Another class of electrochemical measurement is derived from the transport properties of the solution at the solid-liquid interface, such as flow electrification and pressure-wave propagation. Insights gained from these techniques are based on the concept that the motion or flow of an electrolyte solution at a solid surface depends on the space charge characteristics of the liquid-solid interface. Interfacial electrostatic profiles can be derived from these experiments, but the shape of the profiles cannot be determined directly by the experiment but must be assumed in modeling efforts.