(571a) 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.