Ionic conductivity mediated by hydrogen bonding in liquid crystalline 4-n-alkoxybenzoic acids

Andrew Watmough Brown, Alfonso Martinez-Felipe (Corresponding Author)

Research output: Contribution to journalArticle

Abstract

We describe the dielectric response of a series of liquid crystalline 4-n-alkoxybenzoic acids, nOBAs, with different alkyl chains, n = 4, 5, 7 and 8, in planarly aligned cells, as potential anhydrous electrolytes for electrochemical cells. All nOBAs display two modes of dielectric relaxations and conductivity. At moderate-high frequencies, f ∼101–104 Hz, the so-called mode 1 involves fast dipole rearrangements leading to direct current, DC, conductivities in the σdc1 ∼ 10−5 S cm−1 range, which are eventually insensitive to bias fields. At lower frequencies, f ∼10−1 to 101 Hz, the so-called mode 2 is related to slower processes with lower DC conductivities, σdc2 ∼ 10−6 S cm−1, which are further facilitated under sufficiently strong bias fields. Whilst mode 1 can be associated to the presence (and motions) of asymmetric dimers stabilised by hydrogen bonding and free acids in the nematic phase, mode 2 may involve the extension of the hydrogen-bonded network to longer ranges, probably by the formation of catemeric species, and its conductivity increases on heating in both the nematic and isotropic phases. Even though the conductivity values fall below those of benchmark electrolytes used in fuel cells (σdc ∼ 0.1 S cm−1), our results are promising, particularly for non-doped/non-hydrated electrolytes, and highlight the potential of the nOBAs and other hydrogen-bonded liquid crystals as components of electrolytes for ion conductivity.
Original languageEnglish
Pages (from-to)487-496
Number of pages10
JournalJournal of Molecular Structure
Volume1197
Early online date19 Jul 2019
DOIs
Publication statusE-pub ahead of print - 19 Jul 2019

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Ionic conductivity
Electrolytes
Hydrogen bonds
Crystalline materials
Acids
Liquids
Hydrogen
Liquid Crystals
Electrochemical cells
Dielectric relaxation
Dimers
Fuel cells
Ions
Heating

Keywords

  • Liquid crystalline electrolytes
  • Ion hopping
  • Proton conductivity
  • 4--alkoxybenzoic acids
  • Impedance spectroscopy
  • Hydrogen-bonded liquid crystals
  • BEHAVIOR
  • MEMBRANES
  • RELAXATION
  • DIELECTRIC-SPECTROSCOPY
  • MESOMORPHISM
  • MESOGENS
  • 4-ALKOXYBENZOIC ACIDS
  • 4-n-alkoxybenzoic acids
  • SPECTRA
  • TECHNOLOGY
  • INSIGHTS

Cite this

Ionic conductivity mediated by hydrogen bonding in liquid crystalline 4-n-alkoxybenzoic acids. / Brown, Andrew Watmough; Martinez-Felipe, Alfonso (Corresponding Author).

In: Journal of Molecular Structure, Vol. 1197, 05.12.2019, p. 487-496.

Research output: Contribution to journalArticle

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abstract = "We describe the dielectric response of a series of liquid crystalline 4-n-alkoxybenzoic acids, nOBAs, with different alkyl chains, n = 4, 5, 7 and 8, in planarly aligned cells, as potential anhydrous electrolytes for electrochemical cells. All nOBAs display two modes of dielectric relaxations and conductivity. At moderate-high frequencies, f ∼101–104 Hz, the so-called mode 1 involves fast dipole rearrangements leading to direct current, DC, conductivities in the σdc1 ∼ 10−5 S cm−1 range, which are eventually insensitive to bias fields. At lower frequencies, f ∼10−1 to 101 Hz, the so-called mode 2 is related to slower processes with lower DC conductivities, σdc2 ∼ 10−6 S cm−1, which are further facilitated under sufficiently strong bias fields. Whilst mode 1 can be associated to the presence (and motions) of asymmetric dimers stabilised by hydrogen bonding and free acids in the nematic phase, mode 2 may involve the extension of the hydrogen-bonded network to longer ranges, probably by the formation of catemeric species, and its conductivity increases on heating in both the nematic and isotropic phases. Even though the conductivity values fall below those of benchmark electrolytes used in fuel cells (σdc ∼ 0.1 S cm−1), our results are promising, particularly for non-doped/non-hydrated electrolytes, and highlight the potential of the nOBAs and other hydrogen-bonded liquid crystals as components of electrolytes for ion conductivity.",
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author = "Brown, {Andrew Watmough} and Alfonso Martinez-Felipe",
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AU - Brown, Andrew Watmough

AU - Martinez-Felipe, Alfonso

N1 - The authors would like to acknowledge Mathew Abdy and Daniel Zaton for their help preparing the samples, Prof. Corrie Imrie and Prof. John Storey for their continuous advice, and the School of Engineering (University of Aberdeen) for financial support.

PY - 2019/7/19

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N2 - We describe the dielectric response of a series of liquid crystalline 4-n-alkoxybenzoic acids, nOBAs, with different alkyl chains, n = 4, 5, 7 and 8, in planarly aligned cells, as potential anhydrous electrolytes for electrochemical cells. All nOBAs display two modes of dielectric relaxations and conductivity. At moderate-high frequencies, f ∼101–104 Hz, the so-called mode 1 involves fast dipole rearrangements leading to direct current, DC, conductivities in the σdc1 ∼ 10−5 S cm−1 range, which are eventually insensitive to bias fields. At lower frequencies, f ∼10−1 to 101 Hz, the so-called mode 2 is related to slower processes with lower DC conductivities, σdc2 ∼ 10−6 S cm−1, which are further facilitated under sufficiently strong bias fields. Whilst mode 1 can be associated to the presence (and motions) of asymmetric dimers stabilised by hydrogen bonding and free acids in the nematic phase, mode 2 may involve the extension of the hydrogen-bonded network to longer ranges, probably by the formation of catemeric species, and its conductivity increases on heating in both the nematic and isotropic phases. Even though the conductivity values fall below those of benchmark electrolytes used in fuel cells (σdc ∼ 0.1 S cm−1), our results are promising, particularly for non-doped/non-hydrated electrolytes, and highlight the potential of the nOBAs and other hydrogen-bonded liquid crystals as components of electrolytes for ion conductivity.

AB - We describe the dielectric response of a series of liquid crystalline 4-n-alkoxybenzoic acids, nOBAs, with different alkyl chains, n = 4, 5, 7 and 8, in planarly aligned cells, as potential anhydrous electrolytes for electrochemical cells. All nOBAs display two modes of dielectric relaxations and conductivity. At moderate-high frequencies, f ∼101–104 Hz, the so-called mode 1 involves fast dipole rearrangements leading to direct current, DC, conductivities in the σdc1 ∼ 10−5 S cm−1 range, which are eventually insensitive to bias fields. At lower frequencies, f ∼10−1 to 101 Hz, the so-called mode 2 is related to slower processes with lower DC conductivities, σdc2 ∼ 10−6 S cm−1, which are further facilitated under sufficiently strong bias fields. Whilst mode 1 can be associated to the presence (and motions) of asymmetric dimers stabilised by hydrogen bonding and free acids in the nematic phase, mode 2 may involve the extension of the hydrogen-bonded network to longer ranges, probably by the formation of catemeric species, and its conductivity increases on heating in both the nematic and isotropic phases. Even though the conductivity values fall below those of benchmark electrolytes used in fuel cells (σdc ∼ 0.1 S cm−1), our results are promising, particularly for non-doped/non-hydrated electrolytes, and highlight the potential of the nOBAs and other hydrogen-bonded liquid crystals as components of electrolytes for ion conductivity.

KW - Liquid crystalline electrolytes

KW - Ion hopping

KW - Proton conductivity

KW - 4--alkoxybenzoic acids

KW - Impedance spectroscopy

KW - Hydrogen-bonded liquid crystals

KW - BEHAVIOR

KW - MEMBRANES

KW - RELAXATION

KW - DIELECTRIC-SPECTROSCOPY

KW - MESOMORPHISM

KW - MESOGENS

KW - 4-ALKOXYBENZOIC ACIDS

KW - 4-n-alkoxybenzoic acids

KW - SPECTRA

KW - TECHNOLOGY

KW - INSIGHTS

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DO - 10.1016/j.molstruc.2019.07.072

M3 - Article

VL - 1197

SP - 487

EP - 496

JO - Journal of Molecular Structure

JF - Journal of Molecular Structure

SN - 0022-2860

ER -