Black Foam Films Research Articles

Black Foam Films from Aqueous Solutions of a Mixture of Phospholipids and a Permeation Enhancer

The influence of a permeation enhancer on the properties of phospholipid black foam films has been studied through the combination of three complementary techniques: surface tension measurements, X-ray reflectivity, and the “diminishing bubble” method. This permeation enhancer is said to optimize the delivery of active ingredients into or through the stratum corneum: the 4-decyl oxazolidin-2-one. We made films of a complex phospholipid mixture that mimic the behavior of the enhancer in a membrane cell. Mixed phospholipids/4-decyl oxazolidin-2-one/NaCl solutions were studied with various 4-decyl oxazolidin-2-one concentrations. Stable black films were obtained and their thicknesses examined. The evolution of the coefficient of gas permeability with 4-decyl oxazolidin-2-one concentration is also addressed.

Rupture of common black films: Experimental study

The dependence of the mean lifetime of microscopic horizontal common black foam films from sodium dodecyl sulphate (SDS) on the surfactant concentration C is studied at various electrolyte concentrations C el by the thin liquid film microinterferometric technique. These data are used for determination of the surfactant concentration C τ at which the common black films have a constant mean lifetime. Thus the parameter C τ is proposed as a new characteristic of the black foam film stability at different electrolyte concentrations. The C τ ( C el) dependence is obtained within the range 0.1–0.5 mol dm −3 NaCl. The results for the stability of the common black films are compared with those for the Newton black films (foam bilayers). It is shown that the two parameters τ and C τ characterising the stability of the black films are constant above 0.2 mol dm −3 NaCl. This fact allows us to hypothesise that the thinner common black films (thickness below 8.4 nm) rupture by the hole nucleation mechanism analogously to the Newton black films. The statistical analysis of the data for the lifetimes of the SDS black foam films shows that this hypothesis can be adopted for the rupture mechanism of all common black films studied.

Effect of Film Free Energy on the Gas Permeability of Foam Films

The dependence of the gas permeability of foam films on the adsorption density of the stabilizing surfactant at the film surfaces is studied. Recently, it has been found that in black foam films th...

The alveolar surface network: a new anatomy and its physiological significance.

It is generally held that the terminal lung unit (TLU) is an agglomeration of alveoli that opens into the branching air spaces of respiratory bronchioles, alveolar ducts, and alveolar sacs and that these structures are covered by a continuous thin liquid layer bearing a monomolecular film of surfactants at the open gas-liquid interface. The inherent structural and functional instability given TLUs by a broad liquid surface layer of this nature has been mitigated by the discovery that the TLU surface is in fact an agglomeration of bubbles, a foam (the alveolar surface network) that fills the TLU space and forms ultrathin foam films that 1) impart infrastructural stability to sustain aeration, 2) modulate circulation of surface liquid, both in series and in parallel, throughout the TLU and between TLUs and the liquid surface of conducting airways, 3) modulate surface liquid volume and exchange with interstitial liquid, and 4) sustain gas transfer between conducting airways and pulmonary capillaries throughout the respiratory cycle. The experimental evidence, from discovery to the present, is addressed in this report. Lungs were examined in thorax by stereomicroscopy immediately from the in vivo state at volumes ranging from functional residual capacity to maximal volume (Vmax). Lungs were then excised; bubble topography of all anterior and anterolateral surfaces was reaffirmed and also confirmed for all posterior and posterolateral surfaces. The following additional criteria verify the ubiquitous presence of normal intraalveolar bubbles. 1) Bubbles are absent in conducting airways. 2) Bubbles are stable and stationary in TLUs but can be moved individually by gentle microprobe pressure. 3) Adjoining bubbles move into the external medium through subpleural microincisions; there is no free gas, and vacated spaces are rendered airless. Adjacent bubbles may shift position in situ, while more distal bubbles remain stationary. 4) The position and movement of "large" bubbles identifies them as intraductal bubbles. 5) Transection of the lung reveals analogous bubble occurrence and history in central lung regions. 6) Bubbles become fixed in place and change shape when the lung is dried in air; the original shape and movement are restored when the lung is rewet. 7) All exteriorized bubbles are stable with lamellar (film) surface tension near zero. 8) Intact lungs prepared and processed by the new double-embedding technique reveal the intact TLU bubbles and bubble films. Lungs were also monitored directly by stereomicroscopy to establish their presence, transformations, and apparent function from birth through adulthood, as summarized in the following section. Intraalveolar bubbles and bubble films (the unit structures of the alveolar surface network) have been found in all mammalian species examined to date, including lambs, kids, and rabbit pups and adult mice, rats, rabbits, cats, and pigs. Rabbits were used for the definitive studies. 1) A unit bubble occupies each alveolus and branching airway of the TLU; unit bubbles in clusters correspond with alveolar clusters. 2) The appositions of unit bubble lamellae (films) form a network of liquid channels within the TLUs. The appositions are bubble to bubble (near alveolar entrances, at pores of Kohn, and between ductal bubbles), bubble to epithelial cell surface, and bubble to surface liquid of conducting airways. They rapidly form stable Newtonian black foam films (approximately 7 nm thick) under hydrodynamic conditions expected in vivo. 3) Lamellae of the foam films and bubbles tend to exclude bulk liquid and thus maintain near-zero surface tension. At the same time, the foam film formations--abetted by the constant but small retractive force of tissue recoil--stabilize unit bubble position within the network. 4) Unit bubble mobility in response to applied force increases as liquid accumulates within the network (e.g. (ABSTRACT TRUNCATED)

The thickness and contact angle of sodium dodecyl sulfate foam films depending on the concentration of LiCl

In the present study a detailed investigation of the thickness and contact angles of foam films prepared from sodium dodecyl sulfate as a function of LiCl concentration was carried out. Concentration of LiCl was varied in a wide range from 0.05 to 2.0 M. It was found that in the investigated system Newton black foam films are formed at LiCl concentrations higher than 1.4 M. This observation is proved by contact angle measurements and calculated values for the change of interaction free energy between common and Newton black films.

PERMEATION OF GAS THROUGH NEWTON BLACK FILMS AT DIFFERENT CHAIN LENGTH OF THESURFACTANT

The gas permeability coefficients K (cm/s) of Newton black foam films stabilized by four alkyltrimefhylammonium chloride homologues have been measured. The experimental results demonstrate well pronounced dependence: K decreases with increasing surfactant alkyl chain length. The temperature dependence of K has been studied as well. The experimental data are discussed on the basis of the nucleation theory of fluctuation formation of holes in the foam bilayers, assuming that the gas permeation occurs both through holes and through hole-free part of the film (background permeability). The mechanism of permeation through the hole-free film is discussed using the theories of monolayer permeability. The results are in favour of the energy-barrier theory.

Effect of Lipid Phase State and Foam Film Type on the Properties of DMPG Stabilized Foams

The drainage and stability of DMPG (l-α-phosphatidyl-dl-glycerol dimyristoyl) foams were studied by a microconductivity method under conditions where three different foam film types could be formed—thin foam films (TFF), common black foam films (CBF), and Newton black foam films (NBF). Foaming properties were investigated at 20 and 28°C where DMPG is in the gel and liquid-crystalline states. Higher conductivity signals were observed at the higher temperature where DMPG was in the liquid-crystalline state, which is indicative of wetter or more stable foams under these conditions. This effect was observed independent of foam film type. However, for a given phase state, the type of foam films formed significantly influenced the stability and rate of drainage of the foam. Indeed, the water content of the foams, obtained under conditions for formation of different foam films, is ranked in the order TFF > CBF > NBF. When the temperature was increased to 28°C (i.e., in the liquid-crystalline state), CBF and NBF showed a slight decrease in film thickness and an increase in film lifetime and surface molecular diffusion coefficient in the adsorbed layer. It is likely that the fluidity of the interfacial layer is an important factor contributing to DMPG foam stabilization.

Permeability of common black foam films to gas. Part 2

The film permeability coefficients K for permeation of air through common black films (CBF) have been experimentally measured using the stationary bubble method described earlier (R. Krustev, D. Platikanov and M. Nedyalkov, Colloids Surfaces A: Physicochem. Eng. Aspects, 79 (1992), 129.) The dependence of K on LiCl concentration and temperature T have been studied for CBF from sodium dodecyl sulfate (SDS) + LiCl aqueous solutions. The K(T) dependence for the system SDS + NaCl has also been studied. The results prove our hypothesis that the film permeability is determined mainly by the monolayer permeability K ml of the adsorption layers. The K ml values increase with increasing distance between the monolayers (i.e. the film thickness) and tend to a constant value. K ml and K depend on the specific adsorption of the counterions in the dodecyl sulfate monolayer. The CBF with Li + ions are essentially more permeable than those with Na + ions, which are more strongly adsorbed.

Surfactant liquid and black foam film formation and stability in vitro and correlative conditions in vivo

We studied foam film formation by three preparations that are used as surfactant replacement therapy by injection into the lungs of neonatal infants with surfactant insufficiency (“respiratory distress syndrome”). The preparations contain either all putative hydrophobic components of the normal surfactant system (prepared from bovine lung lavage, Infasurf (IN); prepared from minced bovine lung tissue, Survanta (SU)) or a single component of the system, dipalmitoylphosphatidylcholine (Exosurf Neonatal (EX)). Foam film formation is relevant directly to normal surfactant structure and function in vivo in the neonatal period (Pediatr. Res. 12 (1978) 1070–1076). We assessed morphology and stability of liquid to black film formation and its dependence on substrate concentration C, adsorption time, temperature T, “capillary pressure” P c, film drainage time τ 0–1 and black film formation times τ 1–2. We found that (1) in contrast with the other preparations, IN regularly formed stable black films at the lowest C (“threshold C” C t) under all conditions of T (22 and 37°C) and P c (0.3, 0.4, 1.2 and 2.4 × 10 3 dyn cm −2), (2) EX also formed black films but differed from IN in that C t was higher, film integrity required a longer adsorption time and black film formation was blocked (instability) at P c values of 1.2 and 2.4 × 10 3 dyn cm −2 and (3) SU did not form black films but instead formed slowly (long τ 0–1 and τ 1–2), at relatively high C t, viscosity-dependent inhomogeneous atypical (“rheological”) films containing aggregates of material in the preparation. Extrapolation to in-vivo conditions of C, T and P c indicates that both IN and SU (but not EX) may form stable foam films in situ, that film formation by IN is the more efficient process and that stable surfactant foam films, formed naturally in vivo, are consistent with both the in-vitro characteristics described here and correlative lung function in vivo.

Molecular mobility in the monolayers of foam films stabilized by porcine lung surfactant

Certain physical properties of a range of foam film types that are believed to exist in vivo in the lung have been investigated. The contribution of different lung surfactant components found in porcine lung surfactant to molecular surface diffusion in the plane of foam films has been investigated for the first time. The influence of the type and thickness of black foam films, temperature, electrolyte concentration, and extract composition on surface diffusion has been studied using the fluorescence recovery after photobleaching technique. Fluorescent phospholipid probe molecules in foam films stabilized by porcine lung surfactant samples or their hydrophobic extracts consisting of surfactant lipids and hydrophobic lung surfactant proteins, SP-B and SP-C, exhibited more rapid diffusion than observed in films of its principal lipid component alone, L-alpha-phosphatidylcholine dipalmitoyl. This effect appears to be due to contributions from minor lipid components present in the total surfactant lipid extracts. The minor lipid components influence the surface diffusion in foam films both by their negative charge and by lowering the phase transition temperature of lung surfactant samples. In contrast, the presence of high concentrations of the hydrophillic surfactant protein A (SP-A) and non-lung-surfactant proteins in the sample reduced the diffusion coefficient (D) of the lipid analog in the adsorbed layer of the films. Hysteresis behavior of D was observed during temperature cycling, with the cooling curve lying above the heating curve. However, in cases where some surface molecular aggregation and surface heterogeneity were observed during cooling, the films became more rigid and molecules at the interfaces became immobilized. The thickness, size, capillary pressure, configuration, and composition of foam films of lung surfactant prepared in vitro support their investigation as realistic structural analogs of the surface films that exist in vivo in the lung. Compared to other models currently in use, foam films provide new opportunities for studying the properties and function of physiologically important alveolar surface films.

Evolution of white spots in lipid foam black films of DMPC

A new phenomenon in the kinetic behavior of thin liquid films is reported: thickening white spots (lenses) in black foam films of small unilamellar liposomes of dimyristoylphosphatidylcholine (DMPC). The time evolution of the lenses is registered and the shape changes are determined. Such structures form only at temperatures below the main phase transition temperature of the lipid bilayer (gel-liquid crystal first order phase transition).

Lateral mobility of phospholipid molecules in thin liquid films

The Fluorescence Recovery After Photobleaching (FRAP) method was applied to measure the lateral mobility of the fluorescent lipid analog, dioctadecylindocarbocyanine perchlorate (Dil-C18), in microscopic thin liquid films (Foam Films (FFs)). The foam film structures were comprised of two phosphatidylcholine monolayers adsorbed at air/water interfaces which sandwiched a thin liquid core. Lateral diffusion of the DiI molecules in the plane of the monolayers was determined as a function of the thickness of the thin liquid core of the film between the FF monolayers. The results obtained indicated that the diffusion coefficient was strongly dependent both on the distance between the FF monolayers in the range 4 nm to 85 nm (corresponding to the FF thickness) and on the film type. The applicability of the FRAP method for studying the molecular mobility in phospholipid FFs was demonstrated. Considerable differences in the surface diffusion coefficient of Dil were observed, ranging between 2 × 10−8 cm2/s and 22 × 10−8 cm2/s in so called yellow, gray, common black and Newton black FFs. The effect of the presence of polyethylene glycol (PEG-400) in the liquid core of lecithin FFs on surface diffusion was also studied. The surface diffusion results from the FF studies were compared with data from black lipid membranes (BLMs). These structures are related in thickness terms but the molecular orientation in FFs is the reverse of that in BLMs.

Energy-minimizing states of capillary systems with bulk, surface, and line phases

In this work we consider the implications of the minimum-energy principle for a fluid system composed of bulk, surface, and line phases. By analogy with the concept of surface tension for surface phases, line tension is defined as the force, or free energy per unit length, operating in a one-dimensional phase. Such phases typically form the common boundary of several surface phases. The concept of line tension was introduced in a brief footnote by Gibbs (1961) and subsequently developed by a number of researchers. A modern treatment based on Gibbsian thermodynamics may be found in Boruvka & Neumann (1977). The principal effect of line tension is to modify the Young equation that restricts the equilibrium contact angles between the surface phases along their common boundaries (Boruvka & Neumann, 1977). According to the modified equation, line tension affects the contact angles wherever the boundary is curved. This curvature introduces a length scale that can be used to quantify line tension experimentally. Both positive and negative values of measured line tension have been reported. For example, in systems consisting of an oil lens on the surface of water, Langmuir's data yield a positive line tension of approximately 60 uJ/m (Langmuir, 1933), while Gershfeld & Good (1967) and Harkins (1937) report positive values of 5-OxKT 3 and 2-0 x 10~ 5 uJ/m, respectively. Wallace & Schlirch (1988) report positive values ranging from 10 X 10~2 to 2-4 X 10~2 uJ/m for sessile drops on liquid-liquid interfaces. However, negative line tensions varying in magnitude from 105 to 10~ 3 pJ/m have been reported for certain black foam films (Toshev et at., 1988; Kolarov & Zorin, 1979). The line tensions calculated from the data of Ponter & Boyes (1972), Boyes & Ponter (1974), Ponter & Yekta-Fard (1985), and Yekta-Fard & Ponter (1988)

The Shape of the Disjoining Pressure Isotherm – its Effect on the Line Tension of Common Black (Emulsion and Foam) Films

By the systematic direct numerical computation of the line tension of common black films it has been demonstrated that the value and sign of this line tension are very sensitive to the variation of the shape of the disjoining pressure isotherm and this finding may be used to obtain additional information on the surface forces acting in these films from the experimental values of the line tension.

Variations from the Plateau law in foams.

In this paper we study microgeometry of real foam. We suggest an explanation of systematic variations from the classical Plateau law which may be observed in real froths and foams of random structure. We show that the variations in the inclination angles between liquid films forming Plateau borders are conditioned by the variations in disjoining pressure and surface tension in the films separating bubbles of different sizes. Equations for calculating the inclination angles from the isotherm of disjoining pressure are derived. For black foam films the deviations of the inclination angles from the ideal value of 120[degree] are expected to amount up to several degrees.

Surface Diffusion in Phospholipid Foam Films: 1. Dependence of the Diffusion Coefficient on the Lipid Phase State, Molecular Length, and Charge

The surface lateral diffusion properties of a range of pure phospholipid-stabilized black foam films (BFF) were studied by fluorescence recovery after photobleaching. The thin films were formed in a specially constructed chamber and fluorescent-labeled by inclusion of low levels of the anionic surfactant 5- N-(octadecanoyl)aminofluorescein. A systematic investigation of temperature dependence of the surface diffusion coefficient in the range 8-85°C was undertaken with phospholipid BFFs stabilized by DMPG, DMPC, DMPE, DLPE, DPPE, DOPE, and DPPA along with some mixtures (DMPC/DMPG and DLPE/DPPA). It was found that the diffusion coefficient was dependent on the lipid phase state. With the exception of negatively charged DMPG, surface mobility of all lipids in the gel state was due to flow rather than to diffusion. In contrast, above the liquid crystalline phase transition, diffusion predominated and increased with temperature from about 2 × 10 -8 to 9 × 10 -8 cm 2/s, with a different slope for the different lipids. Increases in the hydrophobic chain length of the phospholipids resulted in a decrease in the diffusion coefficient for values obtained at any given temperature above the phase transition, in the order DLPE > DMPE > DPPE. In the case of unsaturated Cl8:1 DOPE, measurable diffusion extended down to 15°C compared to 24°C for DMPC and 45°C for the other PEs. The relative importance of the effects of molecular chain length, unsaturation, and charge is discussed.

Electrical Conduction of Black Foam Films Formed by Lysophospholipids

Abstract The lateral film conductivity along the polar head-groups and the core thickness of film have been measured on the black foam films formed from aqueous solution of 1-palmitoyl-sn-glycero-3-phosphocholine and 1-lauroyl-sn-glycero-3-phosphoethanolamine without and with different concentration of NaCl and CaCl2. It is found that conductivity of each film depends on the core thickness and the type and the concentration of added electrolyte.

Permeability of common black foam films to gas. Part 1

An experimental method for measuring the permeability coefficient K for the permeation of air through black foam films is described. A series of measurements of K for sodium dodecyl sulfate plus sodium chloride aqueous solutions have been performed. Experimental results concerning the dependences of K on surfactant concentration C, NaCl concentration C e1 and temperature T are reported. A stepwise decrease in permeability K at the transition from common black film (CBF) to Newton black film (NBF) has been found, the K values of the thinnest NBF being 2–3 times lower than those of the essentially thicker CBE. The results show that gas permeation through black foam films is mainly determined by the properties of the surfactant layers: monolayers in the case of CBFs and a bilayer in the case of NBFs. The experimental results concerning the permeability of CBFs are discussed on the basis of theories of gas permeation through monomolecular layers.

X-ray scattering by black foam films: New data analysis

X-ray scattering by black foam films: New data analysis

X-ray scattering by black foam films

The x-ray scattering by the three types of black foam films (common black, Newton black, and stratified black films) was experimentally studied. A special device in which flat black films with an area of ca. 2 cm2 can be produced was developed and x-ray diffraction patterns were obtained by a vertical diffractometer. The three types of films differ significantly in their x-ray reflections, which proves that they have different structure. For common black films, the comparison of observed and calculated intensities lead to a model, which corresponds to the three-layer model. The Newton black films exhibit diffraction trace with only one highly asymetric peak and there is, as of yet, no unambigous interpretation. The patterns of the stratified black films have several pronounced sharp peaks corresponding to the areas of different films with a given thickness.