Colloidal metal particles as probes of nanoscale thermal transport in fluids

We investigate suspensions of 3-10 nm diameter Au, Pt, and AuPd nanoparticles as probes of thermal transport in fluids and determine approximate values for the thermal conductance G of the particle/fluid interfaces. Subpicosecond λ = 770 nm optical pulses from a Ti:sapphire mode-locked laser are used to heat the particles and interrogate the decay of their temperature through time-resolved changes in optical absorption. The thermal decay of alkanethiol-terminated Au nanoparticles in toluene is partially obscured by other effects; we set a lower limit G >20 MW m^-2 K^-1. The thermal decay of citrate-stabilized Pt nanoparticles in water gives G≈130 MW m^-2 K^-1. AuPd alloy nanoparticles in toluene and stabilized by alkanethiol termination give G≈5 MW m^-2 K^-1. The measured G are within a factor of 2 of theoretical estimates based on the diffuse-mismatch model.