Article pubs.acs.org/JPCC
Thermoresponsive Assembly of Gold Nanoparticles Coated with Oligo(Ethylene Glycol) Ligands with an Alkyl Head Ryo Iida,† Hideyuki Mitomo,‡ Yasutaka Matsuo,‡ Kenichi Niikura,*,‡ and Kuniharu Ijiro*,‡ †
Graduate School of Chemical Sciences and Engineering, Hokkaido University, Kita 13, Nishi 8, Kita-ku, Sapporo 060-8628, Japan Research Institute for Electronic Science, Hokkaido University, Kita 21 Nishi 10, Kita-ku, Sapporo 001-0021, Japan
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S Supporting Information *
ABSTRACT: This paper presents the thermoresponsive assembly behaviors of gold nanoparticles (AuNPs; 3, 5, and 10 nm in diameter) that are coated with a self-assembled monolayer of oligo(ethylene glycol) (OEG) ligands terminated with alkyl heads. AuNPs (5 nm in diameter) coated with OEG ligands without an alkyl head did not assemble within a temperature range from 20 to 70 °C. However, AuNPs coated with ethyl, iso-propyl, and propyl-headed OEG AuNPs afforded assembly at temperatures of 56, 33, and 19 °C, respectively, indicating that the assembly temperature can be tuned over a wide range by slight changes in the hydrophobicity of the alkyl head. Almost no hysteresis during the heating/cooling cycles was observed for the assembly/disassembly process. The diameter of the AuNPs also affected the assembly temperature, with increases in the diameter of the AuNP affording a lower assembly temperature. The ligand with the shorter alkyl tail length provided the lower assembly temperature of AuNPs than the ligand with longer tail.
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including low-molecular weight (
