Lyophily and Lyophoby
Lyophily and Lyophoby
indexes of the capacity of substances or the bodies formed by them to interact molecularly with liquids.
Lyophily is characterized by intensive interaction, that is, relatively strong attraction between the molecules of a substance (body) and the fluid in contact with them. Lyophoby is characterized by weak interaction. In the most important practical case, that is, interaction of a substance with water, lyophily and lyophoby are called hydrophily and hydrophobicity; in the case of oils and fats, oleophilia (lipophilia) and oleophobia. “Lyophilic” and “lyophobic” are terms applied to macromolecular compounds or to the surfaces of a variety of bodies, including those found in colloidal dispersions. The terms are also used to describe the given atomic groups or radicals of a molecule of a substance that interact in any number of ways with molecules of the solvent.
Lyophilic substances (bodies) dissolve in a given liquid and swell in it or become fully wetted. Lyophobic substances (bodies), on the other hand, neither dissolve nor swell in the liquid and are poorly wetted by it. Substances or surfaces of bodies that manifest lyophily to some liquids may be lyophobic in relation to others. Thus, paraffin, soot, and certain plastics are oleophilic but hydrophobic.
Lyophily and lyophoby are defined by the amount of heat generated in dissolving, swelling, or wetting. A widespread method of evaluating lyophily and lyophoby is to observe the behavior of a drop of liquid applied to the smooth surface of a solid. On a lyophilic surface, the drop spreads completely and forms a thin layer (liquid film); on a lyophobic surface, it does not spread but retains the shape of a lens or flattened sphere. The size of the angle between the surfaces of the drop and the wettable body, called the marginal angle (wetting angle), serves as a quantitative measure of lyophoby.
Lyophily and lyophoby may be chemically or physicochemically altered. Intensification of the interaction of a substance or surface with a surrounding liquid is called lyophilization; reduction of that interaction is called lyophobization. Both these processes have great significance in the production of building and construction materials and in the textile and the pulp and paper industries.
Lyophilization of powders and of fibrous and porous materials facilitates the wetting and saturation of these substances with water or organic fluids (solutions and melts of polymers, resins, petroleum products). Lyophobization of the same materials protects them from unwanted wetting and prevents caking; lyophobization of tissues and smooth surfaces is used to prevent soiling and to decrease adhesiveness. Industrially, the lyophilization and lyophobization of the surfaces of various bodies are often carried out by specially selected surface-active materials or polymerous compounds.
L. A. SHITS