Ordering in Lipid Monolayers Studied by Synchrotron X-Ray Diffraction and Fluorescence Microscopy

Abstract

Synchrotron x-ray diffraction results of phospholipid monolayers at an air/water interface are reported and compared with fluorescence microscopic observations of the fluid-gel lipid phase transition. The pressure-induced transition to an orientationally ordered phase occurs at a pressure ${\ensuremath{\pi}}_{c}$ which is by more than 15 mN/m below a pressure ${\ensuremath{\pi}}_{s}$ where a transition to a positionally ordered phase occurs. Hence there exists an intermediate phase with long-range orientational and short-range positional order.