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. 
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.