Small-angle neutron scattering study of adsorbed water in porous Vycor glass: Supercooling phase transition and interfacial structure

Small-angle neutron scattering by porous Vycor glass at scattering vectors above 0.025 A${̊}^{\mathrm{-}1}$ decays as $Q^{\mathrm{-}n}$. However, both intensity and power-law exponent differ markedly between a dry sample, which has a fractally rough surface with dimensionality D∼2.5, and a water-saturated sample with identical scattering contrast, implying that the pore surfaces undergo gross geometrical changes on drying. The temperature variation of intensity at constant Q confirms the existence of a diffuse supercooling transition centered at about 260 K.