In Situ Observation of Texture of a Dimesogenic Liquid Crystal Compound under Hydrostatic Pressure

• Published in: Molecular crystals and liquid crystals science and technology. Section A, Molecular crystals and liquid crystals Vol. 312; no. 1; pp. 223 - 238
• Main Authors: Maeda, Yoji, Yong-kuk, Yun, Jin, Jung-Il
• Format: Journal Article
• Language: English
• Published: Philadelphia, PA Taylor & Francis Group 01.04.1998; Gordon and Breach
• Subjects: Condensed matter: structure, mechanical and thermal properties; dimesogenic LC compound; Exact sciences and technology; Experimental determinations of smectic, nematic, cholesteric, and other structures; High-pressure optical hot stage; homeotropic orientation; Liquid crystals; optical texture; Physics; pressure-induced crystal polymorph; Structure of solids and liquids; crystallography; Polarizing microscope; Schiff bases; In situ; Fatty ester; Experimental study; Liquid crystals; Texture; High pressure; Pressure dependence; Optical microscopy; Hydrostatic pressure; Benzenic compound; Ethers; Organic compounds; Polymorphism; Steroids
• ISSN: 1058-725X
• DOI: 10.1080/10587259808042442

In situ observation of microscopic texture of an unaligned sample of a dimesogenic liquid crystal compound, N-[4-(6-cholesteryloxycarbonyl)pentyloxy-benzylidene]-4-n-butylaniline, called as KI5, was performed under hydrostatic pressures up to 250 MPa by a polarized optical microscope equipped with a high-pressure optical hot-stage. The spherulites of the pressure-induced crystal polymorph(C II ) of the KI5 compound, different from those of the normal crystal (C I ), were confirmed directly at 100 MPa and higher pressures. The C II spherulites were grown up from the dark field (homeotropic orientation) of the supercooled smectic phase under high pressures. This observation coincides with the experimental results by high-pressure X-ray diffraction and thermal analysis already reported. The temperature region of homeotropic orientation including partial homeotropic region decreases from ca. 70°C at 0.1 MPa to ca. 47°C at 100 MPa, and then the homeotropic state persists to higher temperatures of about 40 ± 5°C under higher pressures. The homeotropic region shifts to high temperature with the C II -S 1 transition line by applying pressures above 60 MPa, suggesting that homeotropic orientation of the KI5 compound occurs immediately after the C II -S 1 transition(melting) at high pressure.