Facile spray coating in preparing anisotropic composites

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 in our previous report showed improvements in both modulus and hardness with higher HNTs orientation. The indentation modulus and hardness both increased by more than 60%. Based on the results from our research scratching tests using Tribolndenter 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 in some sense. This study is aimed to present the detailed inforamtion regarding the processing of successful particle alignment in final composites, and how the processing parameters influecne the final structural features.