Aggregation kinetics and cluster structure of amino-PEG covered gold nanoparticles

Abstract

In this study controlled clustering kinetics is demonstrated for PEG grafted gold nanoparticles, in response to applied environmental stimuli; the temperature and ionic strength of the medium. It is also found that the rate of assembly determines the structure of the prepared clusters. After the system is brought out of equilibrium, time-dependent extinction and dynamic light scattering data are used to follow the evolution of nanoparticle cluster formation in real time. The results show that the rate of assembly increases with increasing ionic strength or temperature of the medium. As a result the nanoparticle cluster size scales with ionic strength and temperature, over a cluster size range from a few particle sizes up to the micron-scale. It is found that, even at the lowest ionic strength, the electric double layer repulsion is eliminated; hence the observed differences in kinetics and in cluster structure arise from modulation of the repulsive steric interactions between nanoparticles. The approach should be extendable to suspensions of other nanoparticle types, where the nanoparticle stability is determined by surface-grafted responsive macromolecules.