Self-assembly of carboxylic acids and hydroxyl derivatives on mica.: A qualitative AFM study

In this paper, we have studied by atomic force microscopy (AFM) the self-assembly of long-chain alkyl linear hydroxyl carboxylic acids and related derivatives on mica to investigate the effect of the number and position of the hydroxyl group in the interaction between molecules. We have observed that hydrogen bonding between secondary hydroxyl groups in mid-chain positions is responsible for an enhanced 2D growth of the monolayer of packed alkyl molecules. The combined presence of secondary and primary (terminal) hydroxyl groups in the same molecule is even more effective in creating an extended one monolayer thick deposit by both secondary to secondary and terminal to terminal (bridging) hydrogen bonding. An additional secondary hydroxyl group in the molecule structure further improves the 2D cross-linking as observed for aleuritic acid (9,10,16-trihydroxyhexadecanoic acid). These observations can be extended to the understanding of the short-range structure and the formation mechanism of some biopolymers such as cutin, a natural polyester supporting the lipidic extracellular membrane that covers the aerial parts of leaves and fruits of plants