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A SAXS study of flow alignment of thermotropic liquid crystal mixtures

DOI: 10.1080/02678290902928542 DOI Help

Authors: Valeria Castelletto (University of Reading) , A. Squires (University of Reading) , I. Hamley (University of Reading, Diamond Light Source) , J. Stasiak (University of Cambridge) , G. Moggridge (University of Cambridge)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Liquid Crystals , VOL 36

State: Published (Approved)
Published: April 2009

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.

Journal Keywords: X-Ray Diffraction ; Nematic ; Smectic ; Mixtures ; Flow Alignment

Subject Areas: Chemistry

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