Recently, Negative Poisson’s Ratio in Modern Functional Materials, a review written by the research team led by Prof. Chen Lang from SUSTech Department of Physics, was published on a famous scientific journal named Advanced Materials (impact factor: 18.96). The review systematically summarizes new advances in negative Poisson’s ratio materials, analyzes methods of regulating the negative Poisson’s ratio of materials such as strain and microstructure, and explains various functional materials’ negative coefficients (negative Poisson’s ratio, negative thermal expansion coefficient and negative compression ratio) and their possible coexistence. Also, potential research orientations and new methods for regulating the negative Poisson’s ratio of materials are proposed.

As a basic flexible variable, Poisson’s ratio is defined as the ratio of transverse contraction strain to longitudinal extension strain in the direction of stretching force. It characterizes the competition between the form distortion and volume deformation of materials volume deformationunder loads, and serves as the most basic metrics to measure the elastic deformation of materials under stress. Poisson’s ratio is now widely applied in materials, mechanics and other fields.

The concept of Poisson’s ratio was put forward by French scientist Poisson 200 years ago. Since then it has been used as a basic parameter in mechanics, serving as an important indicator that measures the deformation of materials. Poisson’s ratio is also closely related with other mechanical properties of materials, such as Young’s modulus and bulk modules. Therefore, the value of Poisson’s ratio can directly influence the mechanical properties of materials. Daily life and experimental results show that the majority of materials in nature have positive Poisson’s ratios (0-0.5). In recent years, Negative Poisson’s Ratio (NPR) begins to win popularity, and becomes a significant branch of researches on materials with negative coefficients. NPR means that there will occur unusual lateral expansion while the material is subjected to tension or pressure. Compared with positive Poisson’s ratio materials, negative Poisson’s ratio materials can greatly strengthen the mechanical properties of materials, i.e., increase the shear modules of materials, enhance plane strain fracture toughness, increase the resistance to indentation, and even repair the material itself after being damaged. With these excellent properties, negative Poisson’s ratio materials play a critical role in functional materials, and are widely used in aviation, the military, mechanical materials, sensors and other industries.

Prof. Chen Lang and Dr. Huang Chuanwei from College of Materials Science and Engineering, Shenzhen University, reviewed new progress in negative Poisson’s ratio materials, including theories on negative Poisson’s ratio materials, researches on natural negative Poisson’s ratio materials, and the preparation of artificial negative Poisson’s ratio materials, especially the phenomenon of negative Poisson’s ratio in today’s popular materials (biological materials, organic materials, 3D printing materials, metal-organic framework materials, carbon nanotubes, black phosphorus, and low dimensional materials such as the epitaxial thin films of electronic oxides). Chen and Huang also explored the variability of Poisson’s ratio with the change of material structures and the external environment (temperature and pressure). They found out negative Poisson’s ratio materials through comparing various ways of regulating Poisson’s ratio, and forecasted the prospect of researches on and application of the mechanical properties of negative Poisson’s ratio materials.  

By looking back on those works, Chen Lang and Huang Chuanwei emphasized that the Poisson’s ratio of materials may vary with the change of structures and external fields, which is the most effective way to explore NPR. But it is always neglected, as it is generally recognized that the Poisson’s ratio of some kind of material is negative. We believe that regulatable Poisson’s ratio will open a window for researches on new materials, and provide new thoughts and developments on the mechanics of materials based on negative Poisson’s ratio. An article on the variability of Poisson’s ratio was published on Advanced Materials (DOI: 10.1002/adma.201601363), which was exclusively reported by Materials Review in China.     

Since Prof. Chen Lang joined in SUSTech, he and his research team have published many articles on first class journals, including Nature Communications. Chen’s researches were supported by Ministry of Science and Technology, Natural Science Foundation of China, SUSTech, Shenzhen Science and Technology Innovation Committee, and Nanshan Science and Technology Bureau.

Link for the review: http://onlinelibrary.wiley.com/doi/10.1002/adma.201601363/full