Chaosheng Yuan

In Situ Observation of Multiple Phase Transitions in Low-Melting Ionic Liquid [BMIM][BF4] under High Pressure up to 30 GPa

In situ characterization of phase transitions and direct microscopic observations of a low-melting ionic liquid, 1-butyl-3-methyl imidazolium tetrafluoroborate ([BMIM][BF(4)]), has been performed in detail by Raman spectroscopy. Compression of [BMIM][BF(4)] was measured under hydrostatic pressure up to ~30.0 GPa at room temperature by using a high-pressure diamond anvil cell. With pressure increasing, the characteristic bands of [BMIM][BF(4)] displayed nonmonotonic pressure-induced frequency shifts, and it is found to undergo four successive phase transitions at around 2.25, 6.10, 14.00, and 21.26 GPa. Especially, above a pressure of 21.26 GPa, luminescence of the sample occurs, which is connected with the most significant phase transition at around this pressure. It was indicated that the structure change under high pressure might be associated with a conformational change in the butyl chain. Upon releasing pressure, the spectrum was not recovered under a pressure up to 1.16 GPa, thereby indicating that this high-pressure phase remains stable over a large pressure range between 30 and 1.16 GPa in low-melting ionic liquid [BMIM][BF(4)]. Although the sample was kept under the normal pressure for 24 h, the spectrum was recovered, and it showed that the phase transition of [BMIM][BF(4)] was reversible. In other words, such a low-melting ionic liquid [BMIM][BF(4)] remains stable even after being treated under so a high pressure of up to 30 GPa.

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.

Controlled synthesis of perovskite lanthanum ferrite nanotubes with excellent electrochemical properties

In this work, we have fabricated a series of perovskite-type oxide LaFeO3 samples using a simple sol–gel method and further calcination treatment. We investigated the morphologies, structures and electrochemical performances of the fabricated samples in detail by controlling the calcination temperature and time. The morphology characterization indicates that when the calcination temperature and time are 700 °C and 3 h, respectively, LaFeO3 presents as a large number of nanotubes with a diameter of 25 nm. Electrochemical performance testing indicates that the tubular LaFeO3 shows excellent electrochemical performance. When 2 M KOH is used as the electrolyte, the LaFeO3 nanotubes exhibit a high specific capacitance of 313.21 F g−1 at a current density of 0.8 A g−1. In addition, the electrode maintains 86.1% of the initial specific capacitance after 5000 cycles at a scan rate of 100 mV s−1, indicating good long-cycle stability. These results indicate that LaFeO3 nanotubes are a novel pseudocapacitance electrode material for application in energy storage devices.

In situ observation of gelation of methylcellulose aqueous solution with viscosity measuring instrument in the diamond anvil cell

Gelation of methylcellulose aqueous solution was investigated by a high-pressure viscosity measurement device which consisted of diamond anvil cell, microscope and CCD. And the temperature and pressure dependence of the viscosity of methylcellulose aqueous solution was measured utilizing a rolling-ball technique. The results showed that sol-gel thermal transition of methylcellulose solution occurred at the temperature of 53 °C under atmospheric pressure. Upon compression, it was indicated that the viscosity showed a dramatic change in the vicinity of the pressure of 500 MPa. Parabolic phase diagram of methylcellulose aqueous solution was constructed, and it showed that the melting point was an increasing function of pressure at the first stage and an decreasing function of pressure at the final stage. The mechanism of sol-gel transformation of methylcellulose aqueous solutions was also discussed, it might be assumed that both hydrogen and hydrophobic bonds were involved with the gel formation in the case of methylcellulose aqueous solution.

An In situ Study on the Orderly Crystal Growth of Pluronic F127 Block Copolymer Blended with and without Ionic Liquid during Isothermal Crystallization

Isothermal crystallization behavior of Pluronic F127 blended with and without an ionic liquid (IL) was investigated by in situ polarized optical microscopy (POM) and Fourier transform infrared spectroscopy (FTIR). For the pure F127, the POM and FTIR results showed that the spherulite size and crystallinity of F127 increased with the melting temperature increasing to 60, 80, and 135°C. This could be explained by the flexibility of the polymer chain at high melting temperatures. For the F127 blended with IL, the POM results showed that the morphology of F127 evolved from spherulite to dendritic segregation and fibrous crystal with the increasing IL content. FTIR results indicated that hydrogen bonds were formed between F127 and IL, and the intensity of the hydrogen bonds became strengthened gradually with increasing IL content. The effect of hydrogen bonds on the morphology evolution of F127/IL is discussed.

Pressure-induced ionic liquid crystal in 1-dodecyl-3-methylimidazolium tetrafluoroborate

The phase behaviors of 1-dodecyl-3-methylimidazolium tetrafluoroborate ([C12MIM][BF4]) had been investigated by means of Raman spectroscopy and polarized optical microscopy under pressure values up to 2.0 GPa at the temperature of 80.0 °C. Upon compression, change in the ratio of peak heights of symmetric and asymmetric CH2 stretching modes of Raman spectra in [C12MIM][BF4] (r(CH2)ss/(CH2)as) indicated that it might experience two successive phase transitions. The structure evolution of the sample, which was investigated through the image analysis from polarized optical microscopy, was found to share many of the known quantitative properties of the smectic A phase of [C12MIM][BF4]. These facts were suggestive of ionic liquid crystal induced by compression in [C12MIM][BF4] under the pressure between 0.25 GPa to 0.60 GPa, which was similar to ionic liquid crystal upon cooling from its melt.