  Understanding the extent of contact between objects is crucial for
surface-driven phenomena in the natural world. While interactions are known to
occur at subnanometer-length scales, the techniques needed to measure such
small-length scales are lacking. We combined two complementary techniques of
attenuated total reflectance infrared (ATR-IR) spectroscopy coupled with an
imaging detector and sum frequency generation (SFG) spectroscopy to
characterize the real contact area between surfaces. Imaging ATR-IR provides
the distribution of airgap separation between the surfaces at larger than
molecular length scales as well as an estimation of the real contact area.
Additionally, SFG directly probes the intermolecular interactions occurring at
molecular scales. Through the combination of these techniques, we show how
contact is achieved for both thin, rigid/glassy polymer films on top of soft
elastomers and rigid/glassy samples. Interestingly, we also show that the
orientation of the molecules in contact is a critically important factor that
influences interfacial interactions rather than just the number of molecular
sites in contact.
