Self-assembly of 5-octadecyloxyisophthalic acid and its coadsorption with terephthalic acid

The structure of the self-assembled monolayer of pure 5-octadecyloxyisophthalic acid (5OIA), and the coadsorption monolayer of 5OIA and terephthalic acid, is investigated using scanning tunneling microscopy (STM) at the liquid-solid interface. 5OIA self-assembles into a monolayer comprised of different structures. For the major phase, 5OIA molecules alternately pack with opposite enantiotopic faces in a lamella, giving lamellae with a chain-to-trough angle of ∼88°. Two adjacent lamellae are assembled together by a hydrogen-bonding network between two carboxylic acid groups from each lamella. In the self-assembled monolayer of the mixture solution of 5OIA and terephthalic acid, 5OIA molecules coadsorb with terephthalic acid and therefore form two stoichiometric multi-component domains. Each domain has a molar ratio of 2:1 for 5OIA and terephthalic acid. For each component (5OIA or terephthalic acid), the two coadsorption structures exhibit opposite chirality.