The solid-liquid interface is an important entity across all disciplines dealing with fluids in contact with solids or soft materials. The understanding and careful tailoring of interfacial properties can make all the difference to the success or failure of a range of vital applications and devices including medical implants, pharmaceutical formulations, catalysts, and energy production and storage devices, among several others. Although the electrical charge at the solid-liquid interface exerts a profound influence on the dynamics and interactions of the interface, we have few, if any, broadly applicable techniques that permit surfaces and their properties to be interrogated in a straightforward fashion.
We are developing a new general, microscopy-based approach to measure the electrical charge of an arbitrary two-dimensional film in contact with any solvent. Because the technique relies on simple wide-field optical imaging, it carries with it all the advantages, simplicity and versatility of that technique – namely, large area, high spatial-resolution direct visualization, as well as high time-resolution that fosters the observation of changes in surface properties as a function of time. The technique permits us to image spatial heterogeneities and charge-altering chemical reactions at interfaces. We are also designing and perfecting a scanning-probe based technique that supports rapid imaging and measurement of surface electrical charge over large sample areas.