Characterization by Ellipsometry of polymerized ultra-thin films formed in a two-dimensional solvent on an oxide surface

Abstract

Surfactants adsorbed onto the surface of suspended mineral oxide particles may be used to position an ultra-thin layer of polymer on the surface of the particles. The polymer layer is formed by what may be viewed as a three-step process. First, solution parameters are varied in such a way as to induce complete coverage of the particle surface with a surfactant bilayer. Monomer introduced into the solution then partitions into the hydrophobic core of the surfactant layer. In situ polymerization is then initiated to form the polymer layer. The surfactant concentration in the bulk is well below the CMC so that solubilization does not occur nor does a latex form. This process was used to construct ultra-thin polymer layers on the surface of glass slides coated with a vacuum deposited aluminum layer, on which an oxide layer had been formed. The films thus constructed consisted of a polystyrene and sodium dodecyl sulfate suprastructure adhereing to the oxide surface. Ellipsometry was employed to calculate: (1) the optical constants of the freshly deposited aluminum, and (2) the thicknesses of the aluminum oxide and polymer layers. In determination of the thicknesses of the aluminum oxide and polymer layers literature values of the refractive indices were used. Under varying reaction conditions, the thickness of the polymer layer could be varied from 3.5 to 13.6 nm. It may be possible to use this process to produce suspensions of greater stability than those obtained by current techniques.