Coating ARMOR

Project title: Integrated Research and Education on the Electro-Mechanical Behavior of Multifunctional Structural Coatings
Source of support: National Science Foundation, CAREER

Multifunctional coatings are materials intentionally encoded with multiple engineering functionalities. In particular, carbon nanotube’s (CNT) unique material properties have motivated engineers to use them as nano-scale building blocks for fabricating strain sensitive coatings that also possess improved mechanical properties/robustness (Fig. 1). Such material-based sensors offers tremendous advantages compared to conventional, discrete, electronic or mechanical-based transducers, since every location of the film or coating is sensitive to external stimuli. The ability to map the two- or three-dimensional electromechanical properties of these multifunctional materials can lead to innovations in spatial sensing for applications such as structural health monitoring. 

Despite this, CNT-based coatings' electromechanical response to applied loads remains poorly understood. Future innovations require the derivation of experimentally validated models and theory that describe their electromechanical behavior. As a step towards this goal, the research objective of this project is to derive and validate the fundamental electromechanical behavior of CNT-polymer thin films. This study began with the derivation of a two-dimensional percolation-based computational model that is physically representative of the CNT-polymer thin film's nano- and micro-structure. Variations of these numerical models were used to explore how changes at the nano- and/or micro-scale affect the electromechanical response at the meso-scale. The initial focus was centered on the strain sensing properties of the CNT-based thin films (Fig. 2) and how strain sensitivity and its nominal electrical properties changed when parameters, such as CNT length, density, geometric shape, and intrinsic gage factor, were varied. 

  • Prof. Yuan-Sen Yang, National Taipei University of Technology

Peer-Reviewed Publications:
  1. B. Lee, K. J. Loh, and Y-S. Yang, 2017, "Carbon Nanotube Thin Film Strain Sensor Models Assembled using Nano- and Micro-Scale Imaging," Computational Mechanics (0178-7675), Springer, 1-11, OnlineFirst. DOI: 10.1007/s00466-017-1391-6
  2. B. Lee and K. J. Loh, 2017, "Carbon Nanotube Thin Film Strain Sensors: Comparison between Experimental Tests and Numerical Simulations," Nanotechnology (0957-4484), IOP, 28(15): 155502/1-14. DOI: 10.1088/1361-6528/aa6382
  3. B. M. Lee and K. J. Loh, 2015, “A 2D Percolation-based Model for Characterizing the Piezoresistivity of Carbon Nanotube-based Films,” Journal of Materials Science (0022-2461), Springer, 50(7): 2973-2983. DOI: 10.1007/s10853-015-8862-y
  4. Y. Zhao, B. R. Loyola, and K. J. Loh, 2011, “Characterizing the Viscoelastic Properties of Layer-by-Layer Carbon Nanotube-Polyelectrolyte Thin Films,” Smart Materials and Structures (0964-1726), IOP, 20(7): 075020/1-11. DOI: 10.1088/0964-1726/20/7/075020

Fig. 1: The scanning electron microscope (SEM) image of a multi-walled carbon nanotube-polymer thin film shows the nanocomposite's dense, percolated morphology.

Fig. 2. The CNT-based thin film computational model successfully predicted the film's electromechanical response due to the application of a one-cycle tensile-compressive load pattern.