Effect of ionic strength on the removal of oils from gold and stainless steel

Modifications to the ionic strength of aqueous surfactant solutions have been examined to determine the effect on oil con tact angles and the removal of the oil from a solid surface. Other variables altered include the solid surface, surfactant concentration, surfactant class and the type of oil. Each individual variable had an affect on the contact angle. The surfaces studied in this case were a gold-coated glass slide and stainless steel. The organic oil hexadecane was used on the gold-coated glass and stainless steel surfaces. A blend oil MAR-TEMP® 355 was used on the stainless steel. Aqueous solutions of anionic surfactant sodium dodecyl sulfate (SOS) and cationic surfactant cetyl trimethyl ammonium bromide (CTAB) were used on both surfaces. The surfactant concentration and ionic strength were found to effect the removal of both oils from a stainless steel surface. The contact angles achieved on the gold-coated glass were greater than stainless steel. Increasing the surfactant concentrations increased the contact angle of both oil droplets on the surfaces. Increasing the ionic strength while maintaining a constant surfactant concentration increased the contact angle of both types of oil droplets on the surfaces in both anionic and cationic surfactants.