AbstractsEngineering

Recent advances in nanocomposites based on conductive carbon nanotubes (CNTs) have led to investigations of using CNT networks as strain sensors. When CNTs are incorporated into a polymer matrix to form electrical networks, the developed conductive nanocomposite becomes sensitive to strain, thus a linear correlation can be found between strain change and electrical conductivity change (i.e., piezoresitivity). To produce reliable nanocomposite sensors, environmental effects, such as humidity, have to be considered. Humidity is one of the most significant environmental factors, because it is present in most environments. Furthermore, polymers and especially epoxies are known to absorb moisture, which affects the electrical conductivity of developed nanocomposites. Humidity therefore can have a larger effect compared to strain on the electrical conductivity, reducing the reliability of the strain sensor. The present study focuses on the understanding on the effect of the humidity and strain on electrical conductivity of CNT-modified epoxy. Experiments were performed and a mathematical model in Matlab was developed to predict these effects. When compared, a conclusion can be drawn about the usefulness of CNT-modified epoxy as humidity sensors or as a strain sensor outside a controlled environment. An aerospace-grade epoxy (EPON 828) and Multi-walled CNTs (MWCNTs) were used for the fabrication of nanocomposites. Experiments involved measuring current while nanocomposites specimens containing different amounts of MWCNTs were exposed to humidity. Similarly, nanocomposites with the same weight percentages of CNTs were subjected to strain while electrical conductivity was monitored. Results suggested that a 2nd order polynomial relationship between humidity and resistance existed, and a linear relationship between strain and resistance. A comparison between experiments and modelling suggest a good agreement as the magnitude of change in conductivity was in the same order of magnitude. Also, a comparison between the results of the humidity and strain suggest that the resistance increase of the nanocomposite due to humidity was four times higher than the resistance increase due to strain. If designed properly, the sensitivity of the electrical resistance of the nanocomposites developed in this study can be used for humidity sensing applications. However, the application of such nanocomposites for strain sensors is limited to the cases in which the correction to humidity change is applied to the sensor.