Phase-separated structures of mixed LB films of silane-coupling agents with polymerization initiating groups and amphiphilic carboxylic acids

We studied the structures of mixed LB films of silane-coupling agents with polymerization initiating groups (SCA-PIGs) and conventional amphiphiles such as long-chain fatty acid and hybrid carboxylic acid having both perfluoroalkyl and alkyl moieties. We used (2-bromo-2-methyl)propionyloxyundecyltriethoxysilane (BUE) and (2-bromo-2-methyl)propionyloxyhexyltriethoxysilane (BHE) as SCA-PIGs. Surface pressure–area isotherms of mixtures of SCA-PIGs and conventional amphiphiles were measured. Additivity rule was found to be held in all the mixed systems studied. Mixed LB films of SCA-PIGs and conventional amphiphiles were fabricated. When SCA-PIGs were mixed with long-chain fatty acids, the fatty acids formed circular domains with diameters on the micrometer length scale in the mixed LB films. In contrast, when SCA-PIGs were mixed with hybrid carboxylic acids, nanostructures were found. The difference in morphology can be due to the difference in homo and hetero intermolecular interactions, affecting the balance between the line tension and dipole–dipole interaction. Optimized conditions for the nanowire formation were obtained for mixed LB films of SCA-PIGs and hybrid carboxylic acids.