Water is the most important liquid for life as well as for the environment. In liquid water there is a hydrogen bonding network that originates from the interactions of H atoms with neighboring O atoms from other water molecules. This network reorganizes itself on the femtosecond (10-15 s) time scale and leads to transient liquid structuring on the nanoscale. Because of its complexity, the relationship between the unique properties of water and its molecular structure have not been solved. Techniques that can provide femtosecond structural information over multiple length scales can help. To do so, we developed nonlinear light scattering and imaging tools to access molecular structural information of aqueous solutions and interfaces. With these methods we have found nanoscale ordering in dilute salt solutions, and probe the structure of aqueous nanoscopic interfaces relevant for biology: lipid droplets, liposomes and water droplets. The optical properties of water can also be used to determine the electrical potential (voltage) of interfaces. This unique readout is useful for chemistry, neurology and device characterization. In this presentation I will give an overview of the field and our findings.
