Cosolvent effect on the phase behavior for the poly(benzyl acrylate) and poly(benzyl methacrylate) in supercritical carbon dioxide and dimethyl ether

Experimental cloud-point data up to 433.2 K and 193.0 MPa are reported for binary and ternary mixtures of poly(benzyl methacrylate) [poly(BzMA)] + carbon dioxide + benzyl methacrylate (BzMA) and poly(benzyl acrylate) [Poly(BzA)] + carbon dioxide + benzyl acrylate (BzA) systems. High-pressure cloud-point data are also reported for Poly(BzMA) + carbon dioxide and Poly(BzA) + carbon dioxide in supercritical dimethyl ether (DME). Cloud-point behavior for the Poly(BzMA) + carbon dioxide + BzMA system was measured in changes of the pressure–temperature (p–T) slope, and with BzMA weight fraction of 50.6, 61.0, 67.2 and 95.0 wt.%. The Poly(BzA) + carbon dioxide + 30.4, 40.7 and 49.4 wt.% BzA systems change the (p–T) curve from upper critical solution temperature region (UCST) to lower critical solution temperature (LCST) region as the BzA concentration increases. With 52.3 wt.% BzA to the Poly(BzA) + carbon dioxide solution, the cloud-point curves are taken on the appearance of a typical lower critical solution temperature boundary. Also, the impact by cosolvent (BzMA and BzA) concentrations for the Poly(BzMA) + DME and Poly(BzA) + DME systems is measured at temperature to 453.2 K and pressure range of 24.6–61.3 MPa.     

Phase behavior measurement for poly(isobornyl acrylate) + cosolvent systems in supercritical solvents at high pressure

We have conducted experiments to obtain cloud-point data of binary and ternary mixtures for poly(isobornyl acrylate) [P(IBnA)] (Mw = 100,000) + isobornyl acrylate(IBnA) in supercritical carbon dioxide (CO₂), P(IBnA) (Mw = 100,000) + dimethyl ether (DME) in CO₂, P(IBnA) (Mw = 100,000) in propane and butane, and P(IBnA) (Mw = 1,000,000) in propane, propylene, butane and 1-butene at high pressure conditions. Phase behaviors for these systems were measured at a temperature range from 323.4 K to 474.1 K and pressure up to 296.7 MPa. The cloud-point curves of P(IBnA) (Mw = 100,000) + IBnA and DME in CO₂ change from upper critical solution temperature (UCST) behavior to lower critical solution temperature (LCST) behavior as IBnA and DME concentration increases, and liquid–liquid–vapor phase behavior appears for the P(IBnA) (Mw = 100,000) + CO₂ + 80.3 wt.% IBnA system. Phase behaviors of P(IBnA) and 50 wt.% IBnA in CO₂ and P(IBnA) in propane and butane show the pressure difference in accordance with Mw = 1,000,000 and Mw = 100,000 of P(IBnA). Also, the solubility curves for IBnA in supercritical CO₂ were measured at a temperature range of (313.2–393.2) K and pressure up to 22.86 MPa. The experimental results were modeled with the Peng–Robinson equation of state (PR-EOS) using a mixing rule including two adjustable parameters. The critical property of IBnA is estimated with the Joback–Lyderson method.     

Phase behavior for the poly[2-(2-ethoxyethoxy)ethyl acrylate] and 2-(2-ethoxyethoxy)ethyl acrylate in supercritical solvents

Pressure-composition (p, x) isotherms were obtained for the carbon dioxide + 2-(2-ethoxyethoxy)ethyl acrylate [2-(2-EE)EA] system at five temperatures (313.2 K, 333.2 K, 353.2 K, 373.2 K, and 393.2 K) and pressure up to 22.86 MPa. The carbon dioxide + 2-(2-EE)EA system exhibits type-I phase behavior with a continuous mixture critical curve. The experimental results for carbon dioxide + 2-(2-EE)EA mixtures are correlated using the Peng–Robinson equation of state (PR-EOS) using mixing rule including two adjustable parameters. The critical property of 2-(2-EE)EA is estimated with the Joback–Lyderson method.Experimental data up to 485 K and 206.6 MPa are reported for binary and ternary mixtures of poly(2-(2-ethoxyethoxy)ethyl acrylate) [P(2-(2-EE)EA)] + carbon dioxide + 2-(2-EE)EA, P(2-(2-EE)EA) + carbon dioxide + dimethyl ether (DME), P(2-(2-EE)EA) + carbon dioxide + propylene and P(2-(2-EE)EA) + carbon dioxide + 1-butene systems. High-pressure cloud-point data are also reported for P(2-(2-EE)EA) in supercritical carbon dioxide, propane, propylene, butane, 1-butene, and DME at temperature to 474 K and a pressure range of (8.45–206.6) MPa. Cloud-point behavior for the P(2-(2-EE)EA) + carbon dioxide + 2-(2-EE)EA system were measured in changes of the pressure–temperature (p, T) slope and with 2-(2-EE)EA mass fraction of 0.0 wt%, 5.9 wt%, 14.9 wt%, 30.3 wt% and 60.2 wt%. With 0.650 2-(2-EE)EA to the P(2-(2-EE)EA) + carbon dioxide solution, the cloud point curves take on the appearance of a typical lower critical solution temperature boundary. The P(2-(2-EE)EA) + carbon dioxide + (0.0–46.6) wt% DME systems change the (p, T) curve from upper critical solution temperature region to lower critical solution temperature region as the DME mass fraction increases. Also, the impact by propylene and 1-butene mass fraction for the P(2-(2-EE)EA) + carbon dioxide + propylene and 1-butene system is measured at temperatures to 454 K and a pressure range of (75.7 to 119.6) MPa.     

High pressure phase behavior of poly[isopropyl acrylate] and poly[isopropyl methacrylate] in supercritical fluid (SCF) solvent and SCF solvent + cosolvent mixtures

Cloud-point data are reported for poly(isopropyl acrylate) [P(IPA)] in CO₂, propane, propylene, butane, 1-butene, and dimethyl ether (DME) and for poly(isopropyl methacrylate) [P(IPMA)] in CO₂. P(IPA) + alkene cloud-point curves are ∼100 °C lower than the P(IPA) + alkane curves, which are close to the P(IPA) + CO₂ curve located at temperatures greater than 130 °C and pressures of 2500 bar. P(IPA) dissolves in pure DME at conditions as mild as 50 °C and 200 bar. Since IPA and IPMA monomers are used as cosolvents with CO₂, binary IPA + CO₂ and IPMA + CO₂ data are reported to complement the ternary cloud-point data. Both monomer + CO₂ mixtures exhibit type-I behavior and both are adequately modeled with the Peng–Robinson equation of state. IPMA is a more effective cosolvent than IPA. The polymer + CO₂ + monomer phase behavior suggests that it is viable to polymerize IPA or IPMA in CO₂ at moderate operating conditions.     

Selective low temperature synthesis of carbon nanospheres via the catalytic decomposition of trichloroethylene

The catalytic growth of structured carbon from a C₂H₄ and C₂HCl₃ feed promoted by Ni/SiO₂ in the presence of H₂ over the temperature range 673 K ≤ T ≤ 1023 K has been examined. The supported Ni phase exhibited an exclusive cubic symmetry (XRD analysis) with a range of Ni particle sizes (TEM analysis) and a net shift in the distribution to larger particles with increasing reduction temperature (from 20 to 36 nm), accompanied by a decrease in H₂ chemisorption. Conversion of C₂H₄ generated hydrogenation (C₂H₆), hydrogenolysis (CH₄) and decomposition (C + H₂) products. Ethane formation was favoured at lower temperatures with C formation increasingly preferred at higher temperatures so that C₂H₄ decomposition was the predominant process at T > 723 K; significant CH₄ production was only observed at T > 900 K. Carbon yield from C₂H₄ passed through a maximum at 773 K and took the form of high aspect ratio graphitic nanofibres with a central hollow core and diameters in the range 5–180 nm. The carbonaceous product has been characterized by a combination of TEM-EDX, SEM, XRD, BET area and temperature programmed oxidation (TPO). Carbon formation from C₂HCl₃ exceeded (by a factor of up to an order of magnitude) that generated via the decomposition of C₂H₄ at the same inlet C:Ni ratio to deliver essentially a carbon yield invariance (9.1 ± 0.3 g_C g_Ni^?1) where 898 K ≤ T ≤ 1023 K, which represents a carbon efficiency (fraction of carbon in the inlet feed that is converted to a solid carbon product) in excess of 96%. Ni/SiO₂ promoted a composite dehydrochlorination/decomposition of C₂HCl₃ to HCl + C. The nature of the carbon product generated from C₂HCl₃ is strongly temperature dependent with a shift from a pseudo-fibrous product at 773 K to a predominant nanosphere formation at 923 K. These nanospheres exhibit a wide diameter range (40–700 nm), a significant Cl content (1.1–2.6%, w/w) and a conglomeration or clustering to give a less ordered carbonaceous product than that generated at the lower temperature (773 K). A tentative carbon growth rationale is presented to account for the observed dependence of carbon structure on carbon-containing precursor and reaction temperature.     

Argon as a potential processing media for natural and synthetic substances

Phase equilibrium data of caffeine, vanillin, o-ethyl vanillin and a natural rosemary extract (containing 73.9% carnosic acid and 14.7% carnosol) in argon have been determined in present work.Solubility data were determined at temperatures of 313.15 K, 333.15 K and 363.15 K and in the pressure range from 0.82 MPa up to 50.27 MPa using a static–analytic method and were compared to solubility data of the same substances in CO₂.Maximal solubility of vanillin in argon was obtained at a temperature of 313.15 K and a pressure of 43.8 MPa, approx. 0.015 g/g. Comparing the solubility data of pure vanillin in argon and in CO₂ higher solubility in argon is observed at lower temperatures and pressures. For o-ethyl vanillin the solubility in argon is higher in comparison to solubility in CO₂ in the entire range of pressure, especially at higher temperatures_.Maximal solubility of caffeine in argon was observed at a temperature of 363.15 K 0.001361 g caffeine/g argon at 38.9 MPa. With increasing pressure solubility increases, while temperature does not have a noticeable impact in the temperature range from 313.15 K to 333.15 K; the solubility increased with increasing temperature to 363.15 K. Similarly, solubility of carnosic acid extract increases with increasing pressure, from about 0.0097 × 10⁻² g substance/g gas at 2.08 MPa and at 313.15 K to 0.0338 × 10⁻² g substance/g gas at 50.27 MPa and at 363.15 K.Solubility of the investigated compounds in argon is a function of both, pressure and temperature. Generally, pressure significantly impacts solubility particularly up to a pressure of 20.0 MPa in case of vanillin and up to 30 MPa in case of o-ethyl vanillin and carnosic acid extract. An additional increase of pressure has only a slight impact on solubility. In the case of caffeine, the impact of pressure on the solubility becomes more evident at pressures higher than 20 MPa.     

Phase equilibria of the propylene glycol/CO2 and propylene glycol/ethanol/CO2 systems

The high-pressure vapour–liquid phase equilibria (P–T–x–y) of the binary mixture propylene glycol/CO₂ have been experimentally investigated at temperatures of (398.2, 423.2 and 453.2) K over the pressure range from (2.5 to 55.0) MPa using a static-analytic method. Furthermore, the high-pressure vapour–liquid phase equilibria (P–T–x–y) of the ternary mixture propylene glycol/CO₂/ethanol at constant temperatures of (398.2, 423.2 and 453.2) K and at constant pressure of 15.0 MPa have been determined using a static-analytic method. Initial concentrations of components in propylene glycol (PG)/ethanol (EtOH) mixture vary from 10 up to 90 wt.%. In general, for binary system it was observed that the solubility of CO₂ in the heavy propylene glycol reach phase increases with increasing pressure at constant temperature. On the contrary, the composition of gaseous phase is not influenced by the pressure or the temperature. On average the solubility of PG in light phase of CO₂ amounts to 30 wt.%. The system behaviour at temperature of 398.2 K was investigated up to 70.0 MPa and a single-phase region was not observed. Above the pressure 60.0 MPa a single-phase region of the system was observed for the temperature of 423.2 K. For the temperature of 453.2 K the single-phase was observed above the pressure of 48.0 MPa. For ternary system it was observed that the composition of heavy phase is slightly influenced by the temperature when the mass fraction of EtOH in initial mixture is higher than 50 wt.%. If the mass fraction of PG in initial mixture is higher than 50 wt.%, the composition of heavy phase is not influenced by the temperature anymore. The composition of the PG, EtOH and CO₂ in light phase remains more or less unchanged and it is not influenced by the conditions.     

Low temperature reaction of point defects in ion irradiated 4H–SiC

The low temperature evolution of point defects induced in SiC by ion irradiation was investigated by deep level transient spectroscopy. The defects were introduced by irradiation with a 7.0 MeV beam of C⁺ ions at a fluence of 6 × 10⁹ cm^? 2. Annealing was then performed in the temperature range of 330–400 K in order to study the change in point defect structure with temperature. The low temperature annealing performed was observed to induce a change in the produced defects. The deep levels related to the S_x (E_C ? 0.6 eV) and S₂ defects (E_C ? 0.7 eV) recovered with annealing while, simultaneously, a new level, S₁ (E_C ? 0.4 eV), was formed. The activation energy of the S₁ defect is 0.94 eV, while the annealing of both the S_x and S₂ levels occurred with activation energy of 0.65 eV.     

Water and ethanol as co-solvent in supercritical fluid extraction of proanthocyanidins from grape marc: A comparison and a proposal

Supercritical carbon dioxide (SC-CO₂) extraction of grape marc was studied using water (W) and ethanol (EtOH) as co-solvent at 15% (w/w), 100 and 200 MPa, and 313.15, 323.15 and 333.15 K to analyze their influence upon total phenols of the extracts. The overall extraction curves were determined and suggested 10 MPa and 313.15 K as the best operating conditions for SC-CO₂ + 15%W extraction, and 10 MPa and 333.15 K for SC-CO₂ + 15% EtOH. The phenolic yields obtained were 63.4 g/kg of extract for SC-CO₂ + 15% W and 38.8 g/kg of extract for SC-CO₂ + 15% EtOH. An alternative method combining Sc-CO₂ + 15% W extraction, followed by SC-CO₂ + 15% EtOH was tested. This procedure provided the best results allowing to obtain the highest phenolic yield (68.0 g/kg of extract), phenol content (733.6 mg GAE/100 g DM), proanthocyanidins concentration (572.8 mg catechin/100 g DM) and antioxidant activity (2649.6 mg α-tocopherol/100 g DM). SC-CO₂ methods were compared with methanol extraction.     

Density and viscosity of the binary polyethylene glycol/CO2 systems

Density of CO₂ saturated solutions of polyethylene glycols (PEGs) of different molecular weight was measured in pressure range from 8.0 MPa up to 47.7 MPa at a temperature of 343 K by a volumetric method. To validate the method density of pure CO₂ was measured at different pressures and a temperature of 293 K. The results were compared to the literature data and the accuracy was better than 2%. The density was between 1.17 g/mL for PEG 1000/CO₂ at 14.5 MPa and 1.78 g/mL for the system PEG 4000/CO₂ at 35 MPa. Further, the data were compared to results, obtained by a gravimetric method using magnetic suspension balance (MSB).Viscosity of CO₂ saturated solutions of polyethylene glycols (PEGs) of different molecular weight at different pressures and at a temperature of 343 K was measured using a high pressure view cell. Also a temperature impact on the viscosity of pure PEGs was observed at ambient pressure. After saturating PEG 1500 with 10 MPa of CO₂ pressure its viscosity decreases from 76.6 mPa s to 2.24 mPa s at 333 K. Further addition of CO₂ and increasing the pressure results in even lower viscosity and the highest viscosity reduction was reached at the highest pressure; at 35 MPa viscosity of the system PEG 1500/CO₂ is only 0.665 mPa s.     

Measurement and correlation of quaternary solubilities of dihydroxybenzene isomers in supercritical carbon dioxide

The equilibrium quaternary solubilities of dihydroxybenzene (resorcinol + pyrocatechol + hydroquinone + SCCO₂) isomers were experimentally determined at 308, 318 and 328 K over a pressure range of 9.8–15.7 MPa by using a saturation method. The effects of temperature, pressure and the components on each other have been thoroughly investigated. The selectivity of SCCO₂ for ternary (resorcinol + pyrocatechol + SCCO₂) and quaternary systems was discussed. A new model equation for quaternary solubilities of solids has been developed by accounting for non-idealities by combining the solution model with Wilson activity coefficient model. The model equation has five adjustable parameters and correlates the quaternary solubilities of current data along with two other quaternary data reported in the literature.     

Phase equilibria of (CO2 + H2O + NaCl) and (CO2 + H2O + KCl): Measurements and modeling

We report experimental measurements of the phase behavior of (CO₂ + H₂O + NaCl) and (CO₂ + H₂O + KCl) at temperatures from 323.15 K to 423.15 K, pressure up to 18.0 MPa, and molalities of 2.5 and 4.0 mol kg⁻¹. The present study was made using an analytical apparatus and is the first in which coexisting vapor- and liquid-phase composition data are provided. The new measurements are compared with the available literature data for the solubility of CO₂ in brines, many of which were measured with the synthetic method. Some literature data show large deviations from our results.The asymmetric (γ–φ) approach is used to model the phase behavior of the two systems, with the Peng–Robinson equation of state to describe the vapor phase, and the electrolyte NRTL solution model to describe the liquid phase. The model describes the mixtures in a way that preserves from our previous work on (CO₂ + H₂O) the values of the Henry's law constant and the partial molar volume of CO₂ at infinite dilution Hou et al. [22]. The activity coefficients of CO₂ in the aqueous phase are provided. Additionally, the correlation of Duan et al. [14] for the solubility of CO₂ in brines is tested against our liquid-phase data.     

Phase equilibria for the binary mixture of n-vinyl pyrrolidone and N,N-dimethylacrylamide in supercritical carbon dioxide

High pressure phase equilibria for the (carbon dioxide + n-vinyl pyrrolidone) and (carbon dioxide + N,N-dimethylacrylamide) systems are measured in a static apparatus at five temperatures of 313.2, 333.2, 353.2, 373.2 and 393.2 K and pressures up to 24.66 MPa. These two systems exhibit maximums in pressure at temperatures between the critical temperatures of carbon dioxide and n-vinyl pyrrolidone or N,N-dimethylacrylamide. The solubility of n-vinyl pyrrolidone and N,N-dimethylacrylamide for the carbon dioxide + n-vinyl pyrrolidone and carbon dioxide + N,N-dimethylacrylamide systems increases as the temperature increases at a fixed pressure. The carbon dioxide + n-vinyl pyrrolidone and carbon dioxide + N,N-dimethylacrylamide systems exhibit type-I phase behavior. The experimental results for the carbon dioxide + n-vinyl pyrrolidone and carbon dioxide + N,N-dimethylacrylamide systems are correlated with the Peng–Robinson equation of state using a mixing rule including binary interaction parameters (k_ij and η_ij).     

Effect of Pb doping on the electrical properties of textured Bi-2212 superconductors

Bi_2−xPb_xSr₂CaCu₂O_y textured materials (x = 0.0, 0.2, 0.4, and 0.6) have been successfully prepared by the laser floating zone technique. Microstructure and electrical properties (J_C and T_C) have been clearly affected by Pb addition. From the E–I curves, slope of the transition between the superconducting and the normal state (n) at 77 K reaches a maximum of about 16 for the 0.4 Pb doped samples. This value is much higher than the typical ones for the Bi-2212 materials. Moreover, when the electrical properties of the 0.4 Pb doped samples are measured at lower temperatures (between 65 and 77 K), n values increase when the temperature is decreased. A maximum n value of 32 has been reached at 65 K which makes this material very attractive for its use as resistive fault current limiters.     

Reactive brazing Cf/SiC to itself and to Mo using the NiPdPtAu-Cr filler alloy

The NiPdPtAu-Cr filler alloy was proposed for joining C_f/SiC composites. The wettability on C_f/SiC composite was studied by the sessile drop method at 1200 °C for 30 min. Under the brazing condition of 1200 °C for 10 min, the C_f/SiC-C_f/SiC joint strength was only 51.7 MPa at room temperature. However, when used a Mo layer, the C_f/SiC-Mo-C_f/SiC joint strength was remarkably increased to 133.2 MPa at room temperature and 149.5 MPa at 900 °C, respectively. At the interface between C_f/SiC and Mo, Mo participated in interfacial reactions, with the formation of Cr₃C₂/Mo₂C reaction layers at the C_f/SiC surface. The improvement in the joint strength should be mainly attributed to the formation of MoNiSi. The C_f/SiC-Mo joint strength was 86.9 MPa at room temperature and 73.7 MPa at 900 °C, respectively. After 10 cycles of thermal shock test at 900 °C the C_f/SiC-Mo joint strength of 71.6 MPa was still maintained.     

Examining the thermo-mechanical properties of novel cyanate ester blends through empirical measurement and simulation

Three cyanate ester monomer or oligomer species: 2,2-bis(4-cyanatophenyl)propane 1, 1-1-bis(4-dicyanatophenyl)ethane 2, and the oligomeric phenolic cyanate (Primaset™ PT30) 3, are blended in various ratios to form binary mixtures, formulated with copper(II) acetylacetonate (200 ppm) in dodecylphenol (1% w/v active copper suspension) and cured (2 K/min to 150 °C + 1 h; 2 K/min to 200 °C + 3 h) followed by a post cure (2 K/min to 260 °C + 1 h). Thermal analysis using DSC reveals good agreement with literature data for the homopolymers: typical polymerisation enthalpies of ca. 97–98 kJ/mol. cyanate are obtained for 1 and 2, with slightly lower values (ca. 80–90 kJ/mol.) obtained for Primaset™ PT30. DMTA data show the possibility of using binary blends of the polymers to yield novel materials with similar thermal and mechanical properties to Primaset™ PT30, while improving the processability of the more highly aromatic oligomer. Two of the homopolymers (1 and 2) and a binary (1:1) blend of the same were simulated. Molecular dynamics experiments reveal good agreement with empirical data generated using DSC, DMTA and TGA.     

Phase equilibrium of two CO2+ biodegradable oil systems up to 72 MPa

A setup based on a static visual synthetic method for determining phase equilibria up to 100 MPa is presented. Solubilities of carbon dioxide (CO₂) in a high-oleic sunflower oil (HOSO) and in an additivated vegetable lubricant (BIO-2T-05) were determined from 298 K to 363 K up to CO₂ mass compositions of 0.42. The experimental device was verified comparing the solubilities of CO₂ in HOSO with values from other laboratory. For both systems, the values of CO₂ solubility show cross-over pressures among the different isotherms. A new equation was used to correlate the solubility data, with deviations in CO₂ mole fraction in the oil-rich phase lower than 1.6%. The prediction ability of Carvalho and Coutinho equation was tested with experimental data. Vapor–liquid–liquid equilibria were also investigated for CO₂ + BIO-2T-05 in the range 288–305 K. Furthermore, densities and viscosities at 0.1 MPa for BIO-2T-05 were measured from 278 K to 373 K.     

Determination and calculation for solubility of m-nitroaniline and its mixture in supercritical carbon dioxide

Equilibrium solubility of m-nitroaniline and p-nitroaniline in supercritical carbon dioxide (SCCO₂) is essential to design the process of SCCO₂ extraction and to investigate the effect of each solute on the solubility in SCCO₂ ternary system. However, the solubility data is not reported so far. We performed the solubility measurements at the temperatures of 308–328 K and in the pressure range of 11.0–21.0 MPa. The experimental results showed the solubility of m-nitroaniline and p-nitroaniline was enhanced in m-nitroaniline + p-nitroaniline + SCCO₂ ternary system. The improvement factor (i), separation factor (μ) and separation efficiency (HE) in the ternary system were defined and calculated, and the best separation result could be obtained at 21.0 MPa and 328 K using SCCO₂ extraction, where the separation efficiency was up to 90.9%. Based on the chemical association theory, a new model was developed to calculate the solubility of mixed solutes in SCCO₂. The correlation result of the new model was tested by about 500 solubility data from 15 kinds of two solutes mixtures in SCCO₂. The correlated result showed that the new model could achieve much better AARD (%) than those of frequently used Sovova and Sovova-T models.     

Phase transitions in single crystal tubes formed from C60 molecules under high pressure

Pure single crystal tubes formed from C₆₀ molecules, with a face-centered cubic (fcc) structure were fabricated by a liquid–liquid interfacial precipitation method using C₆₀ powder. A bulk transition from fcc to a simple cubic structure and a surface transition from (1 × 1) to (2 × 2) have been observed around 246 K (bulk transition temperature T_B) and 214 K (surface transition temperature T_S), respectively, during the measurement of the temperature dependence of electrical resistance. The initiation of the two transitions under pressure was investigated using a piston cylinder high pressure apparatus and it was found that both T_B and T_S increase with increasing pressure. And the C₆₀ molecules at the surface of the tube exhibit the same behavior of that in the bulk at a pressure of about 2.1 GPa.     

Inorganic anion regulated phase transition in a supramolecular adduct: 4-Trifluoromethoxyanilinium hexafluorophosphate-18-crown-6

A new supramolecular adduct 4-trifluoromethoxyanilinium hexafluorophosphate-1,4,7,10,13,16-hexaoxacyclooctadecane ([C₇H₇NOF₃–(18-crown-6)]⁺[PF₆]⁻) was synthesized and separated as crystals. DSC measurement detected that this compound undergoes a reversible phase transition at about 158 K with a heat hysteresis of 4.8 K. The single crystal X-ray diffraction data obtained at 213 K and 113 K suggest that the phase transition undergoes from a high temperature phase with a space group of Pnma to a low temperature one with a space group of P2₁/n, the symmetry breaking occurs with an Aizu notation of mmmF2/m. The driving force of the transition may be ascribed to the order–disorder transformation of the inorganic PF₆⁻ anion. Broad peak dielectric anomaly observed at 157 K further confirms this phase transition.