Liquid dynamics in ZrO2 nanoporous films

Time-resolved Optical Kerr Effect (OKE) measurements were used to determine the orientational dynamics of water and acetonitrile in the bulk and in pores of ZrO2 nanostructured films. The experiments were performed with a home-built OKE microscope, capable of providing the necessary axial resolution (5 μm) to exclusively probe the internal volume of the film. The time constants obtained for the orientational dynamics of the bulk liquids agree with the literature. In the pores, both liquids exhibit slower dynamics, indicating a restricted motion of the molecules at the interface. In the case of water, our data is manifestly incompatible with the existence of a bulk-like population of molecules in the core of the pores, suggesting that the interface induces a long range constraint on the orientational dynamics of the molecules within the nanocavity. The differences observed between the two liquids are interpreted as due to the H-bond character of water, which is absent in acetonitrile.