K. Song, R. Polak, K. Abdalla Askar, M.F. Rubner, R.E. Cohen
Keywords: spray coating, anisotropy, mechanical property, nanotubes
Summary:Anisotropy has been taken advantage in composites to achieve specific mechanical, electrical, magnetic and other functional properties. In composite mechanics, orientation of fiber in polymer matrix will reinforce the composites to the greatest potential along loading direction. Here in this study, with specific dimensions and even dispersion quality, halloysite nanotubes (HNTs) have been studied regarding the orientation influence on mechanical properties in composites . Epoxy based composites including HNTs were prepared using spray coating method, with thin thickness as low as 5 μm. HNTs were aligned by the air flow and maintained by viscous polymers. Upon curing, the HNTs preserved their orientation perpendicular to the film direction, or, in other words, parallel to loading direction. Indentation tests showed improvement in both modulus and hardness with higher HNTs orientation. The indentation modulus and hardness both increased by 60%. Scratching tests using TriboIndenter and Atomic Force Microscopy also showed higher scratching resistance when HNTs were more aligned. Scanning Electron Microscopy and Dynamic Mechanical Analyzer have also proven the degree of orientation. This study is meaningful toward facile processing of mechanical durable composite coatings.