Application of Complementary Experimental Techniques to Characterization of the Phase Behavior of [C16mim][PF6] and [C14mim][PF6]

J. De Roche, C.M. Gordon, M.D. Ingram, C.T. Imrie, A.R. Kennedy, A. Triolo

Research output: Contribution to journalArticle

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Abstract

A range of analytical techniques (DSC, conductivity measurement, Raman spectroscopy, small- and wide-angle X-ray diffraction (S-WAXS), quasi-elastic neutron scattering (QENS), and single-crystal X-ray diffraction) are applied to the characterization of the phase behavior of the low-melting-point liquid crystalline salts 1-hexadecyl-3-methylimidazolium hexafluorophosphate ([C16mim][PF6]) and 1-methyl-3-tetradecylimidazolium hexafluorophosphate [C14mim][PF6]. This is the first time that QENS has been applied to the structural analysis of this type of ionic liquid crystal. For the first time in this class of salts, a low-temperature phase transition is identified, which is assigned to a crystal-crystal transition. Conductivity and QENS data for [C16mim][PF6] suggest that the higher-temperature crystalline phase (CII) has greatly increased freedom in its long alkyl chain and anion than the lowertemperature crystalline phase (CI). This conclusion is supported by single-crystal X-ray diffraction results for [C14mim][PF6]. In both crystalline phases, as well as in the highertemperature mesophase, the structure maintains a monodispersed layer structure with interdigitated alkyl chains. The structure of the mesophase is confirmed as smectic A by the S-WAXS and Raman spectroscopy results. Detailed analysis suggests that in this phase the alkyl chains undergo complete conformational melting. Introduction Ionic liquid (IL) is the term now widely applied to salts that are liquid at or below 100 °C. ILs show great promise as environmentally benign reaction media for many types of chemical processes.1 The key to sustainable technology is achieving an economic benefit with environmental improvements: the use of ILs offers improved performances and greater flexibility for a variety of processes such as biphasic catalysis and organic synthesis,2 separations,3 electrochemistry,4 photochemistry, 5 and liquid crystals,6 potentially leading to economic advantages. ILs are also environmentally
Original languageEnglish
Pages (from-to)3089-3097
Number of pages8
JournalChemistry of Materials
Volume15
Issue number16
DOIs
Publication statusPublished - 13 Jan 2004

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Phase behavior
Elastic scattering
Neutron scattering
Crystalline materials
Ionic Liquids
Liquid Crystals
Salts
Ionic liquids
X ray diffraction
Liquid crystals
Raman spectroscopy
Single crystals
Crystals
Economics
Photochemical reactions
Liquids
Electrochemistry
Structural analysis
Catalysis
Anions

Keywords

  • analytical techniques (DSC
  • conductivity measurement
  • Raman spectroscopy
  • small- and wide-angle X-ray diffraction (S-WAXS)
  • quasi-elastic neutron scattering (QENS)
  • single-crystal X-ray diffraction
  • phase behavior
  • low-melting-point liquid crystalline salts

Cite this

De Roche, J. ; Gordon, C.M. ; Ingram, M.D. ; Imrie, C.T. ; Kennedy, A.R. ; Triolo, A. / Application of Complementary Experimental Techniques to Characterization of the Phase Behavior of [C16mim][PF6] and [C14mim][PF6]. In: Chemistry of Materials. 2004 ; Vol. 15, No. 16. pp. 3089-3097.
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Application of Complementary Experimental Techniques to Characterization of the Phase Behavior of [C16mim][PF6] and [C14mim][PF6]. / De Roche, J.; Gordon, C.M.; Ingram, M.D.; Imrie, C.T.; Kennedy, A.R.; Triolo, A.

In: Chemistry of Materials, Vol. 15, No. 16, 13.01.2004, p. 3089-3097.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Application of Complementary Experimental Techniques to Characterization of the Phase Behavior of [C16mim][PF6] and [C14mim][PF6]

AU - De Roche, J.

AU - Gordon, C.M.

AU - Ingram, M.D.

AU - Imrie, C.T.

AU - Kennedy, A.R.

AU - Triolo, A.

PY - 2004/1/13

Y1 - 2004/1/13

N2 - A range of analytical techniques (DSC, conductivity measurement, Raman spectroscopy, small- and wide-angle X-ray diffraction (S-WAXS), quasi-elastic neutron scattering (QENS), and single-crystal X-ray diffraction) are applied to the characterization of the phase behavior of the low-melting-point liquid crystalline salts 1-hexadecyl-3-methylimidazolium hexafluorophosphate ([C16mim][PF6]) and 1-methyl-3-tetradecylimidazolium hexafluorophosphate [C14mim][PF6]. This is the first time that QENS has been applied to the structural analysis of this type of ionic liquid crystal. For the first time in this class of salts, a low-temperature phase transition is identified, which is assigned to a crystal-crystal transition. Conductivity and QENS data for [C16mim][PF6] suggest that the higher-temperature crystalline phase (CII) has greatly increased freedom in its long alkyl chain and anion than the lowertemperature crystalline phase (CI). This conclusion is supported by single-crystal X-ray diffraction results for [C14mim][PF6]. In both crystalline phases, as well as in the highertemperature mesophase, the structure maintains a monodispersed layer structure with interdigitated alkyl chains. The structure of the mesophase is confirmed as smectic A by the S-WAXS and Raman spectroscopy results. Detailed analysis suggests that in this phase the alkyl chains undergo complete conformational melting. Introduction Ionic liquid (IL) is the term now widely applied to salts that are liquid at or below 100 °C. ILs show great promise as environmentally benign reaction media for many types of chemical processes.1 The key to sustainable technology is achieving an economic benefit with environmental improvements: the use of ILs offers improved performances and greater flexibility for a variety of processes such as biphasic catalysis and organic synthesis,2 separations,3 electrochemistry,4 photochemistry, 5 and liquid crystals,6 potentially leading to economic advantages. ILs are also environmentally

AB - A range of analytical techniques (DSC, conductivity measurement, Raman spectroscopy, small- and wide-angle X-ray diffraction (S-WAXS), quasi-elastic neutron scattering (QENS), and single-crystal X-ray diffraction) are applied to the characterization of the phase behavior of the low-melting-point liquid crystalline salts 1-hexadecyl-3-methylimidazolium hexafluorophosphate ([C16mim][PF6]) and 1-methyl-3-tetradecylimidazolium hexafluorophosphate [C14mim][PF6]. This is the first time that QENS has been applied to the structural analysis of this type of ionic liquid crystal. For the first time in this class of salts, a low-temperature phase transition is identified, which is assigned to a crystal-crystal transition. Conductivity and QENS data for [C16mim][PF6] suggest that the higher-temperature crystalline phase (CII) has greatly increased freedom in its long alkyl chain and anion than the lowertemperature crystalline phase (CI). This conclusion is supported by single-crystal X-ray diffraction results for [C14mim][PF6]. In both crystalline phases, as well as in the highertemperature mesophase, the structure maintains a monodispersed layer structure with interdigitated alkyl chains. The structure of the mesophase is confirmed as smectic A by the S-WAXS and Raman spectroscopy results. Detailed analysis suggests that in this phase the alkyl chains undergo complete conformational melting. Introduction Ionic liquid (IL) is the term now widely applied to salts that are liquid at or below 100 °C. ILs show great promise as environmentally benign reaction media for many types of chemical processes.1 The key to sustainable technology is achieving an economic benefit with environmental improvements: the use of ILs offers improved performances and greater flexibility for a variety of processes such as biphasic catalysis and organic synthesis,2 separations,3 electrochemistry,4 photochemistry, 5 and liquid crystals,6 potentially leading to economic advantages. ILs are also environmentally

KW - analytical techniques (DSC

KW - conductivity measurement

KW - Raman spectroscopy

KW - small- and wide-angle X-ray diffraction (S-WAXS)

KW - quasi-elastic neutron scattering (QENS)

KW - single-crystal X-ray diffraction

KW - phase behavior

KW - low-melting-point liquid crystalline salts

UR - http://dx.doi.org/10.1021/cm021378u

U2 - 10.1021/cm021378u

DO - 10.1021/cm021378u

M3 - Article

VL - 15

SP - 3089

EP - 3097

JO - Chemistry of Materials

JF - Chemistry of Materials

SN - 0897-4756

IS - 16

ER -