Molecular-Level Control over Surface Order in Self-Assembled Monolayer Films of Thiols on Gold

Long-chain ω-hydroxyalkanethiols [HS(CH 2 ) n OH] coordinate to gold surfaces through the sulfur atom and produce ordered, hydrophilic monolayers in which the hydroxyl groups are exposed at the outer surface. Coadsorption of two ω-hydroxyalkanethiols of different chain lengths n resulted in the formation of a monolayer having a disordered surface region that was markedly less hydrophilic than the homogeneous, hydroxylic surface formed from either pure compound. By controlling the composition of the monolayer, it was also possible to control simultaneously the degree of order in the surface and its hydrophilicity. In the monolayers containing a mixture of alkanethiol components, these components apparently did not phase-segregate into macroscopic islands, but were dispersed on a molecular scale.