Department of Physics and Astronomy, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium.
ACS Nano. 2010 Feb 23;4(2):841-8. doi: 10.1021/nn9014517.
The temperature and thickness dependence of the thermal expansivity of ultrathin thin films of poly(tert-butylstyrene) capped between aluminum layers revealed an unusual and intriguing confinement scenario. Below 50 nm, both the glass transition temperature and the thermal expansion coefficients decreased. Such a mixed behavior implies an enhancement of the molecular mobility, without the presence of any free surface, but dead layers. On the basis of a careful analysis of averaged quantities measured by capacitive dilatometry, we deduced a profile of thermal expansivity that explains our experimental data and previous observations in polymer nanocomposites. The effect of density-conformation coupling in proximity of a nonattractive interface allows the coexistence of an immobilized fraction in direct contact with the metal and an excess of thermal expansivity, arising from the long-range effects of packing frustration penetrating inside the bulk-like core of the film.
在铝层之间夹着的超薄聚（叔丁基苯乙烯）薄膜的热膨胀系数随温度和厚度的变化揭示了一种不寻常且有趣的受限情况。在 50nm 以下，玻璃化转变温度和热膨胀系数都降低了。这种混合行为意味着分子迁移率增强，即使没有任何自由表面，也没有死层。基于对电容膨胀法测量的平均量的仔细分析，我们推导出了热膨胀系数的分布，该分布解释了我们的实验数据和以前在聚合物纳米复合材料中的观察结果。在非吸引力界面附近的密度构象耦合的影响使得与金属直接接触的固定部分和由于穿透薄膜块状核心内部的长程堆积受挫效应引起的热膨胀系数的过剩部分能够共存。
