Solid-Like Films at a Moving Interface
Authors: Sutula C.L. , Wilson J.E. 
Published: December 2007

The petroleum literature shows a sporadic but sustained interest insolid-like films adsorbed at oil-water interfaces. A number of investigatorshave described their occurrence, attempts at isolation and some properties. Recently, more attention has been focused on the possible influence of suchfilms in oil production, particularly in waterflooding. Except for the work ofReisberg and Doscher, the influence of adsorbed films on the movement of anoil-water interface near a solid boundary appears uninvestigated. Also, noattention has been given to the possible movement of the film during a liquid-liquid displacement at a solid surface. That the effect of movement of athree-phase interline requires consideration can be illustrated by thefollowing simple experiment. A large, glass bell jar 12 in. in diameter wascleaned and filled with distilled water. After testing the water surface forcontamination, a cleaned glass slide (75 x 50 x 1.5 mm) was immersed verticallyin the water along its length. The slide was held rigidly, almost entirelyimmersed, by attaching it to a mechanism which permitted its withdrawal from orimmersion into the water surface at constant velocity (about 0.1 cm/minute). Talc powder was then liberally sprinkled over the entire water surface and acardboard box was placed over the apparatus to shield the water surface fromair currents. The water interface could be viewed and photographed throughplastic windows mounted over holes in the box. At rest, the talc particles wereuniformly distributed over the water-air surface. No talc particles, however, were found on the surface of the meniscus; i.e., no particles were present onthat part of the water-air surface drawn up from the common level by thewetting of the glass slide (contact angle through water theta, theta 0). Thisexperimental situation is depicted in Fig. 1a which represents the "at rest"configuration of the particles on the water-air surface. As the glass slide wasmoved in a direction which would withdraw it from the surface, the talcparticles for the first time began to ascend the meniscus. Their ascentoccurred in a reasonably coherent front. The particles appeared to move adistance along the surface of the meniscus equal approximately in length to thedistance the glass slide was removed from the water surface. If the motion ofthe slide was arrested, the particles slid down the meniscus and returned tothe common liquid level. If the upward movement of the slide was continued orrestarted, the particles again began ascending the surface of the meniscus(Fig. 1b). Upon reaching the top of the meniscus, the particles began todeposit on the slide to which they adhered. If the direction of motion of theslide was reversed (yet never leaving the water surface) the particles at thecommon level began to move away from the meniscus. Also, particles attached tothe glass slide (from the previous deposition) upon reaching the top of themeniscus, detached and descended the meniscus. This behavior was very strikingbecause the talc particles descended the meniscus in profuse streams ratherthan in a coherent front, as in their ascent (Fig. 1c). However, not allparticles detached from the slide upon meeting the top of the meniscus. Thosewhich did not detach simply remained on the glass slide and were submerged. Asbefore, if the motion of the glass slide was arrested, the particles on themeniscus slid down and adopted the configuration shown in Fig. 1c. A completelyanalogous result was obtained when the experiment was repeated using mercuryinstead of water. In this case, the mercury surface near the glass slide wasdepressed (meniscus below the common mercury level, contact angle &gt;90). After immersing the glass slide, particles were placed upon the mercurysurface. Nearly all the particles slid into the depression and concentratednear the glass slide. If the slide was moved upward, the particles climbed thesides of the depression. attained the common mercury level and moved away fromthe depression. If the motion was arrested, the particles again slid into thedepression. If the slide was moved downward, particles on the common leveldescended the depression. Particles in the depression became submerged, presumably still attached to the surface. If the downward motion of the slidewas stopped. the submerged particles did not reappear. Only when the slide wasmoved in the direction of withdrawal did the particles reappear. If themovement of the slide was continued, the particles again ascended thedepression and moved on the common mercury level away from the slide.