From Simple Liquid to Polymer Melt. Glassy and Polymer Dynamics Studied by Fast Field Cycling NMR Relaxometry: Low and High Molecular Weight Limit
From Simple Liquid to Polymer Melt. Glassy and Polymer Dynamics Studied by Fast Field Cycling NMR Relaxometry: Low and High Molecular Weight Limit
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从简单的液体到聚合物熔体。
DOI：
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
E. Rössler
中科院分区：
文献类型：
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作者：
S. Kariyo;A. Brodin;C. Gainaru;A. Herrmann;H. Schick;V. Novikov;E. Rössler
用快场循环核磁共振研究了1H自旋−晶格弛豫在较宽的温度范围(203GmoL-−1=355和466)在低相对分子质量的邻三苯基、三苯基和低聚聚丁二烯(PB)中的弥散行为(203GmoL−401K)。与以往的FFC核磁共振工作不同的是，我们分析了磁化率形式ω/T1(ω)中的驰豫数据，并应用频率−温度叠加，获得了长达80年的频率主谱。在所有情况下，只有玻璃态动力学(α过程)决定了松弛行为，并且Rouse单位估计为Mr≅500g/mol。提取了10−11−10−6 S范围内的时间常数Tm(T)，与介电谱同时测量的结果吻合较好。对于高分子量的PB(M/GmoL−1=56 500，87 000,314 000和817 000)，在从总光谱中分离出来的低频(ωτα≪1)处观察到明显的聚合物效应。
Fast field cycling (FFC) NMR is applied to study the dispersion of the 1H spin−lattice relaxation in the low molecular weight glass-formers o-terphenyl, tristyrene, and oligomeric polybutadiene (PB, with M/gmol−1 = 355 and 466) over a broad temperature range (203−401 K). Differing from previous FFC NMR works, we analyze the relaxation data in the susceptibility form ω/T1(ω), and applying frequency−temperature superposition, master spectra are obtained covering up to 8 decades in frequency. In all cases solely the glassy dynamics (α-process) determines the relaxation behavior, and the Rouse unit is estimated to MR ≅ 500 g/mol. The time constant τα(T) in the range 10−11−10−6 s is extracted, which agrees well with those measured at the same time by dielectric spectroscopy. For the high molecular weight PB (M/gmol−1 = 56 500, 87 000, 314 000, and 817 000) pronounced polymer effects are observed at low frequencies (ωτα ≪ 1) which are isolated from the total spectrum by subtracting the “glass spectrum” as obtai...