미래를 창조하는 포스텍 화학공학과
제목: Control of nano-particle alignment in colloid and tunable photonic crystal
내용: Self-assembled nematic and lamellar nano-colloids of two dimensional (2D) nanoparticles can exhibit large optical birefringence or photonic crystalline vivid color reflection depending on their orderings. Electrical manipulation of nanoparticle ordering in such colloidal liquid crystals (LCs) may be able to pave a novel pass in the fields of displays, optical devices, and color tunable functional materials, but repeatable control of nanoparticle ordering states is still a highly challenging task owing to their several inherited features such as weak surface anchoring and weak elasticity. Here, we demonstrate an interesting phenomena that the ordering of 2D α-TiP nanoparticles can be electrically and repeatedly switched among meta-stable nematic (or lamellar), isotropic, and anti-nematic orderings, which are observed in optical experiment. In contrast, X-ray scattering results reveal that the microscale ordering of nanoparticles sustains the initial nematic ordering even in the optically isotropic or anti-nematic odering samples. These observations lead to the conclusion that the nanoparticles in colloid form microdomains under the application of electric fields, and the nanoparticles in each microdomain sustains the initial nematic ordering but the microdomains can be redistributed to be isotropic, nematic or anti-nematic ordering. The optically switchable ordering states can be used to fabricate various optical devices using nano-colloids including a swichable photonic crysalline device .
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