Lin Jiahao, Li Peng, Liu Yingjun, Wang Ziqiu, Wang Ya, Ming Xin, Gao Chao, Xu Zhen
MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Key Laboratory of Adsorption and Separation Materials & Technologies of Zhejiang Province, Zhejiang University, 38 Zheda Road, Hangzhou, 310027, P. R. China.
Graphene Industry and Engineering Research Institute, Xiamen University, No. 422 Siming Road, Xiamen, 361005, P. R. China.
ACS Nano. 2021 Mar 23;15(3):4824-4832. doi: 10.1021/acsnano.0c09503. Epub 2021 Mar 8.
The larger size of graphene sheets should intuitively generate higher overall properties of their macroscopic materials. However, this intuitive notion still remains ambiguous. Here, we uncover that the wrinkle formation causes the counterintuitive size predicament of graphene sheets in their macroscopic materials. In the model of graphene oxide assembled papers, we reveal that the giant size of graphene oxide sheets aggravates the formation of larger wrinkles and more microvoids, causing the negative size effect in mechanical strength. A major microscopic origin of the size predicament is the skin wrinkling in the drying process, and the wrinkling behavior follows a general rule of deformation of an elastic thin plate. We use a wrinkle-engineering strategy to depress the spontaneously formed large wrinkles and succeed in the resolution of the size predicament. After wrinkle modulation, an authentically positive size effect reversely appears in which giant graphene sheets generate ultrahigh mechanical strength and superior functionalities of graphene papers. The origin of the size predicament reminds us of the hidden importance of modulating wrinkles for graphene macroscopic materials and provides a guidance of wrinkle engineering for graphene materials with advanced performances.
直观地讲，较大尺寸的石墨烯片材应能使其宏观材料具有更高的整体性能。然而，这一直观概念仍不明确。在此，我们发现皱纹的形成导致了石墨烯片材在其宏观材料中出现违反直觉的尺寸困境。在氧化石墨烯组装纸模型中，我们揭示出氧化石墨烯片材的巨大尺寸加剧了更大皱纹和更多微孔的形成，从而导致机械强度方面的负尺寸效应。尺寸困境的一个主要微观根源是干燥过程中的表面起皱，且起皱行为遵循弹性薄板变形的一般规律。我们采用一种皱纹工程策略来抑制自发形成的大皱纹，并成功解决了尺寸困境。经过皱纹调制后，出现了真正的正尺寸效应，其中巨大的石墨烯片材能产生超高的机械强度和石墨烯纸优异的功能特性。尺寸困境的根源让我们认识到调节皱纹对于石墨烯宏观材料的潜在重要性，并为具有先进性能的石墨烯材料提供了皱纹工程指导。
