Dielectric relaxations in chitosan solution with varying concentration and temperature: analysis coupled with a scaling approach and thermodynamical functions
Dielectric relaxations in chitosan solution with varying concentration and temperature: analysis coupled with a scaling approach and thermodynamical functions
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不同浓度和温度的壳聚糖溶液中的介电弛豫：结合缩放方法和热力学函数的分析
DOI：
10.1039/b922807a
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发表时间：
2010-06
期刊：
影响因子：
3.4
通讯作者：
Zhao, Kong-Shuang
中科院分区：
文献类型：
--
作者：
Liu, Chun-Yan;Zhao, Kong-Shuang
在40 Hz ~ 110 MHz的频率范围内，测量了壳聚糖水溶液的介电性质随浓度和温度的变化关系。在降低电极极化效应的贡献后，壳聚糖半稀溶液的介电谱分别在100 kHz和MHz处出现两个弛豫。利用Cole-Cole函数对所观察到的两种介电弛豫进行了严格的分析，并将可能的弛豫机制分别归结为凝聚态反离子和自由态反离子的涨落.介电增量和弛豫时间对浓度的依赖关系被解释在光的标度性质的水溶液。结果发现，在低频和高频情况下，弛豫时间对Cp的依赖性遵循标度律的预期指数。实验结果与理论分析吻合较好，表明低频弛豫机制是凝聚态反离子的涨落，高频弛豫机制是自由态反离子的涨落.除此之外，该分析进一步支持聚电解质动态行为的标度方法。壳聚糖溶液的介电谱的温度依赖性表明，低和高频率的介电增量一般随温度的升高而减小，这被认为是由于加速的反离子的重取向运动。此外，由弛豫时间计算了低频和高频的活化自由能Ea、活化焓变ΔH和活化熵变ΔS等热力学参数，并从微观角度进行了讨论。
The dielectric properties of chitosan in an aqueous solution with no added salts have been measured as a function of concentration and temperature in the frequency range from 40 Hz to 110 MHz, respectively. After reducing the contribution of the electrode polarization effects, the dielectric spectra of chitosan semidilute solutions show two relaxations at 100 kHz and MHz, respectively. The observed two dielectric relaxations have been strictly analyzed using the Cole-Cole function and the possible relaxation mechanisms were attributed to the fluctuation of condensed counterions and free counterions, respectively. The dependence of the dielectric increment and relaxation time on concentration was interpreted in light of the scaling properties of polyelectrolyte solutions. It was found that the dependence of relaxation time on the Cp follows the expected exponents of the scaling laws, both in the low-frequency and high-frequency cases. The good agreement between experimental results and theoretical analysis suggests that the low- and high-frequency relaxation mechanisms are the fluctuation of condensed counterions and free counterions, respectively. In addition to this, this analysis gives further support to the scaling approach of the dynamic behavior of polyelectrolytes. The temperature dependence of the dielectric spectrum of chitosan solutions showed that the low- and high-frequency dielectric increment generally decreases with the rise of temperature, which is considered to be due to the acceleration of the reorientation motion of the counterions. Moreover, the thermodynamic parameters, such as activation free energy Ea, activation enthalpy change ΔH and activation entropy change ΔS of low- and high-frequency were calculated from the relaxation time, and discussed from the microscopic thermodynamical view.
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影响因子：
6
作者：
De, Ranjit;Das, Bijan
通讯作者：
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影响因子：
5.5
作者：
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影响因子：
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作者：
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通讯作者：
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DOI：
10.1021/la050235u
发表时间：
2005-08
期刊：
Langmuir : the ACS journal of surfaces and colloids
影响因子：
--
作者：
K. Asami
通讯作者：
K. Asami