Exploring the bulk-phase structure of ionic liquid mixtures using small-angle neutron scattering

Abstract

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Dissecting the Vaporization Enthalpies of Ionic Liquids by Exclusively Experimental Methods: Coulomb Interaction, Hydrogen Bonding, and Dispersion Forces

“…Thus, the y-intercept of the n-amine values represents the dispersion interactiond ue to the nitrogen atom, which is also present in all PILs. [22][23][24][25] Forcomparison, we also show the vaporization enthalpies for PILs (red circles) and AILs (red squares) from Figure 2. calculations or molecular dynamics simulations.W eh ave measured the vaporization enthalpies of two sets of ILs, allowing and excluding hydrogen bonding between cations and anions.T he data clearly suggest that protic and aprotic ILs evaporate as ion pairs.M oreover,t he differences in vaporization enthalpies directly allow the extraction of the hydrogen bond energy,which is around 38 kJ mol À1 in the ILs under study.C omparison with vaporization enthalpies of tertiary amines with the linear alkyl chains and n-alkanes additionally allowed the separation of the dispersion energy (10 kJ mol À1 )and finally the Coulomb energy (76 kJ mol À1 )in the PILs I-IV.W ith this approach, we dissected and quantified the interactions of different strengths and directional type in PILs by using purely experimental data.…”

“…[9][10][11][12][13][14][15][16][17][18] Theuse of reduced charges to better describe the transport properties of ILs automatically leads to decreased Coulomb interaction in favor of van der Waals forces without any physical evidence. [22][23][24] In essence,v aporization enthalpies provide information about the total energy,w hich is needed to overcome the overall interaction energy between the liquid constituents. [22][23][24] In essence,v aporization enthalpies provide information about the total energy,w hich is needed to overcome the overall interaction energy between the liquid constituents.…”

“…[19][20][21] Despite improvements in experiment and theory,for example,byconsidering polarizabilities in MD simulations,p redicting and dissecting vaporization enthalpies remains achallenge. [22][23][24] In essence,v aporization enthalpies provide information about the total energy,w hich is needed to overcome the overall interaction energy between the liquid constituents. Form olecular liquids the situation is easy because the gas phase species are represented by isolated molecules.C onsequently,a ccumulation of dispersion interaction for nalkanes with increasing chain length can be easily derived from the experimental vaporization enthalpies.…”

Innenrücktitelbild: Zerlegung der Verdampfungsenthalpien ionischer Flüssigkeiten durch rein experimentelle Methoden: Coulomb‐Wechselwirkung, Wasserstoffbrücken und Dispersionskräfte (Angew. Chem. 25/2019)

“…B. durch Berücksichtigung von Polarisierbarkeiten in MD-Simulationen, bleibt die Vorhersage und Zerlegung von Verdampfungsenthalpien ein schwieriges Unterfangen. [22][23][24] Grundsätzlich liefern Verdampfungsenthalpien Informationen darüber,welche Gesamtenergie notwendig ist, um die Wechselwirkungen zwischen den Komponenten in der flüssigen Phase zu überwinden. Fürm olekulare Flüssigkeiten ist die Situation einfach, da sich die Gasphase aus isolierten Molekülen zusammensetzt.…”

“…Daher repräsentiert bei den Werten der tertiären Amine der Schnittpunktmit der y-Achse die Dispersionswechselwirkung aufgrund des Stickstoffatoms, welches auch in allen untersuchten PILs vorhanden ist. [22][23][24][25] Zum Vergleich sind ebenfalls die Verdampfungsenthalpien der PILs (rote Kreise) und AILs (rote Quadrate) aus Abbildung 2a ufgeführt. In dieser Arbeit zerlegten wir die Gesamtwechselwirkungsenergien in protischen und aprotischen ionischen Flüssigkeiten allein auf Grundlage von experimentell bestimmten Verdampfungsenthalpien und ohne unterstützende Ab-initio-Berechnungen oder molekulardynamische Simulationen.…”