A quartz crystal microbalance study of the removal of solid organic soils from a hard surface in aqueous surfactant solution

A quartz crystal microbalance (QCM) has been employed to monitor the remova l of two model solid organic soils, dotriacontane and tripalmitin, from the hard surface of the QCM crystal in aqueous surfactant solutions of octa-et hyleneglycol mono n-dodecyl ether (C12E8). We have investigated the effect of varying the thickness of the soil coating on soil removal and the effect of soaking the soil in high-purity water for an extended period of time be fore adding surfactant. The QCM results support the view that net soil remo val is preceded by a stage of water and surfactant penetration into the soi l. The rate of penetration and rate of removal depends on the soil type. Wa ter and surfactant take longer to penetrate dotriacontane compared to tripa lmitin coatings. The removal process also occurs over a longer period of ti me in the case of dotriacontane coatings. The percentage of material remove d is less for dotriacontane, compared to tripalmitin coatings. The initial coating thickness on the hard surface does not appear to govern the final p ercentage of soil removed, at least in the thickness range accessible to th e QCM (approximately less than or equal to 800 nm). Immersing the soil coat ed surfaces in water for a relatively long time, hastens the onset of the r emoval stage after surfactant is added but does not significantly influence the rate and extent of removal from the hard surface. (C) 1999 Elsevier Sc ience B.V. All rights reserved.