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首页> 外文期刊>The Journal of Chemical Physics >Dynamics of propylene glycol and its oligomers confined to a single molecular layer - art. no. 244702
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Dynamics of propylene glycol and its oligomers confined to a single molecular layer - art. no. 244702

机译：丙二醇及其低聚物的动力学仅限于单个分子层-艺术。没有。 244702

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The dynamics of propylene glycol (PG) and its oligomers 7-PG and poly-propylene glycol (PPG), with M-w= 4000 (approximate to 70 monomers), confined in a Na-vermiculite clay have been investigated by quasielastic neutron scattering. The liquids are confined to single molecular layers between clay platelets, giving a true two-dimensional liquid. Data from three different spectrometers of different resolutions were Fourier transformed to S(Q, t) and combined to give an extended dynamical time range of 0.3-2000 ps. An attempt was made to distinguish the diffusive motion from the methyl group rotation and a fast local motion of hydrogen in the polymer backbone. The results show that the average relaxation time of this diffusive process is, as expected, larger than the relaxation time averaged over all dynamical processes observed in the experimental time window. More interesting, it is evident that the severe confinement has a relatively small effect on at T = 300 K, this holds particularly for the longest oligomer, PPG. The most significant difference is that the chain-length dependence of is weaker for the confined liquids, although the slowing down in bulk PG due to the formation of a three-dimensional network of OH-bonded end groups reduces this difference. The estimated average relaxation time at Q=0.92 angstrom(-1) for all the observed processes is in excellent agreement with the previously reported dielectric alpha relaxation time in the studied temperature range of 260-380 K. The average relaxation time (as well as the dielectric alpha relaxation time) is also almost unaffected by the confinement to a single molecular layer, suggesting that the interaction with the clay surfaces is weak and that the reduced dimensionality has only a weak influence on the time scale of all the dynamical processes observed in this study. (c) 2005 American Institute of Physics.
机译：通过准弹性中子散射研究了丙二醇（PG）及其低聚物7-PG和聚丙二醇（PPG）的动力学，其中M-w = 4000（约70个单体）被限制在Na--石粘土中。液体被限制在粘土薄片之间的单个分子层中，产生了真正的二维液体。将来自三个不同分辨率的不同光谱仪的数据进行傅立叶变换为S（Q，t），并进行组合，以提供0.3-2000 ps的扩展动态时间范围。试图将扩散运动与甲基旋转和氢在聚合物主链中的快速局部运动区分开。结果表明，正如预期的那样，此扩散过程的平均弛豫时间大于在实验时间窗口中观察到的所有动力学过程中平均的弛豫时间。更有趣的是，很明显，在T = 300 K时，严格限制对的影响较小，这对于最长的低聚物PPG尤其适用。最显着的差异是，对于的链长依赖性，对于受限液体较弱，​​尽管由于形成羟基键合的端基的三维网络而降低了本体PG的速度，区别。对于所有观察到的过程，在Q = 0.92埃（-1）处的估计平均弛豫时间与先前报道的在260-380 K的温度范围内的介电质α弛豫时间极好一致。 tau>（以及介电α弛豫时间）也几乎不受限于单个分子层的影响，这表明与粘土表面的相互作用较弱，并且降维仅对膜的时间尺度有较弱的影响。在这项研究中观察到的所有动力学过程。 （c）2005年美国物理研究所。

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