Unraveling the Effect of Polarized Light and Abrasion in Applicative Customizing of the Azo-Polyimide Morphology

A polyimide containing azo-naphthalene and propylenedioxy units in the side chain was obtained from a fluorinated dianhydride and a triphenylmethane (TPM)-based diamine carrying the photoreceptor. After processing into thin films, this polymer was subjected to a UV laser under different fluence and pulse number conditions. Subsequently, an additional surface rubbing treatment was done, and the results were evaluated for the first time in terms of FTIR dichroism and anisotropy, including optical, morphological, and wettability anisotropies. The polarized ATR-FTIR measurements were used to investigate the spectral changes expressed by different chemical functionalities in correlation with conformational changes experienced by the backbone and the side chain. It evidenced an induced biaxiality in the irradiated films, while the rubbing process caused the reorientation of the side chain, which was superimposed by the direction acquired through the cyclic trans–cis–trans photoisomerization of the azo-naphthalene pendent group. Birefringence measurements emphasized the difference in the molecular ordering produced by the surface modification methods used, showing that rubbing of the samples at lower laser fluence is more beneficial for acquiring highly birefringent layers. A comprehensive description of the polyimide substrate's morphological properties was made to establish suitable interfaces with materials used in electronics. The AFM images provided information about morphology, while the polar graphs of the polar and azimuth angles clarified the orientation and spatial distribution of the surface topography, enabling the examination of the surface structure and direction at the nanometric scale. Surface wettability anisotropy was evidenced via contact angle measurements, showing a higher adhesion for the rubbed and irradiated samples at the interface with certain conducting materials used in electronics.