Anomalously low twist and bend elastic constants in an oxadiazole-based bent-core nematic liquid crystal and its mixtures; contributions of spontaneous chirality and polarity

Shajeth Srigengan, Mamatha Nagaraj, Alberta Ferrarini, Richard Mandle, Stephen Cowling, Mikhail Osipov, Grzegorz Pająk, John Goodby, Helen Gleeson

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Abstract

The splay, twist, and bend elastic constants of an oxadiazole based bent-core liquid crystal have been measured as functions of temperature throughout the nematic phase. The splay elastic constant (K11) behaves similarly to other bent-core systems, though it exhibits rather high values, varying between 8–14 pN. Further, anomalously low, temperature-independent values of both the twist and bend constants (K22 and K33) are found. The combination of such low values of both constants (∼0.15 pN and ∼1.2 pN) and temperature independence has not been observed in any type of nematic material previously. This unusual behaviour has been further investigated using two independent theoretical approaches; a molecular theory based on atomistic simulations of the real molecular structure and an analytical molecular-field theory. Computational calculations show good agreement with the experimental results for both the twist and bend constants. The statistical theory introduces a term related to chiral fluctuations that affects the twist constant, while the inclusion of polarity is known to explain low values of the bend constant. The additional terms enable one to understand the origin of the low values of both elastic constants and to describe their weak temperature dependence. It also offers an explanation for the spontaneous chiral segregation observed in some nematic bent-core systems. Mixtures of this unusual oxadiazole material are made with another similar material (C5-Ph-ODBP-Ph-OC12) that has been extensively studied that exhibits somewhat higher twist and bend elastic constants to explore the behaviour as a function of concentration.
Original languageEnglish
Pages (from-to)980-988
JournalJournal of Materials Chemistry C
Volume6
Issue number5
DOIs
Publication statusPublished - 30 Nov 2017
Externally publishedYes

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Oxadiazoles
Nematic liquid crystals
Chirality
Elastic constants
Liquid Crystals
Temperature
Liquid crystals
Molecular structure

Keywords

  • Liquid Crystals
  • Dielectric Anisotropy
  • Elastic Constants

Cite this

Srigengan, Shajeth ; Nagaraj, Mamatha ; Ferrarini, Alberta ; Mandle, Richard ; Cowling, Stephen ; Osipov, Mikhail ; Pająk, Grzegorz ; Goodby, John ; Gleeson, Helen. / Anomalously low twist and bend elastic constants in an oxadiazole-based bent-core nematic liquid crystal and its mixtures; contributions of spontaneous chirality and polarity. In: Journal of Materials Chemistry C. 2017 ; Vol. 6, No. 5. pp. 980-988.
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Anomalously low twist and bend elastic constants in an oxadiazole-based bent-core nematic liquid crystal and its mixtures; contributions of spontaneous chirality and polarity. / Srigengan, Shajeth; Nagaraj, Mamatha; Ferrarini, Alberta; Mandle, Richard; Cowling, Stephen; Osipov, Mikhail; Pająk, Grzegorz; Goodby, John; Gleeson, Helen.

In: Journal of Materials Chemistry C, Vol. 6, No. 5, 30.11.2017, p. 980-988.

Research output: Contribution to journalArticleAcademicpeer-review

TY - JOUR

T1 - Anomalously low twist and bend elastic constants in an oxadiazole-based bent-core nematic liquid crystal and its mixtures; contributions of spontaneous chirality and polarity

AU - Srigengan, Shajeth

AU - Nagaraj, Mamatha

AU - Ferrarini, Alberta

AU - Mandle, Richard

AU - Cowling, Stephen

AU - Osipov, Mikhail

AU - Pająk, Grzegorz

AU - Goodby, John

AU - Gleeson, Helen

PY - 2017/11/30

Y1 - 2017/11/30

N2 - The splay, twist, and bend elastic constants of an oxadiazole based bent-core liquid crystal have been measured as functions of temperature throughout the nematic phase. The splay elastic constant (K11) behaves similarly to other bent-core systems, though it exhibits rather high values, varying between 8–14 pN. Further, anomalously low, temperature-independent values of both the twist and bend constants (K22 and K33) are found. The combination of such low values of both constants (∼0.15 pN and ∼1.2 pN) and temperature independence has not been observed in any type of nematic material previously. This unusual behaviour has been further investigated using two independent theoretical approaches; a molecular theory based on atomistic simulations of the real molecular structure and an analytical molecular-field theory. Computational calculations show good agreement with the experimental results for both the twist and bend constants. The statistical theory introduces a term related to chiral fluctuations that affects the twist constant, while the inclusion of polarity is known to explain low values of the bend constant. The additional terms enable one to understand the origin of the low values of both elastic constants and to describe their weak temperature dependence. It also offers an explanation for the spontaneous chiral segregation observed in some nematic bent-core systems. Mixtures of this unusual oxadiazole material are made with another similar material (C5-Ph-ODBP-Ph-OC12) that has been extensively studied that exhibits somewhat higher twist and bend elastic constants to explore the behaviour as a function of concentration.

AB - The splay, twist, and bend elastic constants of an oxadiazole based bent-core liquid crystal have been measured as functions of temperature throughout the nematic phase. The splay elastic constant (K11) behaves similarly to other bent-core systems, though it exhibits rather high values, varying between 8–14 pN. Further, anomalously low, temperature-independent values of both the twist and bend constants (K22 and K33) are found. The combination of such low values of both constants (∼0.15 pN and ∼1.2 pN) and temperature independence has not been observed in any type of nematic material previously. This unusual behaviour has been further investigated using two independent theoretical approaches; a molecular theory based on atomistic simulations of the real molecular structure and an analytical molecular-field theory. Computational calculations show good agreement with the experimental results for both the twist and bend constants. The statistical theory introduces a term related to chiral fluctuations that affects the twist constant, while the inclusion of polarity is known to explain low values of the bend constant. The additional terms enable one to understand the origin of the low values of both elastic constants and to describe their weak temperature dependence. It also offers an explanation for the spontaneous chiral segregation observed in some nematic bent-core systems. Mixtures of this unusual oxadiazole material are made with another similar material (C5-Ph-ODBP-Ph-OC12) that has been extensively studied that exhibits somewhat higher twist and bend elastic constants to explore the behaviour as a function of concentration.

KW - Liquid Crystals

KW - Dielectric Anisotropy

KW - Elastic Constants

U2 - 10.1039/C7TC04664B

DO - 10.1039/C7TC04664B

M3 - Article

VL - 6

SP - 980

EP - 988

JO - Journal of Materials Chemistry C

JF - Journal of Materials Chemistry C

SN - 2050-7526

IS - 5

ER -