Comparative study of thiol-free amphiphilic hyperbranched and linear polymers for the stabilization of large gold nanoparticles in organic solvent

Amphiphilic hyperbranched and linear polymers based on the respective palmitic acid modified hyperbranched and linear polyethylenimines have been successfully employed to transfer the citrate-protected 17-nm gold nanoparticles (AuNPs) from water into chloroform without the aid of other compounds. Compared with their corresponding linear analog, the amphiphilic hyperbranched polymers exhibited higher efficiency in transferring the large AuNPs. The chloroform solutions of AuNPs were characterized by UV-vis spectrometry and dynamic light scattering. It was found that aggregated AuNPs existed in the system with the amphiphilic linear polymer as stabilizer, whereas much less aggregated AuNPS could be detected in the system with the amphiphilic hyperbranched polymer as stabilizer. Furthermore the amphiphilic hyperbranched polymers could form relatively homogeneous and densely packed shell around the gold core revealed by transmission electron microscopy. Stability experiments showed that the solution of AuNPs coated with the amphiphilic hyperbranched polymers were more stable than those coated with their linear analogs. Moreover, the AuNPs capped with the amphiphilic hyperbranched polymers could be also stored in dryness for long time. (C) 2009 Elsevier Inc. All rights reserved.