Hysteresis at the Lα-Pαβ Phase Transition in Hen Egg Lecithin

Infrared spectroscopy in the OH and CH stretching region of very thin samples of hydrated egg yolk lecithin reveals an hysteresis at the transition between the two liquid crystalline phases L α (higher temperature phase) and P αβ . Both of these phases havea lamellar structure with alternating hydrophilic and hydrophobic layers, but they differ as to the state of the interiors of the layers. The hysteresis can be explained in terms of a coupling between the structures and the dynamics of adjacent layers.