Common Black Films Research Articles

Relation between ionic surfactant concentration and thickness of foam film stabilized by ionic – nonionic surfactant mixed adsorbed films

In this paper, we compared the thickness of common black films stabilized by four different ionic-nonionic surfactant mixed adsorbed films. For the cetyltrimethylammonium chloride (CTAC) - pentaethyleneglycol monododecyl ether (C12E5), SDS - tetraethyleneglycol monodecyl ether (C10E4), and dodecyltrimethylammonium bromide (DTAB) - tetraethyleneglycol monooctyl ether (C8E4) systems, the foam film thickness measured by using Scheludko–Exerowa glass ring method coincided very well when the foam film thickness was plotted as a function of bulk ionic surfactant (1:1 electrolyte) concentration. In addition, by using the phase diagram of mixed adsorbed film obtained from the thermodynamic analysis of the surface tension data, it was also demonstrated that the surface charge density and surface tension have a minor effect on the equilibrium film thickness. On the other hand, the foam film stabilized by the 1-decyl-3-methyl imidazolium tetrafluoroborate (DMIMBF4) - C10E4 mixed adsorbed film showed much smaller thickness values compared to the above-mentioned systems. Irregular behavior observed in the DMIMBF4 - C10E4 system was discussed based on the specific interaction between imidazolium head groups and BF4- ions through hydrogen bonding in an ion-concentrated environment in the Stern layer.

Responses of soil moisture and photosynthetic characteristics to mulching materials and ridge-to-furrow ratios in rapeseed fields in southwest dryland of China

In order to deal with the frequent seasonal drought and improve water use efficiency and crop photosynthetic efficiency in drylands of southwest China, a field experiment was conducted to investigate the effects of different mulching materials (common white film, common black film, biodegradable film and no film) and ridge-to-furrow ratios (40 cm:40 cm and 40 cm:80 cm) on soil water storage, as well as photosynthetic characteristics, fluorescence parameters and chlorophyll relative content (SPAD) of rapeseed, with the flat planting as the control. The results showed that the average soil water storage under different mulching materials followed the order: ridge with common black film (BR) ≈ ridge with common white film (WR) ≈ ridge with biodegradable film (BDR) ＞ ridge with no film (NR) ＞ flat planting (FP). Meanwhile, ridge-to-furrow ratios did not affect soil water storage. The net photosynthetic rate, stomatal conductance and fluorescence para-meters (Fm, Fv, Fv/Fm, Fv/Fo, qP and qN) of rapeseed under ridge-furrow with film mulching was higher than those under flat planting. Compared with control, SPAD value was improved by 6.1%, 8.6%, 8.5% and 3.6% under WR, BR, BDR and NR, while instantaneous water use efficiency (IWUE) was increased by 18.3%, 11.4%, 16.3% and 10.4% under those treatments, respectively. Rapeseed yield under BR, WR and BDR was significantly higher than that in control, while NR did not increase yield. The treatment of ridge with common black film + 40 cm:40 cm as ridge-to-furrow ratio could gain the highest economic benefit. Ridge-furrow planting of rainfall harvesting could improve soil moisture, increase crop photosynthetic capacity, and raise yield and economic income in rapeseed fields in drylands of southwest China.

Common black film stability and synergetic adsorption in ionic−nonionic mixed surfactant systems

In this paper, the thickness and stability of common black films (CBFs) in two ionic–nonionic mixed surfactant systems were compared based on the phase diagram of the adsorbed film. The mixed surfactant systems examined were (1) cetyltrimethylammonium chloride (CTAC) – n-dodecyl-β-D-maltoside (β-C12G2) and (2) lithium perfluorooctanesulfonate (LiFOS) – tetraethyleneglycolmonooctyl ether (C8E4) systems. When the attraction between the two surfactants in the adsorbed film was weak, the foam film collapsed as the observed bulk composition of the nonionic surfactant, X^2, became 0.09 in system (1). However, the CBF of system (2) was stable up to X^2 > 0.96 due to the strong synergism between the ionic and nonionic surfactants maintaining a high ionic surfactant composition in the adsorbed film, thus leading to a high surface charge density that stabilize the CBF.

Probing pH difference between micellar solution and nanoscale water within common black film by fluorescent dye

The protonation/deprotonation equilibrium of a fluorescent pH probe (carboxy-seminaphthorhodafluor-1, SNARF-1) within the nanoscale water layer confined in common black films (CBFs) has been studied. We find that SNARF-1 molecules feel a more acidic environment in CBFs than when they are in the bulk micellar solution, using the base/acid peak area ratio of the dye to indicate its microenvironment pH. Three surfactants are used to study the dependence of the pH drop versus charge: cationic (cetyltrimethylammonium bromide, CTAB), anionic (sodium dodecylsulphate, SDS) and nonionic (Triton X-100) species. The decrease of CBFs pH versus the pH of the micellar solution is the following: ΔpH ≈ 1.5 for CTAB (pH: 7.0–9.0), ΔpH ≈ 0.8 for SDS, and ΔpH ≈ 0.4 for Triton X-100. With the addition of electrolyte in CBFs, we observe large decrease the amplitude of the pH anomaly, thus suggesting an electrostatic origin of the pH change at nanoscale environment.

Sensing Parts per Million Level Ammonia and Parts per Billion Level Acetic Acid in the Gas Phase by Common Black Film with a Fluorescent pH Probe.

Relying on the nanometer-thick water core and large surface area-to-volume ratio (∼2 × 108 m-1) of common black film (CBF), we are able to use a pH-sensitive dye (carboxy-seminaphthorhodafluor-1, SNARF-1) to detect ammonia and acetic acid gas adsorption into the CBF, with the limit of detection reaching 0.8 ppm for NH3 gas and 3 ppb for CH3COOH gas in the air. Data analysis reveals that fluorescence signal change is linearly proportional to the gas concentration up to 15 ppm and 65 ppb for NH3 and CH3COOH, respectively.

Specific effects of Ca(2+) ions and molecular structure of β-lactoglobulin interfacial layers that drive macroscopic foam stability.

β-Lactoglobulin (BLG) adsorption layers at air-water interfaces were studied in situ with vibrational sum-frequency generation (SFG), tensiometry, surface dilatational rheology and ellipsometry as a function of bulk Ca(2+) concentration. The relation between the interfacial molecular structure of adsorbed BLG and the interactions with the supporting electrolyte is additionally addressed on higher length scales along the foam hierarchy - from the ubiquitous air-water interface through thin foam films to macroscopic foam. For concentrations <1 mM, a strong decrease in SFG intensity from O-H stretching bands and a slight increase in layer thickness and surface pressure are observed. A further increase in Ca(2+) concentrations above 1 mM causes an apparent change in the polarity of aromatic C-H stretching vibrations from interfacial BLG which we associate to a charge reversal at the interface. Foam film measurements show formation of common black films at Ca(2+) concentrations above 1 mM due to considerable decrease of the stabilizing electrostatic disjoining pressure. These observations also correlate with a minimum in macroscopic foam stability. For concentrations >30 mM Ca(2+), micrographs of foam films show clear signatures of aggregates which tend to increase the stability of foam films. Here, the interfacial layers have a higher surface dilatational elasticity. In fact, macroscopic foams formed from BLG dilutions with high Ca(2+) concentrations where aggregates and interfacial layers with higher elasticity are found, showed the highest stability with much smaller bubble sizes.

Comparison of Change in Surface Structure of POPC Surfactant Bilayer on Si Substrate with MIES &amp; UPS

Nanoparticles in the recent times have drawn more attention in the field of electronics and in particular their property of self assembly over another material surface makes them a suitable component in the development of Nanoscale materials. Self organization property of Nanoparticles has opened up whole new possibilities in the construction of 2D nanostructures through deposition of organized bilayer of surfactant called black films on a solid substrate. Newton Black Films which are much thinner than a Common Black Films attracted more interests recently with their ability to form more complex structures. In this article, Newton Black films of POPC (1-palmitoyl-2-oleoyl-phosphaticylcholine) surfactant is formed and deposited on a solid substrate after a certain amount of time and their surface structure were analyzed with time. The experiment is conducted at three different drainage states; un-dried, un-dried with a salt present, and dried; their results are compared with MIES and UPS spectrum. Where, MIES spectra being more sensitive towards surface modification show that the structure becomes more ordered with drainage time and the process gets even faster with the addition of a salt. Comparatively, in MIES the presence of new elements is more clearly observed with the variation in their energy spectra on the drained film substrate than in the un-drained substrate owing to the fact that the drained film has more patterned outermost layer comprised with the new elements.

Thin–Thick Transition of Foam Film Driven by Phase Transition of Surfactant–Alkane Mixed Adsorbed Film

Abstract This paper reports the influence of surface phase transitions of a surfactant–alkane mixed adsorbed film on the foam film thickness. The DLVO free-energy between the adsorbed films is estimated using total-reflection XAFS. The foam film thickness shows discontinuous changes at the surface phase transition. In addition, the foam film thicknesses on either side of the thickness transition were in the range for common black films (CBFs), which shows a striking difference from existing thin–thick transitions between CBF and Newton black films (NBFs).

Thermodynamic studies on thin liquid films IV. Foam film stabilized by sodium dodecyl sulfate

Thermodynamic treatment of thin liquid films in Part III of this series was applied to foam films stabilized by sodium dodecyl sulfate. Miscibility of sodium chloride and sodium dodecyl sulfate in the adsorbed films at the film surfaces and transition between the black films were studied by measuring film thickness and contact angle. A discontinuous change in the thickness and a break on the contact angle vs. concentration curve appeared at the transition. Judging from the phase diagram of adsorption, sodium chloride and sodium dodecyl sulfate are a little miscible in the adsorbed films. The miscibility was ascribed to specific interaction between sodium ion and dodecyl sulfate ion in the adsorbed films. The miscibility in an adsorbed film was compared between the film surface and meniscus and between the common black and Newton black films.

Effect of gas type on foam film permeability and its implications for foam flow in porous media

The aim of this paper is to provide a perspective on the effect of gas type on the permeability of foam films stabilized by different types of surfactant and to present a critical overview of the tracer gas experiments, which is the common approach to determine the trapped fraction of foam in porous media. In these experiments some part of the gas is replaced by a “ tracer gas” during the steady-state stage of the experiments and trapped fraction of foam is determined by fitting the effluent data to a capacitance mass-transfer model. We present the experimental results on the measurement of the gas permeability of foam films stabilized with five surfactants (non-ionic, anionic and cationic) and different salt concentrations. The salt concentrations assure formation of either common black (CBF) or Newton black films (NBF). The experiments are performed with different single gasses. The permeability of the CBF is in general higher than that of the NBF. This behavior is explained by the higher density of the surfactant molecules in the NBF compared to that of CBF. It is also observed that the permeability coefficient, K(cm/s), of CBF and NBF for non-ionic and cationic surfactants are similar and K is insensitive to film thickness. Compared to anionic surfactants, the films made by the non-ionic surfactant have much lower permeability while the films made by the cationic surfactant have larger permeability. This conclusion is valid for all gasses. For all types of surfactant the gas permeability of foam film is largely dependent on the dissolution of gas in the surfactant solution and increases with increasing gas solubility in the bulk liquid. The measured values of K are consistent with rapid diffusion of tracer gasses through trapped gas adjacent to flowing gas in porous media, and difficulties in interpreting the results of tracer-foam experiments with conventional capacitance models. The implications of the results for foam flow in porous media and factors leading to difficulties in the modeling of trapped fraction of foam are discussed in detail. To avoid complications in the interpretation of the results, the best tracer would be one with a permeability close to the permeability of the gas in the foam. This puts a lower limit on the effective diffusion coefficient for tracer in an experiment.

Foam Films as Thin Liquid Gas Separation Membranes

In this letter, we testify the feasibility of using freestanding foam films as a thin liquid gas separation membrane. Diminishing bubble method was used as a tool to measure the permeability of pure gases like argon, nitrogen, and oxygen in addition to atmospheric air. All components of the foam film including the nature of the tail (fluorocarbon vs hydrocarbon), charge on the headgroup (anionic, cationic, and nonionic) and the thickness of the water core (Newton black film vs Common black film) were systematically varied to understand the permeation phenomena of pure gases. Overall results indicate that the permeability values for different gases are in accordance with magnitude of their molecular diameter. A smaller gaseous molecule permeates faster than the larger ones, indicating a new realm of application for foam films as size selective separation membranes.

Foam films from mixed solutions of bovine serum albumin and n-dodecyl-β- d-maltoside

New data for foam films from mixed aqueous solutions of important components non-ionic surfactant “ n-dodecyl-β- d-maltoside” (C 12G 2) and globular protein “bovine serum albumin” (BSA) are presented. Based on the equilibrium surface tension isotherm of mixed aqueous solutions of BSA (10 −6 M) with C 12G 2, obtained by Wilhelmy method it is found that protein–surfactant complexes are formed at concentration region from 3 × 10 −6 to 1.5 × 10 −5 M C 12G 2. Thinning of the films stabilized by mixtures with a composition corresponding to the special points of the isotherm is recorded and compared with this of the individual components. It is found that the films from mixed protein–surfactant solutions, exhibit irregular thinning behaviour and thickness nonhomogeneity. The critical and equilibrium thickness of stable films is measured interferometrically and discussed based on the specificity of interactions between the components. Films from pure BSA solutions are thinnest (11 nm) and their thickness corresponds to Newton black (NB). It is found that the thickness of mixed films is larger (17 nm) than that of films from pure BSA and corresponds to thickness of common black films, irrespectively that they visually look like Newton film (NF). The larger value of these thicknesses is explained with an increase in the thickness of adsorption layers due to the bigger hydrodynamic radius of complexes or reorientation of BSA molecule to the volume face during its displacement by C 12G 2 domains.

Effect of polyelectrolyte/surfactant combinations on the stability of foam films

What happens if polymers are added to a macroscopic foam or to foam films? This is an important question for many technical applications, but it is also important for materials and life science. This paper reviews the effect of the surface composition on the thickness and stability of aqueous foam films containing surfactants and polymers. The surfactant concentration is below the critical micellisation concentration (cmc) and the critical aggregation concentration (cac). The addition of polymers to foam films leads to the formation of surface active polymer/surfactant complexes or to depletion of polymers close to the interfaces, which has a strong effect on the film stability. The review mainly concentrates on the dilute polymer regime (below the overlap concentration c*), and results at the semi-dilute regime (above c*) are briefly reviewed. A principle concept for the relation between the surfactant/polymer combination and the film thickness and stability is developed. It allows the prediction, of whether an unstable Newton black film (NBF) or a stable common black film (CBF) will be formed.

Basic properties of foam films stabilized with tetraethyl ammonium salt of perfluoro octane sulfonate (PFOS)

The paper summarizes the results of a study on the basic properties (film thickness, contact angle film/meniscus and gas permeability) of foam films stabilized with the anionic perfluoro octane sulfonate (PFOS) surfactant. The surfactant was used as a tetraethyl ammonium salt. The dependencies on the electrolyte (NH 4Cl) and surfactant concentration were studied. Strong dependence of the film thickness and the contact angle on the concentration of NH 4Cl and PFOS was observed. Well pronounced transition in the film thickness from common black (electrostatically stabilized) films to Newton black (sterically stabilized) films was registered. The critical salt concentration necessary for the formation of NBF was defined to be 0.1 M NH 4Cl. The contact angles between the films and the meniscus were collected. The gas permeability coefficient ( K, cm/s) was measured at various conditions. The permeability coefficient of NBF decreases with increasing surfactant concentration below the cmc and remains constant above it. The gas permeability of the films depends on the salt concentration, respectively the film thickness in a complicated manner which cannot be explained by simple application of the Fick's law of diffusion.

No Charge Reversal at Foam Film Surfaces after Addition of Oppositely Charged Polyelectrolytes?

The present work deals with control of the stability of ionic surfactant (tetradecyl trimethyl ammonium bromide) foam films by the addition of oppositely charged polyelectrolytes. In the two cases of low and high polyelectrolyte concentrations, a common black film is formed. This is due to an electrostatic repulsion (in the latter case, according to the hitherto assumption) caused by a charge reversal at film surfaces at high polyelectrolyte concentration. But what happens around the nominal isoelectric point (IEP), where the net charge of the whole film is close to zero? Is a Newton black film formed or does the film break? Disjoining pressure isotherms show a strong reduction in stability close to the IEP. The comparison between surface tension and elasticity measurements and disjoining pressure isotherms leads to a surprising conclusion: The stability of foam films seems not to be dominated by the net charge of the polyelectrolyte/surfactant complexes at the surface, which was the former hypothesis, but by the overall net charge of the film.

Inactivation of Pulmonary Surfactant by Lysophosphatidylcholine

ABSTRACTThe aim of the study is to examine the influence of the lysophosphatidylcholine (lysoPC) to surface properties of INFASURF, a replacement lung surfactant, using the methods of thin foam films and Wilhelmy method. By the latter it is shown the change of surface tension (γ, mN/m) during time of the pure INFASURF and their mixture with lysoPC. Foam films are an efficient and useful model for the study of many surface phenomena especially for investigating the surface properties of pulmonary surfactant. Formation and stability of common black foam films (CBF) of pure INFASURF and of mixtures with various concentrations of lysoPC indicate the influence of low concentrations of lysoPC for the stability of CBF from INFASURF. It is proved that the curve W/C (where W is probability and C—concentration) is shifted to the lower concentrations.

Structure of Liquid Films of an Ordered Foam Confined in a Narrow Channel

A bamboo foam is the simplest case of an ordered foam confined in a narrow channel. It is made of a regular film distribution, arranged perpendicularly to the channel. Our work consists of studying the structural properties of several films taken in a drained foam. X-ray experiments highlighted the equality of the equilibrium thickness for each film within a foam. The same thickness was found as by measurements of disjoining pressure isotherms, proving as well that films of a bamboo foam behave like isolated ones. The refinement of X-ray data by a simple model of specular reflectivity showed a significant variation of the electronic distribution of the surfactant layer for a common black film forwarding from one equilibrium state to another. A discussion on the organization of the surfactant molecules to the gas/liquid interface and film is proposed.

Influence of steroid hormone progesterone on the properties of phosphatidyl serine monolayers and thin liquid films

In this work the capability of Progesterone (Prog) to penetrate to phosphatidyl serine (PS) monolayers (detected by equilibrium and dynamic surface tensions) and to induce rupture of PS thin liquid films (TLFs, known as foam films) in presence of Ca 2+ ions is studied. TLF studies reveal that the presence of Ca 2+ ions changes the type of PS films from thicker common black films to bilayer Newton black films and that the addition of Prog results in film destabilization and rupture. The effects of Prog in presence of Ca 2+ ions were observed with the films consisting of negatively charged PS but not of neutral phospholipids. The results correlate with the proposed physiological role of Prog and Ca 2+ in the acrosome reaction. The model of TLFs is used for the first time to study membrane fusion during acrosome reaction and proposes several new qualitative and quantitative parameters for studying of this reaction.

Surface forces in foam films from DPPC and lung surfactant phospholipid fraction

Surface properties of foam films formed from aqueous dispersions of dipalmitoyl-phosphatidylcholine (DPPC) and from solutions of a phospholipid fraction of lung surfactant (TPL) are studied employing the foam film method. Experiments are carried out within a wide range of NaCl concentrations ( C el) and the ranges of C el determining formation of common films (CF), common black films (CBF) and bilayer Newton black films (NBF) are found. The thickness ( h) of the CF and CBF decreases with the increase of C el until the critical electrolyte concentrations ( C el, cr) is reached. The determined C el, cr that characterize the transition to NBF show that C el, cr of the TPL films is an order of magnitude higher than that of the DPPC films. The measured h of the TPL films is higher than that of the DPPC films in the whole C el range. Besides, only the h( C el) curve of the DPPC films outlines a metastable C el range where both CF and NBF are obtained. Both the h( C el) curves and the direct measurements of the disjoining pressure isotherms of the DPPC films (Π( h) isotherms) demonstrate the role of electrostatic repulsive forces for the stability of the phospholipid films The obtained results are compared with the DLVO theory equations and the evaluated potentials of the diffuse electric layer φ 0 ∼ 20 mV for the DPPC films and φ 0 ∼ 100 mV for TPL films show the strong effect of the charged phospholipids in the TPL mixture on the electric properties at the film interfaces.

Characterization of bamboo foam films by neutron and X-ray experiments

We report on small angle neutron and X-ray scattering experiments on single common black films in ordered bamboo foams stabilized by sodium dodecyl sulfate and dodecanol. We observed anisotropic scattering perpendicular to the film. The integrated signal exhibits clear Kiessig fringes over a wide range of diffusion vector q. We were able to fit our data by a single layer (neutron with contrast matching water/SDS) or a “three slabs” (X-ray) reflectivity. We also discuss about the wide range of reflected angle, despite the narrow distribution of incident angles. Though thermal surface fluctuations may induce off-specular reflectivity, we show here a simple geometrical explanation of the phenomenon. This angle distribution is indeed compatible with the curvature of the film.