The structure of thin films. Part IV.—Benzene derivatives. A condition of stability in monomolecular films

Abstract

In Part II of this series of papers (1) it was shown that (with suitable substances) films 1 molecule thick could be obtained on the surface of water, in which the molecules were packed with much the same degree of closeness as in other condensed forms of matter such as solids or liquids. Moreover, under proper conditions, it was shown that the molecules packed themselves, so as to give, for the measurement of the cross-section, some-times that of the hydrocarbon chain, sometimes that of the polar end group, called the "head." Concordant measures were obtained on different substances for the area of cross-section of a saturated normal chain of CH 2 groups, and for some common end groupings such as COOH, COOC 2 H 5 , etc. No check was, however, possible at that time on the measures of the dimensions of the groupings made by this method, as no other method had been applied to the measurement of these groups in condensed forms of matter. Sir W. H. Bragg's measurements of the dimensions of the naphthalene and anthracene molecule within the crystal have made and attempt to measure monomolecular films of substances containing an aromatic nucleus near the head of the molecule very desirable. The present paper describes the results of such and attempt carried out on benzene derivatives.