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Thesis Final ETS Submission.pdf (83.76 MB)

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Mechanical Tension and Electrical Conductivity of Liquid Crystal Filaments

Kress, Oliver Herbert
http://rave.ohiolink.edu/etdc/view?acc_num=kent1437752455

Abstract Details

2015, MS, Kent State University, College of Arts and Sciences / Chemical Physics.
During the NSF funded IRES internship at the Otto-von-Geuricke Univeristy in Magdeburg, Germany, I studied the optical properties and mechanical behavior in the form of line tension of bent-core liquid crystal fiber bundles and verified previously published tension values and temperature dependent behavior. Then, carbon nanotubes were added and it as found that the tension in the fibers decreased by a factor of two instead of increasing as was hoped. A new device for pulling fibers and measuring tension by deflection due to the adhesion of glass beads was built at the LCI. The device was meant to improve upon the device used at O.v.G. Improvements included a smaller heating chamber with better insulation, temperature control, large viewing windows, more stable mounting interface, easier disassembly and the option to quickly modify the device in order to perform a variety of other experiments such as observing behavior due to acoustic driving (based on previous literature), observing optical behavior under a polarizing microscope and introducing probes to measure the electrical properties of fibers. The platform remains modular and makes the addition of new components for carrying out new experiments very simple and straightforward. The addition of carbon nanotubes has scattered results regarding the modulation of fiber tension. It seems that the addition of CNTs to BLC1571 may slightly be decreasing tension while the addition to BLC1688 may be increasing it. In both mesogens, 10wt% CNT yielded the highest tension value above the theoretical surface tension contribution. A reversal of temperature dependence was observed for fibers containing CNT; their tension increased with temperature instead of decreased. A driving rod attached to a speaker was used to acoustically drive a filament of pure BLC1571 in an attempt to replicate the tension values in a different way. The movement of the fiber and the driving rod were captured using a high-speed camera and MATLAB code was written to extract the phase between the rod and the fiber as well as measured their amplitude across a frequency sweep between 40 Hz and 800 Hz. The tension and elastic modulus of fibers was extracted from the fundamental frequency of the fiber and matched the values observed in the bead-hanging experiments. The current through BLCs in bulk and in fiber form, with and without CNTs was measured using a high-precision electrometer with femto-amp current measuring ability and a probe I built capable of measuring current through a pulled fiber in situ. The resistivity of pure BLC1688 in the form of a fluid bridge (in the smectic phase) was found to be on the order of 10! O¿ while for a smectic bridge with 10wt% CNT it was found to be about 10 O¿. When a fiber of pure BLC was pulled, the resistivity fell by 4 orders of magnitude. This corresponds very well to the suggestion that BLCs (in their fiber form) arrange with smectic layers wrapping axially along the fiber length due to the observation by Gardiner et al. that resistivity across smectic layers (which could be assumed to be the case in bulk where the layers are random) is much higher than it is when current is flowing along smectic layers. However, when a fiber with 10wt% CNT was pulled, the resistivity increased by roughly 6 orders of magnitude when compared to the resistivity in bulk form. This corresponds very closely to the observation by Winey et al. that in polymer filaments with 2wt% CNT, that the resistivity varies between 10! O¿ when the CNTs are very well aligned to 10! O¿ when the CNTs are isotropic.25 When the BLC with CNTs is in bulk form, it can be assumed that the CNTs have an isotropic distribution while pulling filaments must cause any CNTs within the fiber to align in the fiber direction since the CNTs are 2 nm wide and between 5 and 30 µm long or longer than the width of a fiber. This alignment could be the cause of the same increase in resistivity by 6 orders of magnitude, and the offset between the range of the resistivity observed by Winey et al and that observed in these experiments could be caused by the difference in resistivity of BLCs versus the polymer they used or from the higher concentration of CNTs used by me. This research is part of a larger study in which results and observations from the work of several group members under the guidance of Dr. Antal Ja'kli are continuously being combined in order to further understand the nature of self-assembling liquid crystal filaments. A paper on the rupture dynamics o BLC fibers made of the same mesogens studied here is in the process of being published and further experiments and results on the topics studied in this thesis are expected to produce future publications. After graduating with my M.Sc. from Kent, I will move to Go¨ttingen, Germany where I have joined the group of Dr. Stephan Herminghaus at the Max Planck Institute for Dynamics and Self-Organization and will work towards receiving my Ph,D from the University of Go¨ttingen. I will be continuing my work on liquid crystal filaments and look forward to maintaining an open collaboration with Dr. Ja'kli’s group at the LCI.
Antal Jákli, Ph.D. (Advisor)
81 p.
Chemistry; Materials Science; Physics

Recommended Citations

Citations

  • Kress, O. H. (2015). Mechanical Tension and Electrical Conductivity of Liquid Crystal Filaments [Master's thesis, Kent State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=kent1437752455

    APA Style (7th edition)

  • Kress, Oliver. Mechanical Tension and Electrical Conductivity of Liquid Crystal Filaments. 2015. Kent State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=kent1437752455.

    MLA Style (8th edition)

  • Kress, Oliver. "Mechanical Tension and Electrical Conductivity of Liquid Crystal Filaments." Master's thesis, Kent State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=kent1437752455

    Chicago Manual of Style (17th edition)

kent1437752455
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© 2015, all rights reserved.
This open access ETD is published by Kent State University and OhioLINK.
Release 3.2.12