Coarse-Grained Molecular Dynamics Simulations on Aggregation and Dispersion Mechanisms of Organically Modified CeO2 Nanoparticles for Electrochemical Sensor Applications
Authors: Nakamura Miho , Jojima Kota , Taniai Ryosuke , Fukushima Shogo , Ootani Yusuke , Ozawa Nobuki , Kubo Momoji 
Published: December 2024

CeO2 nanoparticle with a size between 1 nm and 100 nm has gained many attentions due to its attractive properties such as biocompatibility, good superficial electrical diffusivity, high conductivity, chemical and thermal stability, and significant oxygen transfer ability. CeO2 nanoparticle has been widely employed to develop electrochemical sensors and biosensors because it increases response time, sensitivity, and stability of sensors [1]. For mass production of CeO2 nanoparticles, CeO2 nanoparticles are often handled in organic solvents [2]. To maintain the unique physical properties of CeO2 nanoparticles, it is important to disperse nanoparticles in organic solvents. Especially, CeO2 nanoparticles have low affinity for organic solvents, and they easily aggregate in the organic solvents. Therefore, CeO2 nanoparticles are usually coated with the organic ligands to prevent aggregation and to improve their dispersibility. It is well known that the dispersibility of organically modified CeO2 nanoparticles strongly depends on the solvents, and however the effects of the organic solvents on the aggregation and dispersion of organically modified CeO2 nanoparticles have not been well established.
Therefore, in the present study, we employed a coarse-grained molecular dynamics method for clarifying the aggregation and dispersion mechanism of organically modified CeO2 nanoparticles. We employed our in-house molecular dynamics simulation code “Laich” [3]. Here, decanoic acid ligands are used for organic modification of CeO2 nanoparticles. Figure 1 shows the model of the present simulations. Hexane, tetradecane, cyclohexane, and benzene are used for the organic solvents. After the molecular dynamics simulations, we performed cluster analysis for the final structures (Figure 2). In figure 2, blue is nanoparticle, cyan is not bundled, and other colors are bundled. This figure indicates that ligands are bundled on the large surface and are not bundled on the corner surface of all the models. Table 1 shows the number of bundled parts in the hexane, tetradecane, cyclohexane, and benzene solvents. This table also shows the experimental dispersibility in each solvent [4]. It indicates that the number of non-bundled part corresponds to the experimental dispersibility. It means that the ligands tend to swell in the solvent to disperse organically modified CeO2 nanoparticles. Furthermore, to investigate the solvent penetration in the ligands, the density profile of solvents was calculated and the calculated average relative density of the solvents in the ligands is shown in table 2. Table 2 indicates that the average relative density of the solvents corresponds to the experimental dispersibility. This result suggests that the solvent penetration into the ligands contribute to ligand swelling. Further analysis will be presented in the conference.
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[2] X. Hao, C. Chen, M. Saito, D. Yin, K. Inoue, S. Takami, T. Adschiri, and Y. Ikuhara, Small, 14 (2018) 1801093.
[3] S. Uehara, Y. Wang, Y. Ootani, N. Ozawa, and M. Kubo, Macromolecules, 55 (2022) 1946-1956.
[4] R. J. G. B. Campello, D. Moulovi, and J. Sander, Advances in Knowledge Discovery and Data Mining (2013) 160-172.

Figure 1