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Transient Cooperative Processes in Dewetting Polymer Melts
We have compared the high velocity dewetting behavior, at elevated temperatures, of atactic (aPS) and isotactic polystyrene (iPS) films, with the zero shear bulk viscosity (ηbulk) of aPS being 10 times larger than that of iPS. As expected, for aPS the apparent viscosity of the films (ηf) derived from dewetting was less than ηbulk, displaying a shear thinning behavior. Surprisingly for iPS films, ηf was always larger than ηbulk, even at about 50 °C above the melting point, with ηf /ηbulk following an Arrhenius behavior. The corresponding activation energy of ≈160 ±10 kJ/mol for iPS films suggests a cooperative motion of segments, which were aligned and agglomerated by fast dewetting.