In this microelectric circuit, a slice of carbon fiber is electrically connected to gold/chromium electrodes with platinum/carbon electrodes. Image: Satoshi Matsuo and Nancy R. Sottos.Carbon fiber reinforced polymer composite structures are serving an increasingly important role in aerospace, infrastructure, energy generation and transportation. Yet, the electrical behavior of such composites is challenging to measure or predict because of the electrical conductivity of their constituent carbon fibers and their complex hierarchical microstructures.
In a paper in the Journal of Applied Physics, researchers from the University of Illinois at Urbana-Champaign report the first direct measurement of the transverse electrical resistivity of a single carbon fiber. The researchers combined precise sample preparation with a technique called the van der Pauw method to accomplish this challenging measurement.
"Our experiments confirm that the electrical properties measured transverse to a carbon fiber are not the same as the properties measured along the length the of the fiber," said co-author Nancy Sottos.
When carbon fibers are made, the strong carbon-carbon covalent bonds are aligned in planes parallel to the fiber axis in the longitudinal direction. Only weak van der Waals bonds exist between the planes in the transverse direction, leading to directionally dependent properties.
The researchers used a technique known as the van der Pauw method to accurately measure the resistivity of a carbon fiber in the transverse direction. These resistance measurements were performed on a slice of carbon fiber, cut using a focused ion beam. This slice was connected to electrodes for the electrical resistance measurements.
"Our results reveal that an IM7 carbon fiber is more electrically conductive in the direction parallel to the length," said co-author Satoshi Matsuo.
Previously, the van der Pauw method was mainly used to measure the resistivity of thin films or discs. The researchers cut and manipulated a slice of carbon fiber using a focused ion beam and a needle, which are more commonly used to prepare specimens for transmission electron microscopy.
The researchers are now working on measuring the electrical contact resistance between two carbon fibers. The electrical contact resistance depends on both the electrical resistivity and the contact area, which also varies depending on the angle at which the two fibers cross each other. After that, the researchers plan to measure the transverse electrical resistivity on different types of carbon fibers while varying conditions such as the environmental temperature.
"This procedure may also be applied to other homogenous conductive fibrous materials with a diameter on the order of microns, such as conductive polymer fiber or metallic fiber," said Sottos.
This story is adapted from material from the American Institute of Physics, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.