| Abstract
| - Moisture absorption in poly(4-tert-butoxycarbonyloxystyrene) (PBOCSt) films supported on Al2O3 sputtercoated silicon wafers is measured using neutron and X-ray reflectivity. Accumulation of water at theinterface during moisture exposure results in an apparent film-thickness-dependent swelling for ultrathinPBOCSt films. The swelling of a film on Al2O3 is less than the swelling of a film of the same thicknesson SiOx for films thinner than 20 nm. This is due to comparatively less moisture accumulation at theAl2O3/PBOCSt interface. A simple, zero adjustable parameter model consisting of a fixed water-rich layerat the interface and bulk swelling through the remainder of the film describes the thickness-dependentswelling quantitatively. The influence of four different Al2O3 surface treatments on the moisture distributionwithin PBOCSt films was examined: bare Al2O3, tert-butylphosphonic acid, phenylphosphonic acid, andn-octyltrichlorosilane. Both the phenyl and the octyl surface treatments reduce the accumulation of waterat the polymer/substrate interface. The tert-butyl treatment does not reduce the interfacial waterconcentration, presumably due to insufficient surface coverage.
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