Dependence of the Glass Transition Temperature of Polymer Films on Interfacial Energy and Thickness.
Dependence of the Glass Transition Temperature of
Polymer Films on Interfacial Energy and Thickness.
Fryer, D. S.; Peters, R. D.; Kim, E. J.; Tomaszewski, J.
E.; dePablo, J. J.; Nealey, P. F.; White, C. C.; Wu, W.
Macromolecules, Vol. 34, No. 16, 5624-5634, 2001.
polymer films; temperature; thickness; interfacial
energy; x-ray reflectivity; modified surface energy
The glass transition temperature (Tg) of ultra thin
films (thickness 80-18mm) of polystyrene (PS) and poly
(methyl methacrylate) (PMMA) was measured on surfaces
with an interfacial energy, gsl, ranging from 0.50 to
6.48 mJ/m2. The surface consisted of self-assembled
monolayers of octadecyltrichlorosilane (OTS) that were
exposed to x-rays in the presence of air. Exposure to
x-ray radiation systematically modified the surface by
incorporation of oxygen containing groups on to the OTS.
The interfacial energy for PS and PMMA on the OTS
surface was quantified using the Fowkes-van
Oss-Chaudhury-Good model of surface tension. For both
polymers, the interfacial energy increased with exposure
dose. The Tg of the films was characterized using local
thermal analysis, ellipometry and x-ray reflectivity.
The results from all three methods of measuring Tg
agreed within the resolution of the techniques. The
results from all three methods of measuring Tg agreeded
within the resolution of the techniques. At low values
of gammasl, the Tg of PS and PMMA was below the bulk
value. At high values of gammasl, the Tg was higher that
the bulk value and increased monotonically with
increasing gammasl. The deviation of the Tg from the
bulk value increased with decreasing film thickness. For
a specific film thickness, deltaTg = Tg (film) - Tg
(bulk) scaled linearly with gamma irrespectivie of the
chemistry of the polymer.