[Physicochemical fundamentals on the cleaning of hard surfaces (author's transl)]

The primary process in the cleaning of hard surfaces is the adsorption of the active substance of the detergent at the interfaces: liquid/gas, liquid/liquid, liquid/solid. This primary step in the cleaning process induces secondary processes which in turn are responsible for the soil removal from the surface of the substrate. The first requirement for a cleaning effect is that the dirt and the substrate be well wetted by the cleaning solution as a result of a reduction in surface tension and of the adsorption at the solid/liquid interface. The further secondary processes which effect the removal of dirt vary considerably, depending on the type of dirt (e.g. oils, pigments). In the case of oily and greasy dirt, rolling-up penetration, formation of mixed phases, emulsification and solubilization are of importance. For pigments, the surface pressure of the adsorption layer and the electrostatic repulsion are the determining factors. The processes of pigment dispersion, emulsification and solubilization are, in addition, extremely important for the stabilization of the dirty wash bath and the prevention of deposits on the substrate. The essential active substances of the detergents are surfactant and complexing agents, the first being unspecifically adsorbed by hydrophobic interactions, and the latter specifically by polar interactions. They influence one another mutually and are responsible for an optimal cleaning effect when they occur in suitable mixing ratios; the special constitutional characteristics of the individual surfactant and complexing agents, must also be considered.