A SAXS study of flow alignment of thermotropic liquid crystal mixtures

V. Castelletto, A. M. Squires, I. W. Hamley, J. Stasiak, G. D. Moggridge

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract



We report on the capillary flow behaviour of thermotropic liquid crystal mixtures containing 4-n-octyl-4′-cyanobiphenyl (8CB) and 4-n-pentyl-4′-cyanobiphenyl (5CB). The liquid crystal mixtures are studied in the Nematic (N) and Smectic (SA) phases at room temperature. Polarised optical microscopy (POM), rheology and simultaneous X-ray diffraction (XRD)/capillary flow experiments are performed to characterise the system.

Polarised optical microscopy reveals a dramatic change in optical texture when the 5CB content is increased from 20 to 30% in the mixtures. X-ray diffraction results show that the system goes through a SA–N phase transition, such that the mixtures are smectic for 10–20% 5CB and nematic for 30–90% 5CB. Smectic mixtures flow with the layers aligned along the flow direction (mesogens perpendicular to flow) while nematic mixtures flow with the mesogens aligned in the flow direction. Simultaneous XRD/shear flow experiments show that the SA–N transition is independent of the flow rate in the range 1–6 ml min−1.

The correlation length of the liquid crystal order decreases with increasing 5CB content. Rheology is used to prove that the correlation length behaviour is related to a reduction in the viscosity of the mixture.
Original languageEnglish
Pages (from-to)435-442
JournalLiquid Crystals
Volume36
Issue number4
DOIs
Publication statusPublished - 22 Jun 2009

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Thermotropic liquid crystals
liquid crystals
alignment
capillary flow
Capillary flow
Liquid Crystals
Rheology
rheology
X ray diffraction
Liquid crystals
Optical microscopy
diffraction
microscopy
x rays
Shear flow
shear flow
textures
flow velocity
Textures
Phase transitions

Cite this

A SAXS study of flow alignment of thermotropic liquid crystal mixtures. / Castelletto, V.; Squires, A. M.; Hamley, I. W.; Stasiak, J.; Moggridge, G. D.

In: Liquid Crystals, Vol. 36, No. 4, 22.06.2009, p. 435-442.

Research output: Contribution to journalArticle

Castelletto, V, Squires, AM, Hamley, IW, Stasiak, J & Moggridge, GD 2009, 'A SAXS study of flow alignment of thermotropic liquid crystal mixtures', Liquid Crystals, vol. 36, no. 4, pp. 435-442. https://doi.org/10.1080/02678290902928542
Castelletto, V. ; Squires, A. M. ; Hamley, I. W. ; Stasiak, J. ; Moggridge, G. D. / A SAXS study of flow alignment of thermotropic liquid crystal mixtures. In: Liquid Crystals. 2009 ; Vol. 36, No. 4. pp. 435-442.
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abstract = "We report on the capillary flow behaviour of thermotropic liquid crystal mixtures containing 4-n-octyl-4′-cyanobiphenyl (8CB) and 4-n-pentyl-4′-cyanobiphenyl (5CB). The liquid crystal mixtures are studied in the Nematic (N) and Smectic (SA) phases at room temperature. Polarised optical microscopy (POM), rheology and simultaneous X-ray diffraction (XRD)/capillary flow experiments are performed to characterise the system.Polarised optical microscopy reveals a dramatic change in optical texture when the 5CB content is increased from 20 to 30{\%} in the mixtures. X-ray diffraction results show that the system goes through a SA–N phase transition, such that the mixtures are smectic for 10–20{\%} 5CB and nematic for 30–90{\%} 5CB. Smectic mixtures flow with the layers aligned along the flow direction (mesogens perpendicular to flow) while nematic mixtures flow with the mesogens aligned in the flow direction. Simultaneous XRD/shear flow experiments show that the SA–N transition is independent of the flow rate in the range 1–6 ml min−1.The correlation length of the liquid crystal order decreases with increasing 5CB content. Rheology is used to prove that the correlation length behaviour is related to a reduction in the viscosity of the mixture.",
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