Napolitano Simone, Wübbenhorst Michael
Laboratory of Acoustics and Thermal Physics, Department of Physics and Astronomy, Katholieke Universiteit Leuven, Celestijnenlaan 200D, Leuven, Belgium.
J Phys Chem B. 2007 May 31;111(21):5775-80. doi: 10.1021/jp068721t. Epub 2007 May 5.
In ultrathin polymer films, the coupling between the segmental mobility, precursor of the molecular diffusion, and the crystallization rate is broken down because of interfacial interactions. In particular, in the presence of a reduced mobility layer at the interface with the substrate, the crystallization kinetics slow down at a length scale bigger than the one connected with the deviation from bulk behavior of the structural relaxation. By modeling the influence of the substrate interactions on the parameters governing the temperature evolution of the main relaxation time, it was possible to reproduce the effect of geometrical confinement on the quantities connected to the diffusion-limited crystallization rate. Upon reduction of the thickness or increasing of the substrate interaction, the films show an apparent higher glass stability in terms of an increase of the cold crystallization temperature and of the crystallization time. The deviations from bulk behavior were found to vanish above a crossover temperature as already observed for the phenomena connected to the glass transition.
在超薄聚合物薄膜中，由于界面相互作用，作为分子扩散前驱体的链段迁移率与结晶速率之间的耦合被打破。特别是，在与基底界面处存在迁移率降低层的情况下，结晶动力学在大于与结构弛豫的本体行为偏差相关的长度尺度上减缓。通过对基底相互作用对控制主弛豫时间温度演化参数的影响进行建模，能够再现几何限制对与扩散限制结晶速率相关量的影响。随着薄膜厚度减小或基底相互作用增强，薄膜在冷结晶温度和结晶时间增加方面表现出明显更高的玻璃稳定性。正如在与玻璃化转变相关的现象中已经观察到的那样，发现高于交叉温度时与本体行为的偏差消失。
