用介电谱确定纯回复跃迁
On the Determination of the Transition to Pure Reptation by Dielectric Spectroscopy
摘要：
聚合物熔体显示出一个特征的分子量依赖的弛豫时间，可以与非纠缠和纠缠制度。在高分子量下，轮廓长度波动和约束释放的影响停止，纯蠕动占主导地位。由于介电谱具有很宽的频率范围，它可以在很宽的温度范围内跟踪聚合物的动力学行为，而且它的另一个优点是可以记录含有爬行信息的谱形。在这里，我们调查的明显差异的分子量的发病纯爬行从分子量的依赖性和光谱形状。我们研究了流行的导数方法，并将其与包含高阶项的版本进行了比较。高阶项导致比用更简单的版本确定的那些峰形状和位置更准确的峰形状和位置。如果实验光谱包含电导率和极化贡献，这变得很重要。高阶项需要引入插值函数来分析实验光谱，这使得Havriliak-Negami函数看起来是一种更鲁棒但可靠的确定峰形的工具。我们得出的结论是，分子量的依赖性和光谱形状都可以强烈影响电导率和极化贡献。虽然这留下了过渡分子量的准确值的不确定性，峰形指向爬行和轮廓长度波动的存在下，在聚异戊二烯的分子量大于1000 kg/mol，这将意味着一个10倍以上的阈值分子量比预期从以前的估计使用的分子量依赖性。
英文摘要：
Polymer melts show a characteristic molecular weight dependent relaxation time that can be related to the unentangled and entangled regime. At high molecular weights, influence of contour length fluctuations and con-straint release cease and pure reptation prevails. With the broad frequency range dielectric spectroscopy can fol-low polymer dynamics over a very broad temperature range, with the additional advantage of recording the spec-tral shape which contains information on reptation. Here we investigate the apparent discrepancy in the molecular weight for the onset of pure reptation from the molecular weight dependence and the spectral shape. We examined the popular derivative method and compared it with a version that includes higher order terms. Higher order terms lead to a more accurate peak shape and position than those determined with the simpler version. This becomes important if experimental spectra contain conductivity and polarization contributions. Higher order terms require the introduction of an interpolating function to analyze experimental spectra, which lets the Havriliak-Negami function appear to be a more robust, yet reliable tool to determine the peak shapes. We reach the conclusion that molecular weight dependence and spectral shape can be both strongly affected by conductivity and polarization contributions. While this leaves uncertainties on the accurate value of the transition molecular weight, the peak shape points to the existence of reptation and contour length fluctuations in polyisoprene with a molecular weight greater than 1000 kg/mol, which would imply a ten times greater threshold molecular weight than expected from previous estimates using the molecular weight dependence.
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