Black foam films monolayers

In the method developed by Exerowa, Cohen and Nikolova [144] the insoluble (or slightly soluble) monolayers are obtained by adsorption from the gas phase. A special device (Fig. 2.28) was constructed for the purpose a ring a in the measuring cell of Scheludko and Exerowa for formation of microscopic foam films at constant capillary pressure (see Section 2.1.2.). The insoluble (or slightly soluble) substance from reversoir b is placed in this ring. Conditions for the adsorption of the surfactant on either surface of the bi-concave drop are created in the closed space of the measuring cell. The surfactant used was n-decanol which at temperatures lower than 10°C forms a condensed monolayer. Thus, it is possible to obtain common thin as well as black foam films. The results from these studies can be seen in Section 3.4.3.3. 

As mentioned above, the appearance of black spots (black films) is observed in films from soluble surfactants. It is believed that the solubility of these substances is a necessary condition for formation of black foam films. That is why it is interesting to produce black films, especially NBF, from insoluble (or poorly soluble) surfactant monolayers. Bilayer lipid films formed in aqueous medium from insoluble in organic phase surfactants have been studied largely [e.g. 390]. 

Data on emulsion film formation from insoluble surfactant monolayer are rather poor. It is known, however, that such films can be obtained when a bubble is blown at the surface of insoluble monolayers on an aqueous substrate [391,392]. Richter, Platikanov and Kretzschmar [393] have developed a technique for formation of black foam films which involves blowing a bubble at the interface of controlled monolayer (see Chapter 2). Experiments performed with monolayers from DL-Py-dipalmitoyl-lecithin on 510 3 mol dm 3 NaCl aqueous solution at 22°C gave two important results. Firstly, it was established that foam films, including black films, with a sufficiently long lifetime, formed only when the monolayer of lecithin molecules had penetrated into the bubble surface as well, i.e. there are monolayers at both film surfaces on the contrary a monolayer, however dense, formed only at one of the film surfaces could not stabilize it alone and the film ruptured at the instant of its formation. Secondly, relatively stable black films formed at rather high surface pressures of the monolayer at area less than 53A2 per molecule, i.e. the monolayer should be close-packed, which corresponds to the situation in black films stabilized with soluble surfactants. 

A very suitable method for measurement of the lateral diffusion of molecules adsorbed at the foam film surfaces is Fluorescence Recovery after Photobleaching (FRAP) ([491-496], see also Chapter 2). Measurements of the lateral diffusion in phospholipid microscopic foam films, including black foam films, are of particular interest as they provide an alternative model system for the study of molecular mobility in biological membranes in addition to phospholipid monolayers at the air/water interface, BLMs, single unilamellar vesicles, and multilamellar vesicles. 

In order to determine the infants lung maturity and the necessity of surfactant therapy it is of great importance to substantiate the functionality of the alveolar surfactant, derived via invasive techniques [13], Several techniques and models have been largely used to investigate inteifacial physicochemical properties in vitro and to assess clinical efficiency of ES in vivo the Langmuir monolayer technique in combination with Wilhelmy plate method for surface tension measurements and black foam film method for determination of the ability of ES for stable film formation [14]. The pendant drop method combined with the Axisym-metric Drop Shape Analysis (ADSA) has been also used for similar purposes [4,15-18]. 

Black spot formation discussed here was carried out with foam films from soluble surfactants. The formation of foam films, especially of black films, from insoluble monolayers is also interesting. This will be considered in the next Section. 

Accordingly, the final foam film of Tween 20 equals the diameter of a Tween 20 micelle (Dimitrova et al., 2001) The stratification observed reflects the sequential expulsion of micelles of Tween 20 trapped in the foam film and the final thickness of the film suggests the existence of a Newton black film, covered by two surfactant monolayers (Table 10.2). 

The stability of foams and emulsions depends critically on whether formation of a stable Newton black film or a hole leading to coalescence is favored. Kabalnov and Wen-nerstrom (4) addressed this question by developing a temperature-induced hole nuclea-tion model applicable to emulsions. They point on that the coalescene energy barrier is strongly affected by flic spontaneous monolayer curvature. The aufliors consider a flat emulsion film, covered by a saturated surfactant monolayer, in thermodynamic equi-... 

Adsorption of protein at mobil surfaces as compared with adsorption of proteins from solutions on sohd adsorbents reveals additional phenomena adsorption layers aquire specific rheological properties indicating formation of a new middle phase adsorption can be accompanied by an extension and or stacking of rigid monolayer with nearly ultimate packing by protein and in the case of two liquid immiscible phases by a protein distribution between these phases, evidently in a form of associates of protein with other components of the system. These phenomena remain poorely investigated. Adsorption of a protein on mobil interfaces results in the formation adsorption layer with strong abihty to stabihze foams or emulsions, respectively, and their elements- free and emulsion films, which can be as ultimately thin, black (thickness of such films is of about lOnm). Thermodynamics of black films determines the stability of... 

---