Surface anisotropy from photo-induced bond breaking at polymer surfaces: A sum-frequency vibrational spectroscopic study of polyimide

Abstract

Adsorption and decomposition of formic acid on MgO(001) surface as investigated by temperature programmed desorption and sum-frequency generation spectroscopy: Recurrence induced defect sites Sum-frequency vibrational spectroscopy was used to study how linearly polarized UV irradiation could cause bond breaking and alter the surface structure of a polyimide. The spectroscopic results allowed the determination of an approximate orientational distribution of the polymer backbones at a rubbed surface. They also permitted deduction of rates of bond breaking of the backbones at the surface by UV dosage. The surface anisotropy resulting from bond breaking by linearly polarized UV irradiation was found to be relatively small, suggesting a weak azimuthal anchoring energy for liquid crystal films deposited on such a surface.

Nonlinear Optical Spectroscopic Studies of Polymer Surfaces for Liquid Crystal Alignment: Photo-Irradiated Polyimide and Rubbed Polystyrene Surfaces

“…The quantity QðtÞ is the mode amplitude A q;eff ðU ¼ 90 ; SSPÞ for the phenylene stretch mode presented in Figure 4. From the decay of A q;eff ðU ¼ 90 ; SSPÞ, we find a ¼ ð3:0 AE 0:3Þ Â10 À2 J À1 Á cm 2 , b ¼ ð2:6 AE 0:2Þ Â 10 À2 J À1 Á cm 2 [14]. These values also describe the experimental data of unrubbed PI surface.…”

“…The detailed analysis is described in Ref. [14]. The quantity QðtÞ is the mode amplitude A q;eff ðU ¼ 90 ; SSPÞ for the phenylene stretch mode presented in Figure 4.…”

40.4: New Photoalignment Polymeric Materials with Excellent Photosensitivity and Stability

“…Among these methods, photoinduced anisotropic decomposition of polyimide film has received considerable attention because of their superior properties such as unique photo-and thermal stability to the other methods. In this method, the surface anisotropy of PI films was induced by anisotropic decomposition and with subsequent oxidation of the weakest bonds of polyimide molecule after irradiation of LPUVL, which has been confirmed by spectroscopic measurements [5][6][7]. Due to their low photosensitivity to UV light, however, high exposure energy, and hence, inconveniently long exposure time are required to achieve photoalignment of PIs, especially when the aromatic polyimides are concerned.…”

Tribophysical Interpretation of Polymer Sliding Mechanisms

“…For highly aromatic polymer chains with high stiffness, such as polyimide, chain mobility becomes less important while chemical degradation may occur through intramolecular ring-opening reactions 36 . Referring to Fig.…”