Understanding the properties that lead solutes to form films at interfaces, a priori, is not easy.  Some molecules form monolayers while closely related congeners form multilayers.  Some films consist of monomers acting independently while other films show evidence of collective behavior from molecular aggregates.  Molecular organization and mobility in films will depend sensitively on a balance of forces that include a solute's solvation in bulk solution, solute affinity for a surface and lateral associations between adsorbed solutes themselves.  Using both 2nd order nonlinear optical spectroscopy and time resolved fluorescence in a total internal reflection geometry, we have begun to explore the behavior of different 7-aminocoumarins (7AC) adsorbed to silica/liquid interfaces.  Primary amines form terminal monolayers at silica/methanol interfaces with adsorption energies of ~-35 kJ/mole; tertiary amines show clear evidence of multilayer growth.  The solvatochromic behavior of all 7-AC species show the silica/methanol interface to be remarkably nonpolar.

Molecular film formation at solid/liquid interfaces: Spectroscopic studies of monolayer and multilayer growth

244th National Meeting (2012)

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