Sujeet Kumar Chaurasia

Development of ionic liquid mediated novel polymer electrolyte membranes for application in Na-ion batteries

Polymer electrolyte membranes based on polymer PEO, ionic liquid, 1-butyl-3-methylimidazolium methylsulfate, BMIM-MS, and salt, sodium methylsulfate, NaMS, {PEO + x wt% BMIM-MS for x = 0 and 20 and (PEO + 10 wt% of NaMS) + x wt% BMIM-MS for x = 0, 20 and 60} were prepared and characterized by various experimental techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA)/differential thermogravimetric analysis (DTGA), differential scanning calorimetry (DSC), ac impedance spectroscopy and cyclic voltammetry (CV). The synthesized polymer electrolyte membranes were free-standing and flexible with good mechanical stability. A Fourier transform infrared spectroscopic (FTIR) study showed the complexation of ether oxygen of the PEO backbone with the cations of the Na-salt or IL (BMIM-MS). SEM, XRD and DSC studies show that the crystallinity of the polymer electrolyte membranes decreases on increasing the concentration of IL due to the plasticization effect of the IL. Ionic conductivity of polymer electrolyte membranes was found to increase with the concentration of IL (BMIM-MS) and showed a maximum room temperature (at ∼30 °C) ionic conductivity of ∼1.05 × 10−4 S cm−1 for 60 wt% IL loading. The plasticization effect of the IL enhanced the amorphicity of the polymeric membranes. This optimized composition of polymer electrolyte shows high electrochemical potential window (∼4–5 V), cationic transference number (i.e. tNa+ ∼ 0.46) and also good cycling between ∼2.7 and ∼1.6 V through charging–discharging.

Crystallization behaviour of a polymeric membrane based on the polymer PVdF–HFP and the ionic liquid BMIMBF4

The crystallization behaviour of the polymer poly(vinylidenefluoride)–hexafluoropropylene (PVdF–HFP) in the presence and absence of the ionic liquid (IL) (1-butyl-3-methylimidazolium tetrafluoroborate; [BMIMBF4]) were studied by isothermal and non-isothermal crystallization processes using differential scanning calorimetry. The well-known Avrami equation is used to describe the isothermal crystallization process of pristine PVdF–HFP or PVdF–HFP + x wt% of IL BMIMBF4, where x = 10 and 30, respectively. It was found that the presence of the IL BMIMBF4 in the PVdF–HFP matrix suppresses the crystallization of the polymer PVdF–HFP, resulting in low crystal growth rates. Three kinetic methods (i.e., those of Jeziorny, Ozawa and Mo) were used to analyze the non-isothermal crystallization process. The Avrami equation modified by Jeziorny could only describe the initial stage of crystallization and the Ozawa method failed to describe the non-isothermal crystallization behavior, but Mos method explains the results better.

Effect of ionic liquid on the crystallization kinetics behaviour of polymer poly(ethylene oxide)

Modification in the crystallization kinetics behaviour of the polymer poly(ethylene oxide) due to the incorporation of an ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate; BMIMPF6) has been studied. The PEO + x wt% BMIMPF6 polymer films were prepared by a solution casting technique. Crystallization kinetic parameters, such as relative crystallinity (Xt), crystallization half time (t1/2), crystallization rate constant (K), crystallization rate (G) and Avrami exponents (n), have been determined by both isothermal and non-isothermal techniques using DSC. The experimental results based on both non-isothermal and isothermal methods show that the melt crystallization of PEO slows down significantly with the incorporation of BMIMPF6 in the membranes. The growth of crystallized spherulites has also been monitored by polarizing optical microscope (POM), which confirms that the growth rate of crystallized spherulites slows down on the addition of BMIMPF6 in the polymeric membranes.

Electrical conductivity studies on composite polymer electrolyte based on ionic liquid

PEO: IL(1-ethyl-3-methylimidazolium Tosylate) and (PEO: IL) + xAl2O3 polymer composite films have been obtained by (a) hot press and (b) solution cast techniques. The films prepared by hot press techniques give higher conductivity than their corresponding solution-casted samples. The PEO: IL polymer films conductivity has been found to increase with the amount of IL in PEO polymer matrix at a given temperature. The temperature dependence conductivity of PEO: IL films have been studied and discussed for the films prepared by two preparatory methods (a) hot press and (b) solution cast. The temperature dependence of conductivity exhibited an Arrhenius-type thermally activated behaviour. The ceramic filler Al2O3 concentration-dependent conductivity of PEO + IL (20 wt.%) film shows two conductivity maxima at 2 and 10 wt.%, respectively, which has been explained on the basis of double percolation threshold model.

Isothermal and non-isothermal crystallization kinetics of PVA + ionic liquid [BDMIM][BF4]-based polymeric films

The effect of ionic liquid (IL), 1-butyl-2,3-dimethylimidazolium tetrafluoroborate [BDMIM][BF4], on crystallization behavior of poly(vinyl alcohol) (PVA) has been studied by isothermal and non-isothermal differential scanning calorimetry techniques. The PVA + IL based polymer electrolyte films have been prepared using solution casting technique. To describe the isothermal and non-isothermal crystallization kinetics, several kinetic equations have been employed on PVA + IL based films. There is strong dependence of the peak crystallization temperature (Tc), relative degree of crystallity (Xt), half-time of crystallization (t1/2), crystallization rate constants (Avrami Kt and Tobin AT), and Avrami (n) and Tobin (nT) exponents on the cooling rate and IL loading.

Acoustic wave propagation in barium monochalcogenides in the B1 phase

Temperature dependence of ultrasonic attenuation due to phonon-phonon interaction and thermoelastic loss have been studied in (NaCl-type) barium monochalcogenides [BaX, X = S, Se, Te], in the temperature range 50–500 K; for longitudinal and shear modes of propagation along 〈100〉, 〈110〉, 〈111〉 directions. Second and third order elastic constants have been evaluated using electrostatic and Born repulsive potentials and taking interactions up to next nearest neighbours. Gruneisen parameters, nonlinearity constants, nonlinearity constants ratios and viscous drag due to screw and edge dislocations have also been evaluated for longitudinal and shear waves at 300 K. In the present investigation, it has been found that phonon-phonon interaction is the dominant cause for ultrasonic attenuation. The possible implications of results have been discussed.