Radical re-appraisal of water structure in hydrophilic confinement

[Display omitted] •Water confined in cylindrical silica channels is studied with neutron scattering and computer simulation.•Density distribution across the pore is not uniform and peaks near the surface.•At low temperatures the distribution becomes less uniform, possibly resembling disordered ice.•Significant penetration into silica surface.•Methods can be applied to many other instances of fluids at surfaces. The structure of water confined in MCM41 silica cylindrical pores is studied to determine whether confined water is simply a version of the bulk liquid which can be substantially supercooled without crystallisation. A combination of total neutron scattering from the porous silica, both wet and dry, and computer simulation using a realistic model of the scattering substrate is used. The water in the pore is divided into three regions: core, interfacial and overlap. The average local densities of water in these simulations are found to be about 20% lower than bulk water density, while the density in the core region is below, but closer to, the bulk density. There is a decrease in both local and core densities when the temperature is lowered from 298K to 210K. The radical proposal is made here that water in hydrophilic confinement is under significant tension, around −100MPa, inside the pore.