Effects on pH, surfactant concentration, and surface type on the removal of an oil from a solid surface

Several variables have been examined to determine their effect upon the displacement and removal of an oil from a solid surface. The variables include the nature of the solid surface, the concentration of surfactant, the ionic character of the surfactant, and the pH of the surfactant solution. All of these variables were found to affect the displacement of oil from a solid surface. Two surfaces were tested, stainless steel and optical glass. Greater displacement of the oil occurred when using the stainless steel surface than when using the glass surface. Increasing the concentration of surfactant from below the critical micelle concentration (CMC) to above the CMC while maintaining a constant pH was found to enhance the displacement of the oil from both surfaces. Octylphenol polyglycol ether which is more commonly known as Triton X-100, a nonionic surfactant, yielded greater displacement of the oil from both surfaces than did sodium dodecyl sulfate (SDS), an anionic surfactant, under conditions measured relative to the CMC. Increasing the pH from 6.0 to 10.0 of the surfactant solution while maintaining a constant surface concentration enhanced the ability of a Triton X-100 solution to displace the oil. Decreasing the pH from 10.0 to 6.0 while maintaining a constant surfactant concentration enhanced the ability of an SDS solution to displace the oil from a solid surface. The effect of each of the aforementioned variables was determined by measuring the change in the contact angle of a drop of the oil on a solid surface as a function of time.