Finite Contact Angle Research Articles

Electrochemical investigation of contact angle and of flotation in the presence of alkylxanthates. II. Galena and pyrite surfaces

The contact angle between a nitrogen bubble and galena and pyrite surfaces immersed in methyl-, ethyl- or butyl-xanthates has been determined as a function of the electrode potential and of the quantity of xanthate species formed by interaction with the mineral surface. For galena, the initial chemisorbed xanthate layer was found to be hydrophobic when ethyl- or butyl-xanthates were employed, but hydrophilic for the methyl homologue. The presence of dixanthogen enhanced the contact angle but the metal xanthate diminished it. This conclusion was supported by contact angle studies at a lead electrode. For pyrite the surface was hydrophilic except when dixanthogen was formed, but a significant quantity was required on the mineral surface before a finite contact angle was observed. This behaviour is interpreted in terms of the presence of hydrated iron oxide on the pyrite surface. ��� The potentials at which particulate bed electrodes of galena and pyrite begin to float were determined for ethyl- and butyl- xanthates. The potentials correspond to the regions where chemisorption of xanthate takes place on galena and where significant quantities of dixanthogen are formed on pyrite. ��� With butylxanthate, flotation was inhibited when excessive quantities of xanthate species were present on galena or pyrite. The inhibition arose from flocculation of the mineral particles.

Polymolecular adsorption and capillary condensation in narrow slit pores

Capillary condensation and polymolecular adsorption in narrow slits has been calculated, where the fields of surface forces overlap one another. The calculations were carried out on the basis of macroscopic theory of dispersion forces and the isotherms of lone adsorption layers at the free surface. It has been shown that under the effect of mutual attraction through a gap, polymolecular adsorption films lose their stability long before their thickness has approached the half-width of a flat slit. This results in hysteresis of the capillary condensation in an ensemble of plane-parallel slits. In the case of systems having strong adsorbate—adsorbate interaction, there has been detected the existence of the lower limit of sizes of slit pores, wherein the capillary meniscus can coexist with adsorption films. With a slit width smaller than the critical one, the meniscus is likely to form a finite contact angle with “dry” surfaces of a slit. Thus an explanation has been given of the lower limit of the capillary condensation in an ensemble of flat-surface, slit pores. In the case of strong adsorbate—adsorbent interaction, the coexistence of meniscus with adsorption films within the scope of the approach used is possible in slits of any width. The value of corrections for the surface forces effect to be entered in the calculations of slit pores dimensions has been analyzed on the basis of the capillary condensation data obtained. In wedge-shaped slits there also exists, besides lower limit the upper limit of capillary hysteresis.

Thermodynamics of multiphase fluids in porous media

The basic thermodynamics of multiphase fluids in porous media is formulated, starting from equations originally derived by Laplace, Gauss, Young, and Kelvin. Special attention is paid to the conditions of hydrostatic (Laplace) equilibrium and diffusional (Kelvin) equilibrium, and to the stability of the equilibrium states with respect to displacements arising from flow or condensation/evaporation processes. Detailed discussion is given of capillary condensation in both uniform and nonuniform capillaries, for the case of zero and finite contact angles, and for both one and two liquid components. Immiscible displacement is considered briefly.

Hydrophobic cuticular ledges prevent water entering the air pores of liverwort thalli

Air pore geometry of 14 liverwort species was investigated using light, scanning and transmission electron microscopy to assess their ability to prevent water entering into the air pore and the intercellular space of the thallus. The air pores of 12 species [Marchantia polymorpha L., M. paleacea Bertol., M. nitida Lindenberg & Lehmann in Lehmann, Conocephalum conicum (L.) Wiggers, C. supradecompositum (S.O. Lindberg) Stephani, Grimaldia capensis Stephani, Targionia hypophylla L., Lunularia cruciata (L.) Dum., Reboulia hemisphaerica (L.) Raddi, Oxymitra paleacea Bischoff, Exormotheca bullata (Link) K. Müller (Tüb.), Plagiochasma elongatum Lindenberg & Gottsche] are equipped with hydrophobic ledges which constrict the air pore entrance after the fashion of an iris shutter. As a consequence only liquids having a contact angle of zero degree with the ledges are able to penetrate the air pore. The ledge of Marchantia paleacea was found to have a surface composed of methyl and methylene groups as indicated by the critical surface tension of less than 30.4 dyne cm(-1). Evidence is presented that the ledge is covered with a layer of cutin. It is shown that from the standpoint of protection against water entry these air pores must be considered perfect structures. Plagiochasma rupestre (Forster) Stephani and P. peruvianum Nees & Montagne are exceptional as they do not have ledges around their air pores. As a consequence liquids having a finite contact angle are able to enter through the pores into the thallus. Thus, they are imperfect and must be considered primitive.

Wettability of modified silica surfaces

wettability of silica surfaces was investjgated-by contact angle measurements of water and glycerol. Clean silica surfaces gave zero contact angle for water. Silica surfaces modified with alcohols and silanes, on the other hand, gave finite contact angle values. The actual value of the contact angle depended on the surface tension of the liq uid, the molecular structure and surface coverage of the adsorbed species. The following equation was used to describe the contact angle (θ), on treated silica surfaces:Cos θ = Cos θ1 − (Cos θ1 − Cos θ2) qa/100where θ1 and θ2 are the contact angles on unmodified and modified surface with maximum coverage respectively q is the number of adsorbed molecules per 100Å2 and a is the effective cross sectional area of the adsorbed ,molecule. The cross sectional areas of the alkoxy groups determined from the contact angle values were in close agreement with the calculated values. Résumé La mouillabilité de surfaces de silice fut étudiée par les mesures d'angle de raccordement eau-glycérol. Les surfaces propres de silice ont donné un angle de raccordement zéro pour l'eau. Des surfaces modifiées par l'alcool et les silanes ont donné, d'autre part, des valeurs finies d'angle de raccordement. La valeur de l'angle de raccordement dépend de la tension superficielle du liquide, de la structure moléculaire et de la fraction de la surface couverte par l'espéce adsorbée. L'équation suivante fut utilisée pour exprimer l'angle de raccordement θ sur la surface de silice traitée:Cos θ = Cos θ1 − (Cos θ1 − Cos θ2) qa/100avec θ1 et θ2 les angles de raccordement de surface pour des fractions de surface couverte maximum, θ1 étant pour les surfaces non modifiées et θ2 pour les surfaces modifyées. q représente le nombre de molécules adsorbées par 100° A2, et a est la section effective de la molécule adsorbée. La surface de la coupe transversale des groupes alcoxy déterminée par mesure des angles de raccordement était en accord avec les valeurs calcuIées.

Sizes of bubbles produced by dissolved gas coming out of solution on the walls of pipes in flowing systems

In a liquid that is sufficiently supersaturated with dissolved gas bubbles will form at nucleating cavities on the containing walls. In this paper equations are derived for the drag and surface tension forces on gas bubbles adhering to the walls of pipes in flowing systems. The equations are used to predict the bubble radius on detachment, and give good agreement with some experimenetal results for finite contact angles. The drag force is calculated using values of the drag coefficient obtained from experiments on the terminal velocity of freely rising bubbles and the velocity profile for fully developed turbulent flow in a circular pipe. The surface tension force opposing the drag force arises from the different contact angles upstream and downstream of the bubble. If the liquid exhibits a zero contact angle on the surface the surface tension force is determined by the radius of the nucleating cavity. A method of calculating this radius from superheat or cavitation data is described.

The Effect of Viscous Shear on a Meniscus in an Electrochemical System

Fluid flow in the evaporating meniscus of an electrode‐gas‐electrolyte reacting system has been studied to examine the effect of viscous shear on the meniscus profile. The evaporating meniscus profile, the pressure derivative profile, and the curvature profile for various assumed evaporation profiles were calculated for . Due to the thinness of the meniscus profile in the interline region, large pressure gradients were needed to balance the viscous shear stress. The resulting evaporating meniscus profile was significantly different from the static profile. Depending on the evaporation rate the interline radius of curvature could be micron size for a large meniscus. Heat and mass transfer rates would also be significantly effected by these changes during an electrochemical reaction. Therefore, the effect of viscous shear should not be neglected in analyzing electrochemical processes in a “finite contact angle” meniscus.

Penetration of Stomata by Liquids

Wettability of the leaf surface, surface tension of the liquid, and stomatal morphology control penetration of stomata by liquids. The critical surface tension of the lower leaf surface of Zebrina purpusii Brückn. was estimated to be 25 to 30 dyne cm(-1). Liquids having a surface tension less than 30 dyne cm(-1) gave zero contact angle on the leaf surface and infiltrated stomata spontaneously while liquids having a surface tension greater than 30 dyne cm(-1) did not wet the leaf surface and failed to infiltrate stomata. Considering stomata as conical capillaries, we were able to show that with liquids giving a finite contact angle, infiltration depended solely on the relationship between the magnitude of the contact angle and the wall angle of the aperture. Generally, spontaneous infiltration of stomata will take place when the contact angle is smaller than the wall angle of the aperture wall. The degree of stomatal opening (4, 6, 8, or 10 mum) was of little importance. Cuticular ledges present at the entrance to the outer vestibule and between the inner vestibule and substomatal chamber resulted in very small if not zero wall angles, and thus played a major role in excluding water from the intercellular space of leaves. We show why the degree of stomatal opening cannot be assessed by observing spontaneous infiltration of stomata by organic liquids of low surface tension.

Contact Angle And Interfacial Tension Studies of Some Hydrocarbon-Water-Solid Systems

Abstract An apparatus was built to measure interfacial tensions and contact angles of hydrocarbon-water-solid s:rstems at variable temperatures and atmospheric pressure. Interfacial tensions were measured for benzene, n-dodecane, Klearol and nitrogen against water over a temperature range of 25 to 90 °C. For the n-dodecane-water system, a water-soluble cationic surfactant, a water-soluble nonionic surfactant and an oil-soluble carboxylic acid were added. Relationships among interfacial tension, temperature, surfactant concentration and interface age were determined. Contact angle measurements were made primarily for the n-dodecane-water system on flat quartz and calcite crystal surfaces. An oil-soluble amine, a carboxylic acid, and water-soluble anionic, cationic and nonionic surfactants were used as additives. Without the surfactants, the carefully cleaned solids were completely water-wet. Finite contact angles resulted from contamination or the addition of certain of the surface-active compounds, and were generally accompanied by hysteresis. The magnitude of the contact angles indicates the orientation and degree of packing of surface-active molecules at solid-liquid interfaces, and points out the role of surface charge and polarity in adsorption. Introduction IN CANADA AND THE UNITED STATES, approximately 90 per cent of all the oil produced through the application of enhanced recovery processes is obtained bywaterflooding. The rising cost of exploring for new oil, coupled with the higher cost of applying alternate recovery schemes, creates an incentive for waterfloods to be conducted under conditions favouring most efficient oil recovery. This requires that research be carried out into factors which might significantly improve the immiscible displacement mechanisms. Mungan(1) has shown that interfacial effects in the immiscible displacement of oil from porous media can significantly influence the recovery, and Melrose(2) has recently discussed the role which interfacial phenomena or capillary forces play in determining the extent to which a fluid can be displaced from a porous solid by another immiscible fluid. A general discussion of capillarity was given recently by Schwartz(3). Three factors affect capillary forces in porous media:the interfacial tension between the two fluids,the contact angle between the fluids and the solid surface, andthe pore size and pore size distribution of the porous media. Because of the small pore sizes and the large interfacial areas existing between oil, water and the reservoir rock, the interfacial forces become appreciable and can dominate in the displacement. Moore and Blum(4) estimated that to mobilize residual oil structures, assumed to be several grain sizes in length, through average reservoir rock openings would require a pressure gradient of something like 500 psi/ft - an impossible value to attain in operations. An alternative is to reduce the interfacial tension to low values, say 0.01 dyne/cm, which reduces the pressure requirement to move these same residuals to only 0.33 psi/ft. Chatenever, et al.(5), using microscopic examination of fluid movement in all-glass and all-lucite cells, showed that the residual oil formation and structures we.re significantly different under water-wet and oil-wet situations.

Effect of a Finite-Contact-Angle Meniscus on Kinetics in Porous Electrode Systems

The behavior of the meniscus in a static gas-electrode–gas-electrolyte system has been studied to clarify the mechanism(s) involved in the electrochemical dissolution of gaseous reactants in porous electrodes. Concurrent optical and electrochemical measurements in a specially designed cell, constructed from Teflon and fused quartz, demonstrated conclusively that although metastable thin films could be produced on the electrode by immersion followed by slow draining under high potentials (i.e., > 0.8 V with respect to the normal hydrogen electrode), these films broke down irreversibly at lower potentials, and were never observed to form spontaneously. The most stable configuration was a meniscus with a finite contact angle which was between 1° and 3°. On the basis of the observed geometry of the meniscus and a finite contact angle, a detailed second-order nonlinear nonhomogeneous differential equation of the form d2ηdx2 + F(x) dηdx + A[exp(kη) − exp(k2η)]G(x)[1 + B G(x) exp(k1η)] = 0, where F(x), G(x), A, B, k1, and k2 include only the pertinent experimental conditions (meniscus shape, exchange current, diffusion coefficient, etc.), was derived involving both concentration and activation polarization and the IR drop in the meniscus. This equation was solved numerically in complete form on a digital computer. The computed relations of current to potential were within 10% of the experimentally obtained ones for both H2 and O2 in 1N H2SO4 on Pt electrodes, without the inclusion of “calibrating” factors. The results of the computations show that the meniscus is effectively divided into three regions. In the first, near the tip, the reaction kinetics on the electrode surface is the primary limiting factor. The second region has mixed diffusion and activation limitation up to the zone where the meniscus is so thick that negligible additional currents can be drawn. This zone starts the third (inactive) region which extends down into the bulk of the solution. The experimental conditions (potential, gas pressures, etc.) determine the location of the boundaries of these regions and thus the over-all behavior of the meniscus. At moderate polarizations, over 90% of the current is produced within a very small (10−4–10−5 cm) distance from the meniscus tip.

An adsorption model for contact angle and spreading

The adsorption isotherm for a vapor on a substrate must cross the saturation pressure line at a finite film thickness in the case of those systems for which liquid adsorbate rests on the substrate with a finite contact angle. It is suggested that such isotherms be identified as types VI and VII, depending on the manner of the final asymptotic approach to the P 0 line at infinite film thickness. A semiempirical model is presented, capable of representing type VI and VII isotherms, including the unstable regions. The model allows calculation of contact angles and spreading coefficients from adsorption data alone, and such calculations are illustrated with the use of published data for various vapors adsorbed on glass and on liquid water as substrates. A general purpose of the paper is to emphasize the central role of structural modifications in interfacial regions in determining wetting behavior and to provide a framework for predicting what types of liquid and substrate properties should give very high works of adhesion and very low (even negative) ones.

Adsorption of halides at the mercury-water interface

Summary The capacity of the double layer at a mercury electrode in contact with aqueous KBr solutions was measured at 25°. These results, together with those for other halides, are used to investigate the relation between electrocapillary and capacity measurements. Under most conditions there is no disagreement, but errors can occur in electrocapillary measurements on a positively charged surface in dilute solutions of weakly-adsorbed electrolytes, possibly due to the occurence of a finite contact angle. To obtain accurate surface excesses it is important to make measurements at closely spaced concentrations. The adsorption isotherm of Br − , in common with several other anions, exhibits features which do not seem to be explicable in terms of current theory. The question of specific adsorption of F − is briefly discussed.

Contact angles and adsorption in the system quartz-water-dodecane modified by dodecyl ammonium chloride

Adsorption of dodecyl ammonium chloride was studied in the system quartz-water-dodecane. The distribution of dodecyl ammonium chloride between water and dodecane was measured as a function of pH; the effect of this surfactant on the water-dodecane interfacial tension was also measured. Adsorption of dodecyl amine at the quartz-dodecane interface approached monomolecular thickness, whereas adsorption of this surfactant was very much smaller at the quartz-water interface. In the pure three-phase system the contact angle was zero. Addition of amine resulted in finite contact angles and hysteresis. The contact angles were sensitive to the method of preparation and cleaning of the quartz surface, and also to the concentration of surfactant and pH. The relationship of the observed contact angles to amine concentration and pH was established. Calculations were made which indicated that adsorption equilibrium was not obtained during measurement of dynamic contact angles. By applying the Young equation to the system and by using the estimated true interfacial tensions rather than the equilibrium values, the observed contact angle behavior was satisfactorily explained.

INCIPIENT FAILURE OF SOIL AGGREGATES

SummaryA comparison of the rate of wetting of aggregates taken from a virgin and continuously cultivated Red‐brown Earth has been made. The aggregates were placed on a glass sinter which was connected to a horizontal capillary. The rate of water uptake was obtained from the rate of meniscus travel as water was adsorbed from the sinter by the aggregates.When air‐dry (P/P0≊ 0·50) aggregates were wetted at 2 and 10 cm. water suction the cultivated aggregates wetted more rapidly than the virgin aggregates. At a suction of 30 cm. both groups of aggregates exhibited almost identical rates of wetting. The difference in the rate of wetting could not be attributed to differences in pore structure since both groups of aggregates had almost identical total porosity and clay content and furthermore showed extremely similar rates of wetting when wetted at a low suction with a non‐polar liquid. When aggregates from a virgin and cultivated soil were wetted slowly the pF‐water content relationship was very similar; it was therefore concluded that organic matter did not give rise to a finite contact angle for the water advancing into the virgin aggregates.Because the cultivated aggregates when wetted at 30 cm. and then at 2 cm. ion did suctnot slake when placed in water, whereas cultivated aggregates wetted directly to 2 cm. suction from the air‐dry condition slaked when placed in water, the phenomenon is described as incipient failure. When the cultivated aggregates are wetted at 2 cm. suction the work done by the rapid wetting causes planes of failure to be set up and the soil moves from an over‐consolidated condition to that represented by the n o d or virgin consolidation curve (Croney and Coleman, 1954). It is proposed that the organic matter in the virgin aggregates strengthens the pores against failure and so this material retains its initial pore structure. Mechanical strength measurements on virgin and cultivated aggregates support this hypothesis.