Detergency in spontaneously formed emulsions

We report a microemulsion system with commercial nonionic surfactants, which produces kinetically stable o/w emulsions with sub-micron sized oil droplets, when added to water/brine. These emulsions have shown to be promising for fabric detergency. It is hypothesized that superior detergency could be due to (i) a low value of oil-emulsion interfacial tension (0.01-7 mN/m) even at a low (<= 1 g/l) surfactant concentration, thus effecting rapid emulsification and solubilisation of oily matrix/film present in dirt and (ii) extremely tiny emulsion oil droplets (50-100 nm), which can have easy access to dirt entrapped in the inter-yarn voids. The aim of this work was to investigate the above factors in a model system (cellulose-coated glass slides with attached oil droplets) with a view to detergency. Further, an attempt was made to study changes in contact angles of oil droplets attached to cellulose-coated glass slides immersed in the emulsion system as a function of brine concentration. Correlations were drawn between equilibrium contact angle, interfacial tension and detergency at different brine concentrations through arguments of work of adhesion and showed an excellent match with detergency trends on commercial fabric test monitors. These correlations also provide insights into possible underlying mechanisms that account for detergency at each level of brine concentrations. An important consequence of the work is that superior detergency is achieved when the oil, present in the microemulsion, is physico-chemically similar to those oils which are to be removed from contaminated surfaces. (c) 2006 Elsevier Inc. All rights reserved.