Oil splitting in industrial cleaning systems as studied by conductivity and interfacial tension

Characteristics of emulsion formation and splitting into aqueous and oily phases in simple and formulated surfactant systems were studied via conductivity. In systems composed of mixed nonionic ethoxylated alcohol surfactants, K2CO3, and emulsified n-hexadecane, conductivity decreased linearly with increasing oil volume fraction at HLB (hydrophile-lipophile balance) values of 12.9 and 13.9. The slope of the plot was ca. -3/2, in agreement with the Maxwell expression. At values less than or equal to an HLB of 11.3, conductivity first increased with a small addition of oil and then decreased nearly linearly with subsequent amounts. This was probably due to low HLB surfactants partitioning into the oily phase. When the type of oil was varied, the reduced conductivity also decreased linearly with volume fraction of emulsified oil. The slope was ca. -3/2 for oil weights ranging from very light (n-hexadecane) to very heavy (80W-90 gear oil), also in agreement with the Maxwell expression. Oil separation rates were measured by monitoring the change in conductivity in the lower region of the emulsion (where the aqueous layer formed) during splitting of the oily phase. Heavier oils were found to separate faster than light oils. Oils containing lubricity agents split at the slowest rate. Systems with lower HLB surfactants also displayed slower splitting rates. Splitting rates for a variety of systems, from simple oil and saline systems to more complex formulated systems, over temperatures from 23 to 75 degrees C, were related to oil-aqueous interfacial tension values through a power law expression composed of the maximum splitting rate and the interfacial tension between saline and oil at 23 degrees C.