The effect of the concentration of dispersed particles on the mechanisms of low-frequency dielectric dispersion (LFDD) in colloidal suspensions
The effect of the concentration of dispersed particles on the mechanisms of low-frequency dielectric dispersion (LFDD) in colloidal suspensions
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DOI：
10.1016/s0927-7757(97)00272-0
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发表时间：
1998-09
期刊：
影响因子：
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通讯作者：
Á. Delgado;F. Arroyo;F. González‐Caballero;V. Shilov;Y. Borkovskaya
中科院分区：
文献类型：
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作者：
Á. Delgado;F. Arroyo;F. González‐Caballero;V. Shilov;Y. Borkovskaya
目前有两种机制用于解释电解质溶液中悬浮液的介电常数的低频(kHz范围)色散。第一种是表面扩散机制(SDM)，它将LFDD与外加电场引起的束缚离子沿粒子表面的扩散联系起来。第二种是体积扩散机制(VDM)，它是对经典的电泳弛豫理论在交变场中的推广，将LFDD与自由离子在扩散层中的扩散联系在一起。已经发现VDM比SDM更依赖于粒子浓度，这为分别研究这两种机制开辟了新的可能性。这是因为随着悬浮液中颗粒浓度的增加，体积扩散过程的特征长度随自由电解质体积的减小而减小，而表面扩散的特征长度保持不变。相应地，随着颗粒浓度的增加，VDM效应的驰豫时间必须减小，而SDM机制的驰豫时间必须保持不变。因此，通过改变悬浮液中颗粒的浓度，可以分离SDM和VDM的分散曲线。阐述了一个简单的模型，该模型可用于预测LFDD参数的体积分数依赖关系，特别是其幅值和临界频率。并与体积分数为3%~16%的聚合物胶乳分散体的实验数据进行了比较。结果发现，我们的模型很好地解释了色散的介电行为(LFDD幅值和临界频率对体积分数的依赖关系)，从而证明了VDM在所研究的体系中占优势。根据所提出的模型，对前人的实验数据进行了讨论。
There are two mechanisms which are currently used to explain the low-frequency (kHz range) dispersion of the dielectric permittivity of suspensions in electrolyte solutions (LFDD). The first, the surface diffusion mechanism (SDM), associates the LFDD with the diffusion of bound ions along the particle surface caused by the applied electric field. The second, the volume diffusion mechanism (VDM), follows from the generalization for alternating fields of the classical theory of the relaxation effect in electrophoresis and associates the LFDD with the diffusion of free ions in the diffuse double layer. It has been found that VDM is much more strongly dependent on particle concentration than SDM, opening new possibilities for the investigation of each of these two mechanisms separately. The reason is that when the concentration of particles in suspension increases, the characteristic length for the propagation of volume diffusion processes decreases together with the decrease of the free electrolyte volume, whereas the characteristic length for the surface diffusion remains constant. Correspondingly, when particle concentration is raised, the relaxation time of the VDM effect must decrease, whereas it must remain constant for the SDM mechanism. Thus, by varying the concentration of particles in suspension, one can separate the dispersion curves of SDM and VDM. A simple model is elaborated which can be useful to predict the volume fraction dependence of the parameters of LFDD; in particular, its amplitude and critical frequency. The results are compared with experimental data obtained with polymer latex dispersions of volume fractions ranging from 3 to 16%. It is found that the dielectric behaviour (the volume fraction dependence of both the amplitude and critical frequency of LFDD) of the dispersions is reasonably well explained with our model, thus demonstrating that VDM prevails in the systems studied. Experimental data previously found by other authors are also discussed in the light of the model presented.