Simulation of chiral liquid crystal self-assembly: analogies with the structural formation of biological fibrous composi
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Simulation of chiral liquid crystal self-assembly: analogies with the structural formation of biological fibrous composites Gino De Luca and Alejandro D. Rey Department of Chemical Engineering McGill University, 3610 University Street Montreal, Quebec Canada H3A 2B2 ABSTRACT The wide majority of biological fibrous composites exhibit twisted plywood architectures (planar or cylindrical) for mechanical reasons [1-5]. These supramolecular organizations originate from the passage of the extracellular matrix (surrounding the chiral fibrous molecules) trough a lyotropic cholesteric liquid crystalline mesophase during the structure formation process [1-5]. In this work, we used the well-established Landau-de Gennes theory of liquid crystals in order to develop a fundamental understanding of the supramolecular self-assembly process leading to the planar monodomain (defect-free) twisted plywood architecture [6]. Simulations illustrate the importance of constraining surface in the formation of defect-free (mechanically effective) composites. These results provide a better understanding of tissue morphogenesis which is highly desirable for the development of new bio-inspired synthetic composites. INTRODUCTION Nature produces composites with mechanical properties far beyond to those engineers are currently able to manufacture synthetically [7]. These materials are assembled at ambient temperature and pressure in aqueous environment while made of relatively simple and biodegradable constituents [7]. Given these advantages, natural composites are of a growing interest in applied material science. A major challenge in the field is to produce a synthetic equivalent of these materials. In order to do so, the structure formation process needs to be thoroughly described and understood. Most of the biological fibrous composites have laminated structures called twisted plywoods. In these supramolecular assemblies, fibers are grouped in parallel and form superimposed sheets. The orientation of the fibers is uniform in each of the sheets but slowly changes by a small constant angle trough the thickness of the material. The twisted plywood architecture of biological fibrous composites is responsible for series of arced patterns and periodic extinction of light when seen in cross-section cuts under electron microscopy and polarized light respectively [1-5]. The origin of this organization is the passage of the extracellular matrix (forming the composite) surrounding the chiral fibrous molecules through a lyotropic cholesteric mesophase during the structure formation process and its successive crystallization. This temporary liquid crystalline state of the matrix provides the structural macromolecules with the necessary mobility to self-assemble in the twisted plywood fashion. This spontaneous helical packing at high concentration originates principally from a thermodynamical need for a minimal excluded volume between the long asymmetric molecules [1-6].
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It is well-known that to be mechanically effective the twisted plywood
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