Shape memory polymer materials can be deformed in accordance with established procedures under external stimuli, which makes it a huge application prospect in actuators, sensors, and drug delivery. Due to the low thermal conductivity of the polymer material and the slow chain motion rate, the response speed of the shape memory polymer material still has a large gap compared with other shape memory materials (such as shape memory alloys).
Recently, Zhejiang University's Gao Chao (Communication), Xu Zhen (Communication) team worked with the Marxist-Leninist (Communication) team and other collaborators to break through this problem of speed of response. This work uses a highly stretchable graphene aerogel as a template to build a shape memory network made of polycaprolactone (PCL) nano-films (2.5-60nm) inside. Among them, graphene nanonetworks serve as fast energy conversion and energy injection channels, and PCL nanonetworks serve as fast energy transfer and deformation carriers. The aerogel nanocomposite with PCL / graphene interpenetrating network structure under electrical signal stimulation has a response time of only 50 ms, a response speed of 175 ± 40 mm s-1, and a maximum deformation of about 100%.
The work was published on ACS Nano under the title "Millisecond Response of Shape Memory Polymer Nanocomposite Aerogel Powered by Stretchable GrapheneFramework".
The traditional shape memory polymer composites are mostly prepared by blending with conductive additives, which results in the heat conduction distance from the conductive network to the SMP matrix is generally on the order of microns. However, the thermal conductivity of polymer materials is generally low (such as the polycaprolactone PC used in this article, ~ 0.3 W mK-1), which results in the response time of traditional blended shape memory polymer materials generally in seconds. Above. In this study, a highly stretchable aerogel was used as a template to build a continuous nano-layer of polycaprolactone (2.5-60 nm) on its surface to reduce the heat transfer distance.
The stretchable aerogel used in this research was developed based on the team's 2018 “Highly Stretchable Carbon Aerogels” work (Nat.Commun.2018, 9, 881) Highly stretchable full carbon aerogel elastomer). The graphene aerogel is used as a rapid energy injection and transformation framework to achieve rapid phase transition of SMP. The ultimate result is an ultra-lightweight composite aerogel material with a response time of the order of milliseconds (50 ms) and an elongation of more than 100%.
At the same time, this work used an in-situ TEM sample rod independently developed by Wang Hongtao's research group of Zhejiang University School of Aeronautics and Astronautics to observe the shape memory behavior of graphene / PCL composite sheets under the basic stimulation of composite aerogel.
This fast-responding ultra-light composite aerogel material has broad application prospects, and can be designed as an ultra-fast fuse to protect precision circuits. Under overload conditions, it can be opened in 134 ms to protect electrical appliances. At the same time, it can also be combined with an electromagnet as a micro oscillator.
Professor Gao Chao's doctoral student Guo Fan is the first author of the thesis, and Professor Ma Lie's doctoral student Zheng Xiaowen is the second author of the thesis. Professor Ma Lie of the Institute of Polymer Science of Zhejiang University and Professor Wang Hongtao of the School of Aeronautics and Astronautics of Zhejiang University provided strong support and cooperative guidance for the completion of this work. The thesis has received funding from the National Key Research and Development Program and the National Natural Science Foundation of China.