Emersion of 11-mercapto-1-undecanol-modified Ag substrates from aqueous and nonaqueous solvents: The effect of emersion velocity on emersed solvent layer thickness

The formation and stabilization of the emersed interface is dependent on the interplay of various hydrodynamic (viscosity, emersion velocity) and intermolecular forces (hydrogen bonding, dipole-dipole). In an effort to better define the role of these forces, manual-null ellipsometry has been used to investigate the effect of emersion velocity on the emersed layer thickness of water, methanol, acetonitrile, chloroform, 1-butanol, and 1-pentanol at self-assembled monolayers of 11-mercapto-1-undecanol (11-MUD) on polycrystalline Ag substrates. Emersed solvent layer thicknesses decrease as emersion velocity increases for water, methanol, acetonitrile, and chloroform. In contrast, the emersed layer thicknesses of 1-butanol and 1-pentanol remain relatively constant as the emersion velocity increases over the range of velocities accessible (0.0055-0.037 cm/s). These data suggest that the effect of emersion velocity on the resulting emersed layer thickness depends on the chemical and physical characteristics of the solvent. A descriptive model has been developed to describe the emersion process in terms of the interplay between hydrodynamic and intermolecular forces. According to this model, a shear plane develops at some distance away from the solid surface when the hydrodynamic forces are great enough to overcome the intermolecular forces between the liquid layers that behave as a Newtonian fluid at the molecular level.