Surface Modification Studies of Polyimide Films Using Rutherford Backscattering and Forward Recoil Spectrometry

Abstract

We followed the surface imide ring hydrolysis of fully imidized polyimide films by aqueous base solutions using Rutherford backscattering spectrometry. The hydrolysis reaction was studied using several different polyimide films including spuncast and thermally imidized PMDA-ODA, Kapton-H, and Upilex-S films. The boundary between the modified layer at the surface and the underlying film is a sharp front behind which the conversion of the polyimide into poly(amic acid) is complete and ahead of which there is almost no hydrolysis. The modified layer grows linearly with the time it is exposed to the basic solution. The growth velocity increased strongly with increases in the temperature of the basic solution. Under the reasonable hypothesis that the growth of the modified layer is controlled by the kinetics of the hydrolysis of the imide ring at the interface, we extract an activation energy for this process in Kapton-H films of 60 kJ/mol as compared to 68 kJ/mol for Upilex-S. Using forward recoil spectrometry, we studied the amount of interpenetration when a second layer of deuterium-labeled poly(amic acid) was spun-cast onto the surface-modified PMDA/ODA film. We determined that the interface between the spun-cast layer and the base layer is broader when the modification depth is greater. The fracture energy of such an interface, as measured with a T-peel test, rises rapidly as a function of modification depth and saturates at a value ∼20 times the value for an interface formed from PMDA/ODA polyimide with an unmodified surface.