Lubricant films chemical structure

The concept of the interaction film in lubricant additive action is based on the postulate that material in the rubbing surface and the additive both contribute to the formation of the film by extensive chemical reaction with each other. The additives contain characteristic elements l. g. sulfur, chlorine, phosphorus) in characteristic chemical structures. The material in the rubbing surface is usually metallic iron is the metal most frequently encountered in technological practice. 

In this way, a low-surface-energy, chemically inert lubricant forms a physically smooth and chemically homogeneous lubricating film on the structured surface, which leads to low contact angle hysteresis and a strongly reduced adhesion of the test liquids (e.g., water) to be repelled. The schematic diagram presented in Figure 11 illustrates the physical action principle of slippery liquid infused structured surfaces in comparison to superhydrophobic surfaces based on composite solid-air interfaces. 

An emerging subdiscipline of tribological simulation involves the study of tribochemical reactions—that is, reactions that are activated by pressure and shear. These reactions alter the structure of lubricants and films that are used to protect surfaces from wear. Understanding the effects of these reactions on the intended behavior of these films is of utmost importance. However, simulation studies of tribochemical reactions have been impeded by the difficulty in accurately describing changes in chemical bonding. In a limited number of cases, this can be achieved with the use of reactive FFs, as noted above, whereas in other cases, one must resort to expensive quantum chemical calculations. In this section, we will describe two studies where such methods were used to examine tribochemical reactions. 

Gums are used in industry because their aqueous solutions or dispersions possess suspending and stabilizing properties. In addition, gums may produce gels or act as emulsifiers, adhesives, flocculants, binders, film formers, lubricants, or friction reducers, depending on the shape and chemical nature of the particular gum (2). Considerable research has been carried out to relate the structure and shape (conformation) of some gums to their solution properties (3,4). 

Depending on their chemical composition, molecular structure and molecular weight, silicone compounds are used as liquids, oils and lubricants of various consistency, as elastomers (for sealants, compounds and rubbers), as well as polymers for varnishes, plastic laminates and films. 

The term moisture, usually defined as wetness conferred by an unidentified liquid, is assumed here to be due to water. Thus, the scope of this article is the characterization of and consequences due to relatively small amounts of water associated with solids of pharmaceutical interest. Chemical stability, crystal structure, powder flow, compaction, lubricity, dissolution rate, and polymer film permeability are some properties of pharmaceutical interest that have been demonstrated to be influenced by the presence of moisture. Wet granulation, extrusion, spheronization, tray drying, freeze drying, spray drying, fluid-bed drying, tableting, and aqueous film coating are some unit operations that obviously depend on the amount and state of water present. 

Interest in the properties, structure, chemical modification, and application of thin films of organic polymers has grown enormously in recent years. The impetus for this rebirth derives from the relevance of such materials to adhesion (J,), microelectronics (2) lubrication ( ), and biocompatibility (specifically the Interface between living and nonliving components as occurs with Joint replacements or artificial hearts (4.5 ). These materials have also gained increasing importance in the construction of sensors that are based on electrochemical and... 

---