| Abstract
| - We have examined the adsorption of a nonionic surfactant, penta(ethylene glycol) monododecyl ether(C12E5), at the poly(methyl methacrylate) (PMMA)−water interface using spectroscopic ellipsometry. Thesolid PMMA surface was deposited by spin casting an ultrathin film onto a freshly cleaned silicon wafer.Measurements by both spectroscopic ellipsometry (SE) and atomic force microscopy (AFM) showed thatthe thin PMMA film was uniform with no prominent structural features on the surface. The adsorptionof C12E5 at the solid PMMA−aqueous solution interface was studied using a specially designed cell witha fixed angle of incidence of 75°, and the measurements were made over a wide concentration range aroundthe critical micellar concentration (cmc). It was found that the adsorption is completely reversible and thatthere is no observable penetration of C12E5 into the PMMA. The adsorption was found to reach equilibriumwell within seconds. Although spectroscopic ellipsometry cannot allow a reliable measurement of layerthickness as a result of coupling between refractive indices and layer thickness for ultrathin layers, thesurface excess at a given concentration can be determined reliably. The limiting area per molecule at thecmc was calculated to be 50 ± 3 Å2, in good agreement with the value obtained from a previous neutronreflection study.
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