Solution Miscibility Research Articles

Effect of Solution Miscibility on the Morphology of Coaxial Electrospun Cellulose Acetate Nanofibers.

Coaxial electrospinning (co-electrospinning) technique has greatly expanded the universality of fabricating core-shell polymer nanofibers. However, the effect of solution miscibility on the morphology of co-electrospun products remains unclear. Herein, different cellulose acetate (CA) solutions with high solution miscibility but distinctly different electrospinnability were used to survey the effect of solution miscibility on the co-electrospinning process. The structural characterizations show that co-electrospun products are composed of nanofibers with and without the core-shell structure. This indicates that partial solution mixing occurred during the co-electrospinning process instead of absolute no-mixing or complete mixing. Importantly, the solution miscibility also shows a significant influence on the product morphology. In particular, the transformation from nanofibers to microparticles was realized with the increase of core-to-shell flow ratio during the co-electrospinning of core electrosprayable CA/dimethylacetamide (DMAc) solution and shell electrospinnable CA/acetone-DMAc (2/1, v/v) solution. Results show that the solution miscibility exerts a significant effect on not only the formation of core-shell structure but also the product morphology. This work provides a new insight for the in-depth understanding of the co-electrospinning process.

Wet‐Spinning and Carbonization of Lignin‐Polyvinyl Alcohol Precursor Fibers

AbstractLignin is a promising bio‐based precursor for sustainable carbon fibers. Limiting factors for their development include the brittleness of lignin and the lack of large‐scale production routes. Here, a simple and economic wet‐spinning method, suitable for the fabrication of fibers based on softwood Kraft lignin (KL) and polyvinyl alcohol (PVA), is proposed. These two polymers reveal a partial miscibility in solution, and form metastable dispersions in solid state. KL‐PVA fibers are prepared at a weight ratio of 70:30 and are carbonized without thermo‐stabilization. A tailor‐made temperature program leads to a decreased microporosity on the fiber surfaces. The obtained carbon structures at 1000 °C are found to be poorly ordered, leading to only intermediate mechanical and electrical properties. However, graphitic domains appear at temperatures above 1500 °C and indicate a high potential for the system.

Hollow Polycaprolactone Microspheres with/without a Single Surface Hole by Co-Electrospraying.

We describe the co-electrospraying of hollow microspheres from a polycaprolactone (PCL) shell solution and various core solutions including water, cyclohexane, poly(ethylene oxide) (PEO), and polyethylene glycol (PEG), using different collectors. The morphologies of the resultant microspheres were characterized by scanning electron microscopy (SEM), confocal microscopy, and nano-X-ray computed tomography (nano-XCT). The core/shell solution miscibility played an important role in the co-electrospraying process and the formation of microsphere structures. Spherical particles were more likely to be produced from miscible combinations of core/shell solutions than from immiscible ones. Hollow PCL microspheres with a single hole in their surfaces were produced when an ethanol bath was used as the collector. The mechanism by which the core/shell structure is transformed into single-hole hollow microspheres is proposed to be primarily based on the evaporation through the shell and extraction by ethanol of the core solution and is described in detail. Additionally, we present a 3D macroscopic tubular structure composed of hollow PCL microspheres, directly assembled on a copper wire collector during co-electrospraying. SEM and nano-XCT confirm that microspheres in the 3D bulk structure remain hollow.

Novel aromatic and aromatic–aliphatic poly(thiourea‐amide)s for the extraction of toxic heavy metal ions

AbstractA series of novel aromatic and aromatic–aliphatic diamines [isophthaloyl bis(3‐(3‐aminophenyl)thiourea), terephthaloyl bis(3‐(3‐aminophenyl)thiourea), adipoyl bis(3‐(3‐aminophenyl)thiourea), sebacoyl bis(3‐(3‐aminophenyl)thiourea)] were synthesized starting from the dinitro compounds. Spectroscopic and elemental analyses were carried out for the structure elucidation of the monomers. Three series of poly(thiourea‐amide)s (PTAMs) bearing CS groups were prepared through the condensation of new diamines with the diacid chlorides such as isophthaloyl, terephthaloyl and adipoyl chloride. The ensuing PTAMs were characterized using FTIR, 1H‐NMR and 13C‐NMR techniques. Physical properties of the polymers such as solution miscibility, crystallinity, solution viscosity, molecular weight, and thermal properties were measured. Consequently, good organosolubility of these polymers was experiential in amide solvents as DMAc, DMF, DMSO and NMP. Moreover, PTAMs exhibited ηinh in the range of 0.92–1.56 dL/g and GPC measurements revealed Mw around 607 × 102‐851 × 102. DSC served to envisage the glass transition temperatures (Tg) of poly(thiourea‐amide)s located between 232 and 258°C and the initial decomposition temperatures (T0) probed by thermogravimetry were in the range of 305–419°C. Structure‐property relationship of these polymers was also studied. Eventually, solid−liquid extraction tests of the selected poly(thiourea‐amide)s systems revealed excellent results because these polymers show nearly 100% elimination of lead and mercury cations from water media. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Ordering in binary transition metal alloys

We present the phenomenological thermodynamic modeling of binary alloys which demonstrate solubility of the components at high temperatures, and form intermediate phase near equiatomic composition at lower ones (the so-called sigma-phase). Besides, the regular solution miscibility gap takes place also. The nonequilibrium thermodynamic potential is written out as a sum of the free energy of regular solution and polynomial term of scalar order parameter φ, which describes the σ-phase ordering. There are four parameters in the model: the energy of regular solution mixing, the energy of σ-phase formation at zero temperature, and the widths of temperature and concentration intervals of σ-phase existence in the alloy with frozen-in random distribution of components. Up to now, both phase transitions which take place in a number of transition metals binary alloys (the σ-phase formation and miscibility in the regular solution) have been treated separately. In present work, the standard technique of phase diagram calculation allows us to analyze all possible phase diagrams which may arise in the alloy.

Influence of impact load‐temperature conformity on toughening of poly(vinyl chloride) by core‐shell rubber particles

AbstractThe work focused on the elucidation of several key parameters in toughening poly(vinyl chloride) (PVC) by the methyl methacrylate–butadiene–styrene (MBS) core‐shell particles. Accordingly, blends containing various weight percent of the MBS particles were prepared and characterized by dilute solution viscometry, dynamic light scattering, dynamic mechanical thermal analysis, transmission electron microscopy, and temperature variable impact test. The results showed PVC/MBS solution miscibility in almost all compositions with their maximum thermodynamic affinities at about 17 and 67 wt % of MBS in tetrahydrofurane (THF). In addition, MBS weight percent increase in its blend with the PVC above 10 led to severe impact energy raise with eventual leveling at about 17 wt %. Furthermore, blend toughness and its components miscibility in solution increased in parallel up to 20 wt % of MBS particles. On the other hand, blend toughness declined with test temperature decrease toward impact modifier core Tg at about −30°C even for the sample with 20 wt % of the MBS particles. Finally, the brittle‐ductile transition of the blend containing 20 wt % of the MBS particles comparison with its matrix tan δ‐temperature correlation implied 2500 J/m impact energy equivalence with 90°C sample temperature rise in secondary relaxation activation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Subsolidus phase relations in the ternary system SnO 2–TiO 2–Y 2O 3

Subsolidus phase relations in the ternary system SnO 2–TiO 2–Y 2O 3 have been investigated by means of X-ray powder diffraction. The samples are prepared by solid-state chemical reaction method at 1400 °C. The solid solution miscibility gap at room temperature for the TiO 2–SnO 2 system was determined to be content 22–68 mol% SnO 2, based on accurate determination of lattice parameters as functions of composition. The Y 2Ti 2− x Sn x O 7 forms a complete solid solution with pyrochlore-type structure.

Solution miscibility and phase-change behavior of a polyethylene glycol-diacetate cellulose composite

Polyethylene glycol (PEG) and diacetate cellulose (CDA) exhibit good miscibility in acetone solution. The miscibility is related to the molecular weight of PEG, which increases as miscibility decreases. The phase-change behavior of PEG in composite with CDA prepared from the miscible solution was found to be completely different from that of pure PEG. When the PEG fraction in the composites was less than 85%, PEG within the composite did not melt into liquid; even when the temperature was 40°C higher than the melting point of PEG, the PEG–CDA composite exhibited solid–solid phase-change behavior. Thermal analysis indicated that the PEG–CDA composite had greater enthalpy and exhibited good thermal stability. The PEG–CDA composite that exhibited solid–solid phase-change behavior can be used as a new kind of phase-change material for thermal energy storage and temperature control. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 652–658, 2003

Rheological investigations on the dispersions of sodium alginate and guar gum mixtures at different temperatures

This article reports the rheological properties of the aqueous dispersions of sodium alginate, guar gum, and their blends measured by Brookfield rheometer at 298.15, 303.15, and 308.15K. The blend properties have been measured for five different compositions, in order to understand their compatibility in solution (at lower polymer concentrations, i.e., up to 0.8% (w/w)) as well as in the gel form (at higher polymer concentrations, i.e., up to 3% (w/w) where they can form gels). The solution miscibility of blends was confirmed by calculating the polymer–polymer interaction parameter using the Krigbaum and Wall equation. Rheological properties have been analyzed by using the equations of Bingham, Casson, Power-Law, and IPC Paste Analysis. Gibbs free energy of activation for enthalpy and entropy has also been calculated. Experimental and calculated results have been discussed in terms of the mixing characteristics of the polymers. The data presented here can be useful in pre-formulation studies to develop the controlled release devices for pesticides or drugs.

Estimation of the miscibility of solutes in mixed solvents using a pseudo-binary approach

In predicting the interaction between the solute and solvent mixture in a multicomponent solution system, the solvent mixture is usually considered as a “single liquid.” The present paper is based on this approach. Using this treatment, the solute-(liquid mixture) interaction in the pseudo-binary solution can, within the framework of the lattice theory of solution, be expressed in terms of the interactions between all binary pairs without further assumption. Application of the treatment to problems of polymer solubility in mixed solvent and of solvent mixtures for separation processes are given.

Energetic criteria for solid solution miscibility gap calculations

L'article est une brève synthèse de la théorie énergétique des substitutions isomorphes d'éléments dans les minéraux et les composés inorganiques. Il présente quelques équations fondamentales de la théorie basée sur un modèle cristallochimique simple de solution solide. Les nomogrammes de détermination des limites de substitutions isomorphes en fonction de la température sont données ainsi que quelques exemples de calcul de la lacune de miscibilité dans des systèmes minéraux binaires. La théorie énergétique quantitative permet d'analyser les règles empiriques de l'isomorphisme.