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Friction  2022, Vol. 10 Issue (2): 282-295    doi: 10.1007/s40544-021-0490-8
Research Article     
Mechanical properties of graphene oxide-silk fibroin bionanofilms via nanoindentation experiments and finite element analysis
Hyeonho CHO1,Joonho LEE2,4,Hyundo HWANG3,Woonbong HWANG3,Jin-Gyun KIM2,*(),Sunghan KIM1,*()
1 School of Mechanical Engineering, Chung-Ang University, Seoul 06974, Republic of Korea
2 Department of Mechanical Engineering (Integrated Engineering), Kyung Hee University, Gyeonggi 17104, Republic of Korea
3 Department of Mechanical Engineering, POSTECH, Pohang 37673, Republic of Korea
4 Department of Robotics & Mechatronics, Korea Institute of Machinery & Materials, Daejeon 34103, Republic of Korea
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Understanding the mechanical properties of bionanofilms is important in terms of identifying their durability. The primary focus of this study is to examine the effect of water vapor annealed silk fibroin on the indentation modulus and hardness of graphene oxide-silk fibroin (GO-SF) bionanofilms through nanoindentation experiments and finite element analysis (FEA). The GO-SF bionanofilms were fabricated using the layer-by-layer technique. The water vapor annealing process was employed to enhance the interfacial properties between the GO and SF layers, and the mechanical properties of the GO-SF bionanofilms were found to be affected by this process. By employing water vapor annealing, the indentation modulus and hardness of the GO-SF bionanofilms can be improved. Furthermore, the FEA models of the GO-SF bionanofilms were developed to simulate the details of the mechanical behaviors of the GO-SF bionanofilms. The difference in the stress and strain distribution inside the GO-SF bionanofilms before and after annealing was analyzed. In addition, the load-displacement curves that were obtained by the developed FEA model conformed well with the results from the nanoindentation tests. In summary, this study presents the mechanism of improving the indentation modulus and hardness of the GO-SF bionanofilms through the water vapor annealing process, which is established with the FEA simulation models.

Key wordsgraphene oxide      silk fibroin      layer-by-layer (LbL)      nanoindentation      finite element analysis (FEA)     
Received: 17 September 2020      Published: 17 January 2022
Fund:  National Research Foundation of Korea (NRF) grant that was funded by the Korea Government (MSIT)(NRF-2018R1C1B6002339)
Corresponding Authors: Jin-Gyun KIM,Sunghan KIM     E-mail:;
About author: Hyeonho CHO. He received his B.S. degree in School of Mechanical Engineering from Chung-Ang University in 2019. He is currently a Ph.D. student in Department of Mechanical Engineering at Chung-Ang University. His research interests lie in evaluating mechanical properties of functional nanocomposites and fabricating micro/nano films for electromechanical applications.|Joonho LEE. He received his B.S. and M.E. degrees in Department of Mechanical Engineering from Kyung Hee University in 2019 and 2020, respectively. He is currently a researcher in Korea Institute of Machinery and Materials (KIMM). His research interest is based on kinematics and dynamic contact simulation.|Jin-Gyun KIM. He received his B.S. and M.E. degrees in Civil Engineering from Korea University in 2008 and 2010, respectively, and his Ph.D. degree in ocean systems engineering from Korea Advanced Institute of Science and Technology (KAIST) in 2014. He worked as a senior researcher in Korea Institute of Machinery and Materials (KIMM) from 2014 to 2017. He is currently an assistant professor of Kyung Hee University of Mechanical Engineering. His research area is computational dynamics, vibration, and multiphysics modeling and simulation.|Sunghan KIM. He is an assistant professor of School of Mechanical Engineering at Chung-Ang University. He received his Ph.D. degree in J. Mike Walker ’66 Department of Mechanical Engineering at Texas A&M University in 2015. He worked as a postdoctoral fellow in School of Materials Science and Engineering at Georgia Institute of Technology from 2015 to 2017. His research interests lie in establishing essential design factors to optimize the tribological and mechanical properties of sustainable functional nanocomposites for biological, electrochemical, and mechanical applications.
Cite this article:

Hyeonho CHO,Joonho LEE,Hyundo HWANG,Woonbong HWANG,Jin-Gyun KIM,Sunghan KIM. Mechanical properties of graphene oxide-silk fibroin bionanofilms via nanoindentation experiments and finite element analysis. Friction, 2022, 10(2): 282-295.

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Scheme 1 Overall research outline: bionanofilm fabrication process using LbL assembly technique with graphene oxide (GO) and silk fibroin (SF), GO-SF bionanofilms before and after annealing, and nanoindentation test and FEA.
Fig. 1 Representative AFM topography images (z-scale: 150 nm) of the GO-SF bionanofilms: (a) before annealing and (b) after annealing. (c) 3D topography image of the GO-SF bionanofilm on a Si substrate, and (d) the surface profile data of the GO-SF on the Si substrate to determine the thickness of the bionanofilm.
Fig. 2 Representative load-displacement curves of the GO-SF bionanofilms before and after annealing.
Fig. 3 Results of the indentation modulus and the hardness of the GO-SF bionanofilms before and after annealing: (a) indentation modulus and (b) hardness. Each bar is represented as the mean ± STD.
Fig. 4 (a) Basic formation model of GO-SF bionanofilms before and after annealing. Schematics of the structural changes in the GO-SF bionanofilms before annealing: (b) GO-SF bionanofilms without application of the indentation load, (c) GO-SF bionanofilms with application of the indentation load. Illustrations of the structural changes in the GO-SF bionanofilms after annealing: (d) GO-SF bionanofilms without application of the indentation load, (e) GO-SF bionanofilms with application of the indentation load.
Fig. 5 FEA model of the GO-SF bionanofilm for the nanoindentation characterization.
Fig. 6 Comparison between the experiment and simulation: (a) GO-SF bionanofilm before annealing, (b) GO-SF bionanofilm after annealing. Contour plots of the FEA simulation results: (c) von-Mises stress of the GO-SF bionanofilm before annealing, (d) von-Mises stress of the GO-SF bionanofilm after annealing, (e) strain of the GO-SF bionanofilm before annealing, and (f) strain of the GO-SF bionanofilm after annealing.
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