Relaxation of polymer thin films in isothermal temperature-jump measurements

The dynamic behavior of thin polymer films is of interest in the fabricatio n of microelectronics and optoelectronics and in the coatings industry. It is known that polymer relaxation is affected by film thickness and the part icular substrate/polymer pair. We previously used a spectroscopic ellipsome ter to investigate the glass transition in thin films. In addition to infor mation on the modification of thermal transitions such as the glass-transit ion temperature, the speed of data acquisition in an automated, spectroscop ic ellipsometer, operated at a single wavelength of 780 nm, allows for the direct observation of the isothermal dimensions of a thin polymer film as a function of time after a rapid temperature change. In this article, we dis cuss recent results from the observation of the time dependence of film-nor mal thickness and normalized, in-plane, lateral dimension as well as simple fits to this relaxation behavior in terms of a normalized viscosity and re laxation time. The results support a highly asymmetric initial thermal expa nsion normal to the film followed by close to isotropic relaxation and anis otropic "flow" (the flow in response to the vanishingly small shears of the rmal expansion). These features may clarify issues involving the observatio n of chain confinement in thin polymer films in terms of potential differen ces between equilibrium and dynamic measurements. (C) 2000 John Wiley & Son s, Inc.