FLOW PATTERNS AND DISCLINATION-DENSITY MEASUREMENTS IN SHEARED NEMATIC LIQUID-CRYSTALS .2. TUMBLING 8CB

We examine the behaviour of nematic 4,4'-n-octylcyanobiphenyl (8CB) su bjected to steady torsional shear flow at a temperature where this nem atic is 'tumbling', i.e. the ratio alpha(3)/alpha(2) of Leslie viscosi ties is negative. If the disc rotation speed is gradually increased fr om zero (theta < 10(-6) rad s(-2)), the director eventually departs fr om the shear plane and becomes oriented radially. However, if the disc rotation speed is increased from rest at higher rates, twist wall def ects are created sequentially at the sample meniscus and propagate inw ard with velocity approximate to 0.85 mm s(-1). Eventually, disclinati ons are nucleated. Disclination density measurements reveal that over similar ranges of values of the Ericksen number Er, samples of 8CB hav e roughly ten times the disclination density of the flow-aligning nema tic, 5CB, reported in the preceding paper. Additionally, a transition from a power-law exponent of 0.5 to 1.0 for the dependence of dimensio nless disclination density on Er is observed near Er = 2000, consisten t with theoretical arguments.