Solid-solid Phase Transition Temperature Research Articles

Thermal storage performances of the quaternary ammonium tetrachlorocuprate [1-CnH2n+1N(CH3)3]2CuCl4 (n = 16, 18) multiphase state as high efficient phase change materials (PCMs)

Traditional solid-solid phase change materials (PCMs) have fixed transition temperature due to their composition and structure determination, which impede their practical application in the field of thermal storage. In this work, according to the second law of thermodynamics and the phase equilibrium theory, PCMs can be further improved through form mixtures (molecular alloy) to regulate phase transition temperature and enthalpy for thermal energy storage. Herein, the binary molecular alloy of quaternary ammonium tetrachlorocuprate [1-CnH2n+1N(CH3)3]2CuCl4 (n = 16, C16C3Cu; n=18, C18C3Cu) as solid-solid PCMs were characterized over the entire composition range by DSC and XRD, and were further constructed phase diagram. Thus, a series of multiphase state materials of C16C3Cu-C18C3Cu, such as solid solutions (α, β, γ), intermediate compound ([1-C16H33N(CH3)3][1-C18H37N(CH3)3]CuCl4), and eutectoid compounds (α + γ, β + γ), could be selected from phase diagram to apply as PCMs with solid-solid phase transition temperature in the interval of 49 to 75 °C and enthalpy in the interval of 2.11 to 106.3 J•g−1, so as to extend the thermal performance of [1-CnH2n+1N(CH3)3]2CuCl4 as PCMs to adapt to thermal storage applications under different conditions.

Separation of 2-phenylethanol (PEA) from water using ionic liquids

This work presents some important issues and topics related to chemical thermodynamics of ionic liquids (ILs). It consist of a series of experimental measurements in binary and ternary phase equilibrium systems connected with possible extraction of 2-phenylethanol (PEA) from aqueous phase “in situ” during the bioproduction. New experimental (solid + liquid) phase equilibrium (SLE) data for two binary systems {IL (1) + PEA (2)} and few (liquid + liquid) phase equilibrium (LLE) in binary systems {IL (1) + H2O (2)}, as well as LLE in five ternary systems of {IL (1) + PEA (2) + water (3)} at temperature T = 308.15 K and ambient pressure are reported. The systems are composed of the ILs: N-butyl-N-trimethylammonium bis{(trifluoromethyl)sulfonyl}imide, [N1114][NTf2], (2-hydroxyethyl)-N-trimethylammonium bis{(trifluoromethyl)sulfonyl}imide, [N1112OH][NTf2], N-N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis{(trifluoromethyl)sulfonyl}imide, [N2212OCH3][NTf2], N-methyl-N-trioctylammonium bis{(trifluoromethyl)sulfonyl}imide, [N1888][NTf2], and N-triethyl-N-octylammonium bis{(trifluoromethyl)sulfonyl}imide, [N2228][NTf2], with PEA or water. The miscibility of some of these ILs with water was known from the literature. A differential scanning calorimetry (DSC) was used to determine the melting point and the enthalpy of melting, solid-solid phase transition temperature and enthalpy, as well as glass transition of the ILs. The [N1114][NTf2] and [N1112OH][NTf2] showed complete miscibility in the liquid phase in a binary system with PEA at temperatures higher than the solubility curve. The latest ILs as [N2212OCH3][NTf2], [N1888][NTf2], and [N2228][NTf2] showed complete miscibility with PEA at temperature T = 308.15 K. The solubility of the ILs in PEA decreases in the order [N1114][NTf2] > [N1112OH][NTf2]. All systems revealed immiscibility gap with water (literature and our data). The solubility of water in the ILs increases in the order [N1888][NTf2] < [N2228][NTf2] < [N2212OCH3][NTf2] < [N1114][NTf2] < [N1112OH][NTf2]. The average selectivity of the extraction of PEA from water increases in the following order: [N1112OH][NTf2] (Sav = 130) < [N1114][NTf2] (Sav = 294) < [N2212OCH3][NTf2] (Sav = 319) < [N2228][NTf2] (Sav = 711) < [N1888][NTf2] (Sav = 806). The correlation of the solubility curves in binary systems, and tie-lines in ternary systems was undertaken with the NRTL excess Gibbs energy equation. The model correlates the solubility of the ternary systems with an acceptable average root mean square deviation (σx = 0.0039). Our results of ternary LLE may be used to design future alternative technological processes of the extraction of PEA from the fermentation broth with [N1888][NTf2] or [N2228][NTf2].

Monte Carlo simulations for the free energies of C60 and C70 fullerene crystals by acceptance ratio method and expanded ensemble method

Accurate values of the free energies of C60 and C70 fullerene crystals are obtained using expanded ensemble method and acceptance ratio method combined with the Einstein-molecule approach. Both simulation methods, when tested for Lennard-Jones crystals, give accurate results of the free energy differing from each other in the fifth significant digit. The solid-solid phase transition temperature of C60 crystal is determined from free energy profiles, and found to be 260 K, which is in good agreement with experiment. For C70 crystal, using the potential model of Sprik et al. [Phys. Rev. Lett. 69, 1660 (1992)], low-temperature solid-solid phase transition temperature is found to be 160 K determined from the free energy profiles. Whereas this is somewhat lower than the experimental value, it is in agreement with conventional molecular simulations, which validates the methodological consistency of the present simulation method. From the calculations of the free energies of C60 and C70 crystals, we note the significance of symmetry number for crystal phase needed to properly account for the indistinguishability of orientationally disordered states.

Temperature dependence in interatomic potentials and an improved potential for Ti

The process of deriving an interatomic potentials represents an attempt to integrate out the electronic degrees of freedom from the full quantum description of a condensed matter system. In practice it is the derivatives of the interatomic potentials which are used in molecular dynamics, as a model for the forces on a system. These forces should be the derivative of the free energy of the electronic system, which includes contributions from the entropy of the electronic states. This free energy is weakly temperature dependent, and although this can be safely neglected in many cases there are some systems where the electronic entropy plays a significant role. Here a method is proposed to incorporate electronic entropy in the Sommerfeld approximation into empirical potentials. The method is applied as a correction to an existing potential for titanium. Thermal properties of the new model are calculated, and a simple method for fixing the melting point and solid-solid phase transition temperature for existing models fitted to zero temperature data is presented.

Electrical conductivity, DSC, XRD, and 7Li NMR studies of rotator crystals n-C21H43COOLi x K(1 − x) (0.33 ≤ x ≤ 0.50), n-C m H(2m + 1)COOLi, and n-C m H(2m + 1)COOK (m = 13, 15, 17, 19, and 21)

Differential scanning calorimetry (DSC) thermograms, X-ray diffraction (XRD) analysis, electrical conductivity (σ), and 7Li NMR spectroscopy characterization of n-CmH(2m + 1)COOM solids (M = Li, Na, K; m = 13, 15, 17, 19, 21) and mixed crystals n-C21H43COOLixK(1 − x) (0.25 ≤ x ≤ 0.75) was performed as a function of temperature. DSC thermograms of n-CmH(2m + 1)COOM revealed several solid-solid phase transitions with large entropy changes. Electrical conductivity studies established that n-CmH(2m + 1)COOLi crystals are poor electrical conductors. In contrast, n-CmH(2m + 1)COOK salts were found to have σ values of 10 − 7–10 − 8 S·cm − 1. Since the crystal structures and phase-transition temperatures of both n-CmH(2m + 1)COOLi and n-CmH(2m + 1)COOK crystals were similar, they were able to form mixed crystals with the structure n-CxH(2m + 1)COOLixK(1 − x). DSC thermograms of the mixed crystals showed a small entropy change at the melting point (ΔSmp < 13 J K − 1 mol − 1), in addition, large ΔS values at the solid-solid phase transition temperature. The σ values obtained for mixed crystals were roughly one order of magnitude greater than those determined for n-C21H43COOK crystals. 7Li NMR spectra of the mixed crystals recorded at various temperatures suggested that the self-diffusion of Li + ions was excited in the highest-temperature solid phase. Based on these results, we have classified these mixed crystals as rotator crystals.

Physico-chemical properties and phase behaviour of pyrrolidinium-based ionic liquids.

A review of the relevant literature on 1-alkyl-1-methylpyrrolidinium-based ionic liquids has been presented. The phase diagrams for the binary systems of {1-ethyl-1-methylpyrrolidinium trifluoromethanesulfonate (triflate) [EMPYR][CF3SO3] + water, or + 1-butanol} and for the binary systems of {1-propyl-1-methylpyrrolidinium trifluoromethanesulfonate (triflate) [PMPYR][CF3SO3] + water, or + an alcohol (1-butanol, 1-hexanol, 1-octanol, 1-decanol)} have been determined at atmospheric pressure using a dynamic method. The influence of alcohol chain length was discussed for the [PMPYR][CF3SO3]. A systematic decrease in the solubility was observed with an increase of the alkyl chain length of an alcohol. (Solid + liquid) phase equilibria with complete miscibility in the liquid phase region were observed for the systems involving water and alcohols. The solubility of the ionic liquid increases as the alkyl chain length on the pyrrolidinium cation increases. The correlation of the experimental data has been carried out using the Wilson, UNIQUAC and the NRTL equations. The phase diagrams reported here have been compared to the systems published earlier with the 1-alkyl-1-methylpyrrolidinium-based ionic liquids. The influence of the cation and anion on the phase behaviour has been discussed. The basic thermal properties of pure ILs, i.e., melting temperature and the enthalpy of fusion, the solid-solid phase transition temperature and enthalpy have been measured using a differential scanning microcalorimetry technique.

Ionic conductivity of single crystal LiNaSO 4

The ionic conductivity of single crystal LiNaSO 4 has been investigated for crystal orientation parallel to the a- and c-axis using complex impedancè spectroscopy. The temperature range from 25°C up to the solid-solid phase transition temperature 518°C has been studied. For ionic transport along the c-axis direction the ionic conductivity is only slightly larger than for transport in a direction perpendicular to the c-axis. The results of this study are compared to results for NMR measurements.

Supercooled liquids and solids in porous glass.

Liquid and solid supercooling of molecular oxygen has been observed and studied in well-characterized porous sol-gel glasses. The depression of the solid-solid phase transition temperature was measured as a function of pore size, showing the strong influence of confinement on the solid phases. The liquid freezing-point depression was also measured, and a picosecond optical technique was used to probe the dynamics of the supercooled liquid. The liquid's geometrical confinement is observed to have an important effect on its properties, leading to behavior unlike that of ordinary bulk fluids.

Adjustment of Solid-Solid Phase Transition Temperature of Polyalcohols by the Use of Dopants*

AbstractThe transition temperatures of solid-solid phase changes in selected polyalcohols, “plastic crystals,” can be adjusted by using interstitial and substitutional dopants. An investigation is under way of the structural changes in these during heating and cooling, and of the thermodynamic properties such as the transition, temperatures and enthalpy changes, as a function of the percent of dopant. The purpose of the investigation is to find and evaluate materials having potential value In thermal storage applications. Dopants for pentaerythritol discussed in this report are trimethylolpropane (TMP), ammonia, boron trifluoride, pentaglycerine (PG) and neopentylglycol (NPG).

Mechanism and kinetics of radical reactions in polymers

THE DISCUSSION of this paper will be limited to the subject of free radical generation and decay in irradiated polymers with the greatest emphasis on irradiated polyethylene. Polymers constitute an excellent medium for such a study inasmuch as they can be prepared in film form, which simplifies u.v. and i.r. spectroscopic examinations; they can be irradiated with high energy radiations at 77°K so that certain types of free radicals are frozen in and their reaction studied at a convenient later time by heating above 77°K. Furthermore, on heating to room temperature from 77°K, it is possible to observe not only the kinetics of the decay of certain free radicals but also the kinetics of formation of other free radicals which are not created by the irradiation at 77°K. In addition, on heating above room temperature and through the melting point, additional free radical decay occurs and can be studied. The free radical reactions can also be correlated with mechanical relaxation processes, with the transition from the glassy to the liquid amorphous state and with the fluctuations of density that occur in the solid as a solid-solid phase transition temperature is approached. Thus, there is much to learn from the study of radical reactions in irradiated polymers. It is particularly appropriate to discuss radical reactions in polyethylene this year inasmuch as 1968 marks the 20th anniversary'v?' of the discovery of the irradiation crosslinking in polyethylene which is probably largely a free radical reaction. At this point we should comment on the possibility that some of the observed effects might be due to reactions of charged or electronically excited species rather than of free radicals (although the latter may also exist in excited states or as charged species). For reactions that occur during the irradiation it is difficult to distinguish free radical reactions from others, but due to the fact that electronically excited states usually decay in times of the order of nsec and ions also rather rapidly, by studying free radical reactions subsequent to the irradiation we can observe their reactions uncomplicated by the presence of charged species or electronically excited states. In some very recent work as yet unpublished'] Keyser, Tsuji and Williams have shown that the radiation yield of trapped electrons, G(e-) is 0·5 in Marlex-50 polyethylene, but only 0·1 to 0·2 in a low density polyethylene.v The ESR signal of (e-) was not observed in a y-irradiated polyisobutylene glass at 77°K. The ESR signal due to