Lei Su

Phase transition of [Cn-mim][PF6] under high pressure up to 1.0 GPa

Behavior of the phase transition of an ionic liquid, [Cn-mim][PF(6)], has been investigated under pressures up to 1.0 GPa by using a high-pressure differential thermal analysis (DTA) apparatus. The T versus P phase diagrams of [BMIM][PF(6)] and [EMIM][PF(6)] are constructed. The DTA curve of [BMIM][PF(6)] shows one endothermal valley in heating course at each given pressure, which indicates that a simple phase transition from solid to liquid has taken place under high pressure and that the melting point is an increase function of pressure. However, the DTA curve of [EMIM] x [PF(6)] shows two endothermal valleys in the heating course within the tested pressure range, implying that there may exist another phase. After treatment of [EMIM][PF(6)] at different temperatures under high pressure, the structures of the recovered samples are also investigated by wide-angle x-ray scattering. By considering the results above, it indicates that another crystalline phase exists between the solid and liquid of [EMIM][PF(6)].

Preparation and characterization of a novel ionic conducting foam-type polymeric gel based on polymer PVdF-HFP and ionic liquid [EMIM][TFSI]

Poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP)/ionic liquid (IL) (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [EMIM][TFSI]) polymer gels have been prepared by solvent volatilization with and without ultrasound irradiation, respectively. The gel structure and electrochemical property are characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), Fourier transform infrared (FT-IR), and complex impedance spectroscopy (CIS). It is found that a novel foam-type polymer-ionic liquid gel is prepared with ultrasound irradiation. And, the ultrasound-induced polymer-ionic liquid gel has a higher crystallinity and more diverse crystal size polymer network, comparing with that prepared without ultrasound irradiation. The foam-type gel structure can be explained by the formation of pre-ordered aggregation of molecular chain during the ultrasound irradiation process. The ionic conductivity of the PVdF-HFP/[EMIM][TFSI] gel decline after ultrasound irradiation, which can be attributed to the high crystallinity and looser microstructure. Furthermore, it is found that the ultrasound irradiation can promote the crystalline transition of PVdF-HFP from β to α phase and improve its crystallinity.

In situ solidification of ionic liquid [EMIM][EtOSO3] from melt under high pressure

In situ solidification of 1-ethyl-3-methylimidazolium ethyl sulfate [EMIM][EtOSO3] from melt under high pressure has been investigated by using Raman spectroscopy. The results indicate that [EMIM][EtOSO3] might experience a phase transition at about 2.4 GPa upon compression, which could be identified as solidification to a superpressurized glass by pressure broadening of the sharp ruby R1 fluorescence line. Upon cooling, it solidifies as a glassy state rather than crystallizes at low temperature down to 93 K. These facts are suggestive of a phase transition of liquid to a superpressurized glass induced by compression in [EMIM][EtOSO3], which is similar to the glassy state at low temperature.

A novel method to prepare polymer-ionic liquid gel under high pressure and its electrochemical properties

Sol–gel transition behavior of ionic liquid gel based on poly (ethylene glycol) (PEG) and ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate [EMIM][EtSO4] has been investigated under the pressure up to 250xa0MPa. The Temperature versus Pressure phase diagram of PEG/[EMIM][EtSO4] gel is constructed, and it indicates that the melting point is an increasing function of pressure. Based on the phase diagram, the PEG/[EMIM][EtSO4] gels are prepared by cooling under the pressure of 300xa0MPa and atmospheric pressure, respectively. From the differential scanning calorimetry result of the recovered samples, it is found that PEG/[EMIM][EtSO4] gel prepared under high pressure has a higher crystallinity and smaller crystal size polymer network, comparing with under atmospheric pressure. The cyclic voltammograms and impedance spectra tests indicate that the PEG/[EMIM][EtSO4] gel prepared under high pressure exhibit higher ionic conductivity comparing with atmospheric pressure. It could be speculated these excellent properties might be attributed to the loose gel structure and high ionic density induced by high pressure.

Effect of pressure on the structure and properties of polymeric gel based on polymer PVdF-HFP and ionic liquid [BMIM][BF4]

Poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP)/ionic liquid (IL) (1-butyl-3-methylimidazolium tetrafluoroborate, [BMIM][BF4]) polymeric gels were prepared by cooling method under 0.2, 250, 500, and 750xa0MPa, respectively. The gel structure and electrochemical property were characterized by differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR), complex impedance spectroscopy (CIS), and cyclic voltammetry (CV). It was found that the phase structure of PVdF-HFP/[BMIM][BF4] gel became more orderly while the fracture surface became more irregular with the pressure increasing. FT-IR spectroscopy revealed that ionic liquid (IL) partly complexed with the polymer PVdF-HFP and partly remained dispersed in the matrix, and the relative ratio of them could be changed by high pressure. The ionic conductivity of PVdF-HFP/[BMIM][BF4] gel was increased with the pressure increasing below 500xa0MPa, however, decreased from 500 to 750xa0MPa, which was similar to variation of the amount of uncomplexed IL. It was attributed to the effect of high pressure on ionic density and gel structure of polymer-IL gel. These results indicated that the gel formation under high pressure might be another promising way to prepare IL-GPEs with excellent properties.

High pressure and low-temperature polymorphism in cyclopentanol

The polymorphism of cyclopentanol (C5H10O) has been investigated as a function of temperature at ambient pressure and as a function of hydrostatic pressures to 3.7u2005GPa at room temperature. Differential scanning calorimetry (DSC) and Raman spectra reveal that two plastic phases and two fully ordered crystalline phases are formed during cooling. High pressure Raman and infrared spectra show that cyclopentanol undergoes two-phase transformations. At around 0.6u2005GPa, the liquid cyclopentanol transforms to a solid plastic structure. On further compression to 1.9u2005GPa, one fully ordered crystalline phase is observed. Based on pieces of evidence such as peak splitting and emergence of new peaks, it can be concluded that the ordered crystalline structure has a lower symmetry. In addition, the decrease in the wavenumber of the O–H stretching modes at low temperature and high pressure suggests the ordered crystalline phases are characterized by the formation of hydrogen-bonded molecular chains.

Enhanced Ferromagnetism in Zn0.99Fe0.01O Modified by High Pressure

Polycrystalline bulk sample Zn0.99Fe0.01O was fabricated by a solid-state reaction method and modified by high-pressure treatment technique at a pressure of 5GPa. The structure, morphology and magnetic properties of these samples were investigated in order to clarify the effect of pressure on magnetism of Zn-Fe-O system. It is found that the particle size of the modified samples becomes larger as well as the physical contact between neighboring particles becomes better. All samples show obvious ferromagnetic behaviors at room temperature, and the magnetization of modified samples greatly increases. It is believed that the larger particle size and the closer contact between neighbouring particles resulted from high-pressure treatment cause stronger ferromagnetic exchange interaction in Zn-Fe-O system.

Effects of Substrate Bias on the Microstructure and Properties of a-C:H Films Deposited by MFPUMST

Hydrogenated amorphous carbon (a-C:H) films on silicon wafers were prepared by middle frequency pulsed unbalanced magnetron sputtering technique (MFPUMST) at different substrate bias under the acetylene-argon mixed gases. These films were characterized with Raman spectroscopy, atomic force microscopy (AFM) and nanoindentation. Raman spectra show that the sp3 fraction in a-C:H films increases with increasing substrate bias voltage from 0 to 100 V, and then decreases when the substrate bias above 100 V. AFM and nanoindentation results reveal that the surface roughness and nano-hardness of the films increase with increasing substrate bias voltage from 0 to 100 V, and then decreases when the substrate bias above 100 V. The mechanism of sputtering current on the sp3 fraction is discussed in this paper.