Hesami Mahdis, Steffen Werner, Butt Hans-Juergen, Floudas George, Koynov Kaloian
Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany.
Department of Physics, University of Ioannina, 45110 Ioannina, Greece.
ACS Macro Lett. 2018 Apr 17;7(4):425-430. doi: 10.1021/acsmacrolett.8b00103. Epub 2018 Mar 20.
We studied experimentally the influence of interfaces on the dynamics in thin polymer films at temperatures far above the glass temperature ( + 80 °C). Polyisoprene (PI) was employed as a model system. We examined glass substrate supported films with thicknesses () spanning the range from 10 μm to 10 nm that correspond to / from 400 to 1, where is the polymer radius of gyration. We employed fluorescence correlation spectroscopy (FCS) to monitor the translational diffusion of small fluorescent tracer molecules, dispersed at nanomolar concentrations in the PI matrix. In thick films, a single diffusion process correlated to the bulk segmental dynamics of the matrix polymer was present. However, when the film thickness was smaller than the normal dimension of the FCS observation volume, a second, faster diffusion process appeared, reflecting enhanced segmental dynamics near the free surface. Our results provide direct experimental evidence for the existence of a layer with enhanced mobility near the free surface of supported PI films at temperatures as high as 80 °C above the bulk .
我们通过实验研究了在远高于玻璃化温度（+80°C）的温度下，界面对于聚合物薄膜动力学的影响。聚异戊二烯（PI）被用作模型体系。我们研究了玻璃基底支撑的薄膜，其厚度（）范围从10μm到10nm，对应于聚合物回转半径的400到1倍（）。我们采用荧光相关光谱法（FCS）来监测以纳摩尔浓度分散在PI基质中的小荧光示踪分子的平移扩散。在厚膜中，存在一个与基质聚合物的本体链段动力学相关的单一扩散过程。然而，当膜厚度小于FCS观察体积的正常尺寸时，出现了第二个更快的扩散过程，这反映了自由表面附近链段动力学的增强。我们的结果为在高于本体玻璃化转变温度80°C的温度下，支撑的PI薄膜自由表面附近存在具有增强流动性的层提供了直接的实验证据。
