Schlieren textures in free-standing nematic films: evidence of biaxiality

Conoscopic studies reveal that the nematic phase of 4,4 "-(p-terphenyl)-bis[2,3,4-tri(dodecyloxy)benzal]imine is biaxial, the biaxial angle increasing with decreasing temperature. The schlieren textures exhibited by the nematic phase have been examined. Films sandwiched between glass plates, as well as free-standing films, exhibit a nematic schlieren texture consisting entirely of \s\ = 1/2 or 2-brush disclinations, confirming an earlier suggestion that the absence of 4-brush disclinations is evidence of biaxiality.