Photo-controllable color of sub-micron fibers with dye-doped cholesteric liquid crystal based on coaxial electrospinning technique

  • 陳 哲培

Student thesis: Master's Thesis


This thesis successfully develops photo-controllable colorful DDCLC sub-micron fibers through the coaxial electrospinning technique Experimental results show that different polymer concentrations and feeding rates of the polymer solution and DDCLC can significantly cause different morphologies (appearances) of the formed fibers including beading quasi-continuous and smearing-out types Among these types quasi-continuous LC fibers are practical for further application Quasi-continuous fibers can be successfully fabricated at a polymer concentration of 17 5 wt% and specific ranges of ratio for the feeding rates of sheath (polymer solution) to core (DDCLC) Furthermore the experimental results show that the reflective features (i e reflective color and reflectivity) can all be optically controlled by successive UV- and blue beam-irradiation With the weak UV-irradiation (845 ?W/cm2) only a few azo-chiral molecules become bended cis form through trans-cis isomerizations As a consequence the local order parameter of LCs may slightly decrease thus extending the helical pitch of CLC without distorting the helical axis in the fibers This condition results in the red-shift of the reflective color of LC fibers from blue to green With the blue beam-irradiation following UV-irradiation the cis isomers may revert to the rod-like trans state resulting in the recovery of the helical pitch of the CLC in the fiber cores The color of the fibers then blue-shifts back Under the same conditions of UV-irradiation if the fibers are thicker the recovery time becomes longer because of the higher concentration of induced cis isomer If the intensity of the UV-irradiation is enhanced to 2 75 mW/cm2 the induced massive cis isomers can also considerably disturb the helical structure of the CLC in the cores thus eliminating the color reflectivity of the fibers More defects remain in the thicker fibers after the blue beam-irradiation-induced recovery under the same conditions of UV and blue beam-irradiation This condition is caused by the discrepancies between the confinement strengths and concentration of the residual cis isomer in thicker and thinner fibers Based on the results the optically controllable LC fibers have high potential for use in applications of UV micro-sensors and wearable smart textiles
Date of Award2014 Aug 27
Original languageEnglish
SupervisorChia-Rong Lee (Supervisor)

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