X-ray Scattering Investigations of the Structure of Water and Ice in Periodic Mesoporous Organosilicas

Water is one of the most common materials on Earth and in everyday life. However, with its many anomalies which in many cases get further amplified when supercooled, it is still poorly understood. A particularly interesting case is water under confinement. When water is subject to spatial restrictions, it has been found that the structure of its network is influenced and its equilibrium and dynamical properties vary. An interesting confining matrix for water is found in the form of periodic mesoporous organosilicas (PMOs). These materials enable mesoporous confinement in a broad range of pore diameters with the possibility of tuning the pore wall-water interaction. This is achieved by organic moieties in the pore wall, which can house additional functional groups. These groups can for example have hydrophobic or hydrophilic properties. This thesis investigates the structure of water and ice under confinement in a broad range of PMOs with different pore diameters and pore wall functionalizations, by use of X-ray scattering. A strong dependence of the structure of confined water on the pore functionalization, as well as the pore diameter is found. Pores with smaller diameters and hydrophilic functionalizations lead to a decrease in density when compared to bulk water. Furthermore, a stronger tetrahedral water network is observed in these pores. At lower temperatures, an ice structure with diffuse cubic-like, hexagonal and amorphous contributions is observed. The hexagonal component also exhibits a shift in its lattice parameters when compared to bulk hexagonal ice. In smaller, hydrophilic pores, the ice crystallites are furthermore oriented in specific, preferred angles compared to the pore axis. It is also observed that the PMO host materials undergo a deformation when water is being adsorbed. Specifically, the periodicity of their organic moieties changes in dependence on their interaction with water.