(303e) Surface Dynamics of Macrocyclic Polystyrene Films

Thermally stimulated fluctuations of
the surface of a melt of macrocyclic polymers have been studied for the first
time. The surface fluctuations of macrocyclic polystyrene (cPS) of 2k, 7k, 17k,
and 37k molecular weight (M) were probed using x-ray photon correlation
spectroscopy (XPCS), a recently-developed technique that has already been
applied to study surfaces of linear PS melts.

The surface fluctuations for the cPS
films are slower than those of linear chain analogs for all M. However, the
glass transition temperatures (Tg) of the cyclic chains are higher than those
of the linear analogs, with the discrepancy decreasing with increasing M.  A
continuum hydrodynamic theory of thermally stimulated capillary waves with a
nonslip boundary condition is adequate to rationalize the behavior of the cPS
films. When results from
cPS of different M are plotted as a function of T/Tg the data nearly collapse
to a single curve, indicating that Tg is a key parameter for the surface
dynamics of macrocyclics in the temperature range studied.

Acknowledgements:  NSF support (CBET 0730692)