A new Brillouin scattering analysis of high frequency relaxations in liquids demonstrated at the hypersound relaxation of PPG
A new Brillouin scattering analysis of high frequency relaxations in liquids demonstrated at the hypersound relaxation of PPG
复制标题
液体高频弛豫的新布里渊散射分析在 PPG 的超音速弛豫中得到证明
DOI：
10.1016/0032-3861(96)00154-1
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发表时间：
1996
期刊：
影响因子：
4.6
通讯作者：
M. Pietralla
中科院分区：
文献类型：
--
作者：
H. Krbecek;W. Kupisch;M. Pietralla
提出了一种分析布里渊散射数据的新方法。同时使用两种散射几何，分别测量折射率n（T），我们可以确定对数导数Δ lgM′（ω，T）/Δ lgω = QM，从而能够通过高精度频移测量明确地表征占主导地位的快过程。对于足够窄的弛豫时间分布，可以导出复模量M（ω，T）= M′（ω，T）+ iM″（ω，T）的虚部M″（ω，T）.分析具有Mw = 1000（PPG 1000）的聚（丙二醇）的数据，我们发现显示Arrhenius行为的最快过程。使用已发表的数据，从脉冲表面散射，我们终于可以deconvolute一组三个不同的过程：两个展示Arabius行为和一个显示Vogel-Fulcher-Tammann行为。这三个过程以高准确度描述了数据，并暂时分配给分子运动。在高频率下，观察到的弛豫时间分布变窄到单个弛豫时间。根据这些结果，使用布里渊散射实验的线宽数据来确定弛豫过程的宽度似乎是有问题的。从目前的工作来看，我们相信表面声波实验是最有效的，因为它们可以与布里渊散射实验相结合。
We present a new method to analyse data obtained by Brillouin scattering. Using two scattering geometries simultaneously and measuring separately the refractive index n(T) we can determine the logarithmic derivative ∂lgM′(ω, T)/∂lgω = QMand thus are able to characterize unambiguously the dominant fast processes by high precision frequency shift measurements. For a sufficient narrow relaxation time distribution the imaginary part M″(ω, T) of the complex modulus M(ω, T) = M′(ω, T) + iM″(ω, T) can be derived. Analysing data of poly(propylene glycol) with Mw = 1000(PPG 1000) we find the fastest process to show Arrhenius behaviour. Using published data from impulsive surface scattering we can finally deconvolute a set of three different processes: two exhibiting Arrhenius behaviour and one showing Vogel-Fulcher-Tammann behaviour. These three processes describe the data to a high accuracy and are tentatively assigned to molecular motions. At high frequencies the relaxation time distribution observed narrows to a single relaxation time. In the light of these results it seems questionable to use linewidth data from Brillouin scattering experiments to determine the width of the relaxation process. From the present work we believe the experiments with surface acoustic waves to be the most effective since they can be coupled with Brillouin scattering experiments.