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Anchoring Energy Measurements at the Aqueous Phase/Liquid Crystal Interface with Cationic Surfactants Using Magnetic Fréedericksz Transition

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Department of Chemistry, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan
Cite this: Langmuir 2018, 34, 1, 81–87
Publication Date (Web):December 4, 2017
https://doi.org/10.1021/acs.langmuir.7b03005
Copyright © 2017 American Chemical Society

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    Abstract

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    We constructed the apparatus to observe the Fréedericksz transition of liquid crystal in contact with water. The Fréedericksz transition is a distortion of nematic liquid crystals (LCs) induced by external fields. In the present system, sweeping homogeneous magnetic field was applied to the sample, and the distortion of the LC was visualized with a polarized light microscope with the crossed Nichols configuration. The anchoring energy (WAQ/LC) at the aqueous phase/LC interface was measured in the presence of surfactant from the threshold magnetic field of the Fréedericksz transition. We studied two cationic surfactants: dodecyltrimethylammonium bromide and tetradecyltrimethylammonium bromide. A nematic LC, 4-cyano-4′-pentylbiphenyl (5CB), was examined, which was confined in a copper grid on an octadecyltrichlorosilane-treated microscope glass plate. Measured WAQ/LC were reproducible and showed consistence with the reported region for the water/LC interface. Interfacial excess of surfactants was also measured by the pendant drop method, and the relationship between the obtained WAQ/LC and the interfacial excess was investigated. Experiments showed that an increase in the anchoring energy depends on the surfactant and its interfacial excess. The region of the interfacial coverage, at which WAQ/LC increases, varied with the chain length of the surfactant. The measurement of the anchoring energy will provide new fundamental information on aqueous phase/LC interface.

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    The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.langmuir.7b03005.

    • I. Pendant drop method and estimation of the interfacial concentration. II. Derivation of equation 1. III. Measurement of the thickness of 5CB. IV. Determination of the threshold magnetic field from the oscillation of the transmission intensity. (PDF)

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    Cited By

    This article is cited by 8 publications.

    1. Sangchul Roh, Michael Tsuei, Nicholas L. Abbott. Using Liquid Crystals for In Situ Optical Mapping of Interfacial Mobility and Surfactant Concentrations at Flowing Aqueous–Oil Interfaces. Langmuir 2021, 37 (19) , 5810-5822. https://doi.org/10.1021/acs.langmuir.1c00133
    2. Guillaume Durey, Yoko Ishii, Teresa Lopez-Leon. Temperature-Driven Anchoring Transitions at Liquid Crystal/Water Interfaces. Langmuir 2020, 36 (32) , 9368-9376. https://doi.org/10.1021/acs.langmuir.0c00985
    3. Reza Shadkami, Philip K. Chan. Computational Analysis on the Performance of Elongated Liquid Crystal Biosensors. Micromachines 2023, 14 (10) , 1831. https://doi.org/10.3390/mi14101831
    4. Sophie Ettinger, Charlotte G. Slaughter, Sebastian Hurtado Parra, James M. Kikkawa, Peter J. Collings, A. G. Yodh. Magnetic-field-driven director configuration transitions in radial nematic liquid crystal droplets. Physical Review E 2023, 108 (2) https://doi.org/10.1103/PhysRevE.108.024704
    5. Reza Shadkami, Philip K. Chan. A Numerical Study on the Performance of Liquid Crystal Biosensor Microdroplets. Crystals 2023, 13 (8) , 1237. https://doi.org/10.3390/cryst13081237
    6. Soumita Maiti, Sangchul Roh, Itai Cohen, Nicholas L. Abbott. Non-equilibrium ordering of liquid crystalline (LC) films driven by external gradients in surfactant concentration. Journal of Colloid and Interface Science 2023, 637 , 134-146. https://doi.org/10.1016/j.jcis.2022.12.124
    7. M. Suwa, S. Tsukahara, H. Watarai. Applications of magnetic and electromagnetic forces in micro-analytical systems. Lab on a Chip 2023, 23 (5) , 1097-1127. https://doi.org/10.1039/D2LC00702A
    8. Reza Shadkami, Philip K. Chan. Computational Analysis to Optimize the Performance of Thin Film Liquid Crystal Biosensors. Crystals 2022, 12 (10) , 1463. https://doi.org/10.3390/cryst12101463

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