Doctoral thesis (Dissertations and theses)
Pressure Sensing with Nematic Liquid Crystal and Carbon Nanotube Networks
Murali, Meenu
2020
 

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Keywords :
liquid crystal; carbon nanotubes; pressure sensing; nanoparticles; soft electronics; carbon nanotube sheets; disclination lines; topological defects; nematic force; colloidal inclusions; electrical resistance
Abstract :
[en] The study of colloidal dispersions of nanoparticles in liquid crystals (LCs) is well known. In most of the works, the particles are mixed into the LC to form suspensions with well-dispersed particles. However, when nanoparticles are physically connected to form networks, the overall macroscopic properties of the ensemble are directly linked to the specific properties of the nanoparticles. Carbon nanotubes (CNTs) are excellent electrical conductors possessing extremely high aspect ratio, which results in a very low concentration threshold needed to obtain percolation. Therefore, they form conductive networks with extremely small amounts of CNTs. Another advantage of carbon nanotubes is their capability to transport large current densities without damage by electromigration, maintaining a stable resistance, and having scattering-less paths across several microns. Moreover, the electromechanical properties of CNTs make them an ideal candidate in pressure sensing technology. The doctoral thesis presented here describes two different approaches to integrate and utilise CNTs in an LC matrix. In the first case, we show that a variety of nanoparticles that are dispersed in LC can be attracted and assembled onto a LC defect line generated in a predetermined location, thereby creating a vertical interconnect of nanoparticles. The second consists of CNT sheets mechanically drawn from a CNT forest and an LC cell is then built on top, and the second consists of a template-based assembly of dispersed CNTs onto defect lines in LCs. In this case, we study the electrical and optical properties of CNT sheets in the presence and absence of liquid crystals based on their DC electrical characterization with distributed electrical contacts. Finally, we discuss how these two approaches can be used to successfully fabricate pressure-sensing devices. The pressure response in both these sensors is achieved based on the change in resistance of the CNTs, induced by the structural variations under the external applied pressure. Both the pressure sensors developed here are easy to fabricate, cost-effective, and recoverable owing to the elasticity and softness of the LC.
Disciplines :
Physics
Author, co-author :
Murali, Meenu ;  University of Luxembourg > Faculty of Science, Technology and Medicine (FSTM) > Department of Physics and Materials Science (DPHYMS)
Language :
English
Title :
Pressure Sensing with Nematic Liquid Crystal and Carbon Nanotube Networks
Defense date :
15 December 2020
Number of pages :
155
Institution :
Unilu - University of Luxembourg, Luxembourg, Luxembourg
Degree :
Docteur en Physique
Promotor :
Jury member :
Schilling, Tanja
Defay, Emmanuel 
Poulin, Philippe
Focus Area :
Physics and Materials Science
FnR Project :
FNR10935404 - Materials For Sensing And Energy Harvesting, 2015 (01/10/2016-31/03/2023) - Emmanuel Defay
Funders :
FNR - Fonds National de la Recherche [LU]
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since 20 January 2021

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