Cho Hyeonho, Shakil Ahmad, Polycarpou Andreas A, Kim Sunghan
School of Mechanical Engineering, Chung-Ang University, Dongjak-gu, Seoul 06974, Republic of Korea.
J. Mike Walker '66 Department of Mechanical Engineering, Texas A&M University, College Station, Texas 77843-3123, United States.
ACS Nano. 2021 Dec 28;15(12):19546-19558. doi: 10.1021/acsnano.1c06573. Epub 2021 Nov 22.
Enhancing and manipulating the mechanical properties of graphene oxide (GO)-based structures are challenging because the GO assembly is easily delaminated. We develop nacre-like bionanofilms whose in-plane mechanical properties can be manipulated through water vapor annealing without influencing their mechanical properties in the thickness direction. These bionanofilms are prepared from GO, silk fibroin (SF), and cellulose nanocrystals (CNCs) via a spin-assisted layer-by-layer assembly. The postannealing mechanical properties of the films are determined with atomic force microscopy (AFM) bending and nanoindentation, and it is confirmed that the mechanical properties of the bionanofilms are altered only in the in-plane direction. While AFM bending shows Young's moduli of 26.9, 36.3, 24.3, and 41.4 GPa for 15, 15 annealed, 30, and 30 annealed GO/SF/CNC trilayers, nanoindentation shows reduced moduli of 19.5 ± 2.6 and 19.5 ± 2.5 GPa before and after annealing, respectively. The unaltered mechanical properties of the bionanofilms along the thickness direction after annealing can be attributed to the CNC frame in the SF matrix acting as a support against stress in the thickness direction, while annealing reorganizes the bionanofilm structure. The tunability of the bionanofilms' mechanical properties in only one direction through structure manipulation can lead to various applications, such as e-skin, wearable sensors, and human-machine interaction devices.
增强和调控基于氧化石墨烯（GO）的结构的机械性能具有挑战性，因为GO组装体容易分层。我们开发了类似珍珠母的生物纳米薄膜，其面内机械性能可通过水蒸气退火进行调控，而不会影响其厚度方向的机械性能。这些生物纳米薄膜由GO、丝素蛋白（SF）和纤维素纳米晶体（CNC）通过旋转辅助逐层组装制备而成。通过原子力显微镜（AFM）弯曲和纳米压痕测定薄膜的退火后机械性能，证实生物纳米薄膜的机械性能仅在面内方向发生改变。对于15层、15层退火、30层和30层退火的GO/SF/CNC三层膜，AFM弯曲显示杨氏模量分别为26.9、36.3、24.3和41.4 GPa，而纳米压痕显示退火前后模量分别降低至19.5±2.6和19.5±2.5 GPa。退火后生物纳米薄膜沿厚度方向的机械性能未改变，这可归因于SF基质中的CNC框架在厚度方向上起到了抵抗应力的支撑作用，同时退火使生物纳米薄膜结构重新组织。通过结构操控仅在一个方向上调节生物纳米薄膜的机械性能可带来各种应用，如电子皮肤、可穿戴传感器和人机交互设备。
