Alok Kumar Tripathi

Thermal, electrical and structural studies on ionic liquid confined in ordered mesoporous MCM-41

In the present study, immobilization of different amounts of ionic liquid (IL) 1-ethyl-3-methyl imidazolium tetrafluoroborate [EMIM][BF4] into the pores of ordered mesoporous MCM-41 (Mobil Composition of Matter no. 41) has been accomplished successfully. Differential scanning calorimetry (DSC) and dielectric spectroscopy results indicate the presence of surface adsorbed IL besides, IL confined in pores. The IL adsorbed on the surface of MCM-41 has been removed after washing. DSC and dielectric spectroscopy results and scanning electron microscopy (SEM) confirm the removal of the surface adsorbed IL. Glass transition temperature (Tg) and thermal stability have been found to change as compared to the bulk IL in confinement. An FTIR study shows that the vibrational bands related to the ring of the IL cation shift upon confinement due to the interaction between oxygen of the silica pore wall surface and C–H of the cation ring. Anion [BF4]− also interacts with the pore wall as confirmed experimentally and theoretically. Fluorescence spectra of IL show the blue shift upon incorporation into the ordered mesoporous MCM-41.

Interface and core relaxation dynamics of IL molecules in nanopores of ordered mesoporous MCM-41: a dielectric spectroscopy study

The dynamics of ionic liquid (IL) 1-ethyl-3-methyl imidazolium tetrafluoroborate ([EMIM][BF4]) molecules confined in ordered porous MCM-41 (Mobil Composition of Matter no. 41) with an average pore diameter d = 3.4 nm has been investigated by dielectric measurements. The appearance of a peak in the loss tangent suggests the presence of relaxation in the IL confined ordered mesoporous matrices from which two types of confined states of IL were found; pore wall surface adsorbed IL and core of pore filled IL. The dielectric measurements in the frequency range 1–10 MHz and temperature range 40–100 °C showed that the dynamics of surface adsorbed IL gets slowed down compared to the IL molecules in the core of the pore. The slowest molecular motions of surface-adsorbed ionic liquid results from strong interaction between ionic liquid molecules and the pore wall surface due to which the activation energy is different from the activation energy of bulk IL molecules. Also, Electrode Polarization (EP) phenomenon exists in all the samples and the corresponding peak is shifted towards a higher frequency region as temperature or amount of IL increases. The variation of ac conductivity with frequency obeys Jonscher power law. The dc conductivity increases with increase the IL loading.

Role of ionic liquid [BMIMPF6] in modifying the crystallization kinetics behavior of the polymer electrolyte PEO-LiClO4

We report on the modification in crystallization kinetics behavior of PEO + 10 wt% LiClO4 polymer electrolyte by the addition of an ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6). Three techniques have been used for studying crystallization kinetics, viz., (i) isothermal crystallization technique using DSC, (ii) non-isothermal crystallization technique using DSC, and (iii) by monitoring the growth of spherulites with time in the polymer electrolyte films using a polarizing optical microscope (POM). Results from all the three techniques show that the presence of ionic liquid BMIMPF6 suppresses the crystallization rate due to its plasticization effect. Isothermal crystallization data was well described by the Avrami equation, and Avrami exponent n lies in the range of 1 to 2, which signifies 2D crystal growth geometry occurring in these polymer electrolytes under the investigated temperature range. However, the Avrami crystallization rate constant ‘K’ increases exponentially with crystallization temperature and ionic liquid content as well. However, the non-isothermal crystallization kinetics of these polymer electrolytes is discussed in terms of three different models (Jeziornys, Ozawas and Mos method), and it is found that Mos method better explains the non-isothermal crystallization data. In addition, crystalline morphology and spherulite growth were studied by POM, which shows the suppression in crystallization in the presence of ionic liquid, as confirmed by spherulite growth rate (Gs) analysis.

Continuous Watson wavelet transform

We generalize the results of [2], and using the theory of Watson convolution, the continuous Watson wavelet transform is defined. Some properties related to the Watson wavelet transform are studied.