Temperature dependence of the pulse-height distributions in aliphatic liquid scintillators

The pulse-height distributions for^131mXe in PPO solutions of aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane, 2,4-dimethylpentane, 2,3,4-trimethylpentane, 1-pentene, 1-hexene and 1-heptene are investigated as a function of temperature. The pulse-height distributions are found to be shifted toward higher pulse-heights with decreasing temperature. The count rates of^131mXe remain unchanged with decreasing temperature. The mechanism of the effect is also discussed.     

Temperature dependence of vibrational energy relaxation in liquid oxygen

The energy relaxation of the lowest vibrational level (υ = 1) of liquid oxygen in the electronic ground state was investigated within a wide temperature range (53.4 K ? T ? 96 K). The relaxation time exhibits a peak value of τ′ ≈ 3.1 ms around 65 K and is shorter at lower and higher temperatures. The observed temperature behavior is discussed in view of theoretical models of energy relaxation in liquids.     

Temperature dependence of electrochemical detection for liquid chromatography

The temperature dependence of amperometric response to compounds commonly assayed by liquid chromatography with electrochemical detection is reported. Temperature dependence ranges from 1.5 to 9% change in response per degree. Both diffusion and heterogeneous electron transfer contribute to temperature-induced variability. Controlling the temperature of the chromatographic column markedly reduces the effect of ambient temperature on the electrochemical detector. The efficiency of using different internal standards to compensate for temperature effects is shown to depend on the electrochemical similarity of the standard and the analyte. Several additional approaches to minimization of temperature dependence are discussed. Alteration of detector temperature for the enhancement of signal-to-noise ratio has little advantage.     

Temperature dependence of coarse-grained potentials for liquid hexane

The present molecular dynamics study is an investigation of the temperature (T) dependence of liquid hexane coarse-grained potentials optimized with the Iterative Boltzmann Inversion method. An approach for the derivation of coarse-grained potentials at temperatures T different from the optimization temperature T(0) has recently been proposed for ethylbenzene. This method is based on the use of a T-dependent scaling factor f(T) to generate ethylbenzene potentials at T≠T(0). The approach is here extended to hexane, considering different reference temperatures T(0) and functional forms for f(T). From our simulations, it appears that the accuracy of the temperature transferability depends simultaneously on the T(0) chosen and the analytic form of f(T). Such a behavior is suppressed by the use of a new 2-point interpolation formula to generate coarse-grained potentials as a function of T. This scheme employs a linear interpolation based on the optimization of coarse-grained potentials at two reference temperatures, T(L) and T(U), with T(L)≤T≤T(U). Accurate coarse-grained simulations of liquid hexane can be performed using the new interpolation scheme. The results are encouraging for the use of potential interpolations as a practical means for devising coarse-grained potentials within a wider temperature range.     

Temperature dependence of charge mobility in model discotic liquid crystals

We address the calculation of charge carrier mobility of liquid-crystalline columnar semiconductors, a very promising class of materials in the field of organic electronics. We employ a simple coarse-grained theoretical approach and study in particular the temperature dependence of the mobility of the well-known triphenylene family of compounds, combining a molecular-level simulation for reproducing the structural changes and the Miller-Abrahams model for the evaluation of the transfer rates within the hopping regime. The effects of electric field, positional and energetic disorder are also considered. Simulations predict a low energetic disorder (~0.05 eV), slightly decreasing with temperature within the crystal, columnar and isotropic phases, and fluctuations of the square transfer integral of the order of 0.003 eV(2). The shape of the temperature-dependent mobility curve is however dominated by the variation of the transfer integral and barely affected by the disorder. Overall, this model reproduces semi-quantitatively all the features of experimentally measured mobilities, on one hand reinforcing the correctness of the hopping transport picture and of its interplay with system morphology, and on the other suggesting future applications for off-lattice modeling of organic electronics devices.     

Temperature dependence of physical constants in binary-fluorinated liquid crystal mixtures

The temperature dependence of dielectric constants and splay elastic constants for fluorinated phenyl bicyclohexane (PBC) binary liquid crystal (LC) mixtures is reported. The results show that the proportions of the constituent elements of binary mixtures strongly influence their anisotropic dielectric constants. For mixtures in which meta-para- and ortho-para-fluorine-substituted molecules are in equal proportion, the effectiveness of the anisotropic dielectric is equal to that with a single para-fluorine- substituted compound. The proportions of a mixture seldom affect the threshold voltage and splay elastic constants in an anti-parallel measurement cell.     

Temperature dependence of the dynamic viscosity of liquid mercury

The dependence of the dynamic viscosity of mercury on temperature is calculated and expressed in terms of the cluster associate model, based on the Boltzmann distribution and with normalization at the melting point. The resulting refined equation for mercury viscosity adequately reflects this dependence over the range of the liquid state, including the critical point.     

Temperature dependence of the second-order susceptibility in calamitic ferroelectric liquid crystals

The dij coefficients of the second-order susceptibility tensor for second harmonic generation were detemined for a calamitic ferroelectric liquid crystal (FLC) specifically designed for applications in non-linear optics. The measurements were performed at different temperatures in the SmC* phase. In accordance with the design methodology of these materials, the coefficient along the polar axis d22 is the greatest, and depicts an expected behaviour in the whole range of the ferroelectric phase. On the other hand, the temperature dependence of d21, d23, and d25, is anomalous to some extent, including a sign inversion of d23 at a certain temperature. These results, which contrast with those reported recently for non-calamitic FLCs, were qualitatively interpreted in the light of different conformations which, by virtue of plausible distortions of the molecular core, could coexist in the sample.     

Temperature dependence of electro-optical characteristics of polymer dispersed liquid crystal films

Polymer dispersed liquid crystal (PDLC) films consist of microdroplets of a liquid crystal dispersed in a polymer matrix. Their applications are based on the electrically controllable light scattering properties of the liquid crystal droplets. The effects of temperature on the electro-optical properties of PDLC films have been rarely investigated. In this work, we studied the light transmission on varying the temperature and frequency. It was observed that the transmission at a fixed voltage decreased with increasing temperature above 43°C, independent of frequency. We examined possible origins of this unusual dependence of the transmission on the temperature. It was concluded that conductivity effects due to free ions newly created at high temperatures could be responsible for the unusual behaviour observed.     

Temperature dependence of electro-optical characteristics of polymer dispersed liquid crystal films

Polymer dispersed liquid crystal (PDLC) films consist of microdroplets of a liquid crystal dispersed in a polymer matrix. Their applications are based on the electrically controllable light scattering properties of the liquid crystal droplets. The effects of temperature on the electro-optical properties of PDLC films have been rarely investigated. In this work, we studied the light transmission on varying the temperature and frequency. It was observed that the transmission at a fixed voltage decreased with increasing temperature above 43°C, independent of frequency. We examined possible origins of this unusual dependence of the transmission on the temperature. It was concluded that conductivity effects due to free ions newly created at high temperatures could be responsible for the unusual behaviour observed.     

Temperature dependence of liquid epoxy resin impregnation through polyester non-woven fabric

The temperature dependence of liquid epoxy resin impregnation under atmospheric pressure was measured under the condition that the impregnation was through polyester non-woven fabric sheets, sandwiched between two circular glass plates. It was expected that impregnation would take place to a small extent, because the pressure in the sheet increases to more than atmospheric pressure in the course of impregnation from the perimeter of the circular sheet toward its center, but the liquid resin impregnates to a great extent and impregnating velocity increases with a rise in temperature. This phenomenon can be analyzed by the Kozeny-Carman equation improved by the introduction of the theoretically calculated capillary force in the modeled fiber bed structure and a parameter to postulate gas solubility and diffusion into the liquid resin. An increase in the impregnating velocity with the temperature rise is caused by decrease in the resin viscosity, by increase of the capillary force pressure and by decrease in the gas pressure corrected by a parameter.     

Creep behavior and lifetime prediction of PMMA immersed in liquid scintillator

The creep behavior of PMMA immersed in liquid scintillator at room temperature was experimentally studied with a new type of creep test machine. Both short-term and creep-rupture tensile tests at eight stress levels were performed. A master curve of creep compliance at a reference stress was obtained according to the Time-Stress Superposition Principle. The master curve was compared with the actual long-term creep curve. It demonstrates that the two curves coincide well at short times. However, the actual creep data shows a higher creep rate as time goes on. The actual lifetime is much shorter than that predicted by the master curve. Furthermore, the relationship between long-term creep limited strength and service life was determined. The results can be used to guide the safety design of PMMA vessels for application in a neutrino observatory.     

Temperature dependence of the fluorescence properties of thioflavin-T in propanol, a glass-forming liquid

Steady-state and time-resolved emission techniques were employed to study the nonradiative process of Thioflavin-T (ThT) in 1-propanol as a function of temperature. We found that the nonradiative rate, k(nr), decreased by about 3 orders of magnitude when the temperature was lowered to 88 K. We found remarkably good correspondence between the temperature dependence of k(nr) of ThT and the dielectric relaxation times of the 1-propanol solvent.     

Temperature dependence of solvation dynamics of probe molecules in methanol-doped ice and in liquid ethanol

We have studied the solvation statics and dynamics of coumarin 343 and a strong photoacid (pK* approximately 0.7) 2-naphthol-6, 8-disulfonate (2N68DS) in methanol-doped ice (1% molar concentration of methanol) and in cold liquid ethanol in the temperature range of 160-270 K. Both probe molecules show a relatively fast solvation dynamics in ice, ranging from a few tens of picoseconds at about 240 K to nanoseconds at about 160 K. At about 160 K in doped ice, we observe a sharp decrease of the dynamic Stokes shift of both coumarin 343 and 2N68DS. Its value is approximately only 200 cm-1 at approximately 160 K compared to about 1100 cm-1 at T >/= 200 K (at times longer than t > 10 ps). We find a good correlation between the inefficient and slow excited-state proton-transfer rate at low-temperature ice, T < 180 K, and the dramatic decrease of the solvation energy, as measured by the dynamic band shift, at these low temperatures. We find that the average solvation rate in ice is similar to its value in liquid ethanol at all given temperatures in the range of 200-250 K. The surprisingly fast solvation rate in ice is explained by the relatively large freedom of the water hydrogen rotation in ice Ih.     

Temperature dependence of the structure of Langmuir films of normal-alkanes on liquid mercury

The temperature dependent phase behavior of Langmuir films of n-alkanes [CH3(CH2)(n-2)CH3, denote Cn] on mercury was studied for chain lengths 19< or =n< or =22 and temperatures 15< or =T< or =44 degrees C, using surface tensiometry and surface x-ray diffraction methods. In contrast with Langmuir films on water, where molecules invariably orient roughly surface normal, alkanes on mercury are always oriented surface parallel and show no long-range in-plane order at any surface pressure. A gas and several condensed phases of single, double, and triple layers of lying-down molecules are found, depending on n and T. At high coverages, the alkanes studied here show transitions from a triple to a double to a single layer with increasing temperature. The transition temperature from a double to a single layer is found to be approximately 5 degrees C, lower than the bulk rotator-to-liquid melting temperature, while the transition from a triple to a double layer is about as much below the double-to-single layer transition. Both monolayer and bulk transition temperatures show a linear increase with n with identical slopes of approximately 4.5 degrees C/CH2 within the range of n values addressed here. It is suggested that the film and bulk transitions are both driven by a common cause: the proliferation of gauche defects in the chain with increasing temperature.     

Temperature dependence of self-diffusion in adamantane

Radiotracer experiments show that self-diffusion in the rotator crystalline phase of adamantane proceeds by a vacancy mechanism. The results are in good agreement with those determined from NMR experiments.