Orientation of Discotic Mesophases

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Abstract
The orientation of some fluid (DF) and optically uniaxial columnar (D) discophases by surfaces is examined by optical microscopy. The test materials are 2,3,6,7,10,11 hexa-substituted triphenylenes, including two new compounds exhibiting mesophases at room temperature, and a binary mixture with a DF, phase stable between 57 and 100°C. The alignment with the directors perpendicular to the walls can be obtained on glass surfaces coated with flat molecules possessing six polar side-functions. Similar homeotropic alignments for the DF phase and total normal orientations for the D phase are observed on faces of cleaved apophyllite and muscovite crystals. For the DF phase, the uniform alignment with the directors parallel to the surfaces is obtained using glass surfaces coated with silicon oxides deposited at oblique incidence. Mutual orientations of the D and DF phases are noted. Between two slides and with the parallel alignment, left or right handed twisted fluid discophases with only an infinite-fold screw symmetry axis can be obtained. Displays using optically negative mesophases can be envisaged.