Water Melting Induced Deformation of Ordered Nanoporous Silica: Fid-Bau Portal

Water Melting Induced Deformation of Ordered Nanoporous Silica

Paris, Oskar / Erko, Maxim

Nanoporous silica materials with cylindrical pores of some nanometres in diameter on a highly-ordered hexagonal pore lattice are used as a model system to assess the melting behaviour of water in confinement experimentally. Synchrotron radiation-based small-angle X-ray scattering (SAXS) is used to investigate in-situ the melting of ice in pores of 3.9 nm and 8.9 nm diameter. Besides the well-known melting point depression, the confinement-induced interaction of water with the solid pore walls manifests itself in a temperature-dependent, non-monotonous deformation of the solid host material. This deformation can be monitored as a function of temperature by measuring the pore lattice strain with small-angle X-ray diffraction, allowing to extract nanomechanical properties of the materials. The melting-induced pore lattice deformation is interpreted by a curved phase boundary between the liquid pore water in contact with the solid bulk water phase outside the pores, due to the preferred wetting of the pore walls by the liquid water. Using a simple model based on the generalized Laplace-pressure acting as a negative pressure on the pore walls, the Gibbs-Thomson equation allows a satisfactory description of the experimentally observed strains. Comparison of deduced elastic constants with those obtained from strains induced by capillary condensation for the same samples shows, however, quantitative differences up to 30%. These differences are discussed with respect to possible influencing factors.