Auxetic materials with large negative Poisson's ratios based on highly oriented carbon nanotube structures

Auxetic materials with large negative Poisson's ratios are fabricated by highly oriented carbon nanotube structures. The Poisson's ratio can be obtained down to -0.50. Furthermore, negative Poisson's ratios can be maintained in the carbon nanotube/polymer composites when the nanotubes are embedded, while the composites show much better mechanical properties including larger strain-to-failure (similar to 22%) compared to the pristine nanotube thin film (similar to 3%). A theoretical model is developed to predict the Poisson's ratios. It indicates that the large negative Poisson's ratios are caused by the realignment of curved nanotubes during stretching and the theoretical predictions agree well with the experimental results.