Primary Investigations On Morphologies And Properties Of Chiral Materials

chiral morphology themselves. The unusual optical, magnetic, electric and mechanical properties of chiral materials make them a wide range of promising applications in the fields of biology, medicine, polymer materials, nanoelectromechanical systems (NEMS) and stealth materials. For these chiral materials, the formation mechanism of chiral morphologies and quantitative characterizations of their properties are two critical issues. In this thesis, we preliminarily investigated the underlying physical mechanism of paper twisting and the shape memory effect (SME) and the superelasticity of nanohelices.A series of experiments on paper strips twisting after wetting and redrying have been done. The effects of water content on strips twisting are also investigated. Based on the experimental results and the hierarchical microstructure of paper strips, the physical mechanism of strips twisting is preliminarily given. It is found that strips twisting are mainly induced by the change of helical angle of cellulose chain twining in the cell wall during wetting and redrying of the strips. This is a typical multi-scale chirality transfer. The chiral morphology parameters of paper twisting belts depend on the water content during strips wetting and redrying. From the viewpoint of biomimics, this phenomenon inspire us that we can effectively control and generate the chiral morphology and then even tune the properties of materials by controlling the chirality transfer among different length levels. Two typical of areas are the polymer and gel materials with chiral structures or chiral morpholoiges. Moreover, this study is also helpful in interpreting and understanding the underlying mechanism of chiral growth of many plants in nature.The SME and the superelasticity of nanohelices with chiral morphology are also investigated in this thesis. Based on the surface elasticity theory and nonlinear elastic thin rod model, a nonlinear rod model for nanowires incorporating surface effects is developed to quantitatively investigate the effect of cross-sectional geometry and surface effect on SME and superelasticity of nanomaterials. The results show that the surface effects play an important role in the SME and the superelasticity of nanohelices. Furthermore, SME and the superelasticity can effectively enhance the efficiency of energy storage and retrieval of nanohelices without energy dissipation. This study would be helpful to characterize the mechanical behavior of nanowires with complex morphologes. It suggests that we can design and fabricate the nanohelices or the nanohelices array and other nanohelice-based materials to act as the nanosized energy devices for the purposes of high damping and high efficiency energy storage and retrieval.