title: Controlling gold nanoparticle stability with triggerable microgels.
abstract: The interaction of a photodegradable surfactant (PS, 4-hexylphenylazosulfonate, C(6)PAS) with microgels (MGs) of poly(2-vinyl pyridine) (MGA) in the protonated state (pH 3) has been investigated. Electrophoretic mobility measurements confirm that negatively charged PS interacts with positively charged MGA to form mixed PS-MG complexes. This was sensed by a decrease in the effective PS-MGA charge and a switch in sign of electrophoretic mobility, from positive to negative, with increasing PS concentration. After the addition of extra positive microgels (MGB), the system undergoes coflocculation. Incident UV irradiation was used to photolyze the anionic PS, effectively eliminating the headgroups, thereby lowering the electrostatic interactions between PS and MGA microgel networks. Consequently, a reversal of MGA charge occurred, leading to electrostatic repulsions and causing the MGs to reswell and redisperse, with both MGA and MGB now being positively charged and hence stabilized against coflocculation. Extending this approach, negatively charged gold nanoparticles (AuMES) have been incorporated into the PS-MGA complexes. Atomic absorption spectroscopy (AAS) showed that 100% of the AuMES particles were recovered after coflocculation of (PS-MGA)-AuMES complexes with MGB. Furthermore, approximately 75% of the AuMES could be redispersed after UV irradiation to restabilize the dispersion. This system provides an interesting method for phase separation and gold nanoparticle recovery for reuse and recycling.
authors.affiliation: School of Chemistry, University of Bristol, Bristol BS8 1TS, UK.
authors.forename: Azwan Mat
authors.initials: AM
authors.lastname: Lazim
authors.forename: Melanie
authors.initials: M
authors.lastname: Bradley
authors.forename: Julian
authors.initials: J
authors.lastname: Eastoe