Showing papers on "Miscibility published in 2014"

Investigating miscibility and molecular mobility of nifedipine-PVP amorphous solid dispersions using solid-state NMR spectroscopy.

Abstract: Solid-state NMR (SSNMR) (1)H T1 and T1ρ relaxation times were used to evaluate the miscibility of amorphous solid dispersions of nifedipine (NIF) and polyvinylpyrrolidone (PVP) prepared by three different methods: melt quenching in the typical lab setting, spray drying and melt quenching in the NMR rotor while spinning. Of the five compositions prepared by melt quenching in the lab setting, the 95:5 and 90:10 NIF:PVP (w:w) amorphous solid dispersions were not miscible while 75:25, 60:40, and 50:50 NIF:PVP dispersions were miscible by the (1)H T1ρ measurements. The domain size of the miscible systems was estimated to be less than 4.5 nm. Amorphous solid dispersions with composition of 90:10 NIF:PVP prepared by spray drying and melt quenching in the NMR rotor showed miscibility by (1)H T1ρ values. Variable-temperature SSNMR (1)H T1ρ relaxation measurements revealed a change in relaxation time at approximately 20 °C below Tg, suggesting increased molecular mobility above that temperature.

Thermal properties and miscibility of semi‐crystalline and amorphous PLA blends

Abstract: The focus of this research is the study of the microstructures and miscibility at the interface between semi-crystalline and amorphous PLAs [poly (l-lactic acid)(PLLA) with poly (l,d-lactic acid)(PDLLA), respectively]. The blends are prepared through thermal processing (extrusion and hot-pressing). To increase the area of interface between PDLLA and PLLA, the fibers from PLLA and PDLLA are used. Thermal and microstructures of the blends were studied by differential scanning calorimetry (DSC), polarized optical microscopy (POM), dynamic thermogravimetric analysis(DMA), small-angle X-ray diffraction(SAXS) and wide-angle X-ray diffraction (WAXD). The two PLAs are miscible in molten state. However, phase separation is detected after various thermal treatments, with PDLLA being excluded from the regions of interlamellar PLLA regions when PDLLA content is low, as determined from X-ray diffraction studies. The compatibility between the two PLAs is not perfect in the molten state, since enthalpies of the various blends at Tg are lower than any pure PLA material. The semi-crystalline PLLA fiber can recrystallize alone in the molten amorphous PDLLA, and a higher nuclei density is observed at the interface. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41205.

Amphiphilic self-assembly of alkanols in protic ionic liquids.

Abstract: Strong cohesive forces in protic ionic liquids (PILs) can induce a liquid nanostructure consisting of segregated polar and apolar domains. Small-angle X-ray scattering has shown that these forces can also induce medium chain length n-alkanols to self-assemble into micelle- and microemulsion-like structures in ethylammonium (EA+) and propylammonium (PA+) PILs, in contrast to their immiscibility with both water and ethanolammonium (EtA+) PILs. These binary mixtures are structured on two distinct length scales: one associated with the self-assembled n-alkanol aggregates and the other with the underlying liquid nanostructure. This suggests that EA+ and PA+ enable n-alkanol aggregation by acting as cosurfactants, which EtA+ cannot do because its terminating hydroxyl renders the cation nonamphiphilic. The primary determining factor for miscibility and self-assembly is the ratio of alkyl chain lengths of the alkanol and PIL cation, modulated by the anion type. These results show how ILs can support the self-asse...

Surface morphology of electrospun PLA fibers: mechanisms of pore formation

Abstract: The article elucidates the mechanisms of formation of varying degrees of surface pores/pits on polylactic acid (PLA) fibers during electrospinning. The role of a combination of different parameters in governing pore formation was demonstrated. They include solvent vapor pressure (pv), solvent miscibility/interaction with water, solubility parameter, and relative humidity (RH) within the spinning unit. Our results indicated that traditional mechanisms like thermally induced phase separation (TIPS) and vapor induced phase separation (VIPS) were not responsible in the generation of surface porosity/pits. Instead, higher RH (water vapor, a non-solvent of the polymer), and its miscibility/interaction with solvent(s) were concluded to be relatively more important than the simple presence of a high pv solvent or a combination of high pv and low pv solvent system. Further, content of high pv solvent in solution determined the spherical or elliptical nature of pores/pits by affecting the level of saturation of nearby region of the interface between jet and air during the electrospinning process.

Biorenewable blends of polyamide-11 and polylactide

Abstract: Polyamide-11(PA11) is melt blended with polylactide (PLA) using 0.00 to 0.10 wt% titanium isopropoxide catalyst to investigate potential compatibilizing reactions. Blend properties are characterized by differential scanning calorimetry (DSC), thermogravimetric analysis, dynamic mechanical thermal analysis, and tensile and impact testing. DSC shows two separate glass transition temperatures indicating only partial miscibility. Base etching to remove PLA domains followed by field emission scanning electron microscopy confirms the two phase nature of the blends. Storage and tensile moduli of the blends increase monotonically with increasing PLA content. Interchange reactions during reactive mixing were investigated by 13 degrees C-NMR spectroscopy but the analysis shows little evidence of interchange reactions. This is true irrespective of catalyst level and mixing time over the temperature range from 185 degrees C to 225 degrees C. At the upper end of the temperature range investigated, significant degradation is observed. The combined results indicate that degradation reactions dominate over compatibilizing interchain transreactions. (C) 2013 Society of Plastics Engineers

Morphology and Thermal Properties of Renewable Resource-Based Polymer Blend Nanocomposites Influenced by a Reactive Compatibilizer

Abstract: Partially miscible blends of poly(lactic acid) (PLA) and poly(hydroxybutyrate) (PHB) have been prepared by the melt mixing method. An interpenetrating network structure created by a maleic anhydride (MA) compatibilizer imparted additional interactions between the two matrices, which has resulted in increased miscibility within the blends. A modified interface has been characterized using morphological analysis through FT-IR and SEM analysis. Because MA compatibilization distributed flexible intermolecular hydrogen bonding within the blend matrix, elongation at break and Izod impact strength has been reported at a maximum of 540.17% and 99%, respectively, compared to those of the PLA matrix. Further, incorporation of layered silicates within the optimized composition of the PLA/PHB/MA blend modified the tensile strength by 49%, without compromising its superior flexible characteristics. Simultaneously, the renowned thermal insulating property of exfoliated/intercalated layered silicate works well to promot...

Composition as a Means to Control Morphology and Properties of Epoxy Based Dual-Phase Structural Electrolytes

Abstract: Structural electrolytes were prepared using a fully formulated commercially available high performance epoxy resin (MTM57) and an ionic liquid based electrolyte: lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) dissolved in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI) Through a systematic study, the composition of the formulations was found to have a greater effect than the curing temperature on the morphology and properties of the resulting structural electrolytes The presence of lithium salt is essential to form a structurally homogeneous electrolyte Bicontinuous morphologies containing continuous (coarse) epoxy networks surrounded by connected spherical epoxy nodules were obtained with different length scales upon varying the lithium salt concentration Increasing the LiTFSI concentration improved the miscibility of MTM57 with the electrolyte and decreased the characteristic length scale of the resulting bicontinuous microstructure The properties of the structural electrolytes correlated with the morphology, showing increased Youngs modulus and decreased ionic conductivity with increasing lithium salt concentration The miscibility of the epoxy system with the electrolyte was also improved by substitution of EMIM-TFSI with an equal weight of an aprotic organic solvent, propylene carbonate (PC); however, the window of PC concentrations which resulted in structural electrolytes with bicontinuous microstructures was very narrow; at PC concentrations above 1 wt %, gel-like polymers with no permanent mesoporosity were obtained

New approach of blending polymeric ionic liquid with polybenzimidazole (PBI) for enhancing physical and electrochemical properties

Abstract: Although the use of ionic liquids (IL) in polymeric membranes is known to elevate the electrochemical performance for proton exchange membrane-based fuel cells (PEMFC), they suffer from drawbacks such as IL drain and lowering in mechanical properties that lead to deterioration in PEMFC performance. To mitigate these issues, we report, for the first time, the use of polymeric ionic liquid (PIL), namely, poly(diallyl dimethyl ammonium trifluoride methane sulphonate) (P[DADMA][TFMS]) to be blended with polybenzimidazole (PBI-I) as a membrane material for PEMFC. PBI-I and (P[DADMA][TFMS]) were chosen because they form miscible blends and are suitable for acid doping as a matrix, which can eventually be used as proton conductor. The structure, miscibility and inter-polymer interactions were studied by infrared (IR) spectroscopy and differential scanning calorimetry (DSC). The increase in proton conduction in comparison to the PBI membranes was observed due to the presence of ionic groups of PILs in blend membranes. With the increase in PIL content, the proton conductivity of the composite membranes gradually increased from 0.04 S cm−1 for PBI to 0.07 S cm−1 for the blend membrane at 150 °C. The MEAs were fabricated with PBI-I, PBI-PIL15, PBI-PIL25 and PBI-PIL35. Corresponding single cells were successfully tested at temperatures of 160 °C. The maximum power density and current density obtained were 515 mW cm−2 and 1632 mA cm−2, respectively, for PBI-PIL25-based MEA.

Chemical Control of Hydrodynamic Instabilities in Partially Miscible Two-Layer Systems

Abstract: Hydrodynamic instabilities at the interface between two partially miscible liquids impact numerous applications, including CO2 sequestration in saline aquifers. We introduce here a new laboratory-scale model system on which buoyancy- and Marangoni-driven convective instabilities of such partially miscible two-layer systems can easily be studied. This system consists of the stratification of a pure alkyl formate on top of a denser aqueous solution in the gravitational field. A rich spectrum of convective dynamics is obtained upon partial dissolution of the ester into the water followed by its hydrolysis. The properties of the convective patterns are controlled by the miscibility of the ester in water, the feedback of the dissolved species on its own miscibility, as well as the reactivity of given chemicals in the aqueous solution with the solubilized ester.

Free Volume, Cohesive Energy Density, and Internal Pressure as Predictors of Polymer Miscibility

Abstract: In this paper, we illuminate and predict trends in polymer miscibility using our model understanding of pure component properties. We introduce a new metric that maps a bulk property to a theoretical characteristic parameter, viz. the percent free volume of a polymer melt as a function of the strength of its segment–segment (nonbonded) interaction energy. To this end we apply our simple Locally Correlated Lattice (LCL) model, first to characterize several dozen polymers via pressure–volume–temperature (PVT) data, and then to calculate properties that cannot be directly determined via experiment, such as percent free volume and cohesive energy density, and we rank all of the polymers in terms of these properties. We reveal strong correlations between bulk behavior and theoretical pure component character, and use those correlations to motivate a discussion of what drives polymer miscibility.

Core-Liquid-Induced Transition from Coaxial Electrospray to Electrospinning of Low-Viscosity Poly(lactide-co-glycolide) Sheath Solution

Abstract: Co-electrospinning has demonstrated that polymer solutions below the entanglement concentration can be made into fibers as an encapsulated core in an electrospinnable sheath solution containing a carrier/template polymer. The carrier polymer may require removal at a later stage. This work shows for the first time that without increasing the polymer concentration/molecular weight or needing a template polymer, simply infusing a liquid in the core nozzle can cause the sheath polymer solution (viscosity <20 mPa s) to electrospin instead of electrospray in a coaxial electrified jet. Different from coelectrospinning, the core liquid can be a common solvent such as water and does not require a readily electrospinnable carrier polymer. The process was not limited to one core liquid system; infusing solvents and nonsolvents with different properties in the core generated either beaded fibers or continuous fibers from the sheath solution. The process of fiber formation instead of particle breakup was attributed to the relaxation time of the elastic polymer sheath solution becoming longer than the growth rate of the Rayleigh instability in the compound jet upon the infusion of a second solvent in the core. Key parameters of the process included high surface tension of the core liquid (e.g., water and glycerol), high interfacial tension between the core and the sheath liquids, and electrohydrodynamic operating parameters such as flow rate and applied voltage. Given that charge was transferred from the sheath solution to the core liquid, differences in the dielectric constant and electrical conductivity of the core liquids showed little influence on the process. Fibers also formed irrespective of the miscibility and solubility of the solvent, though in the case of a nonsolvent, a lower miscibility was desirable to minimize polymer precipitation at the core–sheath interface. The process was investigated using poly(lactide-co-glycolide) as a model system, with polycaprolactone and polymethylsilsesquioxane systems presented as two additional examples. This work documents new roles of solvents in coaxial electrohydrodynamic processes and presents a useful method to obtain micro- and nanofibers from low-viscosity solutions without using a template polymer.

Miscibility and Hydrogen Bonding in Blends of Poly(4-vinylphenol)/Poly(vinyl methyl ketone)

Abstract: The miscibility and phase behavior of poly(4-vinylphenol) (PVPh) with poly(vinyl methyl ketone) (PVMK) was investigated by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). It was shown that all blends of PVPh/PVMK are totally miscible. A DSC study showed the apparition of a single glass transition (Tg) over their entire composition range. When the amount of PVPh exceeds 50% in blends, the obtained Tgs are found to be significantly higher than those observed for each individual component of the mixture, indicating that these blends are capable of forming interpolymer complexes. FTIR analysis revealed the existence of preferential specific interactions via hydrogen bonding between the hydroxyl and carbonyl groups, which intensified when the amount of PVPh was increased in blends. Furthermore, the quantitative FTIR study carried out for PVPh/PVMK blends was also performed for the vinylphenol (VPh) and vinyl methyl ketone (VMK) functional groups. These results were also established by scanning electron microscopy study (SEM).

Improvement in toughness of polylactide by melt blending with bio-based poly(ester)urethane

Abstract: Polylactide (PLA) was successfully toughened by blending with bio-based poly(ester)urethane (TPU) elastomers which contained bio-based polyester soft segments synthesized from biomass diols and diacids The miscibility, mechanical properties, phase morphology and toughening mechanism of the blend were investigated Both DSC and DMTA results manifested that the addition of TPU elastomer not only accelerated the crystallization rate, but also increased the final degree of crystallinity, which proved that TPU has limited miscibility with PLA and has functioned as a plasticizer All the blend samples showed distinct phase separation phenomenon with sea-island structure under SEM observation and the rubber particle size in the PLA matrix increased with the increased contents of TPU The mechanical property variation of PLA/TPU blends could be quantitatively explained by Wu's model With the variation of TPU, a brittle-ductile transition has been observed for the TPU/PLA blends When these blends were under tensile stress conditions, the TPU particles could be debonded from the PLA matrix and the blends showed a high ability to induce large area plastic deformation before break, which was important for the dissipation of the breaking energy Such mechanism was demonstrated by tensile tests and scanning electron microcopy (SEM) observations

Miscible blends of polylactide and poly(methyl methacrylate): Morphology, structure, and thermal behavior

Abstract: The miscibility of polylactic acid (PLA) and atactic poly(methyl methacrylate) (PMMA) blends is investigated as a function of composition. The blends quenched from the melt show the presence of a single glass transition temperature dependent on the composition. The equilibrium melting temperature is determined using the Hoffman-Weeks method and a depression is observed with increasing content of the PMMA component. The PLA spherulite growth rate and the overall isothermal crystallization rates decrease with increasing the amount of the amorphous component. The increase of the long period value as a function of the PMMA content in the blend is due to the segregation of PMMA component in the amorphous PLA interlamellar regions. The Lauritzen-Hoffman secondary nucleation theory analysis shows that the segregation of the PMMA in the interlamellar region induces an increase in the surface entropy of folding. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 1168–1177

Thermal and Structural Analyses of PMMA/TiO2 Nanoparticles Composites

Abstract: In the present work, composites of poly (methyl methacrylate)/titanium oxide nanoparticles (100/0, 97.5/2.5, 95/5, 92.5/7.5, 90/10 and 0/100 wt/wt%)were prepared to be used as bioequivalent materials according to their importance broad practical and medical applications. Thermal properties as well as X-ray diffraction analyses were employed to characterize the structure properties of such composite. The obtained results showed variations in the glass transition temperature (Tg), the melting temperature (Tm), shape and area of thermal peaks which were attributed to the different degrees of crystallinity and the existence of interactions between PMMA and TiO2 nanoparticle molecules. The XRD patterns showed sharpening of peaks at different concentrations of nano-TiO2 powder with PMMA. This indicated changes in the crystallinity/amorphosity ratio, and also suggested that the miscibility between the amorphous components of homo- polymers PMMA and nano-TiO2 powder is possible.The results showed that nano-TiO2 powder mix with PMMA can improve the thermal stability of the homo-polymer under investigation, lead- ing to interesting technological applications.

Nanoparticle-driven intermolecular cooperativity and miscibility in polystyrene/poly(vinyl methyl ether) blends.

Abstract: The effect of silver nanoparticles (nAg) in PS/PVME [polystyrene/poly(vinyl methyl ether)] blends was studied with respect to the evolution of morphology, demixing temperature, and segmental dynamics. In the early stage of demixing, PVME developed an interconnected network that coarsened in the late stage. The nAg induced miscibility in the blends as supported by shear rheological measurements. The physicochemical processes that drive phase separation in blends also led to migration of nAg to the PVME phase as supported by AFM. The segmental dynamics was greatly influenced by the presence of nAg due to the specific interaction of nAg with PVME. Slower dynamics and an increase in intermolecular cooperativity in the presence of nAg further supported the role of nAg in delaying the phase separation processes and augmenting the demixing temperature in the blends. Different theoretical models were assessed to gain insight into the dynamic heterogeneity in PS/PVME blends at different length scales.

Synthesis of coffinite, USiO4, and structural investigations of UxTh(1-x)SiO4 solid solutions

Abstract: The miscibility behavior of the USiO4–ThSiO4 system was investigated. The end members and 10 solid solutions UxTh(1–x)SiO4 with x = 0.12–0.92 were successfully synthesized, without formation of other secondary uranium or thorium phases. Lattice parameters of the solid solutions evidently follow Vegard’s Law. Investigation of the local structure with EXAFS reveals small differences between the U and Th environment attributed to different atomic radii of the metal atoms but no implications for a miscibility gap. The data provided confirm complete miscibility for the system USiO4–ThSiO4. The structure of the end members was studied in detail with XRD and discussed with special regard to the oxygen positions and the often neglected Si–O bond length. USiO4 could be obtained without UO2 impurities and the lattice parameters derived from Rietveld refinement as c = 6.2606(3) A and a = 6.9841(3) A. The Si–O distance in USiO4 appears to be 1.64 A, which is more reasonable than earlier reported values.

Data mining of solubility parameters for computational prediction of drug-excipient miscibility.

Abstract: Computational data mining is of interest in the pharmaceutical arena for the analysis of massive amounts of data and to assist in the management and utilization of the data. In this study, a data mining approach was used to predict the miscibility of a drug and several excipients, using Hansen solubility parameters (HSPs) as the data set. The K-means clustering algorithm was applied to predict the miscibility of indomethacin with a set of more than 30 compounds based on their partial solubility parameters [dispersion forces , polar forces and hydrogen bonding ]. The miscibility of the compounds was determined experimentally, using differential scanning calorimetry (DSC), in a separate study. The results of the K-means algorithm and DSC were compared to evaluate the K-means clustering prediction performance using the HSPs three-dimensional parameters, the two-dimensional parameters such as volume-dependent solubility and hydrogen bonding , and selected single (one-dimensional) parameters. Using HSP...

Synthesis and evaluation of novel dental monomer with branched carboxyl acid group

Abstract: To enhance the water miscibility and increase the mechanical properties of dentin adhesives, a new glycerol-based monomer with vinyl and carboxylic acid, 4-((1,3-bis(-methacryloyloxy)propan-2-yl)oxy)-2-methylene-4-oxobutanoic acid (BMPMOB), was synthesized and characterized. Dentin adhesive formulations containing 2-hydroxyethyl methacrylate (HEMA), 2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy) phenyl]propane (BisGMA), and BMPMOB were characterized with regard to real-time photopolymerization behavior, water sorption, dynamic mechanical analysis, and microscale three-dimensional internal morphologies and compared with HEMA/BisGMA controls. The experimental adhesive copolymers showed higher glass transition temperature and rubbery moduli, as well as improved water miscibility compared to the controls. The enhanced properties of the adhesive copolymers indicated that BMPMOB is a promising comonomer for dental restorative materials.

Reduced graphene oxide induced phase miscibility in polystyrene-poly(vinyl methyl ether) blends

Abstract: Graphene oxide and reduced graphene oxide (r-GO) were synthesized by wet chemistry and the effect of r-GO in PS–PVME blends was investigated here with respect to phase miscibility, intermolecular cooperativity in the glass transition region and concentration fluctuation variance by shear rheology and dielectric spectroscopy. The spinodal decomposition temperature (Ts) and correlation length were evaluated from isochronal temperature scans in shear rheology. The r-GO is shown to induce miscibility in the blends, which may lead to increased local heterogeneity in the blends, though the length of cooperatively re-arranged regions (ξ) at Tg is more or less unaltered. The evolution of the phase morphology as a function of temperature was assessed using polarized optical microscopy (POM). In the case of the 60/40 PS–PVME blends with 0.25 wt% r-GO, apart from significant refinement in the morphology, retention of the interconnected ligaments of PVME was observed, even in the late stages of phase separation suggesting that the coarsening of the phase morphology has been slowed down in the presence of r-GO. This phenomenon was also supported by AFM. Surface enrichment of PVME, owing to its lower surface tension, in the demixed samples was supported by XPS scans. The interconnected network of PVME has resulted in significantly higher permittivity in the bi-phasic blends, although the concentration of r-GO is below the percolation threshold.

Effect of poly(ethylene oxide) homopolymer and two different poly(ethylene oxide-b-poly(propylene oxide)-b-poly(ethylene oxide) triblock copolymers on morphological, optical, and mechanical properties of nanostructured unsaturated polyester.

Abstract: Novel nanostructured unsaturated polyester resin-based thermosets, modified with poly(ethylene oxide) (PEO), poly(propylene oxide) (PPO), and two poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) block copolymers (BCP), were developed and analyzed. The effects of molecular weights, blocks ratio, and curing temperatures on the final morphological, optical, and mechanical properties were reported. The block influence on the BCP miscibility was studied through uncured and cured mixtures of unsaturated polyester (UP) resins with PEO and PPO homopolymers having molecular weights similar to molecular weights of the blocks of BCP. The final morphology of the nanostructured thermosetting systems, containing BCP or homopolymers, was investigated, and multiple mechanisms of nanostructuration were listed and explained. By considering the miscibility of each block before and after curing, it was determined that the formation of the nanostructured matrices followed a self-assembly mechanism or a polymerization-induced phase separation mechanism. The miscibility between PEO or PPO blocks with one of two phases of UP matrix was highlighted due to its importance in the final thermoset properties. Relationships between the final morphology and thermoset optical and mechanical properties were examined. The mechanisms and physics behind the morphologies lead toward the design of highly transparent, nanostructured, and toughened thermosetting UP systems.