Parallel Integration of Aligned Carbon Strings in Polymer Matrix: Dielectrophoretic Preparation, Electrical and Electromechanical Characterisation
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.
IdentifiersURN: urn:nbn:no:ntnu:diva-23605Local ID: ntnudaim:8424OAI: oai:DiVA.org:ntnu-23605DiVA: diva2:676948
Raaen, Steinar, ProfessorHelgesen, GeirKnaapila, Matti