A New Intelligent Material Based on Long Carbon Nanotube Arrays

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.