The optically-compensated-bend(OCB) nematic liquid crystal display(LCD) has attracted much attention due to its superior characteristics such as a fast response time and a wide viewing angle.1,2) In the OCB-LCD, a pi-cell is used as the LC layer. The OCB-LCD has one serious drawback in that it needs the initial transition operation from the splay alignment to the bend alignment in the pi-cell by applying high voltage at start-up, and always needs an operating voltage higher than its critical voltage Vc to maintain the bend alignment. To mitigate this problem, the following methods have been proposed. The first method is to complete the transition from the splay alignment to bend alignment quickly by applying a high voltage3) and by forming transition nuclei on the substrate surfaces.4,5) However, this method does not effectively solve the problem because the initial voltage application is indispensable. The other method which aims to make the initial voltage application unnecessary involves polymer stabilization(PS) of the bend alignment by forming a polymer network6,7) or an aligned polymer wall using the optical polymerization of UV curable crystalline monomers or reactive mesogen molecules dissolved within the liquid crystal host. This method is an effective means to solve essentially the problem that OCB-mode has. However, it should be noted that even if PS treatment is used while applying voltage higher than the critical voltage VC, the bend alignment is still not surely stabilized, while the twist alignment is occasionally resultant. In this study, the conditions required for obtaining surely the bend alignment by the PS treatment using a reactive mesogen are investigated. To investigate theoretically the effect of PS on the electro-optical properties of LC cells, we introduced an additional term fstab=1/2Astab[1-(n*nstab)2],8) which expresses the contribution of PS to the free energy density in LC layer. Astab is the PS coefficient and nstab represents the director profile when the PS is carried out. It is thought that the PS coefficient Astab depends on the density of polymer chain generated by photo-polymerization reaction and the manner of interaction between the polymer chain and liquid crystal molecules. Director profiles in the polymer stabilized pi-cell were theoretically investigated taking account of the effect of PS. From these theoretical results, we could predict that the PS coefficient Astab must be larger than the critical value Astabc to confidently stabilize the bend alignment in the pi-cell. This has been experimentally confirmed using our sample cells in which RMM34(Merk) was used as a reactive mesogen.

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