Captive Bubble Technique Research Articles

Estimating the hydrophobicity of coal

Based on contact-angle measurements and the work of adhesion equation, the hydrophobicity of a wide variety of coals was found to decrease with decreasing rank, fixed carbon and total carbon content and with increasing oxygen and hydroxyl content. The estimated hydrophobicity, based on the water-sessile-drop contact angle, is ∼20% for lignite, increases with increasing rank up to a maximum of ∼70% for low (LV) and medium (MV) volatile bituminous coals and then decreases somewhat for anthracite. Using the captive-bubble technique, the calculated hydrophobicity ranges from ∼0% (below HVA bituminous rank) to a maximum of 55% for LV—MV coal. The former estimation is believed to be the more accurate. While the water-sessile-drop contact angle as measured on a polished-coal surface is usually larger than that shown by the captive-bubble method, the two values were found to converge at ∼95% relative humidity. It is proposed that the surface of coal consists of three kinds of sites: strongly hydrophobic, weakly hydrophobic and hydrophilic. The sessile-drop technique measures the total hydrophobic sites whereas the captive-bubble method measures only the more strongly hydrophobic sites. A water film covers the weakly hydrophobic sites preventing their detection by the captive-bubble technique.

Flotation and adsorption studies of chalcopyrite with cupferron

Flotation tests were conducted in a Hallimond tube on chalcopyrite, with a collector system of cupferron and fuel oil. The reagent concentration, pH and conditioning time were studied as variables. The necessity of the fuel oil was verified by conducting experiments without it. Contact-angle measurements have been conducted by the captivebubble technique. From the results it was found that fuel oil is necessary to promote adhesion of the conditioned mineral particles to the air bubbles. Adsorption experiments were carried out in a column apparatus under similar conditions as in flotation, except for the addition of fuel oil. The adsorption density and flotability were high at weakly acidic range where the reagent complexes the metal ions effectively in an aqueous medium.

Studies on the contact angle of the charged silver iodide-solution-vapour interface

Measurements of the contact angle of an air bubble against thin films of silver iodide in an electrolyte solution have been made, using the captive bubble technique, as a function of pAg. The receding contact angle reached its maximum value at a pAg=5.4±0.2. This pAg value coincides closely with the isoelectric point of the silver iodide solution interface. A thermodynamic analysis is given which relates the variation of contact angle to the variation of concentration of potential determining ions and surface charge density.

Wettability of hydrogels. I. Poly (2-hydroxyethyl methacrylate).

The wettability characteristics of the contact lens material, PHEMA, with respect to water have been determined by using the sessile drop, and the captive air bubble techniques of contact angle goniometry. It is concluded that on PHEMA gels water does not spread spontaneously. Large hysteresis has been observed in the advancing and receding contact angles. This suggests that this hydrogel surface is capable of changing its free energy through reorientation of the polymer side chains and chain segments depending on the nature of the adjacent phase. The water content of the gels does not appear to have an effect on water wettability in the hydration range investigated. The minor wettability differences among the various gels studied were most likely due to differences in surface structure and segmental mobility due to inherent variations in the method of preparation. Small but consistent differences were found between the contact angles measured by the captive bubble method and those obtained by the sessile drop method, the former values being higher. These differences may not be method-related artifacts and cannot be explained at the present time.

方鉛鉱浮選における亜硫酸イオンの作用

The actions of sodium sulfite on galena faces have been studied by means of a electron diffraction technique. Interaction of sulfite and xanthate ions with galena depends on a nature of a oxidized state of the cleavage face, pH and a concentration of the reagents. Its primary function on a freshly cleaved face of galena is in a formation of monomolecular film adsorbed on the galenaface. As a substance produced by the action of sodium sulfite onan oxidized face of the galena, lead sulfite is revealed by a electron diffraction technique. Contact angle measurement on the galena face using a captive bubble technique represents that the presence of the sulfite ion in the solution decrease the angle if an oxidized face of the galena is used.

The effect of glass surface chemistry on glass‐epoxy systems

AbstractCarefully controlled experimental techniques were used to study the effect of variations in bulk E glass surfaces on bound life and wetting. Bond life (stability of the bound in the presence of moisture) was determined visually as the time required for hot water to remove an epoxy resin coating from the glass surface. Wetting was determined by the captive bubble technique. Both properties were significantly affected by variations of the glass surface. The bound life studies emphasized the importance of the coupling agent in promoting bound stability in a hot water environment. The only example of the glass surface not treated with a coupling agent that had a satisfactory bound life was the alkali‐deficient glass surface prepared by acid leaching. The surprisingly poor bound lives of the degassed and freshly cleaved (high energy) glass surfaces indicated that the wet strength retention of laminates would be poor when prepared by instantaneously applying epoxy resin without a coupling agent to the glass fibers directly as the fibers are formed. Cleanliness and surface and surface roughness were the only two variables found that promoted wetting. This discrepancy with respect to cleanliness indicated that wetting was not the controlling factor for bond life.

WETTING OF SOLIDS BY SOLUTIONS AS A FUNCTION OF SOLUTE ADSORPTION1,2

The wetting of flat platinum and chromium slides of small surface area by aqueous solutions of decylamine was measured as a function of the adsorption of the amine and the surface tension of the solutions. Adsorption at the solid- solution interface was measured in situ by an optical polarimetric method and wetting was determined concurrently by contact angle measurements employing the captive bubble technique. Adsorption and wetting results for platinum were sharply defined but those for chromium were somewhat obscured by erratic kinetic effects. Multilayer adsorption was observed in all cases, and isotherms on platinum in basic solutions exhibited steps. The observed contact angles of the solutions on platinum rose from 0 deg to a maximum of about 90 deg as adsorption increased, and then fell, sometimes to 0 deg , as adsorption proceeded further. A model is proposed to explain the wetting results which provides a semi-quantitative scheme for computing the behavior of the contact angles from the adsorption isotherms. (auth)