Interfacial Phenomena

The boundary between two phases, the interface between the phases, has very different properties from that of the bulk phase and are important in a variety of chemical engineering processes. The interface may control transport between the phases, e.g., liquid-liquid extraction, reaction at the interface, e.g., heterogeneous catalysis, or accumulation of a component from one of the bulk phases, e.g., adsorption. All of these are examples of interfacial phenomena and all are difficult to study experimentally because of the two-dimensionality of the interface limits the size of the sample (relative to the bulk), although the local (interfacial) concentration may be large compared to the bulk. Special spectroscopies and other surface/interface probes have been developed to study interfacial phenomena at the molecular level. In tandem with experiments, theoretical methods based on first principles approaches are also used to understand the chemistry and physics of the atomic and molecular interactions.

One sub-field of interfacial phenomena (surface science) focuses on the interface between a solid and a low-density gas or partial vacuum. Under these conditions, there are a variety of electron probe spectroscopies that provide fundamental information on the structure of the surface and/or molecules on it. Practical heterogeneous catalysis, as practiced in large scale chemical processing, i.e., refinery and petrochemical production, usually occurs at or above atmospheric pressure and in porous media where photon probe spectroscopies are required for molecular analysis at the interface. Because of the small extent of the interface relative to the bulk, small changes in composition of the interface may have large effects on interfacial properties and these can be exploited for all kinds of chemical processes.