Imprinting the Quasi Bookshelf Texture of a Ferroelectric Liquid Crystal into Nano-scaled Polymer Fibrils
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Imprinting the Quasi Bookshelf Texture of a Ferroelectric Liquid Crystal into Nano-scaled Polymer Fibrils S. H. Kim, S. Suresh, and L.-C. Chien Chemical Physics Interdisciplinary Program and Liquid Crystal Institute Kent state University, Kent, Ohio 44242 ABSTRACT Polymer-stabilized ferroelectric liquid crystals (PSFLCs) are made by photopolymerizing 3% reactive mesogenic monomer on a quasi bookshelf texture of a ferroelectric liquid crystal (FLC). We observe the formation of nano-scaled polymer fibrils templated by the two dimensionally ordered host. The polymer fibrils capture the orientation of the host with thin polymer fibrils interweaving the smectic layers. The SEM study highlights the difference in morphology of the polymer fibrils depending on polymerization conditions; that is, polymerizing with or without the presence of an electric field. The polymer networks suppress the cone of rotation of FLC and thus, facilitate the switching and shorten the response time of the PSFLCs. We observed the threshold-less switching behavior in PSFLCs from samples polymerized with and without the field.
INTRODUCTION Polymer stabilized liquid crystals (PSLCs) have rapidly developed into a unique class of electro-optical materials and play an important role in display1,2 and photonic3,4 technologies. The polymer network morphology of PSLCs, unique among these applications, plays a critical role in the performance of each device.5,6 The polymer network is typically formed via a controllable photopolymerization process using a wide variety of optical pattern forming states of liquid crystal hosts. The resultant polymer networks not only mimic the phase and structures of liquid crystals but also, under applied external field, control the reorientation of liquid crystal molecules in the surrounding area of polymer network. The polymer morphology itself is of considerable interest in the study of polymerization-induced phase separation in orientationallyordered media. Despite reports on polymer stabilized ferroelectric liquid crystals,7-10 the specific morphology of the polymer network and its precise connection to the electro-optical properties of ferroelectric liquid crystal (FLC) system remain open issues. In this paper, we report the study of polymer networks formed in a FLC and the influences of network morphology on electrooptical properties of the composite system.
EXPERIMENTAL DETAILS The CS1024 FLC obtained from Chisso Japan was used as the host (96.85wt%). A mesogenic monomer 1,4’-{bis[4-(6-acryloyloxy)hexoxy] benzoate}-2-methyl-benzene (BBMB6) (3wt%) was used to form polymer networks in CS1024. A small amount of photo initiator Irgacure 369 (0.15wt%) was added to the mixtures of monomer/liquid crystal. The mixtures of FLC/monomer/photoinitiator were loaded into commercial LC cells (with 4 µm CC1.7.1
spacing between anti-parallel rubbed polyimide alignment layers and ITO electrode area of 0.9x0.9 mm2) by capillary action. The FLC mixtures were photopolymerized by UV illumination (the light source has a wavelength of
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