Influence of Mixed Solvents and Temperature on the Solution Properties of Quaternized Polysulfones

Modification of intrinsic viscosity and the preferential adsorption coefficients of quaternized polysulfones with various contents of ionic chlorine in N,N‐dimethylformamide/water and methanol/water mixed solvents was investigated at different compositions and temperatures. The polyelectrolyte effect induced by an enhanced dissociation of the ionizable groups determines both the modification of the swelling degree of the polymer coil and the difference in composition of the mixed solvent inside and outside the coil. The results obtained were correlated with the interaction parameters of the above‐mentioned polymer/solvent/solvent systems.     

Effect of Alkyl Side Chain on the Conformational Properties of Polysulfones with Quaternary Groups

Modification of intrinsic viscosity, temperature coefficient, and preferential adsorption coefficient of polysulfones with different alkyl side groups in N,N-dimethylformamide/methanol and N,N-dimethylformamide/water was investigated at different compositions and temperatures. The specific interactions, such as hydrogen bonding and polyelectrolyte effect induced by an enhanced dissociation of the ionizable groups, determine both the modification of the solvation power of the polymer coil and the difference in the composition of the mixed solvent inside and outside the coil.     

Influence of the Substitution Degree on the Dilute Solution Properties of Cellulose Acetate

Modification of intrinsic viscosity, coil size, and preferential adsorption coefficients of cellulose acetate with various substitution degrees in single and mixed solvents was investigated at different temperatures. Miscibility is attained by specific competitive interactions between the solvent-solvent and solvent-polymer systems, which induce modification in the composition of solvent mixtures both inside and outside the polymer coil. The conformational properties in solutions were correlated with the preferential adsorption coefficients, known as depending on the interaction parameters of the polymer/solvent/solvent systems. The intermolecular interactions observed in the cellulose acetate solutions assure the main properties necessary for obtaining membranes with different applications.     

Effect of phase transformation on optical and dielectric properties of zirconium oxide nanoparticles

Zirconium oxide nanoparticle (ZrO₂) is synthesized by the hydrothermal method at different calcination temperatures. The structural analysis is carried out by X-ray diffraction and Raman spectra. The sample prepared at 400 °C and 1100 °C showed the cubic and monoclinic phase, respectively, and the sample calcined at 600 °C and 800 °C showed the mixed phase with co-existence of cubic and monoclinic phases. Furthermore, the morphology and particle size of these samples were investigated by scanning electron microscope (SEM) and transmission electron microscope (TEM) analysis. The band gap estimated from UV–Vis spectra of ZrO₂ (zirconia) nanocrystalline materials calcined at different temperatures from 400 °C to 1100 °C was in the range of 2.6–4.2 eV. The frequency dependence of dielectric constant and dielectric loss was investigated at room temperature. The low frequency region of dielectric constant is attributed to space charge effects.     

Rheological Properties of Polyethylene Glycol (PEG 35000): An Interpretation of a Negative Intrinsic Viscosity and a High Huggins Coefficient Value

The effect of temperature on the intrinsic viscosity and the Huggins coefficient of polyethylene glycol (PEG 35000) in aqueous solution was studied. The intrinsic viscosity became negative for temperatures higher than 45°C. Two hypotheses are given to explain this tendency. We demonstrated that the mobility and size of the PEG molecules did not give full information concerning the causes of the negative intrinsic viscosity values. The Huggins coefficient variation was also studied. A peak around 45°C was observed where only the hydrodynamic interactions were present, confirming the transition from a soft to a hard sphere conformation. Above 45°C, the decrease of the Hugging coefficient showed that attractive interactions were responsible for the negative intrinsic viscosity values.     

Hypercoiled structures in aqueous solutions of 2-hydroxyethyl methacrylate-methacrylic acid copolymers at low metnacrylic acid content

The behavior of solutions of 2-hydroxyethyl methacrylate-methacrylic acid copolymers in aqueous 2–8M urea was investigated at temperatures ranging from 10 to 50°C at pH from 3 to 8. The molar fraction of methacrylic acid in the copolymer was 0.045 at most. The values of the intrinsic viscosity and Huggins coefficient were determined. Under these conditions, the poly-(2-hydroxyethyl methacrylate) molecules are in a hypercoiled state. In copolymers at a low degree of dissociation, the methacrylic acid units make the degree of coiling even higher, but in the dissociated state this degree is much lower. Hypercoiling is interpreted as a consequence of the association of hydrophobic groups in the molecule of copolymers.     

Viscometric Study of the Gelatin Solutions Ranging from Dilute to Extremely Dilute Concentrations

The viscosity of gelatin solutions with concentrations between 10^?4 and 10^?5 g/cm³, covering the extremely dilute zones, was studied via a photoelectric viscometer, and the effects of the electrolyte, pH, surfactant, urea, and temperature were discussed. The results showed that the reduced viscosity (η_sp/C) of gelatin exhibited a drastic increase with dilution in the extremely dilute aqueous solutions, this being a typical polyelectrolyte effect. The reduced viscosity of gelatin underwent several oscillations with varying pH; the minimum value of the viscosity was at pH = 5.0, corresponding to its isoelectric point, where gelatin exhibited antipolyelectrolyte behavior. The reduced viscosity of gelatin decreased with increasing temperature, which was due to the helix–coil transition in the gelatin solution. The temperature of the helix–coil transition was 30.0°C in gelatin aqueous solution; however the temperature of helix–coil transition decreased to 20.0°C in urea. Upon cooling, the gelatin molecules in aqueous solution underwent a coil–helix transition. Hydrophobic interactions caused chain folding in the presence of the surfactant sodium dodecylsulphate.     

Electrocaloric effect in antiferroelectric PbZrO3 thin films

Antiferroelectric PbZrO₃ thin films have been deposited on Pt(111)/Ti/SiO₂/Si substrate by polymer modified sol–gel route. Temperature dependent P –E hysteresis loops have been measured at 51 MV/m within a temperature range of 40 °C to 330 °C. The maximum electrocaloric effect ～0.224 × 10^–6 K mV^–1 has been observed near the dielectric phase transition temperature (235 °C) of the thin films. The electrocaloric effect and its strong temperature dependence have been attributed to nearly first‐order phase transition. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Sound propagation and viscosity in water short-chain amphiphiles solutions,evidence of percolation phenomena

Summary A water/butoxyethanol solution has been investigated by means of several techniques (viscosity, ultrasound and hypersound) as a function of concentration and temperature. The butoxyethanol molar fraction range investigated was situated between 0.015 and 0.09, while temperature ranged between −10°C and +45°C. We observed the building-up of large structures lowering the temperature, in particular below +15°C. All data coming from different techniques seem to confirm such a picture and indicate that this aggregation phenomenon is a percolation-like process. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Origin of the anomaly in the behavior of the viscosity of water near 0°C

The temperature dependence of the viscosity of water in the range of 240–340 K has been studied by the molecular dynamics method. The analysis of the data has revealed an anomaly in the behavior of the viscosity of water near 0°C. The appearance of this anomaly has been attributed to the formation of cluster structures at a decrease in the temperature.     

Dielectric analysis of the interfacial polarization of alkali treated woven flax fibers reinforced epoxy composites

Dielectric measurements were performed on alkali treated flax fibers reinforced epoxy composites in the frequency range 0.1 Hz–1 MHz and the temperature range 40–170 °C. Two common dielectric relaxations were observed for all composites. The first one appearing at low temperatures was attributed to the water dipoles polarization due to the hydrophilic character of flax fibers. The second one observed at high temperatures was identified to the interfacial polarization. Analysis of this latter using the Havriliak–Negami model showed an improvement of the fibers/matrix adhesion by these alkali treatments. The best adhesion was obtained by the leaching treatment.     

Effect of temperature on the hybrid supercapacitor based on NiO and activated carbon with alkaline polymer gel electrolyte

A hybrid supercapacitor was fabricated with NiO and activated carbon as positive and negative electrode, PVA–KOH–H₂O containing 5 M KOH as alkaline polymer gel electrolyte, respectively. Cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge–discharge measurements were applied to investigate the dependence of the hybrid supercapacitor on the temperatures from − 20 to 40 °C. The results demonstrated that the capacitive performance of the hybrid supercapacitor turned even better with the temperatures rising up from − 20 to 40 °C. The increase of temperature improved the conductivity of the alkaline polymer gel electrolyte, decreased the charge-transfer resistance and made the better contact at the interface between the electroactive materials and the alkaline gel electrolyte at higher operating temperature. The maximum of the specific capacitance and energy density of the hybrid supercapacitor were 73.4 F/g and 26.1 Wh/kg at the current density of 0.1 A/g and the operating temperature of 40 °C, respectively.     

Dielectric Dispersion Study of Poly(vinyl Pyrrolidone)–Polar Solvent Solutions in the Frequency Range 20 Hz–1 MHz

Influence of polar solvents environment and polymer concentrations on the electrical properties (complex dielectric constant, ac electrical conductivity, complex electric modulus and complex impedance) of the solutions of poly(vinyl pyrrolidone) (PVP) in polar solvents, namely water, ethyl alcohol, ethylene glycol, diethylene glycol, poly(ethylene glycol), glycerol, dimethyl sulfoxide and dimethyl formamide, have been investigated in the frequency range 20 Hz–1 MHz at 25°C. Comparative analysis of the dielectric dispersion curves confirms that the solvent molecular size and number of its hydroxyl groups, and the solutions viscosity, are the major factors which governs the PVP chain segmental motion. The ionic conduction and electrode polarization phenomena has a dominant influence on the large increase of complex dielectric constant values of the solutions of PVP‐polar solvent in the lower frequency region. The values of relaxation times corresponding to these phenomena are also reported.     

High Optical Transparency and Low Dielectric Constant Polyimides Containing Trifluoromethyl and Cyclohexane Groups

A series of novel polyimides (PIs) were polymerized from 4,4′-(cyclohexane-1,4-diylbis (oxy))bis(3-(trifluoromethyl)aniline) (1) and 1,4-bis((4-amino-2-(trifluoromethyl) phenoxy)methyl)cyclohexane (2), with two aromatic tetracarboxylic dianhydrides using the typical one-step method. The inherent viscosity of these resulting PIs were in the range of 0.53–0.91 dl/g in N,N-dimethylacetamide (DMAc) at 30°C. They were readily soluble in numerous solvents, such as N-methyl-2-pyrrolidone (NMP), DMAc, N,N-dimethylformamide (DMF), meta-cresol (m-Cresol), and dimethylsulfoxide (DMSO). The PI films showed high optical transparency and were colorless with an ultraviolet-visible absorption cut-off wavelength around 330 nm, and a low dielectric constants of 2.49–2.93 at 1 MHz. The PIs also showed good thermal properties. Their glass-transition temperatures (T _g) were higher than 337°C, and the temperatures of 10% weight loss in air and nitrogen were higher than 412°C and 417°C. Furthermore, the PI films possessed good mechanical properties with tensile strengths of 54–71 MPa, elongations at break of 11.6%–17.3% and low moisture absorption (<1.34%). Due to their properties, these PIs could be considered as materials for photoelectric and micro-electronic applications.     

Solubility of divalent zinc in natrium chloride crystals

The temperature dependence of the solubility of divalent zinc in natrium chloride crystals in a temperature range of 350 to 770°C has been determined by the method of diffusion saturation. The dependence has a retrograde character with a maximum of 5.10^?4 molar fraction of Zn⁺⁺ at 700°C. In the range of temperatures lower than 650°C the experimental results may be well expressed by the relationship

$$C_T = 0 \cdot 132\exp \left( { - \frac{{0 \cdot 458{\text{ }}eV}}{{kT}}} \right)$$     

Effects of preparation method on properties of lithium salt-poly(ethylene oxide) polymer electrolytes

The effects of using different sources of precursor poly(ethylene oxide) (PEO) and acetonitrile solvent on the physical and electrochemical properties of lithium salt-PEO polymer electrolytes were investigated. Although no differences were found due to the use of different types of PEO, the purity of the acetonitrile solvent was found to be critical in controlling the properties of the polymer product. Acetonitrile of nominally relatively low purity produced polymer electrolytes exhibiting largely crystalline type behaviour while the use of nominally high purity solvents gave polymers which were apparently completely amorphous at temperatures above about 50°C. Transport number measurements gave values for the lithium ions of 0.4 at 132°C for the largely crystalline materials and 0.3 at 112°C for the amorphous polymers. Analysis of the acetonitrile solvents revealed the presence of water in the nominally high purity grades and it has been confirmed that water contamination is responsible for the production of the low melting temperature form of the polymer complex.     

Banana fiber strands–reinforced polymer matrix composites

Banana fiber (BF)-reinforced low-density polyethylene (LDPE) unidirectional composites were fabricated by the compression molding process with 40 wt% fiber loading. The fibers were modified with methylacrylate (MA) mixed with methanol (MeOH) along with 2% benzyl peroxide under thermal curing method at different temperatures (50–90 °C) for different curing times (10–50 min) in order to have better compatibility with the matrix. The effect of fiber surface modification on the mechanical properties (tensile and impact properties) of the composites were evaluated. Monomer concentration, curing temperature, and curing time were optimized in terms of polymer loading and mechanical properties. The mechanical properties were found to be improved based on the improved interaction between the reinforcement and the matrix. Optimized BFs were again treated with 2–5 wt% starch solutions and composites made of 4% starch treated BF showed the highest mechanical properties than that of MA treated composites. Scanning electron microscopy (SEM) was performed to get an insight into the morphology of the composites. Water uptake and soil degradation test of the composites were also investigated.     

Evidence of ion pair breaking by dispersed polymer in polymer gel electrolytes

Non-aqueous polymer gel electrolytes containing trifluoromethanesulfonic acid (HCF₃SO₃) and polyethylene oxide (PEO) as the gelling polymer has been studied. The increase in conductivity observed with the addition of PEO to liquid electrolytes has been explained to be due to the breaking of ion aggregates present in electrolytes at higher acid concentrations. The increase in free H⁺ ion concentration upon breaking of ion aggregates has also been observed in pH measurements and viscosity of gel electrolytes has been found to increase with PEO addition. Polymer gel electrolytes containing dimethylacetamide (DMA) have σ ∼ 10⁻² S/cm at room temperature and are stable over −50 to 125 °C range of temperature. Gels based on propylene carbonate (PC) and ethylene carbonate (EC) are stable in the −50 to 40 °C temperature range and loose their gelling nature above 40 °C.     

Evidence of ion pair breaking by dispersed polymer in polymer gel electrolytes

Non-aqueous polymer gel electrolytes containing trifluoromethanesulfonic acid (HCF₃SO₃) and polyethylene oxide (PEO) as the gelling polymer has been studied. The increase in conductivity observed with the addition of PEO to liquid electrolytes has been explained to be due to the breaking of ion aggregates present in electrolytes at higher acid concentrations. The increase in free H⁺ ion concentration upon breaking of ion aggregates has also been observed in pH measurements and viscosity of gel electrolytes has been found to increase with PEO addition. Polymer gel electrolytes containing dimethylacetamide (DMA) have σ ∼ 10⁻² S/cm at room temperature and are stable over −50 to 125 °C range of temperature. Gels based on propylene carbonate (PC) and ethylene carbonate (EC) are stable in the −50 to 40 °C temperature range and loose their gelling nature above 40 °C.     

Exploring low temperature Li+ ion conducting plastic battery electrolyte

We report blend-based plastic polymer electrolyte (i.e., polyethylene oxide (PEO)–polydimethyl siloxane (PDMS)–lithium hexafluorophosphate (LiPF₆)) with substantial improvement in DC conductivity at ambient and subambient temperatures when compared with literature reports. Conductivity variation with salt concentration, investigated within ±30 °C range, indicates an optimum conductivity of 5.6?×?10^?5 S cm^?1 at 30 °C for Ö/Li ~10 with a further lowering by one order at 0 °C and it remains unaltered at ?10 °C. Enhanced conductivity in this blend electrolyte, though lower than two copolymer counterparts, is attributed to very low glass transition temperatures of the host polymers. X-ray diffraction (XRD) and scanning electron microscopy (SEM) suggest an effective blending between the two polymers with an effective interaction between the Li salt and the blend polymer matrix. Raman spectroscopy results indicated that cation (Li⁺) coordination occurs at the C=Ö site in PEO out of the two electron-rich sites (i.e., CÖ and Si–Ö–Si) in the PEO–PDMS blend. The blend electrolytes are predominantly ionic (t _ion ~97 %).