Molecular Interaction in Mixed Monolayers on Aqueous Subsolutions I. Mixtures of Alcohols, Acids and Amines

Abstract

Mixed films are of fundamental importance in biological systems, so mixtures of long chain alcohols, acids, and amines on acidic and basic subsolutions have been investigated. The principal effect of mixing is to change the conditions with respect to the pressure, area, and temperature at which one surfacephase changes into another. In general a mixture of two liquid films gives a monolayer of the same type, with the mean molecular area: a liquid expanded film is made more condensed by admixture of a substance which gives a condensed film, and the condensing action increases with the length of the hydrocarbon chain; an alcohol condenses an acid more than the corresponding acid. The interaction, or departure from the mean value may be either positive or negative, and on acid subsolutions is greatest when one of the components is an amine. Only in amine‐acid mixtures is there an indication of chemical action. The 1 : 1 mixture of stearyl alcohol and stearic acid ``freezes'' at a much larger area than the film given by either component, so the area of the solid mixed film is abnormally high. The area interaction with an amine present is negative, and the potential interaction has a high value and is positive. Calcium ions in a basic subsolution condense a Type II to a solid Type I monolayer.