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Parallel Integration of Aligned Carbon Strings in Polymer Matrix: Dielectrophoretic Preparation, Electrical and Electromechanical Characterisation
Norwegian University of Science and Technology, Faculty of Natural Sciences and Technology, Department of Physics.
2012 (English)MasteroppgaveStudent thesis
Abstract [en]

Carbon black particles have been aligned into string-like assemblies by dielectrophoresis. Particles were dispersed in Dymax Ultra Light-Weld 3094 oligomer mixture, with 0.1 vol.% filler content. This mixture was spread over three different electrode configurations made on glass and silicon substrate by photolithography. Alignment was first tested on the see-through and rigid glass substrate for better visualisation, and then performed on the bendable silicon substrate. The silicon substrate was covered by an insulating silicon oxide layer to separate the electrodes from the conducting silicon. The first configuration consisted of tip-like electrode pairs, with the electrode tips pointing towards each other, with a distance of 30 or 100 µm. The other two electrode configurations consisted of the same tip-like electrode pairs arranged in two-dimensional matrix and radial patterns, with 8 and 15 pairs, respectively. Electric field alignment of carbon black particles was carried out with an alternating electric field with 3-9 kV/cm, followed by photopolymerisation (UV curing) of the matrix, which locks the aligned strings in place. Alignment was obtained for all electrode patterns, and the most successful alignment was obtained with the radial 2D configuration of electrode pairs on rigid glass substrate. The alignment procedure was applied to seven samples with 15 electrode pairs on each sample, and three of these samples resulted in 15 conducting carbon black strings out of 15 possible. The electrical properties were studied in terms of dc measurements and ac-impedance spectroscopy for each string. The resistance of strings varied from 120 k-ohm to 5 M-ohm for the conducting strings, with a mean of 1.03 M-ohm. Alignment on the bendable silicon substrate was influenced by capacitive effects and modication of the electric field between the electrode tips, due to the conducting silicon layer. Carbon black strings were formed in the electrode gaps, but the resistance was signicantly higher than for the strings on glass substrate. Electromechanical properties were studied by bending the substrate, and changes in properties were observed as a result of straining the carbon black strings. A reduction of 80-90% of the current through the aligned strings was obtained with a deflection of 35 µm. This means that by optimising the alignment procedure so that strings with lower resistance would be obtained on silicon substrate, the change in resistance could be measured as a function of deflection, and the aligned strings on the 2D electrode pattern could potentially work as a strain sensor.

Place, publisher, year, edition, pages
Institutt for fysikk , 2012. , 71 p.
URN: urn:nbn:no:ntnu:diva-23605Local ID: ntnudaim:8424OAI: diva2:676948
Available from: 2013-12-08 Created: 2013-12-08 Last updated: 2013-12-08Bibliographically approved

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