Probing diffusion of single nanoparticles at water-oil interfaces

The diffusion of nanoparticles at a water-alkane interface is studied using fluorescence correlation spectroscopy. Hydrophilic and hydrophobic quantum dots of 5, 8, and 11 nm radius are used. A slow-down of nanoparticle diffusion at the liquid-liquid interface is observed. The effect is most evident when the viscosities of both liquid phases are similar, here, at the water-decane interface. In this case, the interfacial diffusion coefficients of the hydrophilic particles are 1.5 times and those of the hydrophobic particles 2 times lower than the corresponding bulk values.