Thermal Transport in Au-Core\nPolymer-Shell Nanoparticles

Abstract

Thermal transport in aqueous suspensions of Au-core polymer-shell nanoparticles is investigated by time-resolved measurements of optical\nabsorption. The addition of an organic cosolvent to the suspension causes the polystyrene component of the polymer shell to swell, and this\nchange in the microstructure of the shell increases the effective thermal conductivity of the shell by a factor of approximately 2. The corresponding\ntime scale for the cooling of the nanoparticle decreases from 200 ps to approximately 100 ps. The threshold concentration of cosolvent that\ncreates the changes in thermal conductivity, 5 vol % tetrahydrofuran in water or 40 vol % <i>N</i>,<i>N</i>-dimethylformamide in water, is identical to the\nthreshold concentrations for producing small shifts in the frequency of the plasmon resonance. Because the maximum fraction of solvent in\nthe polymer shell is less than 20 vol %, the increase in the effective thermal conductivity of the shell cannot be easily explained by contributions\nto heat transport by the solvent or enhanced alignment of the polystyrene backbone along the radial direction.