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Reservoir wettability plays a critical role in determining the fluid interactions, distributions, and flow paths in porous mediums, which is directly reflected in oil production and recovery strategies during a field’s production life. Many factors can influence reservoir wettability characterisation on the laboratory scale such as: sample origin, mineralogical composition, cleaning procedures for further analysis, pressure, temperature, and the oil aging process. The best practice to restore the sample's original wettability by aging processes is unclear, impacting the assessment of contact angle (CA) measurements. This work addresses the oil aging time and experimental conditions associated with the pressure and temperature in CA measurements on rock surfaces from a Brazilian pre-salt reservoir with a predominance of calcite, dolomite, and quartz, respectively. For this purpose, all surfaces used were cleaned with solvents and saturated with synthetic formation water under vacuum conditions. To evaluate the influence of oil aging time on the samples' wettability, the CA measurements, by captive bubble method, were performed on unaged surfaces. The CA measurements were then taken again on the same surfaces after 14 and 42 days of oil aging. To evaluate the pressure and temperature effects on the CA values, the experiments were run at 14.7 psi and 22 °C (room conditions), 14.7 psi and 60 °C and 4000 psi and 60 °C. The results showed a mischaracterization of all surfaces' original wettability due to the cleaning process, showing the higher hydrophilic degree and wettability character of neutral and water-wet surfaces. The oil aging procedure was confirmed to be a fundamental process in restoring the wettability of rock surfaces, requiring more than 14 days to be achieved. Pressure and temperature conditions also matter on CA evaluations. The surface's hydrophobic degree increased as the pressure increased from 14.7 psi to 4000 psi, and the temperature from 22 °C to 60 °C. Furthermore, a higher influence of temperature than pressure was observed to impact CA values. Oil aging and experimental conditions presented a larger effect on increasing the hydrophobic degree of samples with calcite and dolomite predominance than those with quartz predominance.

openaire: EC/H2020/788489/EU//BioElCell Chitin nanofibrils (NCh, ∼10 nm lateral size) were produced under conditions that were less severe compared to those for other biomass-derived nanomaterials and used to formulate high internal phase Pickering emulsions (HIPPEs). Pre-emulsification followed by continuous oil feeding facilitated a "scaffold" with high elasticity, which arrested droplet mobility and coarsening, achieving edible oil-in-water emulsions with internal phase volume fraction as high as 88%. The high stabilization ability of rodlike NCh originated from the restricted coarsening, droplet breakage and coalescence upon emulsion formation. This was the result of (a) irreversible adsorption at the interface (wettability measurements by the captive bubble method) and (b) structuring in highly interconnected fibrillar networks in the continuous phase (rheology, cryo-SEM, and fluorescent microscopies). Because the surface energy of NCh can be tailored by pH (protonation of surface amino groups), emulsion formation was found to be pH-dependent.Emulsions produced at pH from 3 to 5 were most stable (at least for 3 weeks). Although at a higher pH NCh was dispersible and the three-phase contact angle indicated better interfacial wettability to the oil phase, the lower interdroplet repulsion caused coarsening at high oil loading. We further show the existence of a trade-off between NCh axial aspect and minimum NCh concentration to stabilize 88% oil-in-water HIPPEs: only 0.038 wt % (based on emulsion mass) NCh of high axial aspect was required compared to 0.064 wt % for the shorter one. The as-produced HIPPEs were easily textured by taking advantage of their elastic behavior and resilience to compositional changes. Hence, chitin-based HIPPEs were demonstrated as emulgel inks suitable for 3D printing (millimeter definition) via direct ink writing, e.g., for edible functional foods and ultralight solid foams displaying highly interconnected pores and for potential cell culturing applications.

Square millimeters of free-standing graphene do not exist per se because of thermal fluctuations in two-dimensional crystals and their tendency to collapse during the detachment from the substrate. Here we form millimeter-scale freely suspended graphene by injecting an air bubble underneath a graphene monolayer floating at the water–air interface, which allowed us to measure the contact angle on fully free-standing non-contaminated graphene. A captive bubble measurement shows that free-standing clean graphene is hydrophilic with a contact angle of 42° ± 3°. The proposed design provides a simple tool to probe and explore the wettability of two-dimensional materials in free-standing geometries and will expand our perception of two-dimensional materials technologies from microscopic to now millimeter scales., Experimental determination of the contact angle of a two-dimensional film is crucial to understand its wettability characteristics. Here, the authors use the captive bubble method to estimate a contact angle value of 42° ± 3° for a monolayer graphene film.

Subsurface porous formations provide large capacities for underground hydrogen storage (UHS). Successful utilization of these porous reservoirs for UHS depends on accurate quantification of the hydrogen transport characteristics at continuum (macro) scale, specially in contact with other reservoir fluids. Relative-permeability and capillary-pressure curves are among the macro-scale transport characteristics which play crucial roles in quantification of the storage capacity and efficiency. For a given rock sample, these functions can be determined if pore-scale (micro-scale) surface properties, specially contact angles, are known. For hydrogen/brine/rock system, these properties are yet to a large extent unknown. In this study, we characterize the contact angles of hydrogen in contact with brine and Bentheimer and Berea sandstones at various pressure, temperature, and brine salinity using captive-bubble method. The experiments are conducted close to the in-situ conditions, which resulted in water-wet intrinsic contact angles, about 25 to 45 degrees. Moreover, no meaningful correlation was found with changing tested parameters. We monitor the bubbles over time and report the average contact angles with their minimum and maximum variations. Given rock pore structures, using the contact angles reported in this study, one can define relative-permeability and capillary-pressure functions for reservoir-scale simulations and storage optimization.

In this article, we report the measurement of underwater aerophobicity, through the captive-bubble method, for different polymeric coatings employed to protect microscale and nanoscale flexible electronic devices for seawater applications. Controlling the morphology and wettability of the coating, in particular with the incorporation of nanoparticles of fluorinated polymers, allows to adjust the hydrophilic/hydrophobic (aerophobic/aerophilic) character of the surface in order to achieve a more insulating and antibiofouling behavior. Morphological analysis (roughness) and wettability measurements in sessile-drop and captive-bubble methods were provided for some properly selected polymeric coatings. We found that parylene C decorated with poly(vinylidene fluoride) nanoparticles at a higher dispersion concentration (5 mg/mL) exhibits the best compromise between morphology, hydrophobicity, and underwater aerophobicity, with sessile-drop water contact angle of 95.1 ± 2.9° and captive-air-bubble contact angle of 133.1 ± 5.9°. © The Author(s) 2019.

Geological CO2 sequestration has been proposed as an effective solution to mitigate excessive human-emitted CO2 in atmosphere. Knowledge of immiscible two-phase flow of CO2-water/brine is necessary to evaluate the efficiency and safety of geological storage sites. Among forces dominating fluid flow, capillary pressure is highly important because of high uncertainty in measurement due to ambiguous wettability behavior of geomaterials. In particular, time-dependent wettability of geomaterials is of interest for predicting short-term performance of the storage site. After injection of CO2 into an aquifer, both the CO2 and water/brine in rocks pores are unsaturated and tend to dissolve into each other. Present study investigates the variation of contact angle on mica sheet using a captive bubble method at a wide range of pressures and salinities under unsaturated condition. Our results showed a general increase of contact angle with time. Comparison of unsaturated contact angle with previous results in the literature showed a wide span of wettability behavior, ranging from receding to advancing contact angle values reported in the literature. The observed decrease in wettability by time due to heterogeneity and pinning effect of triple line can jeopardize the safety of geological carbon sequestration projects in short-term after injection of CO2.

Reducing liquid surface tension is widely used to increase the efficiency of the centrifugal dehydration in textile wet processing. However, increasing the dehydration efficiency by decreasing fabric surface energy is seldom studied. In this work, the impact of in situ fabric surface energy on residual moisture content (RMC) of fabrics in the dehydration processes was investigated. Different types of fluorocarbon surfactants including cationic, anionic, nonionic and amphoteric were adopted as additives in this study. The liquid surface tension and RMC were efficiently decreased when fluorocarbon surfactants were used. Notably, a cationic fluorocarbon surfactant displays similar surface tension but distinct dehydration efficiency. The in situ fabric surface energy was evaluated by measuring the n-octane contact angle on the cotton fabric surface under the surfactant solution using the captive bubble method. It was found that the cationic fluorocarbon surfactant system gave the lowest fabric surface energy, which was probably because cationic fluorocarbon surfactants are easier to adsorb onto the surface of cotton fabric to form a fluorocarbon layer. The chemical composition (19F, 12C and 16O) analysis of the cotton fabric surface by X-ray photoelectron spectroscopy confirms the hypothesis.

The tooth whitening process is intended to restore the original color of teeth. It consists of the application of oxidizing agents, including hydrogen peroxide. Although these products considerably improve the color of teeth, their effects on other properties of enamel are not fully understood. This work aimed to study the effects of hydrogen peroxide concentration on hydrophilicity, roughness, morphology, and mechanical and tribological properties of human tooth enamel. Human teeth were subjected to bleaching sessions with 6%, 15%, and 35% hydrogen peroxide to achieve a similar level of whitening. The enamel roughness and morphology were characterized by atomic force microscopy and scanning electron microscopy. Vickers microindentation hardness data were obtained. The hydrophilicity was determined using the captive bubble method. Reciprocating, ball-on-flat friction, and wear tests were conducted in artificial saliva using zirconia as the ball and polished enamel as the flat specimens. Although all three test solutions improved tooth color, they also changed the properties of the enamel. Morphological and roughness changes were observed, and there was a decrease in hardness and wear resistance. The wettability was nearly unaffected. It was found that the 15% hydrogen peroxide solution damaged the enamel the least. It was concluded that there is an ideal concentration of hydrogen peroxide for whitening treatments. info:eu-repo/semantics/publishedVersion

Dry eye syndrome is a multifactorial disease of the ocular surface, with clinical findings that include discomfort, visual disturbance, and tear film instability.1 In the United States, it is estimated that 7.8% of women 50 years of age and older2 and 4.34% of men 50 years of age and older3 are affected by dry eye syndrome. Although the International Dry Eye Workshop categorized the types of dry eye as (1) aqueous-deficient and (2) evaporative,1 dry eye syndrome and other ocular surface disorders also involve the interaction between the cellular surface of the eye and the liquid film constituted by the tears.4 It is widely believed that the stability/instability of tear film depends on the surface properties of the epithelium, especially its wettability or degree of retention of tear film in contact with the ocular surface.5–7 Although wetting properties have conventionally been attributed to the presence of a hydrophilic glycocalyx,8 specifically to the highly O-glycosylated membrane-associated mucins of the ocular surface (principally MUC1, MUC4, and MUC16),9 to our knowledge, there are no studies that directly correlate the expression and spatial distribution of cell associated mucins to the physicochemical surface properties of the ocular surface. Immortalized corneal epithelial cell lines have been reported to differentiate, stratify, and express significant amounts of mucins when cultured as a confluent monolayer of cells and stimulated with 10% fetal bovine serum and 10 ng/mL epithelial growth factor (EGF).10 In this work we induced stratification of an hTERT immortalized corneal epithelial (hTCEpi) cell line11 over a period of 6 days and characterized the expression of mucins to correlate with the surface properties of the cells. A standard method to evaluate surface properties is the sessile drop contact angle technique.5–7,12 This widely used method is performed by measuring the contact angle between a drop of liquid and a solid in air. However, measurements of the contact angle of water drops on cell cultures or tissues are misleading because the thin film of liquid covering the surface on hydrated cells impedes the measurement of an angle. Furthermore, if the cell surface is allowed to dry, the contact angle changes values, depending on the moisture level, as observed by Tiffany,7 suggesting the loss of the native state of the cell's surface. To overcome some of the challenges intrinsic to using water as the probe, other liquids can be used to characterize surfaces, such as polar liquids (e.g., glycerol or formamide) or nonpolar lipids (e.g., diiodomethane or benzene). However, polar liquids can disturb the cells due to the difference in osmolarity between the liquid and the cytosol, whereas many nonpolar liquids interact with the phospholipids of the cellular membrane, disrupting it.13 Therefore, the choice of fluid(s) used to measure contact angles of cell surfaces bathed in a fluid environment is critical in determining the interfacial properties. In this work, we used the two-liquid system, where cells are immersed in an isotonic physiologic buffer, and the contact angle is recorded using a nonreactive nonpolar liquid (perfluorocarbon) deposited on the cell surface (Fig. 1A). We also performed the captive bubble method, where the surface of interest is inverted and an air bubble is trapped in contact with the surface (Fig. 1B). Both of these methods permit the measurement of the contact angle and the contact angle hysteresis, which is a measurement that correlates to the uniformity of the surface. For smooth and uniform surfaces, droplets have unique contact angles. However, on heterogeneous surfaces, such as biological surfaces, droplets become pinned by defects and possess an advancing and a receding angle of contact, which may be recorded by tilting the apparatus (Fig. 1C). The intrinsic biochemical make up and surface topography of the ocular surface contribute to this heterogeneity, and the extent to which this promotes the retention of the tear film at the ocular surface is understudied. These measurements allow evaluation of the surface properties at different maturation levels of the glycocalyx during the stratification process of immortalized human corneal epithelial cells. Figure 1 (A) Use of two-liquid method to measure contact angle. In this system, the bulk fluid is PBS and the droplet is a perfluorocarbon. (B) Captive bubble method used to measure contact angle. (C) Tilting of the apparatus to measure the advancing and receding ...

For a water-saturated cap-rock, which consists of a low-permeability porous material, the wettability of the reservoir rock-connate water- CO2 system and the interfacial tension (IFT) between CO2 and connate water are the significant parameters for the evaluation of the capillary sealing. Also, the amount of capillary-trapped CO2 depends on the wettability of reservoir rocks. The wettability of the rock matrix has a strong effect on the distribution of phases within the pore space and thus on the entire displacement mechanism and storage capacity. In this work, the equilibrium contact angles of water/shale system were determined with CO2 for a wide range of pressures at a constant temperature of 318 K by using the dynamic captive bubble method. The results reveal that intermediate-wet conditions and hence possible leakage of CO2 must to be considered at relatively high pressures, however, the salt concentration of the water in the shales plays an important role too. The results show that this estimate is highly dependent on the pore structure, fluid composition and pressure/temperature conditions of the reservoirs. These properties need to be first evaluated before estimates for shale capillarity is used.

International audience; The aim of the present investigation was to compare the in vitro bacterial retention on saliva-coated implant materials (pure titanium grade 2 (cp-Ti) and a titanium alloy (Ti-6Al-4V) surfaces), presenting similar surface roughness, and to assess the influence of physico-chemical surface properties of bacterial strain and implant materials on in vitro bacterial adherence. Two bacterial strains (one hydrophilic strain and one hydrophobic strain) were used and the following were evaluated: bacterial cell adherence, SFE values as well as the Lifshitz-van-der Waals, the Lewis acid base components of SFE, the interfacial free energy and the non-dispersive interactions according to two complementary contact angle measurement methods: the sessile drop method and the captive bubble method. Our results showed similar patterns of adherent bacterial cells on saliva-coated cp-Ti and saliva-coated Ti-6Al-4V. These findings could suggest that bacterial colonization (i.e. plaque formation) is similar on saliva-coated cp-Ti and Ti-6Al-4V surfaces and indicate that both materials could be suitable for use as transgingival abutment or healing implant components. The same physico-chemical properties exhibited by saliva-coated cp-Ti and TAW, as shown by the sessile drop method and the captive bubble method, could explain this similar bacterial colonisation. Therefore, higher values of total surface free energy of saliva-coated cp-Ti and saliva-coated TA6V samples (gamma(sv) approximate to65 mJ/m(2)) were reported using the captive bubble method indicating a less hydrophobic character of these surfaces than with the sessile drop method (gamma(s) approximate to44.50 mJ/m(2)) and consequently possible differences in oral bacterial retention according the theory described by Absolom et al. The number of adherent hydrophobic S. sanguinis cells was two-fold higher than that of hydrophilic S. constellatus cells. Our results confirm that physico-chemical surface properties of oral bacterial strains play a role in bacterial retention to implant materials in the presence of adsorbed salivary proteins. (C) 2004 Elsevier B.V. All rights reserved.

Surface properties of wood and stones are very important in influencing the bonding and finishing of wood and for road construction. Two important surface properties are wettability and surface free energy. Contact angle measurement is a simple, useful and sensitive tool for quantifying the wettability and the surface energy of different materials in contact with pure water and/or aqueous surfactant solutions. Nevertheless, a sessile drop on a real surface shows different contact angle values due to its lack of symmetry or to the loss of volume by capillary action. For this reason alternative techniques which supply an average contact angle value are required. In view of this fact, we applied axisymmetric drop shape analysis-diameter (ADSA-D) using a top view of a sessile drop and axisymmetric drop shape analysis-profile (ADSA-P) with a side view of a captive bubble. Both techniques calculate the contact angle by solving the Young–Laplace equation although with different algorithms, the former needs the maximum drop diameter while the last makes use of the complete bubble profile. ADSA-D was applied to study two wood species (eucalyptus and pine) and ADSA-P with polished rocks of two different compositions (silicate and calcite). The maximum contour of the drop was fitted to an ellipse after being detected and extracted by means of a semi-automatic procedure of image processing. Thus, two different contact angles were found out. The captive bubble method in conjunction with the current ADSA-P technique allows to obtain comfortable, automatic and reproducible measurements of contact angle on porous stones.

Triglyceride wetting properties on solid surfaces of different hydro-phobicities were investigated using three different methods, namely, the sessile drop method for static contact angle measurements, the Wilhelmy method for dynamic contact angle measurements, and the captive bubble method to investigate thin triglyceride film stability. For solid surfaces having a surface free energy higher than the surface tension of triglycerides (tributyrin, tricaprylin, and triolein), a qualitative correlation was observed between wetting and solid/triglyceride relative hydrophobicities. On surfaces presenting extreme hydrophobic or hydrophilic properties, medium-chain triglycerides had a behavior similar to that of long-chain unsaturated ones. On a high-energy surface (glass), tricaprylin showed an autophobic effect subsequent to molecular adsorption in trident conformation on the solid, observed with the three methods. Thin triglyceride films between an air bubble and a solid surface were stable for a short time, for solids with a surface free energy larger than the triglyceride surface tension. If the solid surface had a lower surface free energy, the thin film collapsed after a time interval which increased with triglyceride viscosity. Copyright 2000 Academic Press.

Π/ A isotherms of spread l -DPPC ( l -dipalmitoyl phosphatidylcholine) layers were determined up to the over-compressed state by using the captive bubble method. The influence of solvent vapour in the gas phase on the interfacial behaviour of monolayers was studied as traces of the spreading solution usually stay in the bubble. This was done for two cases; the pendant drop technique with spread 1-monoglyceride monolayer, where the partial pressure of solvents remains constant, and the captive bubble with spread l -DPPC layers, where the partial pressure increases during monolayer compression. Two cases of spreading solvents are distinguished: solvents, which do adsorb at the interface (chloroform), and those, which do not (heptane). Using a model, which takes into account only a small number of accessible parameters, the influence of none adsorbing solvents can be sufficiently described by an increasing cohesion pressure when the partial pressure remains constant. The influence of polar solvents may be quantified by a factor, which considers the apparent increase of the minimum molecular area demand. Spread DPPC monolayers determined by the captive bubble technique show a plateau in the range of about 50 mN m −1 , which depends on the amount of spreading solvent in the atmosphere of the bubble. By monolayer compression, the solvent molecules are squeezed out of the monolayer. Over-compression of the DPPC monolayer occur when all solvent molecules are removed and the surface tension further decreases down to almost zero. In contrast to monolayer collapse the surface pressure do not decrease abruptly for DPPC-layer expansion. This was explained by a monolayer-folding. Both, the process of squeezing out solvent molecules and the over-compression are accompanied by an apparent loss of DPPC molecules, indicated by a shift of the Π/ A isotherms to higher surface coverage. Monolayer cycling leads to a stepwise decrease of solvent molecules in the bubble atmosphere. The solvent molecules are assumed to be irreversibly incorporated into collapsed and lamellar structures, which may be formed by monolayer folds. Over-compressed collapsed or folded structures may be packed together and removed from the interface by forming visible particles. Lamellar structures are discussed as preliminary forms of liposomes, which may also incorporate solvent molecules, remove them during monolayer expansion from the interface, and causing an apparent loss of lipid molecules.

Contact angle measurements with captive bubbles have been used to quantify the wettability of different cellulosic materials in contact with pure water or aqueous protein solutions. The application of a new contact angle technique (axisymmetric drop shape analysis) in combination with atomic force microscopy permits new insights into the wetting behaviour of these hydrophilic surfaces. It was found that the unmodified cellulose membrane has a very smooth and homogeneous surface in the water-swollen state. There is almost no hysteresis between the advancing and receding water contact angles. The chemical modification of the cellulose with diethylaminoethyl groups results in a smooth but heterogeneous water-swollen membrane surface with fewer hydrophilic properties. A water-swollen cellulose acetate film was used as a model surface for wetting measurements with buffered protein solutions. It was found that different proteins (human serum albumin, fibrinogen) yielded different contact angles in their adsorbed state; after the adsorption of fibrinogen the contact angle of the pure aqueous buffer solution on the cellulose acetate was lower than the contact angle measured after the adsorption of human serum albumin.

The captive bubble method was used to describe the wetting characteristics of a number of commercial ultrafiltration (UF) membranes. The membranes belonged to one of two homologous (same material, different cut-off) series made by the same manufacturer. One series was made of polysulphone and the other one of cellulose triacetate. The porosimetric characteristics of the membranes have also been measured. The combined data were used to explain the fouling behaviour of the membranes upon ultrafiltration of solutions containing dextran, whey protein concentrate and silicate sols. The cellulose triacetate series is characterized by lower receding contact angle and smaller contact angle hysteresis and shows better flux behaviour (permeate flux during UF and pure water flux recovery at the end of UF) than the polysulphone series. Within the same series the mean permeability pore size shows a better correlation with membrane flux behaviour than with contact angle hysteresis.

Surface tension-area relations from pulmonary surfactant were obtained with a new apparatus that contains a leak free captive bubble of controllable size. Rat pulmonary surfactant was studied at phospholipid concentrations of 50, 200 and 400 micrograms/ml. At the highest concentration, adsorption was rapid, reaching surface tensions below 30 mN/m within 1 s, while at the lowest concentration, approximately 3 min were required. Upon a first quasi static or dynamic compression, stable surface tensions below 1 mN/m could be obtained by a film area reduction of approximately 50%. After three to four cycles the surface tension-area relations became stationary, and the tension fell from 25-30 to approximately 1 mN/m for a film area reduction of less than 20%. Hysteresis became negligible, provided the films were not collapsed by further area reduction. Under these conditions, the films could be cycled for more than 20 min without any noticeable loss in surface activity. After only three to four consecutive cycles, surfactant films exhibited the low surface tensions, collapse rates and compressibilities characteristic of alveolar surfaces in situ. Remarkably, surface tension and area are interrelated in the captive bubble which may promote low and stable surface tensions. If the surface tension of the captive bubble suddenly increases ('click') because of mechanical vibration or unstable surfactant, the bubble shape changes from flat to more spherical. The associated isovolumetric decrease in surface area prevents the surface tension from rising as much as it would have in a constant-area situation. This feedback mechanism may also have a favorable effect in stabilizing alveolar surface tension at low lung volumes.

Aerosil samples, heat treated and then silylated with various silanes at various temperatures have been characterised by adsorption of ethanol at 293 K. Adsorption isotherms were plotted and the BET specific surface areas were determined. Contact angles were measured by the captive bubble method at the three phase contact line in ethanol, on glass slides similarly modified. Silylation was found to alter the ethanol adsorptive properties on aerosil and increase the contact angles on the glass slides to extents that depend on the silane used as well as the concentration of residual silanols and that of surface silyl groups.

Shortage or malfunction of pulmonary surfactant in alveolar space leads to a critical condition termed respiratory distress syndrome (RDS). Surfactant replacement therapy, the major method to treat RDS, is an expensive treatment. In this paper, the effect of poly(ethylene glycol) (PEG) to improve dynamic surface activity of a bovine lipid extract surfactant (BLES) was studied by axisymmetric drop shape analysis (ADSA) and a captive bubble method. The activity of BLES + PEG mixtures was compared to that of a natural surfactant containing surfactant proteins A and D. When PEG was added into BLES mixtures, the surface tension hysteresis of BLES films was minimized when the films were compressed by more than 50%. PEG also helps to quickly restore surfactant films after film collapse. Thus, as far as surface tension effects go, the findings suggest that PEG might be used as a substitute for surfactant-associated protein SP-A in therapeutic surfactant products, and might also be used to reduce the amount of BLES required in clinical applications.

Fundamental and systematic studies were carried out to make clear the solution conditions where a marked effect of combined collectors on collection occurs in the non-sulfide flotation. Four kinds of collectors such as dodecylamine chloride (DAC), pottassium amyl xanthate (KAX), sodium oleate (NaO1), and sodium dodecylbenzene sulfonate (SDBS) were selected. In a series of flotation system where DAC is combined with one of the other three collectors, the floatability of scheelite was determined in terms of the collector concentration and the pH of solution by means of the captive bubble method. As a consequence, each combination gave a marked collection of the mineral even in the conditions where there is no collection at all by using a single collector alone. The combination of DAC-KAX resulted in the most remarkable collecting action among all the possible combinations. The DAC-SDBS combination was found to be most inferior in the cooperative effect. A remarkable joint effect of combined collectors is considered to be associated with the presence of collector neutral molecules in solution. Furthermore, surface-chemical study of the cooperative action of combined collectors in flotation was also performed by means of surface tension measurements. It was found that the scheelite floatability was closely related to the surface tension change of solutions.

The effect of humidity on the film stability of Bovine Lipid Extract Surfactant (BLES) is studied using the captive bubble method. It is found that adsorbed BLES films show distinctly different stability patterns at two extreme relative humidities (RHs), i.e., bubbles formed by ambient air and by air prehumidified to 100% RH at 37 degrees C. The differences are illustrated by the ability to maintain low surface tensions at various compression ratios, the behavior of bubble clicks, and film compressibility. These results suggest that 100% RH at 37 degrees C tends to destabilize the BLES films. In turn, the experimental results indicate that the rapidly adsorbed BLES film on a captive bubble presents a barrier to water transport that retards full humidification of the bubble when ambient air is used for bubble formation. These findings necessitate careful evaluation and maintenance of environmental humidity for all in vitro assessment of lung surfactants. It is also found that the stability of adsorbed bovine natural lung surfactant (NLS) films is not as sensitive as BLES films to high humidity. This may indicate a physiological function of SP-A and/or cholesterol, which are absent in BLES, in maintaining the extraordinary film stability in vivo.