Abstract:Knudsen effusion mass spectrometry proved to be a valuable method to study the thermodynamics of ionic liquids. The saturated vapor pressure and vaporization enthalpy of [C3MMIM(+)][Tf2N(-)] were accurately determined for the first time. MALDI is also capable of providing indirect information on hydrogen bonding.
“…Therefore, it is very important to highlight those studies that were performed under near-equilibrium conditions. A combination of a Knudsen effusion cell with a small orifice with MS detection has been used by a number of research groups to study the ionic vapour of [C n C 1 Im][NTf 2 ] [ 86 – 89 , 91 ]. All evidence is in agreement with that given already in §4, demonstrating that the equilibrium ionic vapour for [C n C 1 Im][NTf 2 ] ILs is composed of neutral ion pairs.…”
Section: Measuring the Cohesive Energy Density For Ionic Liquids: Ovementioning
confidence: 99%
“…Method 2: measure the amount of ionic vapour in the gas phase produced by IL vaporization. Within Method 2, there are two approaches to determine the amount of ionic vapour in the gas phase: (a) measure the amount of ionic vapour in the gas phase (temperature-programmed MS (TPMS) [ 57 , 63 , 71 – 77 , 86 ], temperature-programmed photoelectron spectroscopy (TPPES) [ 80 ], UV absorption spectroscopy [ 118 ]), (b) measure the amount of ionic vapour that has condensed from the gas phase onto a solid surface (quartz crystal microbalance (QCM) [ 96 , 110 – 112 , 114 – 116 , 119 – 136 ], magnetic suspension balance (MSB) [ 31 ]). Scheme 3.…”
Section: Measuring the Cohesive Energy Density For Ionic Liquids: Ovementioning
confidence: 99%
“…For ILs, both Knudsen effusion [ 56 , 86 – 89 , 91 , 119 , 129 – 133 , 135 , 151 , 152 ] and Langmuir [ 31 , 57 , 63 , 64 , 71 – 77 , 80 , 96 , 106 – 128 ] vaporization methods have been used to obtain Δ vap H . For Langmuir (i.e.…”
Section: Measuring the Cohesive Energy Density For Ionic Liquids: Ovementioning
For ionic liquids (ILs), both the large number of possible cation + anion combinations and their ionic nature provide a unique challenge for understanding intermolecular interactions. Cohesive energy density, ced, is used to quantify the strength of intermolecular interactions for molecular liquids, and is determined using the enthalpy of vaporization. A critical analysis of the experimental challenges and data to obtain ced for ILs is provided. For ILs there are two methods to judge the strength of intermolecular interactions, due to the presence of multiple constituents in the vapour phase of ILs. Firstly, cedIP, where the ionic vapour constituent is neutral ion pairs, the major constituent of the IL vapour. Secondly, cedC+A, where the ionic vapour constituents are isolated ions. A cedIP dataset is presented for 64 ILs. For the first time an experimental cedC+A, a measure of the strength of the total intermolecular interaction for an IL, is presented. cedC+A is significantly larger for ILs than ced for most molecular liquids, reflecting the need to break all of the relatively strong electrostatic interactions present in ILs. However, the van der Waals interactions contribute significantly to IL volatility due to the very strong electrostatic interaction in the neutral ion pair ionic vapour. An excellent linear correlation is found between cedIP and the inverse of the molecular volume. A good linear correlation is found between IL cedIP and IL Gordon parameter (which are dependent primarily on surface tension). ced values obtained through indirect methods gave similar magnitude values to cedIP. These findings show that cedIP is very important for understanding IL intermolecular interactions, in spite of cedIP not being a measure of the total intermolecular interactions of an IL. In the outlook section, remaining challenges for understanding IL intermolecular interactions are outlined.
“…Therefore, it is very important to highlight those studies that were performed under near-equilibrium conditions. A combination of a Knudsen effusion cell with a small orifice with MS detection has been used by a number of research groups to study the ionic vapour of [C n C 1 Im][NTf 2 ] [ 86 – 89 , 91 ]. All evidence is in agreement with that given already in §4, demonstrating that the equilibrium ionic vapour for [C n C 1 Im][NTf 2 ] ILs is composed of neutral ion pairs.…”
Section: Measuring the Cohesive Energy Density For Ionic Liquids: Ovementioning
confidence: 99%
“…Method 2: measure the amount of ionic vapour in the gas phase produced by IL vaporization. Within Method 2, there are two approaches to determine the amount of ionic vapour in the gas phase: (a) measure the amount of ionic vapour in the gas phase (temperature-programmed MS (TPMS) [ 57 , 63 , 71 – 77 , 86 ], temperature-programmed photoelectron spectroscopy (TPPES) [ 80 ], UV absorption spectroscopy [ 118 ]), (b) measure the amount of ionic vapour that has condensed from the gas phase onto a solid surface (quartz crystal microbalance (QCM) [ 96 , 110 – 112 , 114 – 116 , 119 – 136 ], magnetic suspension balance (MSB) [ 31 ]). Scheme 3.…”
Section: Measuring the Cohesive Energy Density For Ionic Liquids: Ovementioning
confidence: 99%
“…For ILs, both Knudsen effusion [ 56 , 86 – 89 , 91 , 119 , 129 – 133 , 135 , 151 , 152 ] and Langmuir [ 31 , 57 , 63 , 64 , 71 – 77 , 80 , 96 , 106 – 128 ] vaporization methods have been used to obtain Δ vap H . For Langmuir (i.e.…”
Section: Measuring the Cohesive Energy Density For Ionic Liquids: Ovementioning
For ionic liquids (ILs), both the large number of possible cation + anion combinations and their ionic nature provide a unique challenge for understanding intermolecular interactions. Cohesive energy density, ced, is used to quantify the strength of intermolecular interactions for molecular liquids, and is determined using the enthalpy of vaporization. A critical analysis of the experimental challenges and data to obtain ced for ILs is provided. For ILs there are two methods to judge the strength of intermolecular interactions, due to the presence of multiple constituents in the vapour phase of ILs. Firstly, cedIP, where the ionic vapour constituent is neutral ion pairs, the major constituent of the IL vapour. Secondly, cedC+A, where the ionic vapour constituents are isolated ions. A cedIP dataset is presented for 64 ILs. For the first time an experimental cedC+A, a measure of the strength of the total intermolecular interaction for an IL, is presented. cedC+A is significantly larger for ILs than ced for most molecular liquids, reflecting the need to break all of the relatively strong electrostatic interactions present in ILs. However, the van der Waals interactions contribute significantly to IL volatility due to the very strong electrostatic interaction in the neutral ion pair ionic vapour. An excellent linear correlation is found between cedIP and the inverse of the molecular volume. A good linear correlation is found between IL cedIP and IL Gordon parameter (which are dependent primarily on surface tension). ced values obtained through indirect methods gave similar magnitude values to cedIP. These findings show that cedIP is very important for understanding IL intermolecular interactions, in spite of cedIP not being a measure of the total intermolecular interactions of an IL. In the outlook section, remaining challenges for understanding IL intermolecular interactions are outlined.
“…One of the specific properties of ionic liquids is their low volatility due to Coulomb interactions between the ions. The classical method for estimating the volatility of ionic liquids is to determine their evaporation enthalpy by various physical and chemical methods: Knudsen effusion mass spectrometry [33][34][35][36][37] or calorimetry [38]. Recently, there have been a significant number of studies where the volatility of ILs was evaluated by thermogravimetry [39][40][41].…”
A number of dicationic ionic liquids with a disiloxane linker between imidazolium cations and bis(trifluoromethylsulfonyl)imide anion were synthesized and characterized. Melting points, viscosity, and volatility in a vacuum were measured; the thermal and hydrolytic stability of ionic liquids were also studied. The dependence of the properties on the structure of substituents in the cation of the ionic liquid was demonstrated.
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