Monomolecular films of phenolic esters.
Abstract The properties of three phenolic esters, characterized by gradual changes in their molecular constitution, have been evaluated in pure monomolecular films, as well as in mixed films with stearic acid. The pressure-area isotherms for the pure compounds reflect a similar orientation for compounds I (resorcinol monoundecanoate) and II (4-chlororesorcinol 1-undecanoate) at the air-water interface. At pressures corresponding to the limiting area per molecule, the molecules are apparently rather erect and anchored to the aqueous subphase surface by the phenolic-OH function; at lower pressures, the molecules are less erect, with their aliphatic chains randomly intertwined. The isotherm characteristics for III (4-chlorophenyl undecanoate), on the other hand, are compatible with an orientation in which the molecule is anchored to the aqueous subphase surface by its ester function, with both the aliphatic chain and the substituted phenyl ring projecting upwards. Isotherms for 1:1 mixtures of each of the phenolic esters with stearic acid indicate that the properties of the mixed films were controlled, generally, by the esters (at low pressures) and by stearic acid (at high pressures), after the esters had been forced out of area-determining positions in the films. The experimentally derived isotherms for the mixtures were compared with those calculated from the isotherms of the pure components, and observed deviations from additive behavior discussed.
Grisan derivatives in pure and mixed monomolecular films.
Abstract Pressure-area isotherms for monolayers of two synthetic grisan derivatives have been determined and correlated with molecular orientations of these entities at the air-water interface. Isotherms for equimolar mixtures of the grisan derivatives with stearic acid, cholesterol, and l -α-lecithin, respectively, are reported. The pressure-area curves show, in general, the predominant influence of the grisan derivatives at low pressures, and ejection of these from the monolayer at intermediate pressure values. At higher pressures the curves reflect largely the properties of the respective lipids. Theoretical curves for the mixtures were calculated assuming additivity, and compared with the corresponding experimentally derived isotherms.
Surface Chemical Phenomena in Lubrication
A remarkable variety of surface chemical phenomena are encountered in lubrication. The more important concern boundary friction, wear prevention, corrosion and its prevention, surface deactivation of pro-oxidant materials, foaming, emulsitication, and detergency. It is convenient to regroup these under the following headings: (a) physical adsorption; (b) chemical reactions a t the solid-liquid interface; (c) colloidal behavior of polar molecules in nonaqueous liquids; and (d) the activity of the liquid lubricant phase as a source or sink for surface-active materials. Not only is each of these subjects still in a state of flux, but lack of time forbids any attempt to cover them thoroughly. There are advantages, however, in presenting recent progress against the broad background of surface and colloidal chemistry; hence our broad title and the above classification. The earliest wear preventives and rust inhibitors added to oils were fatty acids, alcohols, and esters. Such polar-nonpolar molecules (or amphipathic molecules) are still used for mild conditions of loading and temperature. Technical advances have been based on empiricism or on applications (often with amazing extrapolations) of the results of the basic research of Devaux, Hardy, Langmuir, Harkins, Adam, Rideal: McBain, and others. This has been especially true in relating available information of the adsorption and arrangements of amphipathic molecules a t the air-water and the oil-water interfaces to those at the air-oil and solid-oil interfaces. There is little present knowledge of the basic phenomena involved in the adsorption and properties of thin films collected a t the air-oil and oil-water interfaces. I t limits all research on the formation and breaking of foams and emulsions. Even more limited is our knowledge of what happens at the solid-liquid interface. This has been caused by the experimental difficulties and longterm nature of the research required. Modern physical methods and the increasing availability of a wide variety of pure chemicals, however, make this field of research more inviting. Sow Results of Recent Research on Adsorption of Long-Chain Compounds. Concentrations of 0.001 per cent by weight of some polar compounds are able to saturate the surface of metals with adsorbed monolayers. This is responsible for some of the experimental difficulties in studying adsorption a t the liquid-solid interface. If the need for working with such dilute solutions is avoided by using large areas of metal (employing powdered materials, for example), the difliculty of preparing clean, chemically well-defined surfaces of known area is encountered. In the past ten years, great strides have been made in overcoming some of these difficulties, which augurs well for future progress.