The granularity of matter -- details concerning the chemical structure of individual molecules -- are known to become increasingly prominent as the degree of confinement approaches molecular dimensions. Here we use the surface force apparatus (SFA, Figure 1) to study viscoelastic responses of fluids confined between two atomically-smooth mica surfaces. The key point is to impose an oscillatory shear and to observe the response of the confined fluid. Depend upon different surface preparations of the mica, the nanorheological properties of fluids under recleaved, atomically smooth mica surfaces contrast significantly with those under conventional precleaved, atomically rough mica surfaces.
Conventional surface force apparatus (SFA).
Raman spectroscopy provides information about molecular vibrations, which are sensitive to interactions and conformations of the molecules. Moreover, when confocal optics is employed, its spatial resolution along the vertical direction is almost as good as the lateral direction. Here we present a first attempt, by combining Confocal Raman spectroscopy with the SFA technique, to probe the molecular interactions and the near-surface orientations of various polymeric liquids, for instance PDMS (polydimethylsiloxane). By contrasting the Raman signals with and without external shear perturbations, we gain a better understanding of the nanodynamics of polymer liquids at the molecular level.
Confocal Raman/SFA
