Abstract
In this master thesis we perform a systematic investigation of how pore geometry affects the behavior of confined water. The water is confined in nanoporous silica in an amor- phous glass state. Experimental results report that water confined in nanoporous silica has different properties than water in bulk, and since the behavior of water in silica is important for many geological, biological and physical processes we wish to investigate this further. We suspect that a curved surface frustrates the packing or configuration of the water molecules inside the pore, and that the degree of frustration is dependent on the curvature of the pore surface. The studies are based on large-scale molecular dynamics simulations with an inter- atomic potential that allows chemical reactions between atoms in SiO2 and H2 O. We perform simulations of single pore systems, where the pores in the silica have simple geometric shapes with constant Gaussian curvature on the entire pore surface. We simulated six systems with spherical pores of different curvatures, with radii between 1.3 nm and 4.3 nm. In addition we simulated one system with a cylindrical pore and one with plane pore, for comparison. Both structural and diffusive properties are measured on the water inside the pores. We find that the pore could be divided into two regions of different behaviors, the surface region and the confined region. In the confined region, the properties measured are virtually constant, while in the surface region the properties vary with the distance to the pore surface. These regions are separated at the distance dsurf , which for the structural properties is dsurf ∼ 7-8 A, while for the diffusive properties it is dsurf ∼ 9-10 A. The structural properties showed no dependence on the curvature of the pores, which is in disagreement with what we suspected. The diffusive properties showed dependence on the radius of the pore, which is most likely due to varying fraction of water in the surface region compared to the water in the confined region.