Prof. Scott Milner セミナー

Prof. Scott Milner (Penn State Univ) は高分子物理の世界的研究者です。

今回、Milner 先生のご来日の機会にご講演いただけることになりました。是非ともご参加下さいますようお願い申しあげます。

日時:2017年5月29日(月曜日)15:00~16:30

場所:京都大学化学研究所 本館北棟 5F 会議室(N-531C) (アクセス)

講演題目: Simulations of dynamical glass transition in hard spheres and PS thin films

講演概要: We have used simulations of both hard-sphere fluids and polystyrene thin films to explore the dynamical glass transition and reveal cooperativity in local dynamics.

Monodisperse hard spheres are perhaps the simplest glass-forming systems. Their strong tendency to crystallize can be overcome by a “crystal-avoiding” hybrid Monte Carlo method, which biases against the growth of crystalline order. Hard sphere systems are ideal for analysis of how mobility disappears in glassy fluids. We present a purely geometrical criterion that predicts the volume fraction of the dynamical glass transition, which also works well when adapted to soft spheres. To reveal dynamical cooperativity in hard-sphere fluids, we use arrays of “pinned” particles as a field to drive the glass transition. We infer the cooperative length from the array spacing needed to drastically slow the system.

Glassy behavior in polystyrene thin films has been extensively studied experimentally. A free surface “unpins” nearby segments and suppresses the glass transition. We use united-atom MD, taking care to ensure consistent behavior between thin films and bulk. We obtain a film-average Tg from density versus temperature (like ellipsometry experiments), and find Tg shifts with thickness consistent with experiment. We also obtain consistent Tg shifts from short-time dynamics (monomer displacements and bond rotations) versus temperature, which for films of different thickness collapse to a master curve. Finally, we obtain *local* Tg versus depth by applying the same approach to dynamics of segments at different depths, which clearly reveals a mobile surface layer of about 4 nm.

お問い合わせ先: 京都大学化学研究所 分子レオロジー領域 松宮 (email: matsmiya_at_scl.kyoto-u.ac.jp, phone: 0774-38-3136)


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Last-modified: 2017-05-27 (土) 11:56:29 (394d)