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首页> 外文期刊>Journal of Non-Crystalline Solids: A Journal Devoted to Oxide, Halide, Chalcogenide and Metallic Glasses, Amorphous Semiconductors, Non-Crystalline Films, Glass-Ceramics and Glassy Composites >Characteristic size of molecular dynamics in polymers probed by dielectric probes of variable length
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Characteristic size of molecular dynamics in polymers probed by dielectric probes of variable length

机译：变长介电探针探测聚合物中分子动力学的特征尺寸

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摘要

Recently we introduced a rigid-rod type chromophore, E-4,4'-N,N-dibiitylamino-nitro-stilbene (DBANS), that acts as a dielectric and fluorescent probe, and enables the study of molecular dynamics in apolar polymers by dielectric relaxation spectroscopy (DRS). This work focuses on the effect of the probe size and concentration on the specific probe response. For this purpose, a series of probe molecules with core lengths (l) between 0.6 and 2 nm was used to 'dope' polystyrene at concentrations from 0.1 to 1.0 wt%. For all probes, a selective amplification of the intrinsic alpha-relaxation was found that was linear within the whole probe concentration range. Moreover, two clear size effects on the probe dynamics were revealed. At high temperatures, the probe relaxation time obeys tau alpha l(3), which confirmed rotational diffusion as the linking mechanism between the polymeric segmental dynamics and dielectric probe response. The shortest probe revealed an additional Arrhenius-type (beta*) relaxation that was attributed to large angular probe fluctuations involving discrete jumps. Its exclusive occurrence indicates a critical lower probe size (r similar to 0.6 nm) below which the dielectric probe acts also as a 'free-volume probe' as indicated by the pronounced anormality in the tau(beta) (T) dependence. Finally, an attempt was made to relate probe concentration effects on the glass transition temperature (plasticizing effect) to the intrinsic length scale of cooperative dynamics xi. Based on a simple model for local plasticization we have determined a lower bound for in the order of 5 nm. (c) 2005 Elsevier B.V. All rights reserved.
机译：最近，我们引入了一种刚性棒型生色团E-4,4'-N，N-二联环氨基氨基-硝基-苯乙烯-二苯乙烯（DBANS），它可以作为介电和荧光探针，并可以通过以下方法研究非极性聚合物中的分子动力学介电弛豫谱（DRS）。这项工作集中于探针大小和浓度对特定探针反应的影响。为此目的，使用一系列核长度（l）在0.6至2 nm之间的探针分子以0.1至1.0 wt％的浓度“掺杂”聚苯乙烯。对于所有探针，发现固有的α-松弛的选择性扩增在整个探针浓度范围内是线性的。此外，揭示了对探针动力学的两个明显的尺寸影响。在高温下，探针的弛豫时间服从tau alpha l（3），这证实了旋转扩散是聚合物分段动力学与介电探针响应之间的联系机制。最短的探针显示出额外的Arrhenius型（beta *）松弛，这归因于涉及离散跳跃的大角度探针波动。它的排他性出现表明临界探针尺寸较低（r类似于0.6 nm），在该尺寸以下，介电探针也充当“自由体积探针”，如tauβ（T）依赖性的明显异常所指示。最后，尝试将探针浓度对玻璃化转变温度的影响（塑化作用）与协同动力学xi的固有长度尺度联系起来。基于局部增塑的简单模型，我们确定了5 nm的下限。 （c）2005 Elsevier B.V.保留所有权利。

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