6 MeV pulsed electron beam induced surface and structural changes in polyimide

Thin films of polyimide (PMDA-ODA, Kapton) having 50 μm thickness were irradiated with 6 MeV pulsed electron beam. The bulk and surface properties of pristine and irradiated samples were characterized by several techniques such as stress–strain measurements, Fourier Transform Infrared (FTIR), UV–vis spectroscopy, contact angle, atomic force microscopy (AFM) and profilometry. The tensile strength, percentage elongation and strain energy show an enhancement from pristine value of 73–89 MPa, 10–22% and 4.75–14.2 MJ/m3 respectively at the maximum fluence of 4 × 1015 electrons/cm2. This signifies that polyimide being an excessively aromatic polymer is crosslinked due to high-energy electron irradiation. In surface properties, the contact angle shows a significant decrease from 59° to 32° indicating enhancement in hydrophilicity. This mainly attributes to surface roughening, which is due to the electron beam induced sputtering. The surface roughening is confirmed in AFM and profilometry measurements. The AFM images clearly show that surface roughness increases after electron irradiation. Moreover, the roughness average (Ra) as measured from surface profilograms is found to increase from 0.06 to 0.1. The FTIR and UV–vis spectra do not show noticeable changes as regards to scissioning of bonds and the oxidation. This work leads to a definite conclusion that 6 MeV pulsed electron beam can be used to bring about desired changes in surface as well as bulk properties of polyimide, which is considered to be a high performance space quality polymer.