J. Phys. II France
Volume 5, Numéro 8, August 1995
Page(s) 1209 - 1221
DOI: 10.1051/jp2:1995177
J. Phys. II France 5 (1995) 1209-1221

Surface Shear Viscosity and Phase Transitions of Monolayers at the Air-Water Interface

A. Relini, F. Ciuchi and R. Rolandi

Dipartimento di Fisica, Università di Genova, 16146 Genova, Italy

(Received 2 November 1994, revised 14 March 1995, accepted 21 April 1995)

The canal method has been employed to measure the in-plane steady shear viscosity of monolayers of bolaform lipids extracted from the membrane of the thermophilic microorganism Sulfolobus solfataricus. Monolayers were formed with the polar lipid extract (PLE), which is a mixture of several bolaform lipids, each one endowed with two nonequivalent polar headgroups. Viscosities were obtained from the measured flows by using the equation introduced by Joly; this equation contains a semiempirical parameter A, which takes into account the monolayer-subphase mechanical coupling. Measuring the flows for two different substances (PLE and oleic acid) and channel widths, the monolayer viscosities and the parameter A were determined at the same time. The analysis of the viscosity data according to the free area model shows evidences of the molecular conformational changes matching monolayer phase transitions.

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