We perform molecular dynamics simulations to observe the structure and dynamics of water using different water models (TIP3P, TIP4P, TIP5P) at ambient conditions, constrained by planar walls, which are either modeled by smooth potentials or regular atomic lattices, imitating the honeycomb-structure of graphene. We implement walls of different hydroaffinity, different lattice constant, and different types of interaction with the water molecules. We find that in the hydrophobic regime the smooth wall generally represents a good abstraction of the atomically rough walls, while in the hydrophilic regime there are noticeable differences in structure and dynamics between all stages of wall roughness. For a small lattice constant however the smooth and the atomically rough wall still share a number of structural and dynamical similarities. Out of the three water models, TIP5P water shows the largest degree of tetrahedral ordering and is often the one that is least perturbed by the presence of the wall.

Aqueous systems are omnipresent in nature and technology. They show complex behaviors, which often originate in the existence of hydrogen-bond networks. Prominent examples are the anomalies of water and the non-ideal behaviors of aqueous solutions. The phenomenology becomes even richer when aqueous liquids are subject to confinement. To this day, many properties of water and its mixtures, in particular, under confinement, are not understood. In recent years, molecular dynamics simulations developed into a powerful tool to improve our knowledge in this field. Here, our simulation results for water and aqueous mixtures in the bulk and in various confinements are reviewed and some new simulation data are added to improve our knowledge about the role of interfaces. Moreover, findings for water are compared with results for silica, exploiting that both systems form tetrahedral networks.

The phase behavior of a mixture of isobutyric acid and water confined in mesoporous SBA-15 silica material is studied by a combination of solid-state NMR spectroscopy and molecular dynamics (MD) simulations. The combination of these two techniques shows that the iBA-rich phase is close to the pore wall and the water-rich phase is in the center of the pores. The MD simulations reveal that this surprising phase behavior is mainly the result of the minimization of the hydrogen-bonding enthalpy. Moreover, the simulations show also that upon increasing temperature the relative water concentration increases at the pore surface, which is attributed to entropic contributions which lead to a more thorough miscibility. These results solve a long-standing problem of the microphase separation inside these materials.

We perform molecular dynamics simulations to observe the structure and dynamics of SPC/E water in amorphous silica pores and amorphous ice pores with radii slightly larger than 10 Å. In addition to atomically rough pores, we construct completely smooth pores such that the potential felt at a given distance from the pore wall is an averaged atomic potential. As compared to rough walls, smooth walls induce stronger distortions of water structure for both silica and ice confinements. On the other hand, unlike the smooth pores, the rough pores strongly slow down water dynamics at the pore wall. The slowdown vanishes when reducing the atomic charges in the wall, i.e., when varying the hydroaffinity, while keeping the surface topology, indicating that it is not a geometric effect. Rather, it is due to the fact that the wall atoms provide a static energy landscape along the surface, e.g., fixed anchor-points for hydrogen bonds, to which the water molecules need to adapt, blocking channels for structural rearrangement. In the smooth pores, water dynamics can be faster than in the bulk liquid not only at the pore wall but also in the pore center. Changes in the tetrahedral order rather than in the local density are identified as the main cause for this change of the dynamical behavior in the center of smooth pores.

We investigate the microphases of asymmetric AB diblock copolymers confined to thin films in the strong segregation limit under the application of electric fields. We evaluate the free energy of a given set of possible phases and present phase diagrams for diblock copolymers with a cylindrical bulk phase in dependence of the film thickness and the attraction between the confining walls and the A or B monomers. This is done for different field strengths and volume fractions. We find that with increasing field strength structures show a preference for alignment with the field. The alignment is stronger when the permittivity of the minority monomer is larger than that of the majority monomer. Depending on the strength of the wall potential and the film thickness, the walls can become completely wetted by the minority monomer.