title: An ultrasonic study of the thermotropic transition of dipalmitoyl phosphatidylcholine.
abstract: The acoustic absorption of sonicated and unsonicated suspensions of dipalmitoyl phosphatidylcholine has been studied as a function of temperature at frequencies between 0.6 and 4.0 MHz. The absorption at a fixed frequency passes through a maximum at a temperature which is dependent on the sample preparation and history and somewhat dependent on the frequency of observation, with sonicated vesicles exhibiting a temperature of maximum absorption 2--3 degrees C below that found for unsonicated dispersions. The temperature dependence of the absorption at fixed frequency suggests a cooperative process while the frequency dependence of the absorption at fixed temperature indicates that more than a single relaxation time is required to describe the acoustic absorption.
mesh_terms: D008081:Liposomes; D008433:Mathematics; D011663:Pulmonary Surfactants; D013816:Thermodynamics; D014465:Ultrasonics
chemical_list: D008081:Liposomes; D011663:Pulmonary Surfactants