(detergency), a set of physicochemical processes leading to the removal of soil from the surface of a solid. Cleansing action is characteristic of hemicolloidal systems, such as aqueous solutions (more properly, hydrosols) of soaps, synthetic detergents, and a number of naturally occurring compounds.
According to the concepts of P. A. Rebinder, cleansing action consists of wetting, peptization, emulsification, and stabilization of the soil as a highly dispersed phase consisting of tiny droplets or solid particles uniformly distributed in the cleansing solution. Cleansing action results from the presence in the system of surface-active agents, which are capable of forming an adsorptionsolvation protective layer around the dispersed-phase particles or droplets and on the cleansed surface. The high surface activity of such compounds is required for efficient dispersion and removal of soil from the cleansed surface (the substrate). The protective layer prevents the enlargement of the particles of soil that have passed into the cleansing solution and their resorption onto the cleansed surface.
The initial stage of cleansing action is the wetting of the soiled surface. In the case of the most common fat (oil) soils, good wetting may be obtained using cleansing solutions with sufficiently low surface tension (not greater than 30–40 millinewtons per m, or 30–40 dynes/cm). In the presence of a cleansing agent, the liquid soil that is in a thin film on the surface decomposes as a result of thermal motion or mechanical action (friction or mixing) into separate drops, which at first are held by the solid surface and then pass into the cleansing solution. Small aggregates of solid soil, such as soot, also decompose into finer particles (peptization) and are removed from the soiled surface. Once protected by adsorption layers, the liquid drops of fat or solid particles will not be resorbed on the cleansed surface or aggregate with each other.
The emulsification of liquid soils is usually accompanied by their dissolution into micelles of the cleansing agent (solubilization). The introduction of various inactive additives (salts and water-soluble polymers) increases the cleansing action of soaps and especially of synthetic detergents. The combined use of various types of surface-active agents in detergents usually increases the efficiency of the agents.
In addition to aqueous solutions of cleansing agents, nonaqueous systems such as lubricating oils with special surface-active additives may have cleansing action. Such oils are used in industry for cleansing or to prevent the accumulation of dirt on the surfaces of rubbing parts of various mechanisms.
Cleansing action is the result of surface phenomena and processes occurring in microheterogeneous (colloidal) systems in a liquid dispersion medium. The removal of dirt from a surface by dissolution in suitable solvents, as well as through the use of “dry” cleansing agents (pastes and powders) or by mechanical means, is not related to cleansing (or washing) action and is called cleaning.
Nevolin, F. V.Khimiia i tekhnologiia sinteticheskikh moiushchikh
sredstv, 2nd ed. Moscow, 1971. Pisarenko, A. P., K. A. Pospelova, and A. G. Iakovlev. Kurs kolloidnoi khimii, 3rd ed. Moscow, 1969. Page 162.
L. A. SHITS