Synthesis and Characterization of Submicron-Sized and Monodisperse Liquid Crystal Capsules
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1176-Y03-21
Synthesis and Characterization of Submicron-Sized and Monodisperse Liquid Crystal Capsules Yi-Chun Liu , Sheng-Wen Lin and Hui-Lung Kuo Material and Chemical Research Laboratories, ITRI, Hsinchu, Taiwan ABSTRACT Here we developed a new method to prepare the liquid crystal particles by first synthesizing the monodisperse hollow inorganic spheres and then allowing the liquid crystals to infiltrate into the hollow spheres. The resulting liquid crystal colloidal particles have a diameter of 285nm with a low polydispersity of 0.03. DSC thermograms showed a clear peak at around 30 degree, indicating the isotropic-nematic transition of liquid crystals encapsulated in the silica shells. The inorganic shells can prevent liquid crystals inside from leaking out and also hold the spherical shape of colloidal particles after the evaporation of the dispersant. A thin film assembled by the liquid crystal colloidal particles was also prepared in this report. INTRODUCTION The optically anisotropic colloidal particles enable many new studies of both technological and scientific interests in recent years. Especially birefringent colloids from liquid crystal are usually spherical and have tunable optical properties when exposed to external electric/magnetic field. They are therefore believed to be a good candidate for making intriguing optical devices. However, it is challenging to make submicron-sized liquid crystal particles with very low polydispersity using standard emulsion techniques. Here we developed a new method to prepare the liquid crystal particles by first synthesizing the monodisperse hollow inorganic spheres and then allowing the liquid crystals to infiltrate into the hollow spheres. The liquid crystal capsules could serve as a new class of building blocks to construct 3D colloidal crystals that are expected to be used in controlling the propagation of photons. The advantage is that the position of stop band can be tuned over a broad range by simply controlling the refractive index of liquid crystals infiltrated into the hollow particles. In this report, we also prepared a thin film assembled by the monodisperse liquid crystal capsules. . EXPERIMENT Monodisperse polystyrene (PS) spheres were coated with silica shells on the surfaces using a modified Stöber procedure. TEOS which is a commonly used sol-gel precursor was hydrolyzed to amorphous silica at pH>10.The core-shell particles could form stable aqueous suspensions due to the net charges on the surface of silica shells. The size distribution and zeta potential of core-shell particles in aqueous solution were measured by DLS. To obtain hollow spheres of silica, we calcined the sample in air at 500 degrees for 1h to remove the PS macromolecules. The resulting hollow spheres were infiltrated in vacuo with the low molecular-weight liquid crystal 5CB (4’-n-(pentyloxy)-4-biphenylcarbonitrile) which
exhibits nematic phase at 23~35 ℃. The phase transition temperatures of LC encapsulated in hollow silica shells were identified by DSC. A thin film assembled by m
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