On the cooperative nature of the β-process in neat and binary glasses: A dielectric and nuclear magnetic resonance spectroscopy study
On the cooperative nature of the β-process in neat and binary glasses: A dielectric and nuclear magnetic resonance spectroscopy study
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DOI：
10.1063/1.4816374
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发表时间：
2013-08-14
影响因子：
4.4
通讯作者：
Roessler, E. A.
中科院分区：
文献类型：
--
作者：
Bock, D.;Kahlau, R.;Roessler, E. A.
利用介电谱、H-2和P-31核磁共振谱（NMR），选择性地研究了磷酸三丙酯（TPP）/聚苯乙烯（PS/PS-d（3））二元玻璃体系的组分动力学。我们研究了低于T-g的二次（β-）弛豫，这在所有研究的含有TPP的样品中发现，但在纯聚苯乙烯中没有。β-过程的介电谱由活化能的不对称分布描述，在整个浓度范围内基本上没有变化;其最可能的值是E/k与24 T-g一致。β-过程的持久性通过TPP上的P-31 NMR哈恩回波和自旋晶格弛豫实验来证实，所述实验将β-过程的性质确定为与先前研究的或在本工作中重新研究的其他（纯）玻璃中发现的高度空间位阻。对PS-d（3）的相应H-2NMR实验证实了纯PS-d（3）中不存在β-过程，但揭示了混合物中β-过程的明确特征，即，聚苯乙烯单体执行与TPP分子基本上相同类型的二次弛豫。然而，有迹象表明，与纯玻璃的情况相反，PS-d（3）以及TPP分子的一些部分变得固定在混合物中。我们的结论是，在一个二元玻璃的β-过程中引入的一个组件引起高度相似的运动在第二个组件，这可能是作为其合作性质的指示。(C)2013 AIP Publishing LLC.
By means of dielectric as well as H-2 and P-31 nuclear magnetic resonance spectroscopy (NMR) the component dynamics of the binary glass tripropyl phosphate (TPP)/polystyrene (PS/PS-d(3)) is selectively investigated for concentrations distributed over the full range. We study the secondary (beta-) relaxation below T-g, which is found in all investigated samples containing TPP, but not in neat polystyrene. The dielectric spectrum of the beta-process is described by an asymmetric distribution of activation energies, essentially not changing in the entire concentration regime; its most probable value is E/k congruent to 24 T-g. Persistence of the beta-process is confirmed by P-31 NMR Hahn-echo and spin-lattice relaxation experiments on TPP, which identify the nature of the beta-process as being highly spatially hindered as found for other (neat) glasses studied previously, or re-investigated within this work. The corresponding H-2 NMR experiments on PS-d(3) confirm the absence of a beta-process in neat PS-d(3), but reveal a clear signature of a beta-process in the mixture, i.e., polystyrene monomers perform essentially the same type of secondary relaxation as the TPP molecules. Yet, there are indications that some fractions of PS-d(3) as well as TPP molecules become immobilized in the mixture in contrast to the case of neat glasses. We conclude that in a binary glass the beta-process introduced by one component induces a highly similar motion in the second component, and this may be taken as an indication of its cooperative nature. (C) 2013 AIP Publishing LLC.