Rotational dynamics of gold nanoparticles chain in water solution

In this work we report a study on thedetermination of the shape of aggregated gold colloids,obtained by adding pyridine to a solution of puregold nanoparticles prepared by laser ablation in waterstudying their dynamic behavior. We have simultaneouslymeasured the translational and rotationaldiffusion coefficients of dilute solutions of the aspreparedand aggregated gold nanoparticles by polarizedand depolarized dynamic light scattering. Anincrease of the hydrodynamic radius from 26 to135 nm and a decrease of the rotational diffusioncoefficient of two order of magnitude are measuredwith increasing the pyridine concentration, bothcorrelated to the aggregate formation. The dynamicproperties of nanoaggregates have been interpreted byapplying a model which allows a direct evaluation oftranslation and rotational diffusion coefficients of a chain of spherical particles by changing the numberand the relative position of each nanoparticle in theaggregate. The comparison between experimental andcalculated values indicates that an aggregation of lessthan ten isolated nanoparticles produces mainly rodlikechains, while aggregate morphology approachesthe fractal-like configuration with increasing aggregationnumber.