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Platinum cure for poly(dimethylsiloxane) (PDMS) coatings on a thermal gradient (45-140 °C) was carried out to study the effect of temperature on surface chemistry and wetting behavior. The motivation is the interest in surfaces with continuous gradients in wettability for applications such as protein adsorption, controlling bacterial adhesion, directional movement of cells, and biosensors. The Wilhelmy plate method and the advancing/receding drop method were employed for determining the positional dependence of θA and θR. A strong dependence of receding contact angles (θR) on cure temperature was found for Sylgard 184 (S-PDMS) and a Pt-cured laboratory-prepared analogue (Pt-PDMS) of known composition. Cure on the thermal gradient gave rise to striking "Big Dipper" Wilhelmy plate dynamic contact angle curves. High contact angle hysteresis (60-80°) was found for 45 °C cure (CAH = θΔ = θA - θR) but low CAH for 140 °C cure (10-20°). Drop addition/withdrawal using goniometry identified a similar trend. Attenuated total reflectance infrared spectroscopy showed absorptions for Si-OH (3500 cm-1) and Si-H (1250 cm-1) that were correlated with wetting behavior and near-surface chemistry. These studies revealed a complex relationship among hydrosilylation, Si-H autoxidation, and condensation of Si-OH. A model for advancing from a single network due to hydrosilylation to a double network for hydrosilylation plus Si-O-Si from condensation of Si-OH best explains evidence from spectroscopic and contact angle studies. These results are relevant to interactions of Pt-cured silicones at bio-interfaces, as receding contact angles determine work of adhesion, as well as applications that benefit from maximum hydrophobicity and minimizing water roll-off angles.

The densities and surface tensions of [Bmim][TFO]/H2SO4, [Hmim][TFO]/H2SO4 and [Omim][TFO]/H2SO4 binary mixtures were measured by pycnometer and Wilhelmy plate method respectively. The results show that densities and surface tensions of the mixtures decreased monotonously with increasing temperatures and increasing ionic liquid (IL) molar fraction. IL with longer alkyl side-chain length brings a lower density and a smaller surface tension to the ILs/H2SO4 binary mixtures. The densities and surface tensions of the mixtures are fitted well by Jouyban–Acree (JAM) model and LWW model respectively. Redlich−Kister (R–K) equation and modified Redlich−Kister (R–K) equation describe the excess molar volumes and excess surface tensions of the mixtures well respectively. Adding a small amount of ILs (xIL

Exhaled air contains submicron droplets of alveolar lining fluid (ALF), which are generated in the small airways of human lungs and are in fact ALF micro-samples. The trapping of these droplets makes it possible to collect a native material from respiratory tract in a non-invasive manner, which holds great promise for lung diagnostics. In this work, we present an aerosol droplet sampling technique based on the exhaled breath barbotage (EBB) procedure. The proposed technique offers a unique opportunity to accumulate pulmonary surfactant (PS), a major constituent of ALF, on a liquid surface. The Wilhelmy plate method was used to measure the variation of the surface pressure over the surface area for the EBB samples collected in a Langmuir trough. A data processing algorithm was derived to evaluate the surface pressure ( π ) – surface concentration ( Γ ) isotherm from the raw data. With this algorithm, one can restore the isotherm even in the case when the amount of surfactant adsorbed on the surface is unknown. The ( π − Γ ) isotherms found for the samples collected in the groups of healthy volunteers and patients with pulmonary tuberculosis were compared with the isotherms obtained for artificial PS. It has been established that the isotherms measured for healthy people and artificial surfactant coincide, and the isotherms obtained in the TB group have lower inclination, which is indicative of a lower surface activity. The EBB method developed in this study can be used as a diagnostic tool for assessment of the functional status of PS in screening tests and subsequent treatment.

The density and surface tension values are presented that represent the best current knowledge of these properties for members of the homologous series of 1-C n -3-methylimidazolium chlorides. To identify these values, a method was used based on the consistency requirement between selected background experimental data and group contribution models of known best achievable accuracy. The models have been developed using our own and other authors' data. For this purpose 64 and 119 new experimental data on the density and surface tension, respectively, have been measured for [C 1 IM][Cl] and [C n MIM][Cl] with n = 2 , 3, 4, 6, and 10 at temperatures from (263 to 365) K and at the pressure of 0.1 MPa. The density was measured using the buoyancy method while the surface tension was measured by the Wilhelmy plate and du Nouy ring method in parallel. The respective expanded combined uncertainties at the 0.95 confidence level of the resultant means of sets of individual measurements performed at a given temperature do not exceed 1 kg ⋅ m −3 , 0.07 mN ⋅ m −1 and 1 mN ⋅ m −1 . The estimated maximum deviations of the obtained recommended values from the true density and surface tension values are 0.1 kg ⋅ m −3 and 0.15 mN ⋅ m −1 , respectively.

Foreign cations are shown to cause mass transport losses, in particular due to wettability changes in the micro-porous layers (MPL) and the carbon paper substrate, and have a major impact on the durability and the performance of polymer electrolyte fuel cells. We studied the effects of cationic impurities on fuel cell system performance, especially on the water management by employing in-situ and ex-situ contamination methods. Changes in the wettability of the carbon paper surface following the in-situ contamination injection were quantified using the Wilhelmy plate method. The CaSO 4 precipitation on the macro-pores of the carbon paper substrate after the contamination injection causes a higher wettability leading to increased flooding of the carbon paper substrate and consequent mass transport losses. An ex-situ cleaning with an acid solution is shown to be very effective in removing the salt deposits of the carbon paper substrate. During the mitigation, the highly hydrophobic MPL acts as a barrier to the transport of the recovery solution into the membrane-electrode assembly (MEA), therefore isopropanol (IPA) was added to both the contaminant solution and the recovery solution to increase the wettability of the MPL. Wetting force measurements confirm that the added IPA can alter the wettability of the MPL and can render it fully hydrophilic, enabling the transport of the recovery solution into the MEA.

Currently available dynamic surface tension (DST) measurement methods, such as Wilhelmy plate, droplet- or bubble-based methods, still have various experimental limitations such as the large size of the interface, convection in the solution, or a certain “dead time” at initial measurement. These limitations create inconsistencies for the kinetic analysis of surfactant adsorption/desorption, especially significant for ionic surfactants. Here, the “micropipette interfacial area-expansion method” was introduced and validated as a new DST measurement having a high enough sensitivity to detect diffusion controlled molecular adsorption at the air-water interfaces. To validate the new technique, the diffusion coefficient of 1-Octanol in water was investigated with existing models: the Ward Tordai model for the long time adsorption regime (1–100 s), and the Langmuir and Frumkin adsorption isotherm models for surface excess concentration. We found that the measured diffusion coefficient of 1-Octanol, 7.2 ± 0.8 × 10−6 cm2/s, showed excellent agreement with the result from an alternative method, “single microdroplet catching method”, to measure the diffusion coefficient from diffusion-controlled microdroplet dissolution, 7.3 ± 0.1 × 10−6 cm2/s. These new techniques for determining adsorption and diffusion coefficients can apply for a range of surface active molecules, especially the less-characterized ionic surfactants, and biological compounds such as lipids, peptides, and proteins.

Pyridinium-based cations are the second most frequently occurring cations in the commonly studied ionic liquid mixtures - a new prospective field just opened for the property tuning of substances of practical use. To this purpose, a sufficiently accurate knowledge of the properties of pure components is necessary. Presented here are results of a study of the surface tension and 0.1 MPa densities for members of four homologous series consisting of a 1-alkyl-pyridinium or 1-alkyl- m -methylpyridinium cation with m = 2, 3, or 4 and of the bis(trifluoromethylsulfonyl)imide anion. Empirical models are presented, based on the parachor and group contribution approach, which generate recommended surface tension and 0.1 MPa density values for ionic liquids from the studied homologous series including those for which no experimental data are available. The models have been developed both on the basis of data from the literature and on our own data for four ionic liquids with a pyridinium-based cation bearing a propyl side-chain, yet studied poorly in those two respects or even not at all. The presented density data were measured using the buoyancy method with an estimated combined expanded uncertainty at the 0.95 level of confidence U c = 0.8 kg m −3 ( 6 ⋅ 10 − 4 ϱ ) at the most. The du Nouy ring method and the Wilhelmy plate method were used to obtain the data on the surface tension with U c near (0.2 and 0.05) mN m −1 , respectively. The surface tension and buoyancy forces were measured at temperatures from (263 to 365) K using the Krűss K100 Mk2 tensiometer. The deviation of the recommended surface tension and density values from their true values is estimated not to exceed 0.3 mN m −1 and 0.15%, respectively.

The dynamic surface activity in solutions and dynamic spreading on low-energy surfaces of isotridecanol ethoxylates with two different units were investigated by using the Wilhelmy plate, maximum bubble pressure, and contact angle method. The dynamic surface activity was analyzed by using the classical Rosen model, and the dynamic spreading was depicted by decay function. The equilibrium contact angle (θe value) and the spread rate (K value) were suggested to evaluate effectiveness and efficiency of spreading.

This review summarizes some common methods for determining the wettability of powders, especially the contact angle that a liquid would form on powders. The sessile drop, Wilhelmy plate and liquid penetration methods are then briefly compared, especially on the advantages and disadvantages of these techniques. The later part of the review summarizes some experimental details in determining wettability of powders utilizing liquid penetration into a packed column or the Washburn capillary rise (WCR) method based on liquid mass uptake. The discussion is focused on the selection of capillary tube for packing, bottom support, powder properties, reference wetting liquid, and packing method. How each of these parameters influences mass uptake and subsequent wettability determination are also presented, followed with the applicability of mass based WCR for determining the wettability of some powders. The intent of this review is to provide researchers a guide on the proper selection of the method and then the associated details when they apply the mass based WCR experiments for deducing the wettability information of the powders of interest.

Saponins from various botanical origins highly differ in molecular structure. Little is known of the influence of structural differences between the different saponins on interfacial tension, short-term adsorption and foam properties at the air-water interface (a/w). In this study five triterpenoid saponins, with three of these being monodesmosidic and two bidesmosidic as well as one steroid saponin, were analyzed. Interfacial tension isotherms were measured using a tensiometer with a Wilhelmy plate and were fitted using the modified Frumkin model. For characterization of the short-term adsorption at the a/w-interface, two-fluid needle experiments were performed. Foaming, foam stability and foam structure were analyzed using a foaming device. A new method for semi-quantitative analysis of different foam structures was established. Additionally the impact of pH and ionic strength (addition of NaCl) on interfacial tension and foam properties were determined. The short-term adsorption of all saponins was limited by an additional barrier and was not diffusion-limited. Extracts from Quillaja saponaria Molina (QS), Gypsophila (GYP), Camellia oleifera Abel (TS) and Aesculus hippocastanum (ESC) lowered the interfacial tension to 37–42 mN/m and produced stable foams. The steroid saponin from Tribulus terrestris (TT) and the monodesmosidic saponin from Glycyrrhiza glabra (GA) had only poor interfacial and foam properties. Foams made from QS and GYP were only little affected by changes in pH and ionic strength. A reduction of the pH from 5 to 3 increased stability of foams made from GA significantly. Foams made from ESC and TS were negatively affected by increasing ionic strength.

Experimental data over the temperature range from (283 to 365) K are presented on the 0.1 MPa density and (air + liquid) interfacial tension for three 1- C n -3-methylimidazolium iodides with n = 3 , 4, and 6 still poorly or even not studied in these respects at all. The reported density data were obtained using a single-sinker buoyancy method with an estimated combined expanded uncertainty at 0.95 confidence level U c = 1.0 kg · m−3 ( 7 · 10 - 4 ϱ ). The surface tension data were obtained by the Wilhelmy plate method with U c = 0.08 mN · m−1 and by du Nouy ring method with U c = 0.3 mN · m−1. The Krűss K100MK2 tensiometer was used to determine the buoyancy and surface tension forces. The density data obtained for the three studied ionic liquids match a single common group contribution model within their experimental uncertainties, which indirectly supports the data validity. Similar single common model for the surface tension data, based on the parachor, results in two times greater average absolute relative deviation of the data than provide empirical models developed for each ionic liquid separately. For the CH2 parachor group contribution a value of 32.8 (mN · m−1)1/4 mol · cm−3 was obtained, based on surface tension and density data for 33 ionic liquids at T = 298.15 K.

The Langmuir monolayer at an air–water interface shows remarkably different surface pressure (π)–area (A) isotherm, when measured with the surface normal of a Wilhelmy plate parallel or perpendicular to the direction of compression of the monolayer. Such difference arises due to difference in stress exerted by the monolayer on the plate in different direction. In this article, we report the effect of changing the direction of substrate normal with respect to the compression of the monolayer during Langmuir–Blodgett (LB) film deposition on the morphology of the films. The morphology of the LB film of stearic acid is studied using an atomic force microscope. The morphology of the LB films is found to be different due to difference in the stress in different directions. The role of such surface morphology on the alignment of a nematic liquid crystal (LC) in LC cells is studied. The granular texture of LB films of stearic acid supports the homogeneous alignment of the LC whereas the uniform texture supports the homeotropic alignment of the LC.

Organic solutes tend to lower the surface tension of cloud condensation nuclei, allowing them to more readily activate. The surface tension of various dicarboxylic acid aerosol mixtures was measured at 20 °C using the Wilhelmy plate method. At lower concentrations, the surface tension of a solution with equi-molar mixtures of dicarboxylic acids closely followed that of a solution with the most surface-active organic component alone. Measurements of surface tension for these mixtures were lower than predictions using Henning's model and the modified Szyszkowski equation, by ∼1–2%. The calculated maximum surface excess (Γ max ) and inverse Langmuir adsorption coefficient ( β ) from the modified Szyszkowski equation were both larger than measured values for 6 of the 7 mixtures tested. Accounting for the reduction in surface tension in the Kohler equation reduced the critical saturation ratio for these multi-component mixtures – changes were negligible for dry diameters of 0.1 and 0.5 μm, but a reduction from 1.0068 to 1.0063 was seen for the 4-dicarboxylic acid mixture with a dry diameter of 0.05 μm.

This paper describes an improved hydrometer calibration method using a ring type sinker as a reference standard mass. This calibration method can be used for any surface tension and reference temperature design of hydrometer. A suitable dimension of standard ring was used to sink hydrometers into distilled water. The distilled water was used as standard liquid, traceable to a standard solid density determined by hydrostatic weighing method. A tensiometer consisting of balance and Wilhelmy plate was used to measure the surface tension of the distilled water. The calibration results showed an improvement in the calibration range between 0.600 g/ml and 1.000 g/ml with uncertainty in the order of 0.0002 g/ml for hydrometers with scale graduations of 0.0005 g/ml. The differences in measured scale corrections of this method compared to the comparison method indicate a bias smaller than half of the hydrometer graduation. In comparison, this method offers simpler, cheaper calibration with accuracy comparable to other existing hydrometer calibration methods. Furthermore, no harmful chemicals were used as standard liquid especially mixtures of volatile hydrocarbons or aqueous solutions of acids.

Surface tension data were measured by the Wilhelmy plate method for the binary mixtures containing an ionic liquid of the imidazolium dialkylphosphate family and water (methanol or ethanol) at 298.15 K and atmospheric pressure. The enthalpy of vaporization Δ1gHmo and Hildebrand solubility parameter δH for the pure components are estimated from the experimental data, and a perfect correlation is found between surface tension and specific cohesive energy per unit surface area for the imidazolium dialkylphosphate series ionic liquids (ILs). The surface tension as well as the surface tension deviation against the solution composition shows a remarkable difference between the mixtures of an IL with water and with alcohols, which is interpreted qualitatively by the δH values of the corresponding pure components. Some ILs act as a surfactant in aqueous solution, but most of them more like a conventional nonelectrolyte component in the alcoholic solutions.

Experimental data over the temperature range from 263 to 363 K are presented on the air–liquid interfacial tension and 0.1 MPa densities for four ionic liquids with the tris(pentafluoroethyl)trifluorophosphate (FAP) anion and with the 1-(2-methoxyethyl)-1-methylpyrrolidinium, 1-(2-methoxyethyl)-1-methylpiperidinium, N-(3-hydroxypropyl)pyridinium, and 1-(2-hydroxyethyl)-3-methylimidazolium cations. The surface tension data were obtained by the Wilhelmy plate method with an estimated combined expanded uncertainty at 0.95 confidence level of ±0.2 mN m−1. The reported density data were obtained using a single-sinker buoyancy method with an estimated expanded combined uncertainty at 0.95 confidence level ±0.8 kg m−3 (4.6 × 10−4ϱ). The Krűss K100MK2 tensiometer was used to determine the surface tension and buoyancy forces. A value of 224.79 cm3 mol−1 follows for the FAP anion contribution to the ionic liquids molar volume at 298.15 K and 0.1 MPa from the group contribution analysis of the density data. In contrast to the common organic liquids, the studied ionic liquids show a negative value of the temperature derivative of the isochoric thermal volume expansion coefficient in the studied temperature interval.

In this work the studies were performed on the intensity of fouling of the membrane NF90 and NF270 depending on the value of dynamic contact angle, previously determined for these membrane. The NF membranes were used for the separation of broth obtained during the fermentation of glycerol by Lactobacillus casei bacteria. The measurements of dynamic contact angle were carried out using the Wilhelmy plate method. Taped membranes samples (support layer to support layer), wetted for 2 days in deionized water prior to testing, were used to study the contact angle of top layer and its organic fouling. Using deionized water; the contact angle values equal to 27-30o and 53-57o for NF270 and NF90, respectively, were obtained. As a consequence of adsorption of organic compound on the membrane surfaces, the contact angle obtained for both fouled membranes was about 55-56o, and this value was closer to the contact angle of non-fouled NF90 membrane. Therefore, the NF90 membrane was more resistant to organic fouling during the separation of broth.

Experimental air–liquid interfacial tension data and density data are presented for three 1-Cn-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphates (FAP), [CnMIM][(C2F5)3PF3], with n = 2, 4, and 6, measured at atmospheric pressure in the temperature range from 267 K to 360 K using the Krűss K100MK2 tensiometer. The accuracy of the surface tension measurements was checked by employing the Wilhelmy plate and the du Nouy ring methods in parallel. The combined standard uncertainty associated with the Wilhelmy plate method is estimated to be ±0.1 mN · m−1. The density data were obtained using buoyancy method with an estimated standard uncertainty less then ±0.4 kg · m−3 (3 · 10−4ϱ). The chloride anions decrease the density of the tris(pentafluoroethyl)trifluorophosphates of interest up to six times more effectively than they decrease the density of the imidazolium based tetrafluoroborates. A QSPR analysis of the surface tension of imidazolium based ionic liquids with BF4, TFA, DCA, FAP, NTf2, and PF6 anions indicates, that the FAP ionic liquids fit well into the analyzed group of imidazolium based ionic liquids while those having hexafluorophosphate anion show anomalously high deviations of the experimental surface tension from the values predicted by the QSPR model.

Wettability is related to forces or surface tensions (σ) acting at the solid–liquid–vapor interface. Given that surface tensions are difficult to assess directly, contact angles (CA) are used as indicators of the balance of forces acting in the system. In this context, the ES theory was developed as an alternative to assess the σ parameters of the Young's equation. This research evaluates the applicability of a proposed equation of state (ES), which is in theory also able to predict the CA of a sample when two σ parameters of the Young's equation and two fitting parameters (β and α) of the function Φ = (σSL) are known (Φ: molecular interaction parameter, σSL: solid–liquid surface tension). These parameters were determined by different experimental methods assessing the CA, in order to determine which method is more suitable to validate the ES theory: Capillary Rise Method (CRM) and Wilhelmy Plate Method (WPM). For WPM, two modes (advancing and equilibrium CA) were applied. Finally, results of CA between the experimental measurements obtained by WPM and those predicted by the ES were compared. Samples of coarse silt, fine sand, and nonporous glass beads with different levels of water repellency were used as test materials. In line with previous research, all methods showed lower values of σ for samples with increasing hydrophobicity. At the same time, Φ reduces consistently with higher hydrophobicity, up to ≈ 0.5–0.6 based on CRM and WPM-ECA data, and even lower (≈ 0.1–0.2) in WPM-ACA. α increased with higher hydrophobicity, having relatively stable values in samples having σSV > 40 mN m–1. β showed stable values for samples having σSV > 35–40 mN m–1. In hydrophobic samples (σSV < 35 mN m–1), β decreased in calculations based on WPM-ACA data, and to a minor degree in WPM-ECA. The agreement between the CA directly measured (WPM) and those predicted by the ES was low, although better for the WPM-ECA, suggesting that this last approach can be considered more suitable to evaluate the ES theory.

Experimental air–liquid interfacial tension data and density data are presented for two ionic liquids with the 1-Cn-3-methylimidazolium cation, n = 2 and 4, and the dicyanamide anion. The measurements were performed at atmospheric pressure in the temperature range from (278 to 356) K using the Kruss K100MK2 tensiometer. The accuracy of the surface tension measurements was confirmed by employing the Wilhelmy plate and the du Nouy ring methods in parallel. The combined expanded uncertainty at 0.95 confidence level associated with the Wilhelmy plate method is estimated to be 0.1 mN·m–1. The density data were obtained using a buoyancy method with an estimated expanded uncertainty at 0.95 confidence level of 3·10–4ρ. An analysis of the experimental density data, using a group contribution model, performed for eight ionic liquids with the 1-Cn-3-methylimidazolium cation (n = 2, 4, 6) and tetrafluoroborate and trifluoromethanesulfonate and the dicyanamide anion indicates that the uncertainty arising from impurit...

This paper describes the measuring procedure which enables overcoming the base difficulty in application of the vibrating plate (VP) technique to measuring electric surface potential (ΔV) of free solution surfaces, namely loosing the zero level set for the reference sample (water) while replacing it with the solution measured. (The ΔV measurement is performed by comparing two measurements in series, i.e., for the pure interface and that containing a surface film.) Main improvement in the measuring procedure is achieved by (i) applying a flow for exchanging the reference sample with the measured solution and (ii) elimination of an error driven by dependency of the measuring signal on the air gap width. The air gap width is fixed by contact of the bottom edge of a platinum Wilhelmy plate with the solution surface which the plate is simultaneously used for measurement of the surface pressure (Π). The results received with the new methodology for n-decanoic acid, n-decyl-trimethylammonium bromide (C10TABr) and sodium n-dodecyl sulphate (SLS) are discussed.

The amount of available accurate experimental data on the surface tension of ionic liquids is still limited; in many cases the data are rare or even absent. In the present study, air–liquid interfacial tension data were determined experimentally for five 1-Cn-3-methylimidazolium based ionic liquids (n = 2, 4, and 6), three with trifluoromethanesulfonate and two with tetrafluoroborate anion, at atmospheric pressure in the temperature range from 268 to 356 K. The resultant surface tension data are average values of the measurements repeated many times at each set point temperature. The accuracy of the results, was confirmed by employing the Wilhelmy plate and the du Nouy ring methods in parallel, using the Kruss K100MK2 tensiometer. For the Wilhelmy plate data the combined standard uncertainty is estimated to be about 0.05 mN m−1. The data obtained by du Nouy method show about up to seven times greater scatter than those obtained by the Wilhelmy plate method. To the 50 up to now published surface tension values for the five studied ionic liquids the present study adds further 175 data points. In contrast to that of n-alkanes, the surface tension of 1-alkyl-3-methylimidazolium based ionic liquids decreases and their surface entropy increases with the cation alkyl chain length.

The surface characteristics of reverse osmosis membranes and their relation to membrane fouling are systematically investigated by measuring membrane dynamic hysteresis based on the Wilhelmy plate method. Dynamic hysteresis represents the difference between the forces applied to a membrane surface when it is advanced into and withdrawn from a liquid or solution. Our results demonstrate that the chemical surface heterogeneity of various RO membranes could be quantified by measuring their dynamic hysteresis. The chemical heterogeneity was mostly related to the distribution of surface charge rather than average zeta potential. There was a remarkable correlation between the chemical surface heterogeneity and membrane dynamic hysteresis. It was clearly shown that dynamic hysteresis varied substantially with respect to the solution chemistry of test solutions. The dynamic hysteresis of RO membranes measured in the presence of organic foulants was further related to the flux-decline rate determined from bench-scale fouling experiments. It was found that higher flux-decline rate was obtained for RO membranes with larger dynamic hysteresis. Based on the results in this study, it is demonstrated that dynamic hysteresis measurements can be a promising tool for characterizing membrane surfaces as well as assessing membrane fouling.

The surface tension and fluorescence spectra of sodium octyl-[ω-octyloxy-poly(oxyethylene)]-yl-benzene sulfonates (APEnBS) aqueous solutions have been investigated by Wilhelmy plate method and intrinsic probe methods, respectively to study the effect of EO units on their properties. It was discovered that the surface performance of these surfactants was greatly outstanding: the values of critical micelle concentration (CMC) reached to be of the order of magnitude of 10−5 mol/L, the values of surface tension at CMC, γCMC, were between 25.79 to 31.02 mN/m, and the effectiveness and efficiency of surface tension reduction were excellent. The introduction of oxyethylene units to the surfactant molecule evidently improved the solubility of APEnBS. With the increase in EO units, the CMC slightly changed after the first decreased. On the other hand, the surface excess concentration at saturation, Γ max, decreased after the first increased and γCMC increased after the first decreased accordingly. The CMC determin...

A study of the film molecular weight of various proteins is made. Two ranges of surface pressure are examined using in the 0,001-0,02 dynes/cm range a modified Guastalla balance, and, in the 0,02-0,6 dynes/cm range a Wilhelmy plate method or a Marcelin balance. Usually the molecular weights found in both ranges of pressure are in agreement although in some cases those found in the 0,02-0,6 dynes/cm range are not correct due to the shape of the isotherm. The influences of several variables: pH, ionic strength, surface active agent, temperature are investigated. Special mention is to be made of the influence of the substrate temperature on the isotherm of eggalbumin. On the basis of our results, proteins can be classified in two groups: firstly, we find all the proteins giving, when spread at pH 2, a film molecular weight of the same order of magnitude of the osmotic or ultracentrifugation-diffusion molecular weight; secondly, we have the proteins which give a film molecular weight lower than that found in solution. A discussion of the influence of the electrostatic factor and of the flexibility of the protein pattern is made. Finally attention should be paid to the necessity of considering an enthalpy factor in any theory of protein monolayer.

In this work, PEG-stabilized phosphatidylcholine lipid aggregates (disks), mimicking mammalian cell membranes, were introduced as a new biofouling resistant coating for SU-8 polymer microchannels. A rapid and simple method was developed for immobilization of PEGylated phosphatidylcholine disks in microchannels. Microfluidic chips made from SU-8, PDMS, or glass were dynamically coated with the PEGylated disks followed by characterization of their surface chemistry before and after coating. On the basis of the observed changes in EOF and nonspecific protein adsorption, the affinity of the PEGylated disks was shown to be particularly strong toward SU-8. The PEG-lipid coating enabled permanent change in EOF in SU-8 microchannels with an initial value of 4.5 x 10(-8) m(2) V(-1) s(-1), decreasing to 2.1 x 10(-8) m(2) V(-1) s(-1) (immediately after modification), and, eventually, to 1.5 x 10(-8) m(2) V(-1) s(-1) (7 days after modification) for 9 mM sodium borate (pH 10.5) as BGE. As determined by the Wilhelmy plate measurements and microchip-CE analysis of BSA, the PEG-lipid coating also enabled efficient biofouling shield against protein adsorption, similar to that of low amounts of SDS (3.5 mM) or Tween-20 (80 microM) as buffer additives. These results suggest that dynamically attached PEG-lipid aggregates provide stable, biomimicking surface modification that efficiently reduces biofouling on SU-8.

Physical aspects of dynamic hysteresis for characterizing reverse osmosis (RO) membranes have been investigated. Dynamic hysteresis was used as a parameter of showing physical surface characteristics of RO membranes. Automated microbalance was utilized to determine dynamic hysteresis based on the Wilhelmy plate method. Dynamic hysteresis determined with non-polar liquid was related to physical surface characteristics including surface roughness and heterogeneity determined by atomic force microscopy imaging and analysis. A remarkable correlation between dynamic hysteresis and surface heterogeneity was obtained when nonpolar liquid was used during the measurements. Dynamic hysteresis increased as the surface heterogeneity of RO membrane increased.

Summary An accurate method to determine contact angles (CA) of soils as a measure of water repellency is still missing. In the present research, we evaluated and compared different methods to determine the CA of dry soil samples. Experiments were made by using a set of porous materials (silt, sand and glass beads) with different levels of water repellency. The CAs were measured with the Capillary Rise Method (θCRM; liquid penetration into a 3-d system), the Wilhelmy plate method (θWPM; measurement of capillary forces acting on a plane sample) and the Sessile Drop Method (θSDM; optical CA analysis of drop contour on a plane sample). Results were compared with the CAs calculated from capillary rise in long vertical columns ( θ E CR ), where liquid profiles of the final capillary rise of water and ethanol, respectively, were used to derive the contact angle under the assumed equilibrium conditions. The results showed the overestimation of the CA by using the well established bi-liquid CRM technique for porous materials, in particular for material with a low degree of water repellency (CA θ E WPM ), as well as the Sessile Drop CA, θSDM, were close to the ones of θ E CR . We concluded that θ E WPM and θSDM are apparent CA, but nevertheless able to predict the impact of wettability on the final capillary rise which is affected by pore topology as well as by wettability.

The influence of the viscoelastic thermal compression (VTC) of wood on its surface chemistry, wettability, and surface free energy was evaluated. The changes in surface chemistry were studied by means of Fourier transform infrared spectroscopy (FTIR). Wettability was determined on the basis of the contact angle of water, using the Wilhelmy plate method. Surface free energy was determined according to the Owens Wendt Rabel and Kaelble (OWRK) theory, using the contact angle data of diiodomethane and formamide. The studied material was wood of the low-density hybrid poplar (Populus deltoides × Populus trichocarpa), which was densified to three different degrees of densification (63%, 98%, and 132%) using the VTC process. The results, based on the FTIR spectra, revealed that the VTC process caused minor chemical changes on the wood surface. However, wettability changed significantly. The VTC wood surface exhibits rather hydrophobic behaviour. Evaluation of the surface energetics using the OWRK approach showed that total surface free energy dropped significantly due to the VTC process.

The amphipathic character of soyasaponins and their consequent biological and technological properties are well-recognised. However, mainly due to the absence of purified compounds, no data are available on the amphiphilic surfactant properties of individual soyasaponins. In this study we developed a preparative method for the purification of the main soyasaponins species from soy germ. Reversed-phase chromatography (Source 15 RPC) gave a good resolution of the various soyasaponins, and was used for the purification of non- and fully-acetylated soyasaponin Ab, DDMP-conjugated and unconjugated soyasaponins Ba and Bb. For these compounds, the critical micelle concentration (CMC), the minimal attainable surface tension (γCMC) and the surface density (Γmax) were determined using the Wilhelmy plate method. The order of CMC values was as follows: soyasaponin Bb < Ba < βg < αg < Ab < non-acetylated Ab, and the CMC was found to range from 0.56 and to 3.2 g/L. It was concluded that the number of sugar side chains, the presence of acetyl groups and the presence of a DDMP-group are the main factors influencing the CMC of soyasaponins.

A semi-rigid, semi-flexible SU-8 polymer microdevice was designed to measure changes in interfacial tension at an air-water interface. The suspended microtensiometer enclosed a clean air-water interface, with an insoluble surfactant on the exterior. The difference in surface tension between the inside and the outside of the device, called the surface pressure, caused the 850 µm by 3 mm device to deflect. Finite element simulations were performed to predict device behavior prior to fabrication. Finished devices were tested in a Langmuir trough during multiple compression and expansion cycles using large area changes and slow compression speeds. Shorter experiments subjecting the interface to rapid local monolayer concentration variations were also performed. A platinum Wilhelmy plate was used as an independent surface pressure measurement. The microtensiometer had a theoretical resolution of 0.02 mN·m-1 publisher: Elsevier articletitle: Langmuir monolayer characterization via polymer microtensiometers journaltitle: Sensors and Actuators A: Physical articlelink: http://dx.doi.org/10.1016/j.sna.2015.03.041 content_type: article copyright: Copyright © 2015 Elsevier B.V. All rights reserved. ispartof: Sensors and Actuators A, Physical vol:229 pages:110-117 status: published

The equilibrium surface tensionsγ eq of aqueous Pentaethylenglycol-monododecylether (C12E5) solutions at temperature 25 °C were measured by means of Wilhelmy plate method and the determined critical micelle concentration (cmc) is 6.8 x 10-2 mol·m-3. To study adsorption kinetics of aqueous submicellar and micellar solutions, the dynamic surface tensionsγ(t) were measured by means of maximal bubble pressure method. Using the derived equations of adsorption kinetics for submicellar and micellar solutions, the experimental data were analyzed and the adsorption kinetics was studied. For micellar solution (c0>cmc) of C12E5, the demicellization constant $$\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\leftarrow}$}}{k} $$ was calculated.

The surface tensions and densities of aqueous solutions of oxalic, malonic, succinic, maleic, malic, and cis-pinonic acids were measured as a function of the acid mole fraction at 25 °C. These organic acids are typically found in atmospheric aerosols. The surface tensions were measured using the Wilhelmy plate method and were measured also as a function of temperature. The measurable mole fractions were limited by the solubilities of the acids at room temperature. All the acids lower the surface tension of pure water. cis-Pinonic acid lowers the surface tension most effectively. The measured surface tensions were fitted with equations covering the acid mole fraction range from zero to one and assuming a theoretical surface tension of pure, supercooled acids at room temperature. The measured densities were also fitted in a similar way. These equations can be used in model calculations of formation and growth of atmospheric particles.

X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and dynamic wetting measurements with the Wilhelmy plate method were used to characterize layers of three polystyrene-b-poly(acrylic acid) (PS-PAA) diblock copolymers (differing by their block lengths) created by dip coating or spin coating on glass and gold substrata. The copolymer layers were thick and continuous, whatever the substratum, with a preferred exposure of PS chains at the extreme surface for the copolymers with a small PS block. The surface roughness decreased as the PAA/PS block length ratio increased and was larger for dip-coated than for spin-coated layers. The dip-coated layers obtained with the copolymer with the large PAA block presented self-assembled nanostructures of worm-like type. Dynamic wetting measurements showed that the coated layers were able to reorganize, upon immersion-emersion in solution at different pH, due to the deprotonation and swelling of the PAA chains. This phenomenon was dependent on the block length and on the pH. A water contact angle typical of pure PS was obtained with the large PS block. A hydrophilic surface was obtained for the large PAA block after immersion at pH 11. In intermediate situations (large PAA block in water, large PS block at pH 11), the advancing contact angle was dependent on the time of contact with air subsequent to the preceding immersion. This demonstrates the possibility to modulate hydrophobicity-hydrophilicity switching and pH sensitivity of the coatings by the copolymer composition. (C) 2004 Elsevier B.V. All rights reserved.

In this study, the plasma polymerization of ethylene has been used to deposit a polyethylene (PE)-like thin layer on the surface of the selected expanded poly(tetrafluoroethylene) (ePTFE) films. To evaluate the activity of the PE-like surface, acrylic acid (AAc) graft polymerization was carried out for the pretreated films. The modified ePTFE films were characterized by X-ray photoelectron spectroscopy and attenuated total reflection Fourier transform infrared spectroscopies. The surface morphologies of the films were investigated by scanning electron microscopy and atomic force microscopy, and the wettability was evaluated with the sessile drop method and Wilhelmy plate method. It was found that the PE-like surface of the plasma treated specimen can be further grafted by AAc implying that the deposited surface remained active sites. After grafting by AAc, the advancing contact angle (θ a ) and the receding contact angle (θ r ) decreased approximately 40° and 50°, respectively, exhibiting an improvement of the surface hydrophilicity for the modified ePTFE specimens. It was also found that the lap shear strength of the polyAAc–grafted ePTFE specimen, adhered between two stainless steel surfaces by a selected epoxy resin, was enhanced by approximately three times.

Two small hydrophobic proteins, SP-B and SP-C, are responsible for rapid adsorption of pulmonary surfactant to the air/water interface. Despite their physiological importance, the number of protein molecules required to trigger an absorption event remains unknown. To investigate this issue, we varied the protein content of calf lung surfactant extract (CLSE) by dilution with protein-depleted surfactant lipids (neutral and phospholipids, N&PL). Vesicles of a constant size and of composition ranging between 100% N&PL and 100% CLSE were generated by probe sonication. Their adsorption kinetics to an air/water interface were monitored at different temperatures using a Wilhelmy plate to measure surface tension. When plotted versus protein concentration, the adsorption rates during the initial change in surface tension exhibit a diphasic behavior, first increasing rapidly and linearly between 0% and 25% CLSE, and then more slowly at higher concentrations. Direct linearity at low protein content (0-5% CLSE ratio) was confirmed at 37 degrees C. These observations argue against cooperative behavior, for which the adsorption rate would first rise slowly with the protein content, and then increase suddenly once the critical number of proteins on each vesicle is reached. The apparent activation energy E(a) and the free energy of activation DeltaG(0)*, calculated from the temperature dependence of adsorption, further support the view that at least the early stages of protein-induced surfactant adsorption proceeds through a sequence of events involving not several, but a single surfactant protein.

We performed simultaneous measurements of the instantaneous values of the surface pressure versus time, Π(t) (by the Wilhelmy plate method), and the adsorption versus time, Γ(t) (by ellipsometry), for aqueous solutions of a globular protein (β-lactoglobulin, BLG). The resulting dependence Π(Γ) was found to be well described by the Volmer equation of state (when Γ ≤ 1.6 mg/m2, a value corresponding to an almost complete monolayer), for all times and bulk concentrations. The excluded area per molecule, α, turned out to be twice as large as the maximum cross-sectional area of the molecule, ω, in accordance with the theoretical considerations. We processed in the same way available literature data for various proteins (BLG, α-lactalbumin, bovine serum albumin), both for equilibrium and for nonequilibrium adsorbed layers, as well as for spread layers. In all cases, the experimental dependencies Π(Γ) were fitted well by the Volmer equation; the excluded area either was almost exactly twice the maximum cross-sec...

Wilhelmy plate measurements of contact angles with a series of test liquids are used to calculate the surface energies of two poly(ethylene-co-1-butene) random copolymers. Results from five methods of calculation are reported: one-liquid (Good–Girifalco and Neumann), two-liquid (harmonic mean and geometric mean), and three-liquid (Lifshitz–van der Waals acid–base) methods. We find that all five methods are sensitive to the choice of test liquids used for contact angle measurements, as previously reported, but consistent results are obtained if recommended combinations of liquids are used. The mean results of the three-liquid acid–base method are judged to be the most reliable and informative, leading to surface energies of 30.8 mJ/m2 for poly(ethylene-co-1-butene) copolymer composed of 92 mol% ethylene and 30.2 mJ/m2 for copolymer composed of 88 mol% ethylene.

Adsorption of the protein bovine serum albumin (BSA) on gold has been tested at various concentrations in aqueous solution by dynamic contact-angle analysis (DCA) and quartz-crystal microbalance (QCM) measurements. With the Wilhelmy plate technique advancing and receding contact angles and the corresponding hysteresis were measured and correlated with the hydrophilicity and the homogeneity of the surface. With electrical admittance measurements of a gold-coated piezoelectrical quartz crystal, layer mass and viscoelastic contributions to the resonator's frequency shift during adsorption could be separated. A correlation was found between the adsorbed mass and the homogeneity and hydrophilicity of the adsorbed film.

The surface tension−concentration (γ−c) isotherms of soluble surfactants, unlike those of insoluble surfactants, are not sufficient to show whether gas−liquid-phase transitions occur. However, thermodynamic parameters (such as thermal coefficients) can be used to prove the existence of such transitions. The surface thermal coefficient corresponding to (∂γ/∂ ln T)A,P was described by Defay and named bTP. We determined this surface coefficient for a nonionic surfactant, Triton X100 (TX100), both in water and in a salt solution. We used the Wilhelmy plate method to measure the surface tension of TX100 at between 279 and 303 K. The bTP = f (log [TX100]) plot showed a clear peak, which could be attributed to a surface gas−liquid transition. Temperature and salt concentrations did not affect this transition.

Experiments conducted in a modified Langmuir trough are described. Measurements of surface tension were obtained using a Wilhelmy plate, while infrared (IR) images of the water surface adjacent to the Wilhelmy plate were simultaneously recorded. A contaminating surfactant film was allowed to form on the surface while the experiments were being conducted. The data reveal a substantial change in the IR imagery due to the film in all cases. The difference between the appearance of the clean and surfactant-covered regions of the surface is clear and distinct. For some of these experiments the change in the IR imagery is accompanied by no observable change in surface tension. This, along with several other aspects of this work, suggest that IR imagery may be a superior tool, compared to traditional surface tension measurements, for ascertaining the cleanliness of a liquid substrate.

Surfactant transport through the three-phase contact line is studied in relation to the wetting-enhancing effect of surfactants. A specially designed experimental setup is used to simultaneously monitor interfacial adsorption and wetting tension during forced immersion of a hydrophobic or hydrophilic plate into aqueous surfactant solutions. The adsorption at the liquid/solid interface has been measured by ellipsometry, the wetting tension has been determined according to the Wilhelmy plate method, and the adsorption to the liquid/vapor interface has been evaluated from surface tension measurements. The relative importance of different adsorption modes could thereby be grasped. For hydrophobic substrates, the dynamic wetting behavior is strongly affected by surfactant carryover through the advancing three-phase contact line, which appears to be the dominant mode of surfactant transport to the solid/liquid interface. Conversely, for hydrophilic substrates, three-phase contact line carryover of surfactant do...

The surface tensions σ of nonaqueous solutions of n-propyl acetate in caprylic (n-octanoic) acid were measured between 273 and 303 K using the Wilhelmy plate method. Complicated concentration dependences were obtained, different from any previously reported. In addition, independent volumetric and acoustic (sound velocity and absorption) methods were applied. The results are interpreted in terms of formation of weak complexes in the bulk as well as at the surface.

A comparative study was conducted to investigate the effects of pH on the equilibrium and dynamic interfacial tension-lowering activity of a commercial splittable surfactant Triton SP-190 and a common surfactant Triton X-100 at the n-pentadecane/water interface. Equilibrium and dynamic interfacial tensions at the interface of n-pentadecane/aqueous phase containing surfactants were measured by using a Wilhelmy plate tensiometer and a drop volume tensiometer, respectively. It was found that the addition of inorganic acids did not have an effect on the equilibrium and dynamic interfacial tension-lowering activity of Triton X-100 at the interface. However, though the equilibrium interfacial tension-lowering activity of Triton SP-190 was not significantly affected by acids, the dynamic interfacial tension-lowering activity of Triton SP-190 was strongly inhibited at lower pH, resulting in a slower decreasing rate of dynamic interfacial tension. This phenomenon might be explained by the presence of minor surface-active components in the commercial Triton SP-190 surfactant, which dominate the equilibrium interfacial tension behavior at the interface and are not affected by acids. Based on the pH-dependent dynamic interfacial tension data, the percentages of the Triton SP-190 surfactant split under acidic conditions were then estimated. Moreover, the influence of pH was considerably enhanced at small adsorption times and low Triton SP-190 concentrations.

Lipid lateral diffusion in multilamellar stacked bilayers and in monolayers at the interfaces of air/water (A/W) and oil/water (O/W) have been examined. The technique for the diffusion measurement is fluorescence recovery after photobleaching, in conjunction with the Wilhelmy plate method for equilibrium surface pressure. The oil used is heptane, and the lipid is L-α-dilauroylphosphatidylcholine (DLPC). The diffusion in the multi-bilayer system is found to be slower than that in monolayers at the A/W interface by a factor of 2−3. On the other hand, the diffusion at the O/W interface is established to be constant at lower lipid surface density, while that at the A/W interface is faster in the same range of lipid surface density. The difference at the O/W and A/W interfaces, however, diminishes as the surface density increases and eventually disappears altogether at a high enough surface density that is equivalent to 40 A2 per lipid molecule. The observed different diffusion coefficient profile with respect...

The interfacial tensions in two-phase solution systems for extraction of metallic ions from aqueous phase to organic phase by di(2-ethyl-hexyl) phosphoric acid were measured by the Wilhelmy plate method and partly by laser-light scattering method to confirm the accuracy. For copper and iron extraction solution systems, the surface-active species and their interfacial concentrations were identified by comparing the actual behavior of interfacial tension, the pH and extractant concentration dependencies, with the Gibbs–Langmuir equation for adsorption. It was shown that the extractant molecules should be adsorbed at the interface in the form of monomer and its dehydrogenated anion and that in copper extraction solution system non-surface-active 1:2 intermediate complexes should be formed, and in iron extraction solution system strongly surface-active 1:2 intermediate complexes should be formed at the interface. Based on the insights related to the intermediate complexes, reaction schemes at the interface are also discussed.

The critical micelle concentrations (CMC) of nine commercial nonionic surfactants (Tween 20, 22, 40, 60, and 80; Triton X-100; Brij 35, 58, and 78) and two pure nonionics [C12(EO)5 and C12(EO)8] were determined by surface tension and dye micellization methods. Commercially available nonionic surfactants (technical grade) usually contain impurities and have a broad molecular weight distribution owing to the degree of ethoxylation. It was shown that the surface tension method (Wilhelmy plate) is very sensitive to the presence of impurities. Much lower CMC values were obtained with the surface tension method than with the dye micellization method (up to 6.5 times for Tween 22). In the presence of highly surfaceactive impurities, the air/liquid interface is already saturated at concentrations well below the true CMC, leading to a wrong interpretation of the break in the curve of surface tension (γ) vs. concentration of nonionic surfactant (log C). The actual onset of micellization happens at higher concentrations, as measured by the dye micellization method. Furthermore, it was shown that when a commercial surfactant sample (Tween 20) is subjected to foam fractionation, thereby removing species with higher surface activity, the sample yields almost the same CMC values as measured by surface tension and dye micellization methods. It was found that for monodisperse pure nonionic surfactants, both CMC determination methods yield the same results. Therefore, this study indicates that precaution should be taken when determining the CMC of commercial nonionic surfactants by the surface tension method, as it indicates the surface concentration of all surface-active species at the surface only, whereas the dye method indicates the presence of micelles in the bulk solution.

Binary monolayers of l-α-dilauroylphosphatidylcholine (DLPC) and cholesterol were formed at the air/water interface by the successive addition method with chloroform as the spreading solvent at 296 K. Translational diffusion of a probe lipid in the monolayers as a function of cholesterol fraction was examined by the technique of fluorescence recovery after photobleaching in conjunction with epifluorescence microscopy and the Wilhelmy plate method. A transition from biphasic morphology to a visually homogeneous uniphasic monolayer occurred at surface pressures between 13 and 20 mN·m-1, depending on the cholesterol fraction in the monolayer. The lateral diffusion coefficient was found to decrease when surface pressure and/or cholesterol fraction were/was increased. The diffusion coefficients of the probe lipid in the homogeneous monolayers were analyzed on the basis of the free area model. The observed retardation of the diffusion is ascribed to an increase in the in-plane surface viscosity of monolayers. I...

The funnel method presented as a technique for investigating dynamic surface properties at the liquid/air interface consists of a hydrophobic funnel which is moved through a liquid interface in order to compress or expand its area isotropically. A counter-body compensates the displaced liquid by moving in the direction opposite to the funnel movement allowing for a constant liquid phase boundary level. Relaxation processes induced by the funnel movement are monitored by means of the surface tension response measured by a Wilhelmy plate right after expansion/compression of the interface. Studies are preformed with the non-ionic surfactant dodecyl dimethyl phosphine oxide. The relaxation curves depend on the direction and amount of the interfacial deformation. The experimental data are interpreted by a diffusion relaxation theory. Differences between experiment and theory are explained by changes in the effective area during compression or expansion.

L-α- Phosphatidylcholine (DOPC, Dioleoyl) monolayers of different initial surface pressures were spread at the sub-phase surface of a home-made Teflon mini-trough. Surface pressure was measured by the Wilhelmy plate method so as to study the spontaneous membrane insertion of non-ionic surfactant Triton X-100. A formula was deduced to approximately give out the final insertion amounts of Triton X-100 under different initial surface pressures. The results showed that the insertion amount decreased as the initial surface pressure increased and the amount included an `excess' of Triton X-100, which could be used to approximately give out the interaction energy quantity between lipid and Triton X-100 molecules in the monolayer.