The molecular structure of thin films.—Part VI

Abstract

In this paper the results of further experiments on mono-molecular films on water are recorded, the method of experiment being that described in former papers (1). The results are summarized at the end of the paper. The most interesting facts ascertained are that the hydrocarbon chain in the alcohols has sensibly the same cross-section as that of the acids; that the highly unsaturated acids with up to five double linkages in the molecule form expanded films having practically the same properties as the slightly unsaturated oleic acid; that in the substituted acetamides R NH CO CH 3 there is a very definite transition between two condensed films, one of which is solid and the other liquid; and that the four-tentacled molecule, pentærythritol tetrapalmitate, which normally should have its four long chains directed towards the corners of a regular tetrahedron, forms a fairly stable film, with the four chains oriented parallel to each other and perpendicular to the surface. Primary Alcohols . R·CH 2 OH. Pure specimens of five alcohols were prepared by reduction of the ethyl esters of the corresponding fatty acids with sodium and alcohol. Full details of the preparations will be given in another paper. All these compounds formed both condensed and expanded films. The condensed films consisted of two portions, a lower one, less well marked in the shorter chain compounds than in the longer, which cuts the abscissa at an area per molecule of 21·6 sq. A. U., and an upper portion, identical with the line GH of former papers, which has been shown to indicate a close packing of the long chains in the film. Fig. 1 gives the curves determined on tetradecyl and eicosyl alcohols.