SURFACE SHEAR VISCOSITY AND PHASE-TRANSITIONS OF MONOLAYERS AT THE AIR-WATER-INTERFACE

The canal method has been employed to measure the in-plane steady shea r viscosity of monolayers of bolaform lipids extracted from the membra ne of the thermophilic microorganism Sulfolobus solfataricus. Monolaye rs were formed with the polar lipid extract (PLE), which is a mixture of several bolaform lipids, each one endowed with two nonequivalent po lar headgroups. Viscosities were obtained from the measured flows by u sing the equation introduced by Joly; this equation contains a semiemp irical parameter A, which takes into account the monolayer-subphase me chanical coupling. Measuring the flows for two different substances (P LE and oleic acid) and channel widths, the monolayer viscosities and t he parameter A were determined at the same time. The analysis of the v iscosity data according to the free area model shows evidences of the molecular conformational changes matching monolayer phase transitions.