Abstract

The present study focuses on the microstructural characterization of polyurea after extended UV exposure using a mechanics-based, atomic force microscope (AFM) investigation. Extended exposure to UV radiation resulted in photo-degradation with subsequent photo-oxidation reactions causing an increase in the surface roughness associated with crack nucleation. The crack opening and length were found to increase considerably with the rise in UV exposure duration. The crack growth was modeled using linear elastic fracture mechanics (LEFM) since the mechanical properties of the surface degraded layer were found to be within the limits of applicability of the theory. Force-distance measurements performed on the surface of the samples revealed a significant increase in the local modulus after 4.5 weeks of exposure. The local modulus was found to reach a steady limit after 7.5 weeks of UV radiation. The adhesive tip-sample forces resolved from the AFM force-displacement measurements indicated a drastic decrease after 3 weeks of exposure due to embrittlement of photo-oxidized exposed surface.Radiation effect; Microstructure; Polymers; LEFM

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