Depth-dependent inhomogeneous characteristics in supported glassy polystyrene films revealed by ultra-low X-ray reflectivity measurements
Depth-dependent inhomogeneous characteristics in supported glassy polystyrene films revealed by ultra-low X-ray reflectivity measurements
复制标题
DOI：
10.1038/pj.2014.80
复制
发表时间：
2014-12
期刊：
影响因子：
2.8
通讯作者：
Chunming Yang;Kohei Ishimoto;Syunsui Matsuura;Naoki Koyasu;I. Takahashi
中科院分区：
文献类型：
--
作者：
Chunming Yang;Kohei Ishimoto;Syunsui Matsuura;Naoki Koyasu;I. Takahashi
这项研究报告了支撑在Si衬底上的聚苯乙烯薄膜的玻璃化转变的X射线反射率测量，并以0.14至0.01 C min-1的低加热速率加热。在0.14 C min-1的加热速率下，玻璃化转变温度Tg与低至6 nm的膜厚度无关。然而，在0.04 C min− 1的加热速率下，Tg值随着厚度的减小而减小。Tg的降低在0.01 C min− 1的超低加热速率下最为显著。此外，随着薄膜厚度的减小，玻璃态α玻璃的线性热膨胀系数在0.14 C min− 1的加热速率下略有降低，而α玻璃在0.01 C min− 1的超低加热速率下表现出显著增加。用积分模型拟合α玻璃值得到的热膨胀系数重建深度剖面表明，随着升温速率的降低，界面死层的厚度减小，而自由表面区的体积分数增加。所观察到的降低Tg可以归因于表面和界面效应扰动的玻璃化转变动力学的薄膜在较慢的探测条件下。
This study reports X-ray reflectivity measurements of the glass transition of polystyrene thin films supported on Si substrates and heated at low heating rates that ranged from 0.14 to 0.01 C min− 1. At a heating rate of 0.14 C min− 1, the glass transition temperature T g was independent of the film thickness down to a thickness of 6 nm. However, at a heating rate of 0.04 C min− 1, the value of T g decreased with decreased thickness. The reduction in T g was most significant at the ultra-low heating rate of 0.01 C min− 1. Furthermore, with decreased film thickness, the linear thermal expansivity in the glassy state α glass slightly decreased at a heating rate of 0.14 C min− 1, whereas α glass exhibited a significant increase at the ultra-low heating rate of 0.01 C min− 1. Reconstructed depth profiles of thermal expansivity, which were obtained by fitting the α glass values using an integral model, indicated a decrease in the thickness of the interfacial dead layer with a decrease in the heating rate, whereas the volume fraction of the free surface region increased under this condition. The observed reduction in T g can be attributed to surface and interface effects perturbing the glass transition dynamics of the thin films under slower probing conditions.