Multiscale Model for the Extreme Piezoresistivity in Silicone/Nickel Nanostrand Nanocomposites
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INTRODUCTION
MANY sensor technologies are based upon exploitation of the piezoresistive properties of various materials. Such technologies use the change in resistance of the sensor induced by an applied load to determine a displacement. Most commonly, thin foils made of piezoresistive metals are used as strain gages. Unfortunately, accurate strain measurement using these gages is limited to about 5 pct elongation.[1] Conductive polymeric materials show great promise as an alternative that could measure much larger strains.[2–5] We developed a unique silicone/nickel nanostrand (silicone/NiNs) nanocomposite that has been shown to respond to strains of up to 50 pct elongation.[4,5] However, understanding of the piezoresistive mechanism in these composites is limited. The resistivity of typical filled polymer composites increases under tension and decreases in compression; OLIVER K. JOHNSON, formerly a Research Assistant with Brigham Young University, Provo, UT 84602, is now a Doctoral Student with the Massachusetts Institute of Technology, Cambridge, MA 02139-4307. Contact e-mail: [email protected] CALVIN J. GARDNER, formerly a Research Assistant with Brigham Young University, is now a Doctoral Student with the University of California-San Diego, La Jolla, CA 92093. DANIEL B. SEEGMILLER, Research Assistant, and DAVID T. FULLWOOD, Associate Professor, are with Brigham Young University. NATHAN A. MARA, Technical Staff Member, and ANDREW M. DATTELBAUM, Scientist, are with the Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, NM 87545-0001. PHILIP J. RAE, Technical Staff Member, is with the Structure/Property Relations Group, Materials Science and Technology Division, Los Alamos National Laboratory. GEORGE C. KASCHNER, Technical Staff Member, is with the Nuclear Materials Group, Materials Science and Technology Division, Los Alamos National Laboratory. THOMAS A. MASON, Research Engineer, is with the Detonator Technology Group, Weapon Systems Engineering Division, Los Alamos National Laboratory. GEORGE HANSEN, President, is with Conductive Composites, LLC, Heber City, UT 84032-2256. Manuscript submitted March 21, 2010. Article published online September 23, 2011 3898—VOLUME 42A, DECEMBER 2011
however, silicone/NiNs nanocomposites decrease in resistivity under both tensile and compressive loads.[6] Understanding of the piezoresistive mechanism that is operative in these nanocomposites is essential for their use in sensor technologies and for the optimization of the same. We present a multiscale semiempirical model based upon quantum mechanical principles that describes the macroscopic composite resistivity as a function of strain. We also developed a novel technique to study the charge transport mechanism in silicone/NiNs nanocomposites using conductive nanoindentation. The results of these experiments allow for the accurate determination of an essential model parameter: the barrier height. We describe our experimental results as well as the preliminary results of the aforementioned model.
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