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The material biocompatibility of hydrogel and silicone hydrogel (SiHy) contact lens (CL) is of paramount importance in CL wear because a decrease in CL wettability reduces wearer comfort and increases wearer dropout. The aim of this study is to report on the repeatability and agreement between two different software programs that measure the contact angle with the captive bubble method in marketed CLs, which will help to translate this information into clinical practice.The contact angle of 23 different CLs was measured with the captive bubble method using 2 software programs: FTÅ200 and ImageJ. Three consecutive measurements were conducted for each CL. Reproducibility, repeatability, and agreement values were calculated according to the British Standards Institute and the International Organization for Standardization.All methods showed good repeatability values in both CL materials (coefficient of variation1.51%, Sw2.26°, intraclass correlation coefficient0.89, and the range of limits of agreement was between 7.22° and 7.57°). Higher concordance was achieved between the spherical and nonspherical options when using FTÅ200 software than when using ImageJ software. Statistically significant differences (P0.05) between the 2 software programs were found, and they ranged between 5° and 10°.The captive bubble method showed great repeatability in measuring the contact angle in marketed CLs with both software programs (FTÅ200 and ImageJ) assessed in this study. However, differences in the measured contact angles suggest that these techniques are not interchangeable. Therefore, standardization is recommended for contact angle measurement in hydrogel CL materials to facilitate comparisons, to improve clinical use of this information, and to analyze their impact in CL user comfort.

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.

Metallic microchannels have been widely applied in two-phase heat transfer devices to satisfy the high heat flux cooling requirements of compact devices, but the pool boiling heat transfer and bubble dynamics over metallic microchannels have been rarely reported. Herein, we investigate the pool boiling heat transfer and bubble dynamics over V-shaped open microchannels prepared on copper by ultrafast laser micromachining. The open microchannels are of various channel widths, 100 μm and 50 μm, and of depth-to-width ratios varying from 0.5 to 2. In addition to the conventional methods used for studying boiling, we utilized the captive bubble method and the capillary tube method to analyze the bubble dynamics and the surface wickability, respectively. We find that for the microchannels with a channel width of 100 μm, the critical heat flux (CHF) and the heat transfer coefficient (HTC) increase with the increase of depth-to-width ratio; but the opposite trend is observed for the microchannels with a channel width of 50 μm. We propose that the surface wickability affects the boiling heat transfer more significantly with the increase of heat flux. For narrow and deep V-shaped microchannels, there is a mismatch between the bubble removal rate and the liquid supplying rate and thus leading to the deteriorated boiling heat transfer. We also demonstrate that the wickability of pyramidal microstructures is much higher than V-shaped microchannels. The CHF and HTC of pyramidal microstructures increase by 5-40% and 35-157%, respectively, compared to the V-shaped microchannels with identical structural spacing and depth.

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.

Reverse cationic flotation is the most known beneficiation method for the separation of fine hematite particles from silicates. In this process, the depression of the hematite surface is an essential factor. Thus, the development of environmentally friendly depressants plays a critical role. Tannin (TA) as a natural and eco-friendly organic reagent has not yet been considered for such a purpose. Through the reverse cationic flotation, the depression effect of TA was investigated by single and mixture of minerals. Micro-flotation tests and wettability analysis based on contact angle measurements by the captive bubble method (CBM) were conducted. The surface adsorption mechanism of TA on the hematite and quartz was explored through turbidity, zeta-potential measurements, surface adsorption tests, and Fourier transform infrared (FT-IR) analyses. The micro-flotation results indicated that TA could selectively depress more than 90% of hematite, while its effect on quartz floatability was negligible (

The interaction of the confined gas with solid surface immersed in water is a common theme of many important fields such as self-cleaning surface, gas storage, and sensing. For that reason, we investigated the gas-graphite interaction in the water medium. The graphite surface was prepared by mechanical exfoliation of highly oriented pyrolytic graphite (HOPG). The surface chemistry and morphology were studied by X-ray photoelectron spectroscopy, profilometry, and atomic force microscopy. The surface energy of HOPG was estimated by contact angle measurements using the Owens–Wendt method. The interaction of gases (Ar, He, H2, N2, and air) with graphite was studied by a captive bubble method, in which the gas bubble was in contact with the exfoliated graphite surface in water media. The experimental data were corroborated by molecular dynamics simulations and density functional theory calculations. The surface energy of HOPG equaled to 52.8 mJ/m2 and more of 95% of the surface energy was attributed to dispers...

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.

One of the most effective ways to reduce carbon dioxide (CO2) emissions is sequestration in geological reservoirs. CO2 sequestration in coal formations enhances the methane production from coalbeds (ECBM) in addition to storing CO2. CO2 can be stored in coalbeds in three ways: free gas phase in the pore space or the cleat network system, adsorbed molecules onto the organic surface of the coal, and dissolved in the groundwater within the coal. The performance of this process is dependent on the wettability behavior of the coal–water–CO2 system. This paper presents an investigation of the effect of the formation water salinity on the wettability behavior of highly volatile bitumen coal. The captive bubble method was used to measure the contact angle in coal–water–CO2 systems at pressures up to 2000 psi. The contact angle (CA) was measured at different NaCl concentrations (0–20 g/L). The CO2 adsorption isotherm on the coal surface was examined at different water salinities (0–20 g/L NaCl). Zeta-potential mea...

In this paper, a novel captive bubble method is designed to measure the liquid contact angle on the cementitious material surface. The surface free energy is calculated from the contact angle based on the Young’s equation. The experimental results show that cement pastes with different w/c ratios (0.3, 0.4, 0.5 and 0.6) share a highly similar adhesion work, although the components of surface free energies of samples change with increasing w/c ratio. To estimate the wettability of cement pastes, a critical surface energy is proposed to interpret the hydrophilic feature of the cementitious materials. Moreover, the interaction between sodium chloride solution and surface of the cement pastes is obtained, and the result shows a decline of the dispersion component for each specimen while values of polar components rise.

Both theory and experiments demonstrate that gas-wetness cannot always be overlooked and the gas-wet degree affects gas-well production greatly in gas condensate reservoirs. In the study, two quantitative methods have been introduced, the sessile drop and the captive bubble, and the corresponding wettability indexes, including gas-wetting parameter in the sessile drop method and gas contact angle in the captive bubble method. Gas-wetness of various substrates, such as Paraffin wax, plastics, glass, and iron plate, has been compared. Experimental results show that with the decrease of surface free energy, the hydrophobic and oleophobic and aerophily property gets enhanced. Particularly, air against water was preferentially wet on the Paraffin wax surface ( = 0.258, = 70.53°). Moreover, gas-wetness against water on the substrate surface is stronger than gas-wetness against oil on the same surface. The study is of great importance for study on gas-wetness.

This paper presents CO2-brine wettability of sandstones and minerals composing the sandstones. The measured contact angles are used further to analyse the effect of wettability on fines migration during CO2 injection. Limited data are available to assess the effect of minerals' wettability on fines migration. We use the captive bubble method to measure contact angle of CO2-brine on Berea and Obernkirchener sandstones, and their mineral components. X-ray powder diffraction (XRD) and x-ray fluorescence (XRF) analysis show that these sandstones consist primarily of five minerals: quartz, kaolinite, chlorite, microcline, and muscovite. All contact angles were measured under a pressure of 5.5 MPa–13.8 MPa at temperatures of 38 °C and 55 °C. Scanning electron microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) analyses are performed on mineral surfaces before and after measurements to examine surface changes after contact with CO2 and brine. The contact angle of the two types of sandstone indicates that their wettability was not clearly related to pressure and temperature. Quartz is found to be strong water-wet. Kaolinite, chlorite, and muscovite are found to be weak water-wet at 38 °C, whereas Microcline and muscovite show neutral-wettability at 55 °C. For chlorite, the contact angle is found to increase for the first 30 min, which is not observed for other minerals. SEM images reveal surface changes in kaolinite, chlorite, and muscovite after their exposure to CO2-saturated brine. SEM images also reveal heterogeneity in microcline sample, which accounts for the disagreement of our measurements with literature. For strong water-wet fines (contact angle

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

The oxidation state of the surfaces of titanium-based biomaterials strongly depends on their previous history. This factor affects the titanium wettability and it probably conditions the success of the implanted biomaterials. However, the separate role of the pollution and oxidation states of metallic titanium surfaces remains still controversial. To elucidate this, it is required to standardize the initial surface state of titanium in terms of roughness and surface chemistry, and then, to monitor its wettability after the corresponding treatment. In this work, we studied finely polished surfaces of commercially pure titanium (cpTi) which were subjected to cleaning surface treatments. X-Photoelectron spectroscopy was used to characterize the surface chemistry and the oxide film thickness. The contact angle hysteresis in underwater conditions was measured with the growing/shrinking captive bubble method, which allowed for mimicking the real conditions of implantable devices. The water wettability of smooth...

In this work, a modification to the captive bubble method was proposed to test the advancing and receding contact angle. This modification is done by adding a pressure chamber with a pressure control system to the original experimental system equipped with an optical angle mater equipped with a high speed CCD camera, a temperature control system and a computer. A series of samples with highly hydrophilic, hydrophilic, hydrophobic and superhydrophobic surfaces were prepared. The advancing and receding contact angles of these samples with highly hydrophilic, hydrophilic, and hydrophobic surfaces through the new methods was comparable to the result tested by the traditional sessile drop method. It is proved that this method overcomes the limitation of the traditional captive bubble method and the modified captive bubble method allows a smaller error from the test. However, due to the nature of the captive bubble technique, this method is also only suitable for testing the surface with advancing or receding contact angle below 130°. © 2014 Elsevier B.V. All rights reserved.

Gas-well production will be increased greatly after altering the wettability of porous media from preferential liquid-wetting to preferential gas-wetting in gas-condensate reservoirs. Moreover, the degree of gas wetness strongly affects the production. Thus, the study of gas-wet quantitative measurement methods is of great significance. The wetting ability parameter of gas versus liquid ζG-L is calculated from the proposed formula in the sessile drop method, and the gas contact angle θ G in the captive bubble method was separately used to measure gas wettability and propose the wettability criteria. Also, the concept of gas wettability was defined. After treated by fluorocarbon polymer (Zonyl8740), glass slides, and glass capillary tubes got tested on gas wetness. The results show that with the increase of the concentration of Zonyl8740 solution, the surface free energy of glass slides decreases and gas-wetness of them is enhanced. And capillary tube rise tests showed the same conclusion, demonstrating th...

The characterization of wetting properties (by contact angles) of several undersea artificial (glass plates,) and natural (stones, sand layers, soft-bottom structures, aquatic macrophytes, sediments, and seafloor communities) solid substrata in the Baltic Sea brackish water (Gulf of Gdansk). The studies were performed under laboratory and field conditions using a novel captive bubble air-pipette computer microscope system. A set of the surface wettability parameters: the apparent surface free energy γ SV , adhesive layer film pressure Π, work of adhesion W A , and work of spreading W S were determined to quantify the wetting properties of model substrata using the contact angle hysteresis (CAH) approach. The useful technique to measure in situ the contact angle giving reproducible and accurate values of CA turned out to be a captive bubble method, for fully hydrated interfacial layers of highly hydrophilic and porous nature met at seabed ( Rodrigues-Valverde et al., 2002 ). CA measurements revealed mostly hydrophilic nature of the studied solid material (CA SV ↓,W A ↓, W S more negative). The adhesion of biofouling was correlated both with CAH and the dispersive interaction term γ SV d of the total γ SV . Monitoring of the artificial substrata of the hydrophilic nature with a CA technique can be used to observe the development of the organisms community i.e., microfouling, and to carry out a comprehensive study of surfaces of the submerged macrophytes ( Potamogeton lucens in particular). Since aquatic macrophytes can act as bio-indicators of water chemistry their surface wettability may reflect plant surface erosion and organic matter accumulation state being of particular value in biological assessment of ecosystems status.

UNLABELLED The ability of food gels to hold water affects product yield and organoleptic quality. Most researchers believe that water is held by capillarity such that gels having smaller mean pore diameter and a more hydrophilic surface hold water more tightly. To date, however, only qualitative evidence relating pore size to water holding (WH) properties has been provided. The present study sought to provide quantitative confirmation of this hypothesis. Scanning electron microscopy coupled with image analysis was used to measure pore size, and water contact angle with the gel surface was measured by the captive bubble method, in both model polyacrylamide gels and heat-induced protein (minced chicken breast) gels. These were related to water lost during cooking of meat pastes to form gels (cooking loss (CL)), as well as water lost upon centrifugation (expressible water (EW)) or by capillary suction (CSL) of all prepared gels, as inverse measures of WH. As predicted by the Young-Laplace equation for calculating capillary pressure, the presumed mechanism of WH, gels with lower water losses exhibited a more hydrophilic surface (smaller contact angle). Yet, both lower CL and CSL correlated with larger mean pore diameter of gels, not smaller as had been expected. Polyacrylamide gels varied more in WH than did prepared meat gels, yet only the capillary suction method was sensitive enough to detect these differences. PRACTICAL APPLICATION The ability of gels to hold water is important for economics of processing, food quality, and food safety. This study investigated the prevailing theory for how gels hold water, capillarity. Both the pore sizes of gel microstructures and the degree of hydrophilicity of the polymers comprising each gel were quantitatively assessed and related to water holding (WH) properties, and this was the first report using such methodologies. It appeared that the degree of hydrophilicity was much more important explaining WH properties than pore size, and that future research of this kind should be carried out.

Contact angle measurement is conducted to determine surface hydrophilicity of RO membrane with the intention of predicting membrane performance or fouling potential. Most researchers of membrane technology have used contact angles without considering effective factors for contact angle measurement such as measurement time, drop volume and membrane sample preparation. In fact, significantly different contact angles are reported even on the same RO membrane. In this study, contact angles were measured by the sessile drop method and captive bubble method and were compared with various conditions such as measurement time, drop volume, membrane sample preparation and liquid type in the commercialized RO membranes. As a result, sessile drop method showed unreliable contact angles, which varied dramatically with the preparation conditions. On the other hand, the captive bubble method, which represents conditions closer to the real RO membrane process, showed reproducible contact angles. For the different commercially available RO membranes, similar hydrophilicity was observed. Overall, the captive bubble method appears to be a more adequate method for measuring contact angle of RO membranes.

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 ...

Porous silica thin films were prepared on silicon wafers by an aerosol flame deposition (AFD) process, and dependence of their characteristics on sintering temperature was investigated. At sintering temperatures ranging from 1270 °C to 1320 °C, films with continuous micro-pores were deposited. As the sintering temperature increased, the pores of the film were getting smaller with more uniform distribution and the thickness and surface roughness decreased. The films were found to be hydrophilic when tested by the sessile drop method and the captive bubble method. And, zeta potentials of the films in a KCl solution sharply decreased to the minimum value at pH 8 and increased again as pH increased. The minimum value for the film prepared at sintering temperature of 1320 °C was −87 mV.

This work sought to undertake a comprehensive investigation of the measurement errors associated with contact angle assessment of curved hydrogel contact lens surfaces. The contact angle coefficient of repeatability (COR) associated with three measurement conditions (image analysis COR, intralens COR, and interlens COR) was determined by measuring the contact angles (using both sessile drop and captive bubble methods) for three silicone hydrogel lenses (senofilcon A, balafilcon A, lotrafilcon A) and one conventional hydrogel lens (etafilcon A). Image analysis COR values were about 2 degrees , whereas intralens COR values (95% confidence intervals) ranged from 4.0 degrees (3.3 degrees , 4.7 degrees ) (lotrafilcon A, captive bubble) to 10.2 degrees (8.4 degrees , 12.1 degrees ) (senofilcon A, sessile drop). Interlens COR values ranged from 4.5 degrees (3.7 degrees , 5.2 degrees ) (lotrafilcon A, captive bubble) to 16.5 degrees (13.6 degrees , 19.4 degrees ) (senofilcon A, sessile drop). Measurement error associated with image analysis was shown to be small as an absolute measure, although proportionally more significant for lenses with low contact angle. Sessile drop contact angles were typically less repeatable than captive bubble contact angles. For sessile drop measures, repeatability was poorer with the silicone hydrogel lenses when compared with the conventional hydrogel lens; this phenomenon was not observed for the captive bubble method, suggesting that methodological factors related to the sessile drop technique (such as surface dehydration and blotting) may play a role in the increased variability of contact angle measurements observed with silicone hydrogel contact lenses.

Contact angle measurement has been an indispensable tool for surface characterization and wetting study due to its simplicity and versatility. In this chapter, major measurement techniques for static contact angle, sliding angle, and advancing/receding angle are overviewed. Critical procedural details including sessile-drop dispensing, drop size, drop profile capturing, and analysis are highlighted and discussed. Best practices on measuring sliding and advancing/receding angles are recommended with support of publications from leading researchers. It is our hope that the techniques described within will be used as guidelines for the research community.

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.

In this study, the surface characteristics of three major materials which are widely used in food industry, glass, polyethylene (PE) and stainless steel (SS 316), were studied. The hydrophilicity, hydrophobicity and surface free energy (SFE) of those surfaces were determined by contact angle measurements prior and after plasma polymerisation treatment. The modification of the surfaces was carried out at low pressure and low temperature plasma conditions by using different monomers with functional properties. Phenol and 1,1,1,3,3,3-hexaflouroisopropylacrylate (HFIPA) were used to produce hydrophobic materials with low surface energy, and hydroxyethylmethacrylate (HEMA), ethylenediamine (EDA), polyethyleneglycolethylethermethacrylate (PEGEEMA) and polyethyleneglycolmethacrylate (PEGMA) were used to produce hydrophilic materials with higher surface energy. The effects of monomer flow rate, exposure time and discharge power parameters were optimized by comparing surface characteristics before and after plasma polymerisation treatments. Contact angle measurements were performed by using the captive bubble technique, and the geometric mean equation was used to calculate the surface free energy values. Air and n-octane bubbles with different polarity were used to determine the changes on the surface energy including the dispersive and polar components. Polyethylene was the most hydrophobic material among the materials used in this study related to its air contact angle and γsw values. γsw value was found 38.91 mJ/m2 for polyethylene. Glass was determined as the most hydrophilic material (γsw: 1.11 mJ/m2) among the used surfaces, and its surface energy (γsv) was 58.95 mJ/m2. The contact angle and SFE values were affected by monomer flow rate, exposure time and power parameters used for all modification processes. The equilibrium between etching and deposition processes can be controlled by these plasma parameters. Therefore, we tried to optimize plasma parameters according to the results from contact angle and surface energy data.

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.

Palliative treatment for obstructive jaundice by endoscopic biliary stent insertion is a recent commonly used method. Unfortunately, stent reobstruction may occur within 3 to 6 months as a result of bacterial adhesion and formation of biofilm. Bacterial adhesion was postulated as the initial step of stent clogging and the bacterial enzyme activity of β-glucuronidase led to the deposition of calcium bilirubinate. In this study, surface sulfonation of the polyethylene lumen was postulated to improve the patency of the biliary stent. Surface modification with sulfonated group formation was carried out with fuming sulfuric acid containing 20 wt % sulfuric trioxide (SO3). The reaction time varied from 1 to 3 h at room temperature. ATR-FTIR and ESCA techniques showed that the surface amount of sulfonated functionalities increased with sulfonation time. The contact angle of the sulfonated PE, determined by the sessile drop technique, decreased compared to that of unmodified PE, but cannot be detected by the captive bubble method because of the high surface hydrophilicity. SEM micrographs indicated that the sulfonated PE inner lumen remained relatively smooth after extended sulfonation reaction. Adhesion of Escherichia coli to the sulfonated PE stents after 48-h bile perfusion was about 10- to 20-fold less than that to the unmodified PE, as observed by SEM and surface spreading method. These results indicated that the surface sulfonated groups could effectively decrease the adhesion of E. coli in human bile, probably attributable to the hydrophilic repellence between the bacterial cell membrane and sulfonated groups. This finding suggested that the sulfonated PE tubing could prolong the patency period of plastic stents and may be of great potential as a biliary stent in a real clinical setting. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2450–2457, 2004

Cell attachment and spreading to titanium-based alloy surfaces is a major parameter in implant technology. In this paper, substratum surface hydrophobicity, surface free energy, interfacial free energy and surface roughness were investigated to ascertain which of these parameters is predominant in human fibroblast spreading. Two methods for contact angle measurement were compared: the sessile drop method and the captive bubble two-probe method. The relationship between surface roughness and the sessile drop contact angles of various engineered titanium surfaces such as commercial pure titanium (cp-Ti), titanium–aluminium–vanadium alloy (Ti–6Al–4V), and titanium–nickel (NiTi), was shown. Surface free energy (SFE) calculations were performed from contact angles obtained on smooth samples based on the same alloys in order to eliminate the roughness effect. SFE of the surfaces have been calculated using the Owens–Wendt (OW) and Van Oss (VO) approaches with the sessile drop method. The OW calculations are used to obtain the dispersive (γd) and polar (γp) component of SFE, and the VO approach allows to reach the apolar (γLW) and the polar acid–base component (γab) of the surface. From captive bubble contact angle experiments (air or octane bubble under water), the interfacial free energy of the different surfaces in water was obtained. A relationship between cell spreading and the polar component of SFE was found. Interfacial free energy values were low for all the investigated surfaces indicating good biocompatibility for such alloys.

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.

The interfacial charge formation of self-assembled monolayers (SAMs) of thiol derivatives on gold was investigated by streaming potential and streaming current measurements in aqueous electrolyte solutions. All experiments were performed at a slit channel formed by two parallel sample plates. For the first time, ζ potentials of planar SAM−solution interfaces were determined experimentally. Surface pK values were calculated from the pH dependence of the ζ potential. Monolayers carrying ω-carboxylic moieties show a shift of the pK toward the alkaline direction as compared to the carboxy-terminated alkanethiol molecules in solution. Contact angle titrations using a captive bubble method confirmed the dissociation behavior of monolayers with acidic groups. Monolayers of methyl-terminated thiols exhibit ζ potential−pH plots that account for unsymmetrical ion adsorption. Models of the electric double layer are discussed to describe the interface between self-assembled monolayers and electrolyte solutions. Two c...

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.

A new general approach for improving polymer substratum biocompatibility is proposed. In a first example, polysulfone (PSf) film was modified by covalent end-on grafting of poly(ethylene glycol) (PEG) (2, 5, and 10 kDa) using well-defined, photoreactive α-4-azidobenzoyl β-methoxy PEG conjugates (ABMPEG). After adsorption from aqueous solution, ABMPEG was photografted under wet conditions onto PSf, where the degree of surface functionalization could be controlled through the applied ABMPEG concentration during adsorption. Attained surface characteristics, after changing systematically ABMPEG concentration, molecular weight, and the ratio of binary ABMPEG mixtures, were monitored by air−water contact angles (CA, captive bubble method) and partially also by X-ray photon spectroscopy (XPS). For ABMPEG 10 kDa adsorption kinetics and grafting efficiency as a function of applied concentration were evaluated by both CAs and fibronectin (FN) adsorption (in situ ellipsometry) to surfaces modified at different degre...

Two different methods for investigating monolayer properties are presented, the micro-film balance and the captive bubble method. Both require the elimination of traces of the spreading solvent in the atmosphere, as in the micro-film balance experiment a drop is kept in a small hermetically closed chamber and in the captive bubble method the monolayer is spread inside a bubble. The influence of different organic spreading solvents on the surface tension at the air/water interface was checked for the two methods. The surface tension of water was measured by the micro-film balance when exchanging the air in the chamber after spreading. Using a small amount of methanol as solvent, similar results in the captive bubble experiments are obtained. In the presence of a monolayer, traces of solvents interact with the monolayer molecules and can be removed only immediately after spreading. In such cases, a good agreement with surface pressure isotherms determined by a Langmuir trough is achieved. When different amounts of chloroform, heptane and methanol are evaporated in the cell atmosphere, the π/A isotherms of 1-monoglycerid monolayers change dramatically up to atmosphere saturation by the hydrocarbons. These changes could not be removed by air exchange in the cell. Therefore, the micro-film balance is applicable in investigating interactions between monolayer and gas phase. Taking into account these results, dipalmitoyl phosphatidylcholine monolayers were investigated by both the captive bubble and the micro-film balance. The results of both methods are in good agreement when the methodological requirements stated above are met.

Purpose: To present contact-angle measurements of commercially available intraocular lenses (IOLs) in air and in water to facilitate the understanding of how various OLs might interact in different environments. Setting: Laboratory. Methods: Five commercially available IOLs were studied: AMO® DuraLens® PS-59NB™, AMO PhacoFlex® SI-26NB™, AMO PhacoFlex II® SI-30NB®, Chiron® ChiroFlex® C10UB, and Alcon® AcrySof® MA60BM. The AMO soft acrylic model AR40™, currently under clinical study, was also evaluated. Contact-angle measurements were made in air and in water using sessile drop and captive bubble methods. Results: The sessile drop method indicated that all materials were hydrophobic in air. The captive bubble method differentiated materials based on their polar and dispersive forces. Conclusion: Contact-angle measurements differed depending on the test conditions. Proper choice of contact-angle measurement method can generate useful information about a material surface and its potential biomaterial interactions.

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.

For measuring the properties of lung surfactant, we provide formulas for calculating the surface tension, area, and volume of captive air bubbles in aqueous media. Only measurements of bubble height (h) and diameter (d) are required. Data processing has been automated using standard video capture hardware and software, and our own image-processing and -analyzing programs. Our polynomials in h/d describe the ratios of actual bubble surface area and volume to that of a spherical bubble having the same diameter. For surface tension, a polynomial in h/d describes the ratio of the surface tension of a flat semi-infinite bubble to the surface tension of the measured bubble of the same height. Coefficients for the area and volume polynomials were obtained from h and d, and measured areas and volumes of revolution of calibrating bubbles. Coefficients for the surface tension polynomial were obtained analytically from a published polynomial in h/d [3]. Results using these polynomials agree satisfactorily with those obtained independently [4] using bubble perimeter measurements.

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.