Zhu Xiangyu, Yang Chao, Wu Pingwei, Ma Zhenqian, Shang Yuanyuan, Bai Guangzhu, Liu Xiaoyan, Chang Guo, Li Ning, Dai Jingjie, Wang Xitao, Zhang Hailong
State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China.
School of Mechanical and Electronic Engineering, Qingdao Binhai University, Qingdao 266555, China.
Nanoscale. 2020 Feb 27;12(8):4882-4894. doi: 10.1039/c9nr07861d.
A deep understanding of the shaping technique is urgently required to precisely tailor the pore structure of a graphene aerogel (GA) in order to fit versatile application backgrounds. In the present study, the microstructure and properties of GA were regulated by freeze-casting using an ice crystal template frozen from -10 °C to -196 °C. The phase field simulation method was applied to probe the microstructural evolution of the graphene-H2O system during freezing. Both the experimental and simulation results suggested that the undercooling degree was fundamental to the nucleation and growth of ice crystals and dominated the derived morphology of GA. The pore size of GA was largely regulated from 240 to 6 μm via decreasing the freezing temperature from -10 °C to -196 °C but with a constant density of 8.3 mg cm-3. Rapid freeze casting endowed GA with a refined pore structure and therefore better thermal, electrical, and compressive properties, whereas the GA frozen slowly had superior absorption properties owing to the continuous and tube-like graphene lamellae. The GA frozen at -196 °C exhibited the highest Young's modulus of 327 kPa with similar densities to those reported in the literature. These findings demonstrate the diverse potential applications of GA with regulated pore morphologies and also contribute to cryogenic-induced phase separation methods.
为了使石墨烯气凝胶（GA）的孔结构能够精确适配多种应用背景，迫切需要对其成型技术有深入的了解。在本研究中，通过使用从-10℃冷冻至-196℃的冰晶模板进行冷冻铸造来调控GA的微观结构和性能。应用相场模拟方法来探究冷冻过程中石墨烯-H₂O体系的微观结构演变。实验和模拟结果均表明，过冷度是冰晶成核和生长的关键因素，并主导了GA的最终形态。通过将冷冻温度从-10℃降至-196℃，GA的孔径在很大程度上从240μm调节至6μm，但其密度保持在8.3mg cm⁻³不变。快速冷冻铸造赋予GA精细的孔结构，从而使其具有更好的热学、电学和压缩性能，而缓慢冷冻的GA由于其连续的管状石墨烯薄片而具有优异的吸附性能。在-196℃冷冻的GA表现出最高的杨氏模量，为327kPa，其密度与文献报道的相近。这些发现展示了具有调控孔形态的GA的多种潜在应用，也为低温诱导相分离方法做出了贡献。
