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Dynamics of Surface Fluctuations on Macrocyclic Melts
A hydrodynamic continuum theory (HCT) of thermally stimulated
capillary
waves describing surface fluctuations of linear polystyrene melts
is found to describe surface fluctuations of sufficiently thick films
of unentangled cyclic polystyrene. However, for cyclic polystyrene
(CPS) films thinner than 10<i>R</i><sub>g</sub>, the surface
fluctuations are slower than expected from the HCT universal scaling,
revealing a confinement effect active over length scales much larger
than <i>R</i><sub>g</sub>. Surface fluctuations of CPS films
can be slower than those of films of linear polystyrene analogues,
due to differences between the glass transition temperatures, <i>T</i><sub>g</sub>, of the linear and cyclic chains. The temperature
dependences of the surface fluctuations match those of bulk viscosities,
suggesting that whole chain dynamics dictate the surface height fluctuation
dynamics at temperatures 25–60 °C above <i>T</i><sub>g</sub>. When normalized surface relaxation rates of thicker
films are plotted as a function of <i>T</i>/<i>T</i><sub>g</sub>, a universal temperature behavior is observed for linear
and cyclic chains