Cross-linked epoxy network films were cast onto silicon wafers with a variety of surface treatments. X-ray reflectivity was used to characterize their electron density and thermal expansion in the rubbery state. A transition from bulk to confined expansion occurs in the range of 200 to 400 , where thinner films exhibit smaller rubbery expansion coefficients. The thermal expansion behavior of the epoxy films was independent of the substrate surface treatment, which varied in both surface energy and the strength of bonding interactions with the polymer. The thickest epoxy films displayed typical rubbery thermal expansion values for temperatures above the bulk polymer glass transition temperature. The thinnest epoxy films (< 120 ) exhibited typical glassy expansion values even at temperatures (20 to 40) degrees C above the bulk polymer glass transition temperature, independent of the surface treatment.
and Wu, W.
Influence of Cross-link Density on the Thermal Properties of Thin Polymer Network Films, Langmuir, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=852081
(Accessed May 29, 2023)