Ordering of Glass Rods in Nematic and Cholesteric Liquid Crystals

The orientational assembly of glass rods (3 x ~15 μm) in nematic, twisted nematic, and cholesteric liquid crystal cells was observed and quantified with optical microscopy. At this size, the rods were affected strongly by gravity and sedimented to the bottom of the cells. Temporal visualization of the sedimentation process (induced by flipping the cell over) shed insight into the effect the liquid crystal order had on the glass rod orientation. For nematic and twisted nematic geometries, the glass rods were aligned parallel to the local director orientation. Control experiments indicate that the rod alignment is not due to capillary flow induced artifacts from fabrication of the sample or due to interactions with the buffed substrates. As evidence, the glass rods rotated 90 degrees as they fell from the top to the bottom of a twisted nematic cell. More complex behavior was observed for cholesteric cells depending on the pitch length. A computational model was developed to predict the elastic energy of the system as a function of the angle between the long axis of the glass rod and the cholesteric liquid crystal director. The model predicted that the elastic energy of the system was minimized when the glass rods remained parallel to the cholesteric liquid crystal director when the pitch was sufficiently long, which agrees with experimental results. ©2011 Optical Society of America OCIS codes: (160.3710) Liquid crystals; (160.1585) Chiral media; (160.2100) Electro-optical materials; (160.0160) Materials. References and links 1. T. Hegmann, H. Qi, and V. M. Marx, “Nanoparticles in liquid crystals: synthesis, self-assembly, defect formation and potential applications,” J. Inorg. Organomet. Polym. Mater. 17(3), 483–508 (2007). 2. M. D. Lynch and D. L. Patrick, “Controlling the orientation of micron-sized rod-shaped SiC particles with nematic liquid crystal solvents,” Chem. Mater. 16(5), 762–767 (2004). 3. J. D. Mougous, A. J. Brackley, K. Foland, R. T. Baker, and D. L. Patrick, “Formation of uniaxial molecular films by liquid-crystal imprinting in a magnetic field,” Phys. Rev. Lett. 84(12), 2742–2745 (2000). 4. J. B. Pendry, “A chiral route to negative refraction,” Science 306(5700), 1353–1355 (2004). 5. P. R. Evans, G. A. Wurtz, W. R. Hendren, R. Atkinson, W. Dickson, A. V. Zayats, and R. J. Pollard, “Electrically switchable nonreciprocal transmission of plasmonic nanorods with liquid crystal,” Appl. Phys. Lett. 91(4), 043101 (2007). 6. W. Cai, and V. Shalaev, Optical Metamaterials: Fundamentals and Applications (Springer Science + Business Media, 2010). 7. L. Cseh and G. H. Mehl, “The design and investigation of room temperature thermotropic nematic gold nanoparticles,” J. Am. Chem. Soc. 128(41), 13376–13377 (2006). 8. L. Li, J. Walda, L. Manna, and P. Alivisatos, “Semiconductor nanorod liquid crystals,” Nano Lett. 2(6), 557–560 (2002). 9. G. N. Karanikolos, N.-L. Law, R. Mallory, A. Petrou, P. Alexandridis, and T. J. Mountziaris, “Water-based synthesis of ZnSe nanostructures using amphiphilic block copolymer stabilized lyotropic liquid crystals as templates,” Nanotechnology 17(13), 3121–3128 (2006). 10. K. Wu, K. Chu, C. Chao, Y. Chen, C. Lai, C. Kang, C. Chen, and P. Chou, “CdS nanorods imbedded in liquid crystal cells for smart optoelectronic devices,” Nano Lett. 7(7), 1908–1913 (2007). #155093 $15.00 USD Received 20 Sep 2011; revised 4 Nov 2011; accepted 4 Nov 2011; published 8 Nov 2011 (C) 2011 OSA 1 December 2011 / Vol. 1, No. 8 / OPTICAL MATERIALS EXPRESS 1536 Report Documentation Page Form Approved OMB No. 0704-0188 Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number.