Infrared Spectroscopic Study of Chemically lnduced Dewetting in Liquid Crystalline Types of Self-Assembled Monolayers

Self-assembled monolayers (SAMs) were prepared by chemisorption of n -hexadecanoic acid ( 1 ), 4-hexadecyloxybenzoic acid ( 2 ), and 4‘-hexadecyloxybiphenyl-4-carboxylic acid ( 3 ), molecules with liquid crystalline properties, onto air-exposed silver substrates to produce films with essentially identical CO 2 - /Ag interfaces. Brief H 2 S exposure leads to immediate −CO 2 H formation and film reorganization. Both the 1 and 2 SAMs dewet into discrete crystallites with their alkyl chain c -axes aligned near parallel to the substrate plane. In contrast, the 3 SAM reorganizes into a uniform, quasi-2-D, network of hydrogen-bonded CO 2 H groups at the film/substrate interface in which the c -axes remain near perpendicular to the substrate plane. Upon extended storage in air, oxidation of the sulfided Ag surface layer induces a near complete return of the 1 SAM to its original state, while the 2 and 3 SAMs show only partial reversal. These results demonstrate the interplay between intermolecular and interfacial interaction forces and their effects on dynamic restructuring of highly organized monolayers under chemical stress.