ALKYL GROUP DEPENDENCE OF THE SURFACE-INDUCED ASSEMBLY OF NONIONIC DISACCHARIDE SURFACTANTS

N-Alkylmaltonamide nonionic diblock surfactants of varying hydrophobic segment lengths were synthesized, and their surface active properties on highly oriented pyrolytic graphite were characterized by atomic fo rce microscopy (AFM). The N-alkylmaltonamide surfactants are composed of maltose, a hydrophilic disaccharide, with amide-linked alkyl groups of varying length, from octyl to octadecyl. All the surfactants readi ly adsorb uniformly onto the hydrophobic graphite surface from solutio n. Surfactants with alkyl lengths of 10 or more carbons exhibit epitax ial adsorption on graphite, forming ordered hemicylinders with a diame ter that increases with increasing surfactant length. The solution con centration necessary for inducing surface ordering decreases with incr easing alkyl chain length. N-Octadecylmaltonamide, which is insoluble in water, adsorbed from methanol solution without ordering and upon so lvent replacement with water, assembled into hemicylinders. Once forme d, the surfactant structures appeared stable in pure water and under h igh scanning forces. The effects of alkyl chain length on surface-indu ced assembly and molecular packing are discussed from the viewpoint of surfactant composition and adsorbed configurations.