How microscopic chirality is reflected in macroscopic scale to form various chiral shapes, such as straight helicoids and spiral ribbons, and how the degree of macroscopic chirality can be controlled are a focus of studies on the shape formation of many biomaterials and supramolecular systems. This article investigates both experimentally and theoretically how the chiral arrangement of liquid crystal mesogens in twist-nematic-elastomer films induces the formation of helicoids and spiral ribbons because of the coupling between the liquid crystalline order and the elasticity. It is also shown that the pitch of the formed ribbons can be tuned by temperature variation. The results of this study will facilitate the understanding of physics for the shape formation of chiral materials and the designing of new structures on basis of microscopic chirality.
Dynamic High Contrast Reflective Coloration From Responsive Polymer/Cholesteric Liquid Crystal Architectures10/24/2011
We report on high reflectivity CLC structures (R > 50%) whose wavelength can be thermally tuned reversibly by a de-swelling/re-swelling transition unique to ordered solvent-gel systems. The system contains no chiral dopant and the coloration is completely induced by a responsive chiral structured gel. The de-swelling transition, leading to blue tuning, occurs at the nematic-isotropic transition of the liquid crystal, which is a result of a mismatch in the orientational energy of the isotropic liquid crystal and the anisotropic gel. The re-swelling transition subsequently occurs at the nematic-isotropic transition of gel, due to the miscibility of the isotropic liquid crystal and the isotropic gel, which induces a red-shift in the coloration. Examination of varying clearing point liquid crystal solvents, contact angle measurements, and white light optical profilometry localized thickness measurements shed light on this de-swelling/re-swelling transition. A dynamic, high reflectivity cell was demonstrated by combining both a left-handed chiral gel with a right handed chiral gel, both of whose initial periodicities were equal. Heating of this so-called hyper-reflective cell drove reversible and large scale wavelength changes (100's of nm) while maintaining large reflectivity (R similar to 90%).