Photodesign and fabrication of surface relief gratings on films of polyimide-based supramolecular systems obtained using host-guest strategy

Abstract

New supramolecular structures were attained by an original approach based on mixing the concepts of polyamidic acid (PAA) host and an azochromophore guest with hydrogen bonding intermolecular interactions. The materials have been obtained and characterized for use as liquid crystal (LC) alignment layers. The azochromophore was introduced in the PAA solution in different ratio followed by casting on glass plate and thermal treatment to realize a film with imide structure, confirmed by Fourier-transform infrared spectroscopy (FTIR). Thermal analyses indicated that the dye loading in the polymer host slightly reduces the temperature of thermal decomposition from 508 to 466 °C, while glass transition temperature ranges between 244 and 213 °C. UV–Vis data proved that the samples exposure at the wavelengths of 355 nm is beneficial for surface relief gratings (SRGs) formation. Atomic force microscopy (AFM) evidenced the surface structuring of the samples and the changes in the spatial and functional contact area characteristics as a function of azo-dye amount. The attained grating periodicity was about 1 μm, while the depth ranged between 35 and 100 nm depending of the system composition. Surface anisotropy, bearing properties and fluid retention are enhanced upon chromophore incorporation. LCs anchoring energy increases with azochromophore percent up to 22.9 ∙ 10 −16 μJ/m 2 , which is desirable for LC display applications. • Supramolecular structures, based on a polymer matrix and an azo-dye, are achieved. • Transparent flexible polyimide films with heat resistance up to 466 °C are attained. • As the azo-dye loading increases LASER-made SRGs depth increases from 37 to 81 nm. • Anisotropy, bearing and fluid retention are enhanced upon azo-dye incorporation. • LC anchoring energy increases with azochromophore percent up to 22.9 ∙ 10 −16 μJ/m 2 .