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Professor Lei XU and Dr. Xiangying Shen and Dr. Chenchao Fang, post-doctoral fellows, from the Department of Physics of The Chinese University of Hong Kong (CUHK) have collaborated with scientists from Mainland China to discover a novel topological and elastic transition in packing derived networks, and have achieved smart metamaterials with widely-adjustable elasticity, demonstrating a huge potential for applications in building materials, anti-vibration materials and impact protection materials. This study is also the first to reveal the new connection between elasticity and network topology. The findings have been recently published in the prestigious scientific journal Nature Materials.

Using network topological transition to realise the smart metamaterials with widely-adjustable elasticity

In the classic Chinese novel Journey to the West, Monkey King’s golden staff can magically expand and shrink at will. In real life, scientists have long been exploring a new material which can be freely adjusted in its hardness, compression and expansion properties so that it can become very soft and easy to compress when its profile is changed under external stress, and become very rigid and difficult to compress when resistance to external stress is required. This new type of material will be very useful in areas of industries and daily life. Realising these magical functions is closely related to the control of the elastic properties of the material.

Topological transition is the transition of system topology from one to another; for example, a pancake and a donut have two different topologies. By achieving a topological transition in a special packing derived network, the research team of Professor Lei Xu has designed a unique network structure based on the packing of particles, and observed a new topological elastic transition. By adding or reducing network connections near this topological transition, the team successfully realised the free adjustment of elastic modulus in which the soft, hard, expanding and shrinking properties of the materials can be widely adjusted.

First-time discovery of the close connection between topology and elasticity

This research discovered the close connection between topology and elasticity for the first time on the theoretical front and successfully produced a new type of smart elastic metamaterials, in the form of a fabricated smart spring system and 3D-printed metamaterials with freely adjustable elastic properties, in the laboratory. These materials are expected to have huge applications in building materials, anti-vibration materials and impact protection materials.

Professor Lei XU said, “Our research reveals the relationship between the elastic properties of the network system and the topological structure, which provides inspiration for the practical design of multi-functional smart metamaterials. This discovery also makes an important contribution to both scientific frontier research and real life applications.”

Supported by funds received from the Research Grants Council of Hong Kong, the National Natural Science Foundation of China and the Guangdong Natural Science Fund, this research was mainly carried out by two outstanding post-doctoral fellows in the Department of Physics at CUHK, Dr. Xiangying SHEN and Dr. Chenchao FANG under the supervision of Professor Lei XU. The CUHK team members also include Dr. Hau Yung LO, Dr. Zhipeng JIN, Mr. Shixiang TANG, and Dr. Hongchuan SHEN.

The research in Professor Lei XU’s laboratory focuses on soft condensed matter physics, which studies everyday phenomena such as drop splashing, water freezing and particle packing. Through these common everyday phenomena, Professor Xu hopes to discover new physics and novel materials to improve people’s everyday life.

The full journal paper can be found at https://www.nature.com/articles/s41563-021-01046-8.