Abstract
Vertical alignment of liquid crystal (LC) was achieved in an easy and effective way: in situ photopolymerization of dodecyl acrylate (DA) monomers initiated by polyimide based on 3,3′,4,4′-benzophenonetetracarboxylic dianhydride and 3,3′-dimethyl-4,4′-diaminodiphenyl methane (BTDA-DMMDA PI). The alignment behavior and alignment stabilities were characterized by a polarizing optical microscope (POM), which showed a stable vertical alignment after 12 h of thermal treatment. The chemical structures, morphology, and water contact angles of alignment films peeled from LC cells with and without DA monomers were analyzed by means of a Fourier transform infrared spectrometer (FTIR), a scanning electron microscope (SEM), and a contact angle tester, separately. The results confirmed that the DA monomers underwent self-polymerization and grafting polymerization initiated by the BTDA-DMMDA PI under ultraviolet irradiation, which aggregated on the surfaces of PI films. The water contact angles of the alignment films were about 15° higher, indicating a relative lower surface energy. In conclusion, the vertical alignment of LC was introduced by the low surface free energy of PI films grafted with DA polymer and intermolecular interactions between LC and DA polymers.
Highlights
A liquid crystal (LC) alignment layer is a crucial component of liquid crystal displays (LCDs), which has a great influence on the LCDs’ optical and electrical performance in terms of view angles, response time, and voltage holding ratio, among others
Fourier transform infrared spectrometer (FTIR) is useful for comparing the chemical structures of alignment layers before and after UV
Thiscaused result an elevation of contact angles and the reduction of total surface free energy, contributing to revealed that the dodecyl acrylate (DA) monomers grafted onto the PI film caused an elevation of contact angles and the vertical alignment of LCfree
Summary
A liquid crystal (LC) alignment layer is a crucial component of liquid crystal displays (LCDs), which has a great influence on the LCDs’ optical and electrical performance in terms of view angles, response time, and voltage holding ratio, among others. Polymers 2017, 9, 233 the PSVA technology showing strength through its fast response, high transmittance, and simple manufacturing process [18] has been widely investigated This technology is conducted as follows: the LC cell containing LC and UV-curable monomers is UV-irradiated under a voltage larger than the Freedericksz transition voltage, and the pretilt angle is fixed by the polymer networks formed during UV irradiation. Discovered that the pretilt angle of homogeneous alignment polyimide (PI) film was controlled using photocurable monomer (NOA65) without photoinitiator Inspired by these results, we proposed using photosensitive PI as a photoinitiator to initiate long alkyl monoene to obtain a uniform and stable vertical alignment. The chemical structure and morphology of the PI films peeled from LC cells with and without DA monomers, as well as the alignment behavior and its thermal stability, were characterized and analyzed This will provide the vertical alignment method with a simple procedure and free of additional micromolecular initiators
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