Nanomechanical Properties of Teflon Amorphous Fluoropolymer -MWCNT Bilayer Films
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Nanomechanical Properties of Teflon Amorphous Fluoropolymer -MWCNT Bilayer Films R. L. Schoeppner1, A. Qiu1, D. D. Stauffer2, R. C. Major3, J. L. Skinner4, T. Zifer4, G. O’Bryan4, A. Vance4, W. W. Gerberich2, D. F. Bahr1, N. R. Moody4 1
Mechanical and Materials Engineering, P.O. Box 642920, Washington State Univeristy, Pullman, WA 99164, U.S.A. 2 Chemical Engineering and Materials Science, 421 Washington Ave SE, University of Minnesota, Minneapolis, MN 55455, U.S.A. 3 Hysitron Inc., 10025 Valley View, Minneapolis, MN 55344, U.S.A. 4 Sandia National Laboratory, P.O. Box 969 MS9402, Livermore, CA 94551-0969, U.S.A. ABSTRACT Teflon amorphous fluoropolymer (TAF) multi-walled carbon nanotube (MWCNT) suspensions have the potential for creating conductive coatings on insulating films for numerous applications. However, there are few studies on polymer MWCNT suspension properties and even fewer that use Teflon. To define mechanical and electrical property relationships, bilayer films of TAF-MWCNT were created with differing concentrations of MWCNTs. Nanoindentation revealed that addition of 8 wt% MWCNTs to TAF increased the elastic modulus by about 25% and hardness by about 15%. Conducting indentation showed 8 wt% MWCNT films exhibit uniform stable conductance once indentation depth exceeds several hundred nanometers. Films with lower concentrations of CNTs were insulating. The two techniques provide a unique description of structure property relationships in this suspension film system. INTRODUCTION Carbon nanotubes have become increasingly useful in the fabrication of conductive nanoparticle filled polymer materials [1] owing to their processability and unique combination of mechanical, electrical, and magnetic properties. Films with insulating and conducting surfaces on opposite sides are particularly interesting for use in applications where variable electrical properties over a short length scale are desired, but properties of the polymer must be maintained. There have been several studies involving polymer MWCNT suspensions [2-4] but very few using Teflon. TAF is ideal for electrical applications due to its low dielectric constant and high chemical resistance. A recent patent discusses the use of fluoropolymers as a binder for CNT coatings [5] to increase electrical conductivity, thermal resistance and interfacial adhesion; which suggests TAF would be a useful polymer for the conducting bilayer film. Multi-walled carbon nanotubes are desirable for this application due to their high conductivity (>100 S/cm), high aspect ratios (~1000:1) and relatively low cost compared to single-walled nanotubes. In their pristine form, MWCNTs are not readily soluble in many solvents; however, the surface can be functionalized to improve solubility. Mixtures of functionalized and non-functionalized MWCNTs are combined with TAF to create the conductive films characterized in study. Nanoindentation is one of the most accepted methods of mechanical characterization for small volumes [6]. Instrumented indentation measures load as a functi
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