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 10R_g, the surface fluctuations are slower than expected from the HCT universal scaling, revealing a confinement effect active over length scales much larger than R_g. Surface fluctuations of CPS films can be slower than those of films of linear polystyrene analogues, due to differences between the glass transition temperatures, T_g, 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 T_g. When normalized surface relaxation rates of thicker films are plotted as a function of T/T_g, a universal temperature behavior is observed for linear and cyclic chains.