Anomalous ultrasonic absorption in a nematic and a polymesomorphic liquid crystal

Ultrasonic absorption measurements were carried out in a nematic liquid crystal, p-(p prime -ethoxyphenylazo) phenylundecylenate (EPAPU) and a polymesomorphic liquid crystal p-n-decyloxybenzoyl-p-cresol (DBC) with nematic and smectic phases, at a frequency of 2 MHz. The transition temperatures of these liquid crystals observed through thermal microscopy are given. An ultrasonic flow detector, UFD67 (ECIL) facilitated absorption measurements. The ultrasonic cell was a double walled cylindrical vessel with providsion for circulating glycerol at any desired temperature. The temperature was controlled to plus or minus 0. 2 degree C by circulating glycerol through the cell from a thermostat. A quartz crystal was fixed at the bottom of the generating cell. The ultrasonic pulses generated from the transmitting crystal propagate normally from the crystal till they are reflected back from the reflector at the top. The reflector can be moved up and down, the position of which can be determined accurately by a micrometer screw attached to it.