Structural transition in liquid cobalt

The temperature dependence of kinematic viscosity of liquid cobalt in the range 1490–1700°C and the influence of the degree of cobalt overheating on its overcooling were studied by viscometry and differential thermal analysis. It was found that liquid cobalt undergoes a structural transition near 1595°C, which manifests itself as a sharp change in the viscosity and the activation energy for viscous flow at this temperature and is accompanied by a considerable increase in crystallization ability.     

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.     

Effect of Temperature on Cononsolvency of Polyvinylpyrrolidone in Water/Methanol Mixture

The behavior of polyvinylpyrrolidone in mixed water/methanol solvents was studied by rheoviscosimetry over a temperature range of 20°C–40°C. For the lower temperatures of this range, the intrinsic viscosity variation of the polymer vs. methanol molar fraction shows structural transitions (coil–globule–coil). This transition, which is usually attributed to the cononsolvency phenomenon, agrees with our previously published results obtained by dynamic light scattering. For higher temperatures, near 40°C, the intrinsic viscosity increase shows an expansion of the polymer over the alcohol molar fraction range 0.2 < X _A < 0.5. This last result can be attributed to the water/alcohol complex destruction under temperature increase. The “excess viscosity” of the polymer-mixed solvents vanishes with increasing temperature and becomes positive at 40°C. So, the polymer chain tends to transit from a globular to an ideal chain in the middle composition range of the mixed solvents.     

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.     

Differential thermal analysis at high pressures—VII: Phase behaviour of solid methanol up to 3kbar

The phase behaviour of solid methanol was investigated from -196°C to the melting temperature and up to 3 kbar, using a low-temperature high-pressure dta apparatus. The melting temperature rises from -98°C at 1 atm to -64°C at 2775 bar. Solid methanol exhibits a transition at atmospheric pressure at approximately -115°C; the transition has a strong tendency to superheat and to occur at -110°C. The transition temperature rises from approximately -115°C at 1 atm to -81°C at 2725 bar. Small impurities of water induce a “second transition” at -117.3°C that must be attributed to the water-methanol eutectic. Volume changes accompanying the phase transition have been calculated using the Clausius Clapeyron equation.     

Experimental Investigation on the Thermal Conductivity and Viscosity of Silver-Deionized Water Nanofluid

Abstract

This article presents an experimental investigation where the thermal conductivity and viscosity of silver-deionized water nanofluid is measured and studied. The mixture consists of silver nanoparticles of 0.3, 0.6, and 0.9% of volume concentrations and studied for temperatures between 50°C and 90°C. The transient hot-wire apparatus and Cannon-Fenske viscometer are used to measure the thermal conductivity and kinematic viscosity of nanofluid, respectively. The thermal conductivity increases with the increase in temperature and particle concentrations. A minimum and maximum enhancement of 27% at 0.3 vol% and 80% at 0.9 vol% are observed at an average temperature of 70°C. The viscosity decreases with the increase in temperature and increases with the increase in particle concentrations. The effect of Brownian motion and thermophoresis on the thermo-physical properties is discussed. Thus, an experimental correlation for thermal conductivity and viscosity, which relates the volume concentration and temperature, is developed, and the proposed correlation is found to be in good agreement with the experimental results.     

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.     

Self-diffusion of nematic liquid crystals in the isotropic phase near the nematic-isotropic transition

Self-diffusion coefficients of two nematic-liquid crystals, PAA and MBBA, were measured by the spin-echo technique over a temperature-range ≈30°C above the nematic-isotropic transition. For both systems, activation energies derived from such measurements agree fairly well those determined earlier from viscosity data.     

Effect of deuteration on the electrical conductivity,dielectric constant and phase transitions in LiNH4SO4

Measurements of dc conductivity and dielectric constant show that deuteration causes an upward shift of the high temperature phase transition point from 186.5 to 191°C and a downward shift of the low temperature transition point from 10 to -1.5°C in LiNH₄SO₄. Mechanisms of phase transitions and of electrical transport in the crystal are discussed.     

Dynamic mechanical characterization of relaxations in poly(oxymethylene), miscible blends,and oriented filaments

Multifrequency dynamic mechanical analysis (DMA) data were obtained for molded poly(oxymethylene) (POM) and its blends from-150°C to 150°C. Because of the high crystallinity, the assignment of the glass transition in POM has been controversial in the literature. Low and high glass transition temperature (T _g) phenolated compounds, including poly(vinyl phenol), were found to be miscible with POM. The shift of the β transition in the POM blends favors an assignment of the β transition detected at ?3°C(1 Hz), not the ?80°C γ transition, as the T _g in semicrystalline POM because the latter is invariant with diluent. The peak at the β transition in pure POM is weak and can only be seen clearly by DMA measurements on samples that have not “aged” at ambient temperature. This is further evidence that the β transition arises from a cooperative glass-transition-like motion. The γ transition is not influenced by aging because it is due to a concerted localized main chain motion. The β transition of an oriented POM filament can be seen in the DMA flexural loss spectrum at-18°C (1 Hz), but not in a tensile loss spectrum. The broad a relaxation was detected at about 110°C (1 Hz) in molded POM and its blends, while it was shifted to about 135°C in the higher crystallinity, oriented system. The α peak is also independent of diluent, consistent with a crystalline origin for this transition, as was proposed earlier.     

Determination of inelastic critical scattering at a first order phase transition in the CDW structure of 1TTaS2 using Mössbauer diffraction

We report Mössbauer diffraction measurements of the temperature dependence of the elastic and inelastic intensities at the (100) Bragg reflection in 1TTaS₂. These measurements use a newly developed microfoil conversion electron (MICE) spectrometry. They cover the temperature range from 19°C to 100°C, bracketing the first order 1T₁ to 1T₂ phase transition in the charge density wave structure at 79°C. The elastic Bragg peak shows a discontinuity at the phase transition as reported by Moret and Colella. The inelastic scattering shows a significant peak near the phase transition. This peak is interpreted as inelastic critical scattering at this first order phase transition.     

Temperature dependence of morphology of supermolecular structures growing in the thin layer melt of fractions of poly(ethylene oxide)

Poly(ethylene oxide) fractions with molecular weights in the range from 1.55 × 10³ to 1.5 × 10⁵ were studied. The optical microscopic observations of the morphology of supermolecular structures grown isothermally from the melt were used to determine the dependance of structural-morphological changes on temperature. Two morphological transitions were established: (1) a high temperature transition at 49 [Ptilde] 3° C from hedritic structures to positive spherulitoids and (2) a low temperature transition at 38 [Ptilde] 2° C from positive spherulitoids to negative spherulites. It is supposed that the transition from hedrites to positive spherulitoids proceeds through a transition from b-axis-oriented lamellae with tilted chains to [401] lamellae with chains perpendicular to the lamellar surface.     

Photo-induced change of viscosity of glassy selenium below its glass transition temperature

The viscosity of g-Se at temperatures between 25 °C and glass transition temperature of g-Se, T_g, was measured by the thermomechanical analysis (TMA). The samples were exposed by halogen light, which passes through penetration silica indentor. The exposure leads to higher rate of penetration.The viscosity of the g-Se decreased during exposure of the samples near its T_g. The photo-induced change of viscosity decreased with increasing temperature. The photo-induced decreasing of viscosity depended on intensity and wavelength of exposure light. Process of the photo-induced change of viscosity was not stable. The Raman spectra revealed that the process of photo-induced decrease of viscosity is not connected with changes of g-Se structure.     

A Spin Label Study of the Effects of Hydrostatic Pressure and Temperature on Cellular Lipids

Rabbit alveolar macrophages were labeled with fatty acid-derived spin labels and the effects of both hydrostatic pressure and temperature upon the fluidity of cell lipids were observed. The alveolar macrophage membrane is significantly more fluid than the erythrocyte membrane, with a value of 2T of 52.1 ± 0.7 gauss as compared to a literature value of 56.2 ± 0.8 gauss for erythrocyte ghosts. Arrhenius plots of the effects of temperature upon membrane lipids exhibit a constant slope as the temperature is reduced until a temperature of 2–3°C is obtained, at which point an abrupt change of slope is encountered indicating a lipid phase transition. When the temperature is held constant and hydrostatic pressure is applied in increasing increments, membrane lipids again exhibit a gradual, consistent decrease in fluidity. Moderate pressures in the range of atmospheric to 4000 psi were employed; and for the cells studied, an increase in pressure of 1000 psi appears roughly equivalent to a temperature reduction of 1°C. When hydrostatic pressure is applied in combination with reduced temperature, the temperature at which the lipid phase transition takes place is shifted from 2–3°C to approximately 10°C.     

Raman scattering from three phases in LiIO3

We studied the temperature dependence of the Raman spectrum of LiIO₃, from room temperature up to t ～ 350°C. Two discontinuous changes in the spectrum are observed as temperature increases. The first one is reversible and occurs in a temperature range between 215°C and 260°C, depending upon sample origin (single crystal or powder) and thermal history. The second occurs at t ? 290°C and becomes irreversible once the samples are heated above 340°C. Each phase has a characteristic spectrum, distinct from that of the other two. Although the occurence of these phase changes are in complete agreement with studies made with X-ray diffraction and differential thermal analysis (DTA), it is at variance with previous Raman and infrared work which report no qualitative change in spectrum at the α ? γ phase transition. We believe this disagreement comes about because our measurements are the first ones so far to have actually passed through the transition.     

Temperature Effect on the Elasticity of Acrylamide-n-Isopropylacrylamide Copolymers

Acrylamide (AAm) – N-isopropylacrylamide (NIPA) copolymers were prepared via free radical crosslinking copolymerization with various weight percentages (wt%) of AAm and NIPA. The temperature dependence of the compressive elastic modulus, G, and toughness, U_T, of the PAAm- NIPA copolymers due to a volume phase transition was found using a compressive testing technique. It was observed that the compressive elastic modulus increased comprehensively when the temperature was increased between 30°C and 60°C. The PAAm- NIPA copolymers presented higher values of the compressive elastic modulus than pure NIPA above the lower critical solution temperature (LCST) (NIPA exhibits a volume phase transition from hydrophilic to hydrophobic in water at 31°C) and their compressive elastic modulus and toughness had a strong temperature dependence.     

X-ray investigation of the transition I→II of NH4I at temperatures between 22° and −163°C

The lattice parameters of modifications I and II of NH₄I at temperatures between 22° and ?39°C were determined at twelve different temperatures by using the same Debye-Scherrer method as in the case of NH₄Br[1]. At the assumed transition temperature, ?16°C, the molar volume was found to increase by 16.96% with increasing temperature. By using a low temperatureX-ray diffractometer, the half time (50% mod. I and 50% mod. II) of the transition I→II of NH₄I was determined at different temperatures between ?23° and ?163 C° for four different particle sizes. It was found that, closely below the transition temperature, the needed supercooling increased with decreasing particle size.     

Birefringence of SbSI and SbSeI crystals at the region of antiferroelectric phase transition

Anomalous behavior has been observed in the temperature range of T = 140–145 °C. The electric current I(T) of SbSI and SbSeI crystals along the c(z) axis changes significantly at the region of the antiferroelectric phase transition when DC voltage is applied. The peak positions are observed at 140 °C and 145 °C for SbSI and SbSeI, respectively. The birefringence spectra show temperature-dependent changes upon retardation m, confirming the antiferroelectric phase transition for both crystals. The peak positions observed from the optical measurements do not differ from the electrical measurements, showing the transition point at 140?°C and 145?°C for SbSI and SbSeI, respectively.     

First observation of a wetting phase transition in low-angle grain boundaries

The wetting phase transition at low-angle intercrystallite grain boundaries has been experimentally observed. In contrast to the high-angle grain boundaries with the misorientation angels θ > 15°, the low-angle grain boundaries (θ < 15°) are not continuous two-dimensional defects, but constitute a discrete wall (network) of lattice dislocations (edge and/or helical). The theory predicts that, depending on θ, either a continuous layer of the liquid phase or a wall (network) of microscopic liquid tubes on wetted dislocation nuclei is formed at completely wetted low-angle grain boundaries. It has been shown that the continuous liquid layers at low-angle grain boundaries in the Cu-Ag alloys appear at the temperature T _wminL = 970°C, which is 180°C higher than the onset temperature T _wmin = 790°C and 50°C lower than the finish temperature of the wetting phase transition at high-angle grain boundaries, T _wmax = 1020°C.     

A Rheological Study of Xanthan Polymer for Enhanced Oil Recovery

This study explored the potential application of xanthan gum as a polymer-flooding agent for oil recovery applications in a specific Devonian oil field. Rheological measurements using oscillatory and steady shear were carried out to examine the change in shear viscosity when the polymer was applied under reservoir conditions. The xanthan rheological properties were described by the Herschel–Bulkley and Ostwald models to characterize its non-Newtonian behavior. As expected, the results showed that higher xanthan concentrations raised the polymer viscosity and increased the degree of shear thinning. Addition of alkalis caused the viscosity of the xanthan solutions to decrease, but they maintained their shear-thinning properties. Polymer solutions in typical oil field brine increased in viscosity by ca. 400% for 720 hours storage time. On the other hand, as expected, the solutions lost their viscosity gradually with increasing temperature. However, at reservoir temperature (68°C), the polymer solutions kept more than 60% of their initial viscosity. In oscillatory deformation tests it was observed that all the measured viscoelastic properties were influenced by temperature and confirmed that xanthan solution behaved as a weak-gel. An order-disorder transition exists within the xanthan-brine solutions which responds to changes in solution concentration, temperature and alkalis.