Perez-de-Eulate Natalia G, Sferrazza Michele, Cangialosi Daniele, Napolitano Simone
Centro de Física de Materiales (CSIC-UPV/EHU), Paseo Manuel de Lardizábal 5, San Sebastián 20018, Spain.
Departamento de Física de Materiales, University of the Basque Country (UPV/EHU), San Sebastián 20018, Spain.
ACS Macro Lett. 2017 Apr 18;6(4):354-358. doi: 10.1021/acsmacrolett.7b00129. Epub 2017 Mar 20.
When cooled at constant rate, a 25 nm thin film of poly(4--butylstyrene) vitrifies 50 K lower than in bulk. This record sets the largest depression in thermal glass transition temperature () ever observed upon confinement at the nanoscale level. Same as for other supported polymer layers, this reduction in has been attributed to the presence of a free surface, the ensemble of molecules at the interface with air remaining in the liquid state also at temperatures well below bulk . Here, we verify that such tremendous shifts can be erased upon prolonged annealing in the liquid state, hinting at a metastable nature of confinement effects. We demonstrate that the recovery of bulk behavior and the manifestation of the free surface are enslaved to the kinetics of irreversible adsorption of chains on the supporting substrate.
当以恒定速率冷却时，聚（4-丁基苯乙烯）的25纳米薄膜玻璃化的温度比本体低50K。这一记录是在纳米尺度受限条件下观察到的热玻璃化转变温度（）的最大降幅。与其他支撑聚合物层一样，这种的降低归因于自由表面的存在，与空气界面处的分子集合在远低于本体的温度下也保持液态。在这里，我们证实，在液态中长时间退火后，这种巨大的转变可以消除，这暗示了受限效应的亚稳态性质。我们证明，本体行为的恢复和自由表面的表现受制于链在支撑基底上不可逆吸附的动力学。
