General Aspects of Soil Removal

The soil that accumulates on fabrics is generally of an oily nature and contains particles of dust, soot, and the like. Thus soil may be either a solid, a 

The cleaning process proceeds by one of three primary mechanisms solubilization, emulsification, and roll-up [229]. In solubilization the oily phase partitions into surfactant micelles that desorb from the solid surface and diffuse into the bulk. As mentioned above, there is a body of theoretical work on solubilization [146, 147] and numerous experimental studies by a variety of spectroscopic techniques [143-145,230]. Emulsification involves the formation and removal of an emulsion at the oil-water interface the removal step may involve hydrodynamic as well as surface chemical forces. Emulsion formation is covered in Chapter XIV. In roll-up the surfactant reduces the contact angle of the liquid soil or the surface free energy of a solid particle aiding its detachment and subsequent removal by hydrodynamic forces. Adam and Stevenson s beautiful photographs illustrate roll-up of lanoline on wood fibers [231]. In order to achieve roll-up, one requires the surface free energies for soil detachment illustrated in Fig. XIII-14 to obey 

adding surfactants to minimize the oil-water and solid-water interfacial tensions causes removal to become spontaneous. On the other hand, a mere decrease in the surface tension of the water-air interface, as evidenced, say, by foam formation, is not a direct indication that the surfactant will function well as a detergent. The decrease in yow or ysw implies, through the Gibb s equation (see Section III-5) adsorption of detergent. 

In addition to lowering the interfacial tension between a soil and water, a surfactant can play an equally important role by partitioning into the oily phase carrying water with it [232]. This reverse solubilization process aids hydrody-namically controlled removal mechanisms. The partitioning of surface-active agents between oil and water has been the subject of fundamental studies by Grieser and co-workers [197, 233]. 

The experimental study of detergency ranges from the very practical to the molecular surface-sensitive approaches discussed in this book. In more practical studies, model 

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