Thermochimica Acta, Vol.616, 61-68, 2015
Anchoring transition driven by short range ordering in calamitic-discotic composites
We report investigations at atmospheric as well as elevated pressures on a host calamitic nematic liquid crystal doped with a discotic material exhibiting a novel anchoring transition (ANT), not present in the pure host. The change over from the substrate-surface determined planar to the homeotropic orientation occurs at a specific temperature that is governed by, as seen from X-ray and Frank bend and splay constants data, the short-range ordering changing from that for a columnar nematic to that of a standard nematic. Applied pressure diminishes the tendency for the orientation change thereby enhancing the range of the planar alignment finally annulling ANT. We ascribe the observed features to the competition between the anchoring energy of the aligning surface and the tendency of the structure to be parallel to the surface creating frustration and leading to ANT. Phase diagrams involving ANT have been constructed at atmospheric as well as elevated pressures. (C) 2015 Elsevier B.V. All rights reserved.