COLL 416 |
| Dimo Platikanov, M Nedyalkov, and V Petkova. Department of Physical Chemistry, University of Sofia, BLVD James Bourchier 1, 1126 Sofia, Bulgaria |
| Bilayer foam films (Newton black films) stabilized by soluble or insoluble phospholipid adsorption layers have been studied using two experimental methods: 1)The behaviour of a small floating bubble with black foam film on its top has been studied during the spontaneous or forced variation of the bubble size. The contact angle film/bulk and the gas permeability coefficient of the bilayer film can be determined. 2) The dynamic film tension of the bilayer film has been determined from the capillary pressure and curvature of a semibubble obtained on the orifice of a fine capillary tube, both parameters being changed by controlled variation of the gas pressure. Two types of aqueous solutions of dimyristoyl phosphatidyl choline (DMPC) have been used: a) Molecular solution in 47.5% ethanol & water mixture (soluble adsorption layers); b) Vesicle suspension in water obtained through sonification (insoluble adsorption layers). Dimyristoyl phosphatidyl glycerol (DMPG) was added in some cases. The results show very strong effect of the insolubility of the phospholipid. The film tension, which is constant in dynamic conditions for bilayer films from simple soluble surfactants, varies with the time for the films from phospholipids, the variations being most expressed for the insoluble bilayers. The results have been interpreted by Frumkin’s equation of state modified for bilayers. The contact angles essentially vary with increasing or decreasing the film and bubble size, dynamic hysteresis being observed. The addition of the electrically charged DMPG to DMPC solutions increases the contact angles and their dynamic hysteresis, but very much decreases the gas permeability of the bilayer films. The dynamic properties of black films from natural lung alveolar surfactant have been studied as well. The results are discussed in connection with the data for the thickness and structure of the bilayer films obtained by X-ray reflectivity measurements. |
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ACS Award in Colloid and Surface Chemistry Symposium Honoring Clay Radke
Division of Colloid and Surface Chemistry |