Berlin 2012 – scientific programme

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O: Fachverband Oberflächenphysik

O 12: Surface dynamics

O 12.9: Talk

Monday, March 26, 2012, 18:00–18:15, H 2013

Probing diffusion of single nanoparticles at water/oil interfaces with fluorescence correlation spectroscopy — Dapeng Wang, Hans-Jürgen Butt, and •Kaloian Koynov — Max Planck Institute for Polymer Research, Mainz, Germany

A good understanding of the dynamics and self organization of nanometer-sized objects, e.g., molecules, macromolecules and nano-particles (NPs) at immiscible liquid/liquid interfaces is not only of fundamental interest for the soft mater physics and cell biology, but is also very important for a number of technological applications in material synthesis, pharmacy, microfluidics and nanotechnology. Here, we show that the fluorescence correlation spectroscopy (FCS), a method based on measuring the fluctuations of the fluorescent light intensity caused by the diffusion of fluorescent species through a very small observation volume, is very well suited for studies of NPs diffusion on liquid/liquid interfaces as it offers the possibility to monitor fast diffusing, nanometer size objects at extremely low surface coverage. We used FCS to study the diffusion of fluorescent semiconductor nanoparticles (quantum dots) on planar water/oil interfaces. The effects of several important parameters, i.e. the particles size, their surface functionalization (hydrophobic/hydrophilic) and the oil phase viscosity were systematically explored. Most notably, a significant slow-down of nanoparticle diffusion at the water/oil interface was observed. The effect was most evident when the viscosities of both liquid phases were similar, i.e. at the water/decane interface.