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Tailoring Piezoresistive Sensitivity of Multilayer Carbon Nanotube Composite Strain Sensors

Department of Civil & Environmental Engineering, University of Michigan Ann Arbor, MI 48109, USA

J.P. Lynch

Department of Civil & Environmental Engineering, University of Michigan Ann Arbor, MI 48109, USA, jerlynch{at}umich.edu, Department of Electrical Engineering & Computer Science, University of Michigan Ann Arbor, MI 48109, USA

B.S. Shim

Department of Chemical Engineering, University of Michigan Ann Arbor, MI 48109, USA

N.A. Kotov

Department of Chemical Engineering, University of Michigan Ann Arbor, MI 48109, USA

In recent years, carbon nanotubes have been utilized for a variety of applications, including nanoelectronics and various types of sensors. In particular, researchers have sought to take advantage of the superior electrical properties of carbon nanotubes for fabricating novel strain sensors. This article presents a single-walled carbon nanotube (SWNT)-polyelectrolyte (PE) composite thin film strain sensor fabricated with a layer-by-layer (LbL) process. Optimization of bulk SWNT-PE strain sensor properties is achieved by varying various LbL fabrication parameters, followed by characterization of strain-sensing electromechanical responses. A resistor and capacitor (RC)-circuit model is proposed and validated with electrical impedance spectroscopy to fit experimental results and to identify equivalent circuit element parameters sensitive to strain. Experimental results suggest consistent trends between SWNT and PE concentrations to strain sensor sensitivities. Simply by adjusting the weight fraction of SWNT solutions and film thickness, strain sensitivities between 0.1 and 1.8 have been achieved. While SWNT-PE strain sensitivity is lower than some metal-foil strain gauges ($2), the LbL method allows for precise tailoring of the properties (i.e., strain sensitivity, resistivity, among others) of a high-capacity (±10,000 µm m^-1) homogeneous multilayer strain sensor.

Key Words: carbon nanotube composite • electrical impedance spectroscopy • layer-by-layer • nanotechnology • strain sensor.

This version was published on July 1, 2008

Journal of Intelligent Material Systems and Structures, Vol. 19, No. 7, 747-764 (2008)
DOI: 10.1177/1045389X07079872


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