The surface relaxation dynamics of supported star-shaped polymer thin films are shown to be slower than the bulk, persisting up to temperatures at least 50 degrees above the bulk glass transition temperature . This behavior, exhibited by star-shaped polystyrenes (SPSs) with functionality f = 8-arms and molecular weights per arm Marm < Me (Me is the entanglement molecular weight), is shown by molecular dynamics simulations to be associated with a preferential localization of these macromolecules at the free surface. This new phenomenon is in notable contrast to that of linear chain polymer thin film systems where the surface relaxations are enhanced in relation to the bulk; this enhancement persists only for a limited temperature range above the bulk . Evidence of the slow surface dynamics, compared to the bulk, for temperatures well above Tg and at length and time scales not associated with the glass transition has not previously been reported for polymers.
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机译：已显示，负载型星形聚合物薄膜的表面弛豫动力学要比块状晶体慢，并且可以保持到比块状玻璃化转变温度至少高出至少50度的温度。 org / 1998 / Math / MathML“ id =” M1“ display =” inline“ overflow =” scroll“> T g 批量 。这种行为由功能为f = 8臂且每臂分子量Marm T g 批量 。相对于整体而言，对于远高于Tg的温度以及在与玻璃化转变无关的长度和时间范围内，表面动力学较慢的证据，以前尚未见过聚合物的报道。
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