Surface/interface order in liquids with electrostatic correlations: X-ray scattering studies

PROJECT SUMMARY Intellectual merit: Normal (isotropic) liquids, both metallic and nonmetallic, are now known to stratify near surfaces and interfaces, i.e. to form layers. The objective of this project is a detailed and systematic study of such ordering phenomena. A class of molecular liquids called “Madrid liquids” has been identified as likely to have high critical temperatures (Tc) and low melting temperatures, and thus ideal systems for studies of surface layering at low T/Tc without preemption by freezing. The dependence of surface layering in such liquids on temperature and surface tension will be investigated and compared with theoretical descriptions. Lateral order at the surface will be characterized near and below the melting transition, where surface melting is predicted. Ordering of these liquids at their free surfaces will be compared with the ordering at liquid-solid interfaces, to try to learn whether the trends can be explained within a common framework. Interfaces between water and solid substrates (both hydrophilic and hydrophobic) will be studied under flow conditions where slip is reported to occur at the interface. The primary experimental probes to be used are synchrotron X-ray reflectivity and surface scattering. Broader impacts: Liquid surfaces and interfaces play crucial roles in physics, chemistry, geology, biology, etc., and in a large variety of real-world processes and products such as lubrication,adhesion, filtration, oil recovery, wetting/spreading/coating, aerosols and emulsions, etc. The knowledge gained from the proposed studies will help us learn how and why liquids behave differently at surfaces and interfaces, and may help in designing systems with specific surface/interface behaviors. Thus, such studies may lead ultimately to technological benefits for society. For example, an increased understanding of interface structure and its relation to slip during flow may lead to more efficient ways of transporting fluids. This project will integrate research and teaching by training graduate students in an interdisciplinary environment, and also by giving them experience in the use of synchrotron facilities, an area in which infrastructure development and operation have been constrained by a shortage of junior personnel. The results of this research will be disseminated through traditional scientific channels, through web pages,through the media when possible, and through graduate and undergraduate courses in liquid-state physics that are being developed.