New strategies and implications for the photoalignment of liquid crystalline polymers

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The photoalignment of liquid crystalline materials has been studied extensively over the past two and a half decades and has recently become of technological importance in the liquid crystal display panel industry. This review introduces recent attempts at the photoalignment of liquid crystalline polymers and focuses on two aspects. First, strategies to ensure effective in-plane alignment of photoresponsive mesogens are highlighted. Despite the numerous investigations reported to date, film systems have not been well optimized in terms of realizing efficient photoreactions that consider the mesogen orientations. Second, new photoalignable systems composed of block copolymers with surface-grafted polymers and block copolymer films are introduced. The photoalignment processes in these mesoscopic systems involve strong cooperative motion of the different hierarchical size features. In the course of these approaches, a new strategic platform, photoalignment of liquid crystalline polymers via commanding from the free surface, is proposed. These approaches are expected to offer new concepts and possibilities for smart light-responsive materials and systems. This review introduces recent attempts in the photoalignment processes of liquid crystalline polymers focusing on the two aspects. First, the strategies to ensure effective in-plane alignment of the photoresponsive mesogens are summarized. Despite many investigations reported so far, the film systems have not been optimized for efficient photoreaction. Second, new photoalignable systems involving block copolymer frameworks such as surface-grafted polymers and block copolymer thin films are introduced. The photoalignment processes in such mesoscopic systems involve strong cooperative motions among different hierarchical size features. Based on these approaches, a new strategic platform, photoalignment via a command surface at the free surface, is further proposed.