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. A clear slowdown of the mobility of hydrophilic and hydrophobic quantum dots at planar water–alkane interfaces is observed by fluorescence correlation spectroscopy. The effect is most evident when the viscosities of both liquid phases are similar, i.e., at decane–water interfaces. 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.