydrofuran. The phase behavior of block copolymers of the ethers is influenced by both composition and topology (blocky versus random, block arrangement). It appears that the ether oxygens in polyethers enhance the solubility of such polymers (relative to simple hydrocarbons) through specific interactions with CO2, but only if the ether oxygen is in a readily accessible position.

Formation of integrally skinned asymmetric polyetherimide nanofiltration membranes by phase inversion process

Abstract: Integrally skinned asymmetric polyetherimide (PEI) membranes were prepared by the phase inversion process from casting solution containing dimethylformamide (DMF) as a solvent and 1,4-dioxane as a cosolvent. Deionized water was used as a coagulation medium in preparing asymmetric membranes. The effect of 1,4-dioxane was investigated by measuring casting solution properties, permeation properties, and membrane structures. Various effects of polymer concentration, evaporation time, and coagulation bath temperature were also studied. Low miscibility of 1,4-dioxane with coagulant (water) resulted in reducing membrane pore size. The molecular weight cutoff values of asymmetric membranes could be controlled by changing the amount of 1,4-dioxane in the casting solution. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1300–1307, 2002; DOI 10.1002/app.10452

Miscibility, melting, and crystallization of poly(trimethylene terephthalate)/poly(ether imide) blends

Abstract: Miscibility, melting, and crystallization behaviors of solution-blended poly(trimethylene terephthalate) (PTT)/poly(ether imide) (PEI) blends have been investigated using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and polarized light microscopy (PLM). These blends show a single and composition-dependent glass transition temperatures over the entire composition range, implying that these blends are fully miscible in the amorphous region. The enthalpy of the middle endotherm melting of the primary crystallization decreases with increasing PEI content in the blend. Recrystallization of PTT during heating scan in DSC is either retarded or fully inhibited by the presence of PEI. In nonisothermal crystallization, the depression of crystallization temperature of PTT also depends on the blend composition and cooling rate; the presence of PEI decreases the PTT segments migrating to the crystallite-melt interface. The effects of temperature and PEI content on the spherulite growth rate of PTT were evaluated by PLM. The spherulite growth rate decreases with the increase of the PEI content, implying that it is a thermodynamically dominant process. Both thermodynamic and kinetic factors cause total inhibition of PTT crystallization at higher PEI content in the blend. © 2002 John Wiley & Sons, Inc. J Appl Polym Sci 84: 850–856, 2002; DOI 10.1002/app.10367

Guidelines To Creating a True Molecular Composite: Inducing Miscibility in Blends by Optimizing Intermolecular Hydrogen Bonding

Abstract: Blending a liquid crystalline polymer (LCP) with an amorphous polymer to create a molecular composite offers a method to utilize the desirable properties of a LCP at a more modest cost. However, ve...

Miscibility of cellulose acetate with vinyl polymers

Abstract: Binary blend films of cellulose acetate (CA) with flexible syntheticpolymers including poly(vinyl acetate) (PVAc), poly(N-vinyl pyrrolidone) (PVP),and poly(N-vinyl pyrrolidone-co-vinyl acetate) [P(VP-co-VAc)] were preparedfrommixed polymer solutions by solvent evaporation. Thermal analysis by DSC showedthat CA of any degree of substitution (DS) was not miscible with PVAc, but CAwith DS less than 2.8 was miscible with PVP to form homogeneous blends. Thestate of mixing in CA/P(VP-co-VAc) blends was affected not only by the DS of CAbut also by the VP/VAc copolymer composition. As far as CAs of DS<2.8 andP(VP-co-VAc)s with VP contents more than ca. 25 mol% were used,theCA/copolymer blends mostly showed a miscible behaviour irrespective of themixing ratio. FT-IR measurements for the miscible blends of CA/PVP andCA/P(VP-co-VAc) revealed the presence of hydrogen-bonding interactions betweenresidual hydroxyls of CA and carbonyls of N-vinyl pyrrolidone units, which maybe assumed to largely contribute to the good miscibility.

Miscibility and Crystallization Behavior of Crystalline/Crystalline Polymer Blends. Poly(ester carbonate)/Poly(l-lactic acid)

Abstract: Miscibility and Crystallization Behavior of Crystalline/Crystalline Polymer Blends. Poly(ester carbonate)/Poly(l-lactic acid)

Effect of tacticity on coil dimensions and thermodynamic properties of polypropylene

Abstract: Small-angle neutron scattering (SANS) has been used to measure the chain dimensions of syndiotactic polypropylene (s-PP) in the melt, using mixtures of 1H- and 2D-labeled molecules. This leads to a segment length 7.6 A normalized to a four-carbon repeat unit, which is in excellent agreement with a prediction based on a correlation of chain conformation and the plateau modulus obtained from rheology. The s-PP segment length is substantially higher than the values of 6.2 A previously obtained for isotactic polypropylene (i-PP) in the melt and 5.6 A in a low-molecular-weight “polymeric solvent”. We have also studied its effect on the thermodynamics of polyolefin blends by investigating the miscibility of s-PP with a range of atactic poly(ethylene/ethylethyelene) (PEEx) random copolymers, with x% ethylethylene, and comparing this with i-PP. The miscibility “window” of i-PP with PEEx ranges from x = 63−96% ethylethylene, while that of s-PP is shifted to x = 53−73%, in qualitative agreement with the concept tha...

Liquid-liquid equilibrium of the aqueous two-phase system water + PEG 4000 + potassium phosphate at four temperatures: Experimental determination and thermodynamic modeling

Abstract: The effect of temperature on the liquid−liquid equilibrium for the aqueous two-phase system water + poly(ethylene glycol) 4000 + potassium phosphate was studied by determining 29 tie lines at 10 °C, 14 tie lines at 15 °C, 23 tie lines at 20 °C, and 15 tie lines at 30 °C, to give a total of 81 tie lines at four different temperatures. The results show a transition of miscibility: at 10 °C, the pair water + salt is completely miscible and the pair PEG + water is partially miscible, while, at higher temperatures, the pair water + salt becomes partially miscible and the pair PEG + water becomes completely miscible. Experimental results were correlated with a mass fraction-based NRTL activity coefficient model. New interaction parameters were estimated with the Simplex method and the maximum likelihood principle. The mean deviations between the experimental and calculated compositions in both equilibrium phases are below 1.7%.

Miscibility and Phase Structure of Blends of Poly(ethylene oxide) with Poly(3-hydroxybutyrate), Poly(3-hydroxypropionate), and Their Copolymers

Abstract: The miscibility and phase behavior of poly(ethylene oxide) (PEO) blends with poly(3-hydroxybutyrate) (P(3HB)), poly(3-hydroxypropionate) (P(3HP)), and poly(3-hydroxybutyrate-co-3-hydroxypropionate)s (P(3HB-co-3HP)s) have been investigated by differential scanning calorimetry (DSC) and high-resolution solid-state 13C nuclear magnetic resonance (NMR). Four bacterial P(3HB-co-3HP) samples with 3HP contents of 15, 25, 46, and 76 mol % have been used in order to investigate possible influence of the sequence structure of P(3HB-co-3HP)s on the miscibility and phase behavior of blends. These four P(3HB-co-3HP) samples have different thermal properties and crystallizability depending on the 3HP contents. The DSC thermal behavior of the blends revealed that the blends of PEO with P(3HB), P(3HP), and P(3HB-co-3HP)s were miscible over the whole composition range but the crystallization of blend components followed by phase separation exerted much influence on the phase structure of the blends. The results from solid...

Miscibility Behavior and Specific Interaction of Phenolic Resin with Poly(acetoxystyrene) Blends

Abstract: Full Paper: The miscibility behavior and specific interaction of phenolic resin with poly(acetoxystyrene) (PAS) blends were examined using differential scanning calorimetry (DSC), fourier-transform infrared (FT-IR) spectroscopy and solid-state NMR. This phenolic/PAS blend is fully miscible, as indicated by a single glass-transition temperature, due to the formation of inter-hydrogen bonding between the hydroxyl group of the phenolic resin and the carbonyl group of PAS. The DSC study indicates that this phase-separation exothermic peak area is closely related to the interaction between the components. Furthermore, 13 C solid-state NMR and FT-IR spectroscopies were used to study the extent of specific interaction with various compositions and degrees of inter- and intramolecular hydrogen bonding. Moreover, the inter-association equilibrium constant and the related enthalpy of this phenolic/PAS blend were determined and used to predict the free energy and fraction of the hydrogen bonding according to the Painter‐Coleman association model.

Miscibility and adhesive properties of ethylene vinyl acetate copolymer (EVA)-based hot-melt adhesives. I. Adhesive tensile strength

Abstract: A series of ethylene vinyl acetate copolymers (EVA) were blended with some tackifier resins that are made from wood extracts, and possible relations between their miscibility and properties as hot-melt adhesives (HMA) were investigated. From our previous report on miscibility of various EVA-based HMAs, we chose some blends that represent some of typical miscibility types and measured their adhesive tensile strengths. When the blends were miscible at testing temperatures, the temperature at which the maximum value of adhesive tensile strength was recorded tended to move toward higher temperature as tackifier content of blends increased. This result corresponds to the glass transition temperature (Tg) of the blends that became higher as tackifier content of blends increased when blend components were miscible. In terms of HMA performances, we suggest that factors other than miscibility affect absolute values of adhesive tensile strength more directly than miscibility; this idea has to be investigated further in a future study. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 719–725, 2002