Equilibrium and metastable states in lecithin films

We have considered whether lecithin surface films below the gel-liquid crystal transition temperature, Tc, are in unique physical states. In general, below Tc, equilibrium films do not exist when surface pressures, pi, exceed about 0.1 dyn/cm. Since surface pressure-surface area isotherms of lecithi...

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Bibliographic Details
Published in:Biophysical journal 1977-06, Vol.18 (3), p.301-310
Main Authors: Horn, L.W., Gershfeld, N.L.
Format: Article
Language:English
Subjects:
Atmospheric Pressure
Biophysical Phenomena
Biophysics
Membranes, Artificial
Phosphatidylcholines
Pulmonary Surfactants
Surface Properties
Temperature
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Summary:We have considered whether lecithin surface films below the gel-liquid crystal transition temperature, Tc, are in unique physical states. In general, below Tc, equilibrium films do not exist when surface pressures, pi, exceed about 0.1 dyn/cm. Since surface pressure-surface area isotherms of lecithin films below Tc always encompass pi's much greater than 0.1 dyn/cm, the film states are metastable. We show that the film properties under these conditions depend strongly on the history of the film, particularly the method of film formation. Lecithin surface films below Tc are thus in arbitrary metastable states, so that pi-area isotherms are difficult to interpret. The physical significance of such isotherms remains to be determined. The utility of pure lecithin surface layers below Tc as models for biological systems is also challenged by our results.
ISSN:0006-3495
1542-0086
DOI:10.1016/S0006-3495(77)85615-4