Bittermann Marius R, Grzelka Marion, Woutersen Sander, Brouwer Albert M, Bonn Daniel
Van der Waals-Zeeman Institute, Institute of Physics, University of Amsterdam, Science Park 904, 1098 XH, Amsterdam, The Netherlands.
TiFN, P.O. Box 557, 6700 AN, Wageningen, The Netherlands.
J Phys Chem Lett. 2021 Apr 1;12(12):3182-3186. doi: 10.1021/acs.jpclett.1c00512. Epub 2021 Mar 24.
The macroscopic viscosity of polymer solutions in general differs strongly from the viscosity at the nanometer scale, and the relation between the two can be complicated. To investigate this relation, we use a fluorescent molecular rotor that probes the local viscosity of its molecular environment. For a range of chain lengths and concentrations, the dependence of the fluorescence on the macroscopic viscosity is well described by the classical Förster-Hoffmann (FH) equation, but the value of the FH exponent depends on the polymer chain length. We show that all data can be collapsed onto a master curve by plotting the fluorescence versus polymer concentration, which we explain in terms of the characteristic mesh size of the polymer solution. Using known scaling laws for polymers then allows us to quantitatively explain the relation between the FH exponent and the polymer chain length, allowing us to link the nano- to the macroviscosity.
一般来说，聚合物溶液的宏观粘度与纳米尺度下的粘度有很大差异，两者之间的关系可能很复杂。为了研究这种关系，我们使用了一种荧光分子转子来探测其分子环境的局部粘度。对于一系列链长和浓度，荧光对宏观粘度的依赖性可以用经典的福斯特 - 霍夫曼（FH）方程很好地描述，但FH指数的值取决于聚合物链长。我们表明，通过绘制荧光与聚合物浓度的关系图，所有数据都可以汇聚到一条主曲线上，我们从聚合物溶液的特征网眼尺寸角度对此进行了解释。然后，利用已知的聚合物标度律，我们能够定量解释FH指数与聚合物链长之间的关系，从而将纳米粘度与宏观粘度联系起来。
