1. Composites of Carbon Nanotubes and PDMS for strain gauge applications
Gonzatto Neto (UNIFESP), E. F. Antunes (INPE) , F.H.Cristovan(, E.Antonelli2, E. F. Antunes(USP), U.A.Mengui (INPE), E.J.Corat 1
Recent literature has demonstrated the use of polymeric composite of carbon nanotubes as strain gauges [1,2]. In this work, membranes of vertically-aligned carbon nanotubes (VACNT) were produced by spin coating of PDMS (Ezsil 44) diluted in tholuene. The VACNT films were produced on 1cm2 Ti6Al4V square substrates by microwave plasma chemical vapor deposition (MWCVD), with a gas mixture of N2/H2/CH4 [3]. The thickness of VACNT film and membrane are is ~15 um, and ~1mm, respectively. DC and AC electrical characterization of the membranes were performed under tensile strain, with comercial electrometer (Keytlhey), and impedancimeter (SolartronThe piezoresistivity with high linearity (but with histeresis) was demostrated. Nyquist diagram shows capacitive effects, and the resistivity shows changes depending on the input signal amplitude, which probably affect the field distribution.
São José dos Campos/SP - Brazil
Production of Vertically Aligned Carbon Nanotubes (VACNTs)
Electromechanical properties under tensille strain
VACNT films on Ti substrates by Microwave Plasma
Parameters:
Wheaststone Bridge + Data aqcuisition system (0-10V)
Keithley Electrometer -10 to 10 V
Manual mode or stteper motor
I x V
R x V
MW-CVD Reactor
STEP BY STEP
Ti substrate
Heating at 480oC
TiN + óxidos
10 nm Fe film
e-beam evaporation
Gauge Factor
Hysteresis Curve
Lo = 11,4 cm, Ro= depend on strain
Fe nanoparticles
H2/N2 Plasma
VACNT Deposition
H2/N2 /CH4
1,2: Microwave source and waveguide
3: Plasma Chamber; 4: Vacuum system; 5: Heating Control
Work Pressure: 30 Torr, Temperature: 850oC,
H2/N2 /CH4 : 90/10/14 sccm
Photos, HRSEM Images and Raman spectroscopy
Impedance Spectroscopy – AC under tensile
Ti , Ti/Fe and Ti/CNT
Raman Spectra
Parameters: Solartron Impedancimeter - 1 Vrms / 1Hz - 10MHz
Bode Diagram
Fe Nanoparticles
VACNT
Raman Shift (cm-1)
Frequency (Hz)
3D Plot
Silicone Membrane for Strain Sensors
Transference of VACNT films to silicone rubber membrane
Deposição
MWCNT
Spin Coating of PDMS (Ezsil 44) + Tholuene
20x20 mm
80oC/20 min
1000rpm
Nyquist Diagram
Low Frequency
Resistive Gauge Factor
Capacitive Gauge Factor
Conclusion
Peel off membrane
Flexible membranes of vertically-aligned carbon nanotubes were succesfully produced by silicone infiltration by capillary effect.
Electrical characterization of composite membranes showed that is possible to develop strain gauge sensors based on piezoresistance (low frequencies or DC) or piezocapacitance . The higher capacitive gauge effect was reach at 2,5 MHz.
The electronic conduction in this composite is dominated by both percolation (102 S/m) and tunneling (lower electric field showed higher gauge factors).
It is possible to increase the gauge factor at electrical percolation limiar, future work should be explore films with lower density of nanotubes. Small strain range should be also studied.
Acknowledgements To SPONSORs
FAPESP and CNPq (Brazilian Agencies for funding research) for financial support and scholarships.
VACNT Film - Silicone infiltration - Conductive VACNT/Silicone Membrane
Hu, Ning, Karube, Yoshifumi, Yan, Cheng, Masuda, Zen, Fukunaga, Hisao. Tunneling effect in a polymer/carbon nanotube nanocomposite strain sensor. Acta Materialia, 56(2008)
Y. Li, W. Wang,  K. Liao,  C. Hu, Z. Huang, Q. Feng. Piezoresistive effect in carbon nanotube films. Chinese Science Bulletin 48(2003)
 L. Cai, L. Song, P. Luan, Q. Zhang, N. Zhang, Q. Gao, D. Zhao, X. Zhang, M. Tu, Feng Yang, W. Zhou, Q. Fan, Jun Luo, W. Zhou, P. M. Ajayan, S. Xie. Super-stretchable, Transparent Carbon Nanotube-Based Capacitive Strain Sensors for Human Motion Detection. Scientific Reports 3, Article number:3048 (2013) doi: /srep03048.
W. Obitayo, T. Liu A Review: Carbon Nanotube-Based Piezoresistive Strain Sensors. Journal of Sensors  2012 (2012), Article ID 652438, 15 pages.
 S. Tadakaluru, W. Thongsuwan, P. Singjai. Strechable and Flexible High Strain Sensor Made using carbono nanotubes and grafite films on natural rubber. Sensors 14 (2014)
Stretchable and Flexible High-Strain Sensors Made Using Carbon Nanotubes and Graphite Films on Natural RubberStretchable and Flexible High-Strain Sensors Made Using Carbon Nanotubes and Graphite Films on Natural Rubber
Alamusi, N. Hu, H. Fukunaga, S. Atobe, Y. Liu, J. Li, Piezoresistive Strain Sensors Made from Carbon Nanotubes Based Polymer Nanocomposites. Sensors 11(2011)