Browsing by Author "Yogendra Lal Verma"

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Behaviour of ionic liquid adsorbed on the surface of nano silica particles and in confined system of silica matrices
(Elsevier B.V., 2020) Yogendra Lal Verma; Manish Pratap Singh; Santosh Kumar; Ravindra Dhar; Rajendra Kumar Singh
This paper presents studies on behaviour of a solid ionic liquid (IL); 1-butyl-2,3-dimethylimidazolium hexafluorophosphate [BMMIM][PF6] based ionogels obtained by two different techniques, first by physical confinement of IL into nano porous silica matrix and second by adsorption of IL on the outer surface of nano silica particles. The properties of samples have been investigated using various experimental techniques like N2-sorption measurements, TEM, DSC, TGA, and FTIR. It has been observed that the properties of IL have been affected more in confined geometry of silica pores as compared to the adsorption on the surface of nano silica particles. Loading of IL initially increases size and volume of pores while decrease the surface area by ~ 23 %. However, further increase in loading of IL does not produce significant change. This might be explained on basis of π-π stacking of imidazolium ring and an additional π-π stacking association between imidazolium cations. The Fourier transform infrared (FTIR) results show that stronger interaction of IL with the silica pore wall surface in confined matrix while weaker interaction due to the interfacial interaction of nano silica particles with the ions of the IL in surface adsorbed IL. The interactions and method of confinement of IL have been found to be the key parameters that determine the properties of confined and adsorbed IL. © 2020 Elsevier B.V.
Changes in dynamical behavior of ionic liquid in silica nano-pores
(Institute for Ionics, 2014) Manish Pratap Singh; Yogendra Lal Verma; Abhishek Kumar Gupta; Rajendra Kumar Singh; Suresh Chandra
Dielectric relaxation measurement has been carried out on an ionic liquid (1-butyl-3-methyl imidazolium hexafluorophosphate, [BMIM][PF6]) confined in nano-porous silica matrix. Two dielectric relaxation peaks have been observed in the confined ionic liquid (IL) while there is only one relaxation peak for bulk IL. Confinement results in layering of some IL molecules near the pore wall while other molecules, less affected by pore wall interaction, remain in the central core. The two relaxation peaks are assigned to the different dynamical behaviors of the central core and layered IL molecules. © 2013 Springer-Verlag Berlin Heidelberg.
Conformational States of Ionic Liquid 1-Ethyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide in Bulk and Confined Silica Nanopores Probed by Crystallization Kinetics Study
(American Chemical Society, 2015) Yogendra Lal Verma; Rajendra Kumar Singh
The nonaqueous sol-gel process has been used to synthesize the ionogels by confining ionic liquid (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide; [EMIM][TFSI]) into silica gel matrices. The present study is concerned mainly with probing the conformational states of the IL ([EMIM][TFSI]) through crystallization kinetics study of the bulk and confined ionic liquid (IL) in nanopores of silica matrix. The crystallization kinetics has been studied by the isothermal method using differential scanning calorimetry (DSC). For bulk IL, DSC result shows three crystallization peaks due to different conformations of IL molecules. DSC results show that one of these crystallization peaks disappears upon confinement due to interaction of IL molecules with the silica pore wall surfaces. The crystallization kinetics of bulk and confined IL is quantified using the Avarami analysis. Confinement of IL results in a decrease of the Avarami exponent, indicating one-dimensional crystal growth. To support the results obtained from crystallization kinetics study, investigate the properties of confined IL, and to study the morphological properties of silica gel matrices, some other characterization techniques, viz. TGA, XPS, FTIR, BET, SEM, and TEM, have been used. The XPS and FTIR results show the change in the binding energy of constituents of IL molecule and vibrational bands related to IL, respectively. BET, SEM, and TEM analyses display the uniform pore structures in IL confined silica matrices. © 2015 American Chemical Society.
Dynamical properties of EMIM-SCN confined in a SiO2 matrix by means of 1H NMR relaxometry
(Royal Society of Chemistry, 2017) Danuta Kruk; Milosz Wojciechowski; Yogendra Lal Verma; Sujeet Kumar Chaurasia; Rajendra Kumar Singh
1H nuclear magnetic resonance relaxometry is applied to investigate the translational and rotational dynamics of ionogels composed of an ionic liquid (IL): 1-ethyl-3-methyl-imidazolium-thiocyanate (EMIM-SCN) confined in a nanoporous SiO2 matrix. The relaxation studies were performed in the frequency range of 4 kHz-40 MHz and the temperature range of 223-248 K for different concentrations of the IL; the ratio (no. of moles of IL/no. of moles of SiO2) yields: 1/2, 3/5 and 7/10. A thorough analysis of this large set of experimental data was performed assuming the existence of two fractions of the liquid: a core fraction (near the pore center) and a surface fraction (near the confining walls). It was shown for all concentrations that the confinement does not significantly affect the translational motion near the pore center compared to the dynamics in bulk. The diffusion coefficients in the surface fraction are considerably smaller compared to the core fraction (from one to two orders of magnitude) and the difference becomes larger with increasing temperature. The diffusion coefficients become smaller for higher concentrations-this effect is not large, but visible. Very importantly, it was shown that, despite the interactions with the surface, the diffusion in the surface fraction remains of 3D character. As far as rotational dynamics in the surface fraction is concerned, it slows down compared to the bulk (and the core fraction), but this effect is of the order of factor 2-3. © the Owner Societies 2017.
Effect of temperature on electrochemical performance of ionic liquid based polymer electrolyte with Li/LiFePO4 electrodes
(Elsevier B.V., 2017) Himani Gupta; Shalu; Liton Balo; Varun Kumar Singh; Shishir Kumar Singh; Alok Kumar Tripathi; Yogendra Lal Verma; Rajendra Kumar Singh
Poly ethylene oxide based polymer electrolytes containing salt lithium bis(trifluoromethylsulfonyl)imide and ionic liquid 1-butyl-3-methyl pyridinium bis(trifluoromethylsulfonyl)imide are synthesized. The prepared polymer electrolytes are found to be thermally stable up to 340–360 °C. Ionic conductivity is observed ~ 2.5 × 10− 5 S cm− 1 at 25 °C and 2.3 × 10− 4 S cm− 1 at 40 °C for 30% IL containing polymer electrolyte. Also, ionic transference number > 0.99 and cationic transference number ~ 0.41 with electrochemical window ~ 5.2 V at 25 °C is observed for the electrolyte containing 30% IL. The highest Li+ ion conducting polymer electrolyte is further optimised for battery application. The specific discharge capacity of the prepared cell (Li/polymer electrolyte/LiFePO4) is found to be 106 mAh g− 1 at 25 °C and 160 mAh g− 1 at 40 °C up to 25 cycles with 0.1 C current rate. The increment in discharge capacity at higher temperature may be due to the better electrode-electrolyte contact. Decrement in cell resistance is also observed at higher temperature. © 2017
Effect of ultrasonic irradiation on preparation and properties of ionogels
(2012) Yogendra Lal Verma; Manish Pratap Singh; Rajendra Kumar Singh
Silica-gel matrices containing ionic liquid (IL) 1-butyl-3- methylimidazolium hexafluorophosphate viz. ionogels have been synthesized using one-pot nonhydrolytic sol-gel method and taking tetraethyl orthosilicate (TEOS) as starting precursor. Effect of ultrasonic irradiation on pore parameters of ionogels and vibrational properties of the IL upon confinement in the porous matrix has been investigated. The synthesized gels have been characterized by BET, DSC, TGA, and FTIR. BET analysis shows some changes in the pore parameters due to ultrasonic irradiation. DSC results indicate shift in glass transition temperature upon confinement of the IL. The FTIR spectra show changes in vibrational bands on confinement, particularly, the bands related to the imidazolium ring; aliphatic chain and anion PF 6 - of the IL are found to shift upon confinement in porous silica matrix obtained due to ultrasonic irradiation. Ultrasonic irradiation has been found to affect the gelation dynamics and kinetics and pore parameters. © 2012 Yogendra Lal Verma et al.
Electrochemical characterization of ionic liquid based gel polymer electrolyte for lithium battery application
(Institute for Ionics, 2018) Shishir Kumar Singh; Himani Gupta; Liton Balo; Shalu; Varun Kumar Singh; Alok Kumar Tripathi; Yogendra Lal Verma; Rajendra Kumar Singh
High molecular weight polymer poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP), ionic liquid 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIMFSI), and salt lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)-based free-standing and conducting ionic liquid-based gel polymer electrolytes (ILGPE) have been prepared by solution cast method. Thermal, electrical, and electrochemical properties of 80 wt% IL containing gel polymer electrolyte (GPE) are investigated by thermogravimetric (TGA), impedance spectroscopy, linear sweep voltammetry (LSV), and cyclic voltammetry (CV). The 80 wt% IL containing GPE shows good thermal stability (~ 200 °C), ionic conductivity (6.42 × 10−4 S cm−1), lithium ion conductivity (1.40 × 10−4 S cm−1 at 30 °C), and wide electrochemical stability window (~ 4.10 V versus Li/Li+ at 30 °C). Furthermore, the surface of LiFePO4 cathode material was modified by graphene oxide, with smooth and uniform coating layer, as confirmed by scanning electron microscopy (SEM), and with element content, as confirmed by energy dispersive X-ray (EDX) spectrum. The graphene oxide-coated LiFePO4 cathode shows improved electrochemical performance with a good charge-discharge capacity and cyclic stability up to 50 cycles at 1C rate, as compared with the without coated LiFePO4. At 30 °C, the discharge capacity reaches a maximum value of 104.50 and 95.0 mAh g−1 for graphene oxide-coated LiFePO4 and without coated LiFePO4 at 1C rate respectively. These results indicated improved electrochemical performance of pristine LiFePO4 cathode after coating with graphene oxide. © 2018, Springer-Verlag GmbH Germany, part of Springer Nature.
Electrochemical investigations of Na0.7CoO2 cathode with peo-natfsi-bmimtfsi electrolyte as promising material for na-rechargeable battery
(Springer Science and Business Media, LLC, 2018) Varun Kumar Singh; Shishir Kumar Singh; Himani Gupta; Shalu; Liton Balo; Alok Kumar Tripathi; Yogendra Lal Verma; Rajendra Kumar Singh
We report herein the development of a sodium polymer battery consisting of solid polymer electrolyte (SPE) system (polymer + ionic liquid and salt) as an electrolyte and sodium cobalt oxide as cathode material. Solid polymeric membranes (SPMs) were synthesized using polymer polyethyleneoxide (PEO), ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIMTFSI) (10–40 wt.%), and sodium bis(trifluoromethylsulfonyl)imide (NaTFSI) salt. Na0.7CoO2 cathode material was prepared using solid-state reaction route. These solid polymeric membranes were optimized using various experimental techniques such as thermogravimetric analysis, differential scanning calorimetry, and electrochemical impedance spectroscopy (EIS). It was found that the membrane containing 40 wt.% of IL has high room temperature (~ 30 °C), ionic conductivity (~ 4.1 × 10−4 S cm−1), Na+ transference number (~ 0.39), and good thermal stability. The optimized polymeric membrane shows high electrochemical potential window (~ 3.6 V) vs. Na/Na+, a specific discharge capacity of ~ 138 mAhg−1 (at 0.1 C rate) and maximum coulombic efficiency (~ 99%) for the prepared cell Na | SPE | Na0.7CoO2. Thus, the membrane containing 40 wt.% IL polymer electrolyte and Na0.7CoO2 as cathode is promising material for the formation of sodium rechargeable battery. ©Springer-Verlag GmbH Germany, part of Springer Nature 2018
Electrochemical study of Ionic Liquid based polymer electrolyte with graphene oxide coated LiFePO4 cathode for Li battery
(Elsevier B.V., 2018) Himani Gupta; Shalu Kataria; Liton Balo; Varun Kumar Singh; Shishir Kumar Singh; Alok Kumar Tripathi; Yogendra Lal Verma; Rajendra Kumar Singh
Ionic Liquid (IL) based polymer electrolytes using polymer poly ethylene oxide (PEO), salt lithium bis(fluoromethylsulfonyl)imide and IL N-propyl-N-methylpyrrolidinium-bisfluorosulfonylimide (PYR13FSI) are synthesized by solution cast method. Using different experimental techniques, good thermal stability and wide electrochemical window are observed for synthesized polymer electrolytes. Maximum Li+ conductivity is found for 10% IL containing polymer electrolyte so, it is used in Li cell preparation. LiFePO4 (LFP) cathode and graphene oxide wrapped LFP cathode (GO-LFP) are also prepared to observe the effect of graphene oxide coating in electrochemical performance of the Li cell. From charge –discharge process, high specific discharge capacity (~163 mAh g−1 at 0.1 C) is found for GO-LFP as compared to LFP cathode. GO-LFP cathode shows good cyclability and Coulombic efficiency up to 100 cycles. High charge-discharge capacity of GO-LFP is noticed even at higher current rate. © 2018 Elsevier B.V.
Improved electrochemical performance of EMIMFSI ionic liquid based gel polymer electrolyte with temperature for rechargeable lithium battery
(Elsevier Ltd, 2018) Shishir Kumar Singh; Shalu; Liton Balo; Himani Gupta; Varun Kumar Singh; Alok Kumar Tripathi; Yogendra Lal Verma; Rajendra Kumar Singh
Free-standing, ﬂexible ionic liquid based gel polymer electrolyte (ILGPE) membranes containing polymer PVdF-HFP, imidazolium-based ionic liquid EMIMFSI with lithium salt LiTFSI are synthesized and characterized by various techniques. Thermal, electrochemical and electrical properties of prepared ILGPE membranes are investigated by thermogravimetric analysis, linear sweep voltammetry, cyclic voltammetry and impedance spectroscopy techniques. Prepared membranes are found to be thermally stable upto 200 °C. The ionic conductivity is found to be ∼3.8 × 10−4 S cm−1 at 25 °C and ∼6.0 × 10−4 S cm−1 at 50 °C for 40 wt% IL containing GPE. Lithium transference number and lithium ion conductivity of 40 wt% IL containing GPE shows the maximum value ∼0.4 and ∼1.5 × 10−4 S cm−1 respectively with electrochemical window ∼4.7 V versus Li/Li+ at 25 °C. The 40 wt% IL containing GPE is used for battery application because of its better compatibility with lithium electrode compared to other prepared ILGPEs. The discharge capacity attains a maximum value ∼141.2 mAh g−1 and ∼160.3 mAh g−1 at 25 °C and 50 °C respectively at 0.1C. About ∼99% Coulombic efficiency is obtained upto 100th cycles at 50 °C. These results indicate that the Li/40 wt% IL containing GPE/LiFePO4 cell shows high Coulombic efficiency, good charge-discharge capacity and cyclic stability upto 100th cycles. © 2018 Elsevier Ltd
Ionic liquid assisted synthesis of nano-porous TiO 2 and studies on confined ionic liquid
(2012) Yogendra Lal Verma; Manish Pratap Singh; Rajendra Kumar Singh
Nanoporous anatase form of TiO 2 powder was synthesized by non-hydrolytic solgel method with and without ionic liquid (1-ethyl-3- methylimidazolium ethyl sulphate) [EMIM] [EtSO 4]. The prepared nanoporous TiO 2 powders were characterized by Thermogravimetric Analysis, Differential Scanning Calorimetry, Fourier Transform Infrared Spectroscopy, BrunauerEmmetTeller N 2 gas adsorptiondesorption isotherms, X-ray diffraction and transmission electron microscopy. Confinement of ionic liquid (IL) in porous TiO 2 resulted in change in the glass transition temperature (T g), shift in the CH vibrations wave number of alkyl chain and ring of the ionic liquid and increase in surface area of the TiO 2 particles prepared with IL. TiO 2 particles obtained without ionic liquid were amorphous in nature whereas TiO 2 particles obtained after the incorporation of ionic liquid were of poly-crystalline (anatase) form. © 2012 Elsevier B.V.
Ionic liquid based polymer gel electrolyte membranes for lithium ion rechargeable batteries
(Electrochemical Society Inc., 2016) Shalu; Liton Balo; Himani Gupta; Varun Kumar Singh; Shishir Kumar Singh; Alok Kumar Tripathi; Yogendra Lal Verma; Rajendra Kumar Singh
Li-ion conducting polymeric membranes containing 1-butyl-3-methylimidazolium tetrafluroborate (BMIMBF4), polymer poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP), and Lithium bis(trifluoromethanesulfonyl)imide) (LiTFSI) salt have been synthesized and characterized by various techniques. The synthesized polymeric membrane have good free-standing characteristics, good thermal stability (300-400 °C) and also have a wide electrochemical window (ECW) ∼ 4.0 to 4.50V. The room temperature ionic conductivity of the membrane (PVdF-HFP+20 wt.% LiTFSI) + 60% BMIMBF4 was found to be 1.7mS.cm-1. © The Electrochemical Society.
Ionic liquid template assisted synthesis of porous nano-silica nails
(Royal Society of Chemistry, 2014) Yogendra Lal Verma; Rajendra Kumar Singh; Il-Kwon Oh; Suresh Chandra
Our planned strategy to obtain porous materials was to synthesize porous silica at a fast gelation rate which can be attained by using non-hydrolytic sol-gel route with high ionic liquid (IL)-loading. Then the silica might get drawn into a tubular spring-like structure that would cage the ionic liquid within its fold and some ionic liquid might get into the pores of the silica spring. To test this strategy, we used a mixture of tetra methyl ortho-silane and ionic liquid in such a ratio that the resulting product, SiO2IL, has a content of IL as high as 85-92 wt%. Interestingly, the experimental results described in this paper have proved the validity of our strategy to obtain "porous" nano-silica particles (sometimes, "porous nail" structures also resulted). This journal is © the Partner Organisations 2014.
Preparation and characterisation of ionic liquid confined hybrid porous silica derived from ultrasonic assisted non-hydrolytic sol-gel process
(Elsevier, 2014) Yogendra Lal Verma; Abhishek Kumar Gupta; Rajendra Kumar Singh; Suresh Chandra
A series of porous silica matrices have been synthesized using ionic liquid (IL) 1-ethyl-3-methylimidazolium thiocyanate ([EMIM][SCN]) by nonhydrolytic sol-gel method with and without ultrasonic irradiation during gelation. The properties of IL confined silica gel matrices so prepared have been studied using N2-sorption measurement (BET characterisation for determining pore parameters), pulse echo technique (for sound velocity and hence elastic modulus determination), DSC, TGA, FTIR, TEM, SEM and fluorescence techniques. From the N2-sorption measurement, it has been found that BET surface area increased (due to creation of pits on the surface caused by ultrasonic irradiation) while pore volume, average pore size and porosity for ultrasonicated samples decreased. Elastic modulus of the samples containing IL in silica matrices have been found to change with IL content. Glass transition temperature and thermal stability of the IL have been found to increase upon confinement in silica gel matrices. FTIR spectra (experimental as well as computed) show changes in vibrational bands of IL on confinement in pores of silica matrices. Particularly, for ultrasonic assisted samples, the bands related to the imidazolium ring, aliphatic chain and anion SCN of the IL are found to shift upon confinement. Optimised geometry of the IL in porous matrix shows interaction of these groups with the oxygen present on silica pore wall. Fluorescence spectra of samples containing IL shows a shift compared to the bulk IL. © 2014 Elsevier B.V. All rights reserved.
Quasi solid-state electrolytes based on ionic liquid (IL) and ordered mesoporous matrix MCM-41 for supercapacitor application
(Springer New York LLC, 2017) Alok Kumar Tripathi; Yogendra Lal Verma; Shalu; Varun Kumar Singh; Liton Balo; Himani Gupta; Shishir Kumar Singh; Rajendra Kumar Singh
Quasi solid-state electrolytes (QS-SEs) based on an ionic liquid ([EMIM][FSI]) immobilized in ordered mesoporous silica MCM-41 using physical imbibition process have been developed. Supercapacitor assembly obtained using activated carbon electrodes and QS-SEs can be operated up to 2 V and exhibit good specific capacitance of 30 F g−1. The specific energy and power densities of the supercapacitor are found ~17 Wh kg−1 and 1000 W kg−1, respectively, at 1 mA cm−2 current density and exhibit good cycle performance at room temperature. © 2017, Springer-Verlag GmbH Germany.
Role of reduced precursor and solvolytic reagent molar ratio on preparation and properties of ionogel
(Academic Press Inc., 2016) Abhishek Kumar Gupta; Yogendra Lal Verma; Manish Pratap Singh; Rajendra Kumar Singh
In the present study, ionogels have been synthesized by immobilizing IL (1-ethyl-3-methylimidazolium tetrafluoroborate) in silica gel matrices using non-aqueous route. In this process, tetraethyl orho-silane (TEOS) as a precursor to silicon dioxide and formic acid as a solvolytic gelating reagent in reduced molar ratio 1:4 were used. We find that reduced molar concentration of formic acid results the formation of ionogels having less number of closed pores (totally isolated from their neighbours), larger density and stable monolithic form. TEM and SEM measurements are used to visualize the morphology of sample and closed pores present in the sample. N2-sorption measurement is used to measure the pore parameters of the silica matrices which shows the mesoporous structure. DSC and TGA results show the change in phase transition temperature and thermal stability of IL upon confinement in silica matrices. Moreover, ionic conductivity of bulk and confined IL is measured using impedance spectroscopy and it has been found that it increases with increasing the temperature as well as concentration of IL in ionogels. Apart from these characterization techniques, ionogels have been characterized using FTIR and fluorescence spectroscopy which exhibit the change in vibrational frequencies and fluorescence behaviour of confined IL. © 2016 Elsevier Inc.
Studies on an ionic liquid confined in silica nanopores: Change in T g and evidence of organic-inorganic linkage at the pore wall surface
(2014) Abhishek Kumar Gupta; Yogendra Lal Verma; Rajendra Kumar Singh; Suresh Chandra
Ionic liquid (IL) 1-ethyl-3-methylimidazolium ethyl sulfate [EMIM][EtSO4] has been immobilized in silica matrix by using nonhydrolytic one-pot sol-gel method, with tetraethyl orthosilicate (TEOS) used as precursor and formic acid as a reagent. The glass transition temperature (Tg) of the confined IL was ∼20 C higher than the bulk IL. The thermal stability of IL also increased upon confinement. These changes are explained on the basis of interactions between the inorganic SiO2 pore wall surface and the organic cation [EMIM]+ and anion [EtSO 4]- of the ionic liquid. Quantum mechanical calculation based on DFT has been used to show that the oxygen of SiO2 interacts with the C-H of the imidazolium ring of [EMIM]+ cation and the surface Si atoms interact with S-O of the [EtSO4]- anion. The latter has led to Si-O-S linkages, which have been experimentally confirmed by FTIR studies. The silanol OH group is also likely to interact but less dominantly as compared to the earlier discussed interaction. These interactions have also led to changes in the fluorescence spectra of the confined IL. © 2013 American Chemical Society.
Thermal, electrical and structural studies on ionic liquid confined in ordered mesoporous MCM-41
(Royal Society of Chemistry, 2015) Alok Kumar Tripathi; Yogendra Lal Verma; Rajendra Kumar Singh
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. © The Royal Society of Chemistry.
Viscoelastic, surface, and volumetric properties of ionic liquids [BMIM][OcSO4], [BMIM][PF6], and [EMIM][MeSO3]
(American Chemical Society, 2014) Manish Pratap Singh; Satish Kumar Mandal; Yogendra Lal Verma; Abhishek Kumar Gupta; Rajendra Kumar Singh; Suresh Chandra
Thermophysical properties viz. surface tension, viscosity, density, and ultrasonic velocity of three ionic liquids 1-butyl-3-methyl imadazolium octyl sulfate [BMIM][OcSO4], 1-butyl-3-methyl imadazolium hexafluorophosphate [BMIM][PF6], and 1-ethyl-3-methyl imadazolium methanesulfonate [EMIM][MeSO3] have been measured in a wide temperature range. Experimental data so obtained have been used to calculate isentropic compressibility, isothermal expansion coefficient, surface entropy, surface enthalpy, and critical temperature (temperature where the distinction between liquid and gas phase vanishes and the surface tension tends to zero). Structure-property correlation for different ILs is also discussed. © 2014 American Chemical Society.