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The interactions between gold nanoparticles modified with mercaptoacetate and a cationic polyelectrolyte, poly (dimethyldiallylammonium chloride) (PDC) have been investigated. As a comparison, a system containing the modified gold nanoparticles and a cationic surfactant, hexadecyltrimethylammonium bromide (HTAB) is also studied. The average sizes of the modified gold nanoparticles used are 5.7 and 12.9 nm, respectively. Most of experiments have been performed under a fixed concentration of the modified gold nanoparticles with various PDC concentrations at pH 3 and 8. UV-vis spectroscopy and transmission electron spectroscopy reveal that at pH 8, the modified gold nanoparticles with small size are gradually aggregated with an increase of PDC concentration, whereas those with large size are aggregated at low PDC concentration, but at higher PDC concentration the gold nanoparticles are well separated. At pH 3, the modified gold nanoparticles for both sizes show a dispersion-flocculationredispersion sequence. These interactions are predominantly induced by the electrostatic attractions between negatively charged nanoparticles and positively charged PDC which are affected by pH. In the case of the modified gold nanoparticles-HTAB system, the modified gold nanoparticles show a dispersion-flocculation-redispersion sequence. The redispersion occurs by the formation of HTAB bilayer on the nanoparticles. Key-words: Interaction of nano gold with polymer, Thiol-modified gold particle, Poly (dimethyldiallylammonium chloride), Aggregation, UV -vis spectroscopy

Interactions between Thiol-modified Gold Nanoparticles and a Cationic Polyelectrolyte