Polyimide films tailored by UV irradiation: Surface evaluation and structure-properties relationship

This study focuses on a detailed comparative investigation of the changes inflicted by the UV irradiation of some polyimide films. In this regard, three aromatic polyimides were synthesized via conventional, high-temperature, polycondensation reactions in solution, followed by conventional casting towards polyimide thin films. The obtained materials were subjected to 10 h of UV irradiation and various techniques were used to assess the chemical and topographical changes it produced. The FT–IR evaluation provided evidence of the breakage of the imide cycle. Variations in the water contact angle values suggested a shift in the occurrence of hydrophobic and hydrophilic groups on the surface of the polyimide films. SEM analysis showed no major changes in films' morphology after UV irradiation, while EDX measurements emphasized the connections between the structure of each polyimide and the changes in its surface chemistry. Cell behavior was closely related to the surfaces’ wettability and revealed that UV irradiation enhances cell proliferation on polyimide films. It was assumed that the hydrophobicity induced by certain structural elements led to a different exposure of the imide cycle to UV irradiation through distinct polymer chains orientation.