Understanding the properties of aqueous mixtures has important implications in applications ranging from enhanced oil recovery to biochemical processes. While there has been considerable effort invested in understanding the bulk properties of aqueous mixtures, very few studies have concentrated on their behavior in interfacial systems. Interfacial properties, which are important for applications like coatings and chemical separations, are defined by the molecular structuring of the fluid at the interface. The goal of this thesis is to understand and alter the wetting of solid surfaces by aqueous mixtures. In particular, we study the partitioning of aqueous mixtures of polar and non-polar molecules to different surfaces. What makes aqueous mixtures interesting is the hydrogen bonding nature of water that plays very different roles in the partitioning of polar and non-polar components of the aqueous mixtures. In this thesis, hydrogen bonding is modeled using a thermodynamic perturbation theory due to Wertheim. The theory, included in a classical Density Functional Theory framework, is used to study the molecular structure and interfacial properties of the system. We extend and apply the theory to study a number of aqueous mixtures. Key contributions of this thesis include

1. Predicting the interfacial properties of aqueous mixtures of short alcohols close to a hydrophobic surface
2. Extension of the first order perturbation theory to study the competition between intra and intermolecular hydrogen bonding of molecules in the presence of an explicit water-like solvent
3. Studying the effect of physical conditions and surface chemistry on the wetting of different surfaces by water-oil mixtures
4. Analyzing molecular simulation models for water-alkane interactions through a solubility study