Black Film Method

Black Film Method for Assessment of Foetal Lung Maturity... 

The results on formation and stability of black foam films, on the first place those on bilayer foam films (NBF) (see Sections 3.4.1.2 and 3.4.4) have promoted the development of methods which enable lung maturity evaluation. The research on stability of amphiphile bilayers and probability for their observation in the grey foam films laid the grounds of the method for assessment of foetal lung maturity created by Exerowa et al. [20,24]. Cordova et al. [25] named it Exerowa Black Film Method. It involves formation of films from amniotic fluid to which 47% ethanol and 7-10 2 mol dm 3 NaCl are added [20,24]. In the presence of alcohol the surface tension of the solution is 29 mN m 1 and the adsorption of proteins from the amniotic fluid at the solution/air interface is suppressed, while that of phospholipids predominates. On introducing alcohol, the CMC increases [26], so that the phospholipids are present also as monomers in the solution. The electrolyte reduces the electrostatic disjoining pressure thus providing formation of black foam lipid films (see Sections 3.4.1.2 and 3.4.4). 

Black-Ground Method. The relative scattering power is determined from the tristimulus values Y of the pigmented medium applied in various film thicknesses to black substrates. Compared with the gray paste method, the black-ground method has the advantage that it is not restricted to any particular test medium. Apparatus spectrophotometer or tristimulus colorimeter. 

Comparable to thiophene, pyrrole is a five-membered heterocycle, yet the ring nitrogen results in a molecule with distinctly different behavior and a far greater tendency to polymerize oxidatively. The first report of the synthesis of polypyrrole (PPy) 62 that alluded to its electrically conductive nature was published in 1968 [263]. This early material was obtained via electrochemical polymerization and was carried out in 0.1 N sulfuric acid to produce a black film. Since then, a number of improvements, which have resulted from in-depth solvent and electrolyte studies, have made the electrochemical synthesis of PPy the most widely employed method [264-266]. The properties of electrosynthesized PPy are quite sensitive to the electrochemical environment in which it is obtained. The use of various electrolytes yield materials with pronounced differences in conductivity, film morphology, and overall performance [267-270]. Furthermore, the water solubility of pyrrole allows aqueous electrochemistry [271], which is of prime importance for biological applications [272]. 

III.B. The Role of Thermal Fluctuations on the Transition from Common Black Films to Newton Black Films. The method described in the previous section will be now applied to thin films with fluctuating interfaces, with the interaction energy calculated as in section II.G. For low values ofthe external pressure, the enthalpy has two metastable minima at Zk and 2c, and a stable one at 2 - 0 (the former two correspond to the Newton and to the common black films, respectively, and the latter implies the rupture of the film), separated by two maxima located at Z and 22 (see Figure 7a). At metastable equilibrium the distances between the surfaces are distributed between 21 and 22 for the Newton black film and between z2 and 2 —°° for the common black film. The stability of the metastable states depends on the chance for a small area S of the interface to reach the... 

This method gained a significant improvement with the introduction of the contemporary infrared technique with a Fourier transformer (FT-IR), permitting to obtain measurable values of adsorption of the infrared light even from single black foam films. The thickness of the aqueous core is derived from the adsorption at 3400 cm 1 which is related to the OH stretching vibration of the water molecules. Umemura et al. [114] have employed the polarised Fourier transformed infrared spectra for the study of the water content of NaDoS black films. The cell used to form films of ca. 2 cm2 area is illustrated in Fig. 2.19. By fitting the calculated curved of polarised FT-IR spectra to the respective experimentally obtained... 

Bubble of size of the order of tens of micrometers floating on the surfactant surface only little deviates from the spherical shape. This fact has been used in the method of diminishing bubble [128,129] which allows to measure the contact angle of the black film, the linear tension of the contact line film/meniscus and the coefficient of the gas permeability through the film. Fig. 2.24 presents the scheme of this device. 

A freely floating bubble of very small size is used in the diminishing bubble method [ 134] (Fig. 2.24) for the estimation of K by measuring the radii of the bubble R and the black film r with respect to time t. K is calculated from [135]... 

It is interesting to apply the method of n(h) isotherms at high capillary pressures to studying the multilayer structure of black films. The first results obtained refer to biostructures (see Chapter 11) and lamellar structures in solubilising solutions (see Section 3.4.2.5). 

Additional data about the structure of black films are obtained by X-ray diffraction method. The first steps [336,338] have been performed with vertical foam films in a frame in a horizontal scanning diffractometer. Black films from decyltrimethyl ammonium decyl sulphate and NaBr solutions have been studied. The film thickness was calculated using a model of the mean electron density projection on the film normal. However, there was no indication whether the films were CBF or NBF. Platikanov et al. [339,340] used a new device for investigation of a horizontal black films from aqueous NaDoS solution (see Section 2.2.6). They found essentially different X-ray diffraction traces for the three types of black films CBF, NBF and stratified black films. This indicates their different structure. Precise X-ray reflectivity measurements with CBF and NBF films from NaDoS and NaCl aqueous solutions [341-343] provided more details about their structure. The data obtained for the thicknesses of the respective layers which detail the film structure are given below... 

Platikanov, D., Nedyalkov, M., and Nasteva, V., Line tension of Newton black films. 11. Determination by the diminishing bubble method, J. Colloid Interface Sci., 75, 620, 1980a. 

In 1979 [10] researchers at IBM in San Jose, led by Diaz, reported that polypyrrole (PP) could be obtained as a freestanding film by electrochemical oxidation of pyrrole in acetonitrile. The polymer was produced at the electrode surface and could be peeled off as a flexible, relatively dense, shiny, blue-black film. Polypyrrole had been already synthesized electrochemically from aqueous sulfuric acid solutions in 1969 by Gardini and co-workers [11], but the poor mechanical and electrical properties of the material obtained discouraged further developments of this synthetic method. 

Hard, black films can be generated by electrochemically polymerizing thieno(3,2- )thiophene (Fig. 17c) in acetonitrile [345]. The conductivity was only 10" S cm" as measured using a two-probe method. Cyclic voltammetry indicated that the oxidation process is reversible. The isomer thieno(2,3- )thiophene (Fig. 17d), in which the sulfur atoms are on the same side of the molecule, has been polymerized but demonstrates no reversible electroactivity [346]. 

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]. 

---