The solution-state property of three-dimensional self-assembled monolayers (3D SAMs) on CeO2 nanoparticles (NPs) has been found to seriously affect dispersion of the NPs. The chain length and solvent-dependent changes in the properties of SAMs were investigated by using various n-alkanoic acid SAMs on CeO2 NPs and various nonpolar organic solvents. NMR and DSC were employed to analyze solution-state behavior of the 3D SAMs. A scaling approach on the chain length and the grafting density of the SAMs could characterize the behavior of SAMs in solution: whether the SAMs were swelling or not. The solvent quality (good or poor) for SAMs was also important for the swelling of the SAMs. In addition, the volume of the solvent molecule was also a critical parameter. The swollen SAMs could provide effective repulsion to overcome van der Waals attraction between NPs. Combining our scaling analysis on solution-state behavior of the 3D SAMs and the experimental results of dispersion of the CeO2 NPs, a criterion for the 3D SAMs to obtain well-dispersed surface-modified NPs was proposed.
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