Molecular Hopping on Attractive Surfaces

Transport at the solid-liquid interface determines the efficiency of many chemical separations, biomolecule sensors, and catalytic reactions.  In previous single-molecule imaging experiments and Monte Carlo simulations, we have shown that a wide variety of molecules undergo intermittent hopping at the solid-liquid interface.  In this mode of transport, molecules make displacements across the surface by hopping through the bulk fluid. There is typically a broad distribution of waiting times between hops, indicative of the spectrum of binding strengths.  In previous studies, we found that changes in the waiting time distribution led to differing levels of molecular mobility. In this study, we changed the composition of the overlying fluid phase to change the attraction between the molecules and the surface and showed that longer hops across the surface became more probable when the surface was less attractive.  This work provides further evidence that the molecules hop through the bulk phase and gives a general strategy for increasing molecular mobility at the solid-liquid interface.