Glass transition and dynamics of semiflexible polymer brushes

The glass transition and dynamics of densely grafted semiflexible polymer brushes are studied by molecular dynamics simulation. The glass transition temperature (T_g) increases with the polymer rigidity. The local glass transition temperature (T_g,local) is estimated from the temperature-dependent dynamics of individual segments including the lateral position fluctuation and lateral mean square displacement. Different from the flexible polymer brush, T_g,local of semiflexible polymer brushes is roughly independent of the segment height. Our simulation reveals that the glass transition is in synchronism with an abrupt change of the chain conformation in semiflexible polymer brushes. When the temperature drops to near T_g, the semiflexible polymer chains elongate, tilt, and become more ordered. Moreover, enhanced segmental dynamics is observed at temperatures just above T_g for the semiflexible polymer brushes.