Concentrated colloidal dispersion of decanoic acid self-assembled monolayer protected CeO 2 nanoparticles up to 77 wt% i
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Concentrated colloidal dispersion of decanoic acid self-assembled monolayer protected CeO2 nanoparticles up to 77 wt% in nonpolar organic solvents Toshihiko Arita1, Jungwoo Yoo1, Yu Ueda1 and Tadafumi Adschiri2 1 Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1, Katahira, Aoba-ku, Sendai, 980-8577, Japan 2 WPI Research Center: Advanced Institute for Materials Research, Tohoku University, 2-1-1, Katahira, Aoba-ku, Sendai, 980-8577, Japan ABSTRACT Self-assembled monolayers (SAMs) of decanoic acids were prepared on cerium oxide nanoparticles (NPs). The dispersion of the NPs was improved by increasing the packing density of decanoic acid SAM on the NPs. Highly concentrated ceria nanofluids more than 22 vol% (about 77 wt%) in cyclohexane and trans-decalin were achieved, according to the criterion to the packing density and chain length of the alkanoic acid of the SAM to disperse the ceria NPs in nonpolar organic solvents proposed previously. Temperature effect on the dispersion was also examined and it was turned out that the dispersion was strongly enhanced with activation of Brownian motion. INTRODUCTION In order to perfectly disperse inorganic nanoparticles (NPs) in hydrophobic organic solvents, surface control of the polar NPs' surface is promising. Actually, surface modifications of NPs by organic surfactants have succeeded to disperse NPs and already been recognized as a common technique [1,2]. However, when one thinks about dispersion at very high NPs content, total packaging (design) of nanofluid (hybrid material) is very important. Because inter particle distance at very high particle concentration is smaller than the thickness of electric double layer which plays important role for dispersion, the repulsive force other than electrostatic repulsion between particles should be employed. Osmotic repulsion between two highly packed selfassembled monolayer (SAM) of surface modifiers in swollen state would be a candidate for the alternative repulsive force. In our former studies, individual factor which affects osmotic repulsion (dispersion of NP) in organic solvents, e.g., packing density of surface modifier on NP [3], size and size distribution of NP’s core [4], solvent quality [3,4], and chain length of surface modifier [5] been experimentally investigated and associated with dispersion of the NP in organic solvents [5]. As a result of the series of investigations, perfect dispersion of the CeO2 NP at very high content (50 wt%, 8.2 vol%) in cyclohexane was achieved [6]. In this study, more condensed dispersion (77 wt%, 23 vol%) of the decanoic acid SAM-protected CeO2 NP in transdecalin was prepared. In addition, the temperature effect on the stability of dispersion in transdecalin and benzene was examined and discussed.
EXPERIMENT DETAILS The decanoic acid-modified CeO2 NPs were synthesized by supercritical hydrothermal method [7,8]. Then, as-synthesized decanoic acid SAMs on the NPs were purified via poorsolvent precipitation method [3]. Obtained decanoic acid SAM protect
