Effect of cosolvent on the lateral order of spontaneously formed amphiphilic amide two-dimensional crystallites at the air-solution interface

Abstract

At low temperature (5-12 o C), uncompressed films of insoluble amphiphilic molecules C 19 H 39 X, where the head group X contains one (CONH 2 , 1) or two (CONHC 2 H 4 CONH 2 , 2) amide groups, spontaneously form two-dimensional (2D) crystalline clusters over aqueous subphases containing soluble amide or carboxylic acid molecules. These crystallites were detected and their structures were studied using grazing incidence X-ray diffraction (GID). In the presence of subphases containing carboxylic acid (RCO 2 H, R=H, CH 2 Cl) at sufficiently high concentrations, a loss of diffraction signal was observed for 1, while amide and less concentrated acid subphases did not show such a destructive effect