Using light to study boundary lubrication: spectroscopic study of confined fluids.

Several instrumental developments to examine the spectroscopic response of molecularly thin fluids confined between mica sheets are described. They are predicated on using a redesigned surface forces apparatus where dielectric coatings, transparent to light at needed optical wavelengths, retain the ability to measure interferometric thickness at other optical wavelengths. Examples of recent measurements are presented using confocal laser Raman spectroscopy to evaluate how molecules orient as well as to perform chemical imaging. Other examples are presented using confocal fluorescence recovery after photobleaching to evaluate translational diffusion of confined polymer melts. The advantage of separating the mechanical average (force and friction) from direct information about structure and mobility at the molecular level is stressed.