Ellison Christopher J, Torkelson John M
Department of Chemical Engineering, Northwestern University, Evanston, Illinois 60208-3120, USA.
Nat Mater. 2003 Oct;2(10):695-700. doi: 10.1038/nmat980. Epub 2003 Sep 21.
Despite the decade-long study of the effect of nanoconfinement on the glass-transition temperature (T(g)) of amorphous materials, the quest to probe the distribution of T(g)s in nanoconfined glass formers has remained unfulfilled. Here the distribution of T(g)s across polystyrene films has been obtained by a fluorescence/multilayer method, revealing that the enhancement of dynamics at a surface affects T(g) several tens of nanometres into the film. The extent to which dynamics smoothly transition from enhanced to bulk states depends strongly on nanoconfinement. When polymer films are sufficiently thin that a reduction in thickness leads to a reduction in overall T(g), the surface-layer T(g) actually increases with a reduction in overall thickness, whereas the substrate-layer T(g) decreases. These results indicate that the gradient in T(g) dynamics is not abrupt, and that the size of a cooperatively rearranging region is much smaller than the distance over which interfacial effects propagate.
尽管对纳米限域对无定形材料玻璃化转变温度（T(g)）的影响进行了长达十年的研究，但探究纳米限域玻璃形成体中T(g)的分布这一目标仍未实现。在此，通过荧光/多层方法获得了聚苯乙烯薄膜中T(g)的分布，结果表明表面动力学增强会影响薄膜内部数十纳米处的T(g)。动力学从增强态到本体态的平滑转变程度在很大程度上取决于纳米限域。当聚合物薄膜足够薄以至于厚度减小会导致整体T(g)降低时，表面层T(g)实际上会随着整体厚度的减小而增加，而基底层T(g)则会降低。这些结果表明，T(g)动力学中的梯度并非突然变化，并且协同重排区域的尺寸远小于界面效应传播的距离。
