A New Intelligent Material Based on Long Carbon Nanotube Arrays
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A New Intelligent Material Based on Long Carbon Nanotube Arrays Vesselin Shanov1, YeoHeung Yun2, Mark J. Schulz2, Ram Gollapudi2, Sergey Yarmolenko3, Sudhir Neralla3, Jag Sankar3, Yi Tu4, Srinivas Subramaniam1 1-Department of Chemical and Materials Engineering, University of Cincinnati, Cincinnati, Ohio 45221-0012; 2-Department of Mechanical, Industrial, and Nuclear Engineering, Smart Materials Nanotechnology Laboratory, University of Cincinnati, Cincinnati, Ohio 452210072; 3-Department of Chemical and Mechanical Engineering, North Carolina A&T State University, Greensboro, NC 27411; 4-First Nano, Inc., Carpinteria, CA 93013. Abstract Highly aligned multi-walled carbon nanotube (MWCNT) arrays were synthesized on Si wafers. Water vapor was used to enhance the catalyst performance, which enabled continuous growth of MWCNT arrays for up to 3 hours. Various types of Fe patterning on a Si substrate with a multilayered structure were tested. MWCNT arrays up to 4 mm long were grown by Chemical Vapor Deposition (CVD). Environmental scanning electron microscopy was used to characterize the MWCNT morphology and showed that the nanotubes typically reveal a 20 nm outer diameter and 8 nm inner diameter. To investigate applications, a nanotube tower 1 mm x 1 mm x 4 mm in size was grown and peeled off the Si wafer. Each tower contains millions of individual nanotubes with 20-30 nm diameters. Electrochemical actuation of one MWCNT tower was demonstrated in a 2M NaCl solution. The MWCNT tower actuator operated up to 10 Hz without significantly decreasing strain. Only 2 volts was needed to obtain 0.15% strain. The aligned nanotube morphology of the tower is the reason for the high strain in the axial direction. Also, the measured electrical volume resistivity of the material was in the range of 0.1 ohm ⋅ cm. The results presented suggest nanotube array towers can be considered a novel intelligent material. Introduction Smart materials can have piezoelectric, pyroelectric, electrostrictive, magnetostrictive, piezoresistive, electroactive, and other sensing and actuating properties with no moving parts. Piezoelectric ceramic materials produce a charge when strained and expand when a voltage is applied, which makes them the most useful smart material today. However, the hard piezoceramic materials are heavy and brittle, and the strain is only 0.15%. Recently, smart materials based on nanotechnology have shown the potential to improve the way we generate and measure motion in devices from the nano to the macro scale in size. The mechanical and electrical properties are coupled in Carbon Nanotubes (CNT) which is a characteristic of smart materials. In experimentation with dry carbon nanotube actuators, no significant piezoelectric effect was observed. There is predicted to be a piezoelectric effect in boron nitride nanotube bundles which may be about twenty times smaller than for piezoelectric ceramic materials. The boron nitride material is not readily available commercially for making a new smart material. The first nanot
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