Liquid oily soils, removal from surfaces

The removal of liquid oily soils from surfaces is generally understood in terms of three basic mechanisms the roll - back of droplets of oily soil, the surfaces of which are modified by the presence of an adsorbed layer of surfactant direct emulsification of macroscopic droplets of soil and the direct solubilization of the oily soil into surfactant micelles or other interfacial phases formed (1-3). 

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... 

The phenomena at the liquid/liquid interface are of outstanding importance for the removal of oily soil from the surface. The interfacial tension is one of the decisive parameters in the rolling-up process. This parameter vary considerably, de-... 

We also describe the spreading of a thin surfactant laden aqueous film on a hydrophilic solid, i.e., one in which the dynamic contact angle is small. In such a case, the osmotic pressure gradient generated by the nonuniform distribution of surfactant micelles in the liquid film can drive fhe spreading process. The mofivation for this study comes from the need to understand the detergent action involved in the removal of an oily soil from a soiled surface. This paper presents an overview of our recent work. 

The most frequently discussed topic in washing is the role of solubilisation processes. Many investigators [76] attract attention to the fact that the surfactant concentration in a washing solution is much lower than CMC, and in this connection, solubilisation of oils is principally excluded due to absence of surfactant micelles. At the same time, the review of recent works [85, 86] show that solubilisation can play a dominant role both in washing fabrics and in the removal of soils from solid surfaces. These views are based on the following mechanisms. Surfactants adsorb at w/o interfaces under formation of densely packed adsorption layers which leads to a high local surfactant concentration as compared with the rather low concentration in the washing solution. After that, noticeable penetration of water into the oily soil is possible, under formation of liquid-crystal phases. Then, mesomorphic phases are swelled and destroyed under the formation of emulsion droplets. 

Fundamental principles leading to the removal of oily soil from the solid substrate by the so-called roll-up mechanism, in which liquid oil is displaced from the surface by the washing solution in the form of dispersed tiny droplets [60], are essentially the same as those evoked in the attachment of air bubbles onto a mineral surface. 

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