Departamento de Física Aplicada I, Facultad de Ciencias, Universidad de Málaga, 29071 Málaga, Spain.
J Phys Chem B. 2010 May 13;114(18):6134-43. doi: 10.1021/jp102350d.
In this contribution, the dynamic (or alternating current (AC)) electrophoretic mobility of spherical colloidal particles in a realistic salt-free concentrated suspension subjected to an oscillating electric field is studied theoretically using a cell model approach. Such a suspension is a concentrated one (in charged solid particles) in an aqueous solution without any electrolyte added during the preparation. The ionic species in solution can solely be: (i) the "added counterions" stemming from the particles (for example, by ionization of particle surface ionizable groups), (ii) the H(+) and OH(-) ions from water dissociation, and (iii) the ions produced by the atmospheric CO(2) contamination. The corrections related to water dissociation and CO(2) contamination in suspensions open to the atmosphere have turned out to be tremendous in many of the experimental situations of interest in direct current (DC) electric fields. Thus, it is mandatory to explore their influence in the more complex situation of AC electrophoresis. The results confirm the importance of ions produced by water dissociation and those originated by the acidification of the aqueous solution in suspensions contaminated with atmospheric CO(2), for low to moderate particle volume fractions, where the role of the added counterions is screened by the other ionic species. It is worth mentioning that, for high particle charges, two Maxwell-Wagner processes develop in the mobility frequency spectrum, respectively linked to the diffuse layer relaxation and to the relaxation of a condensed layer of counterions located very close to the particle surface. This is the so-called ionic condensation effect for highly charged particles, already described in the literature, and which for the first time will be studied in detail in realistic salt-free systems. The dynamic electrophoretic mobility will be numerically computed throughout a wide frequency range and compared with the cases of pure and realistic salt-free conditions. In addition, the competition between different relaxation processes associated to the complex electric dipole moment induced on the particles by the field, the particle inertia, as well as their influence on the dynamic response, will be explored for pure and realistic cases.
在这项贡献中，我们使用细胞模型方法从理论上研究了在无盐浓缩悬浮液中球形胶体颗粒在振荡电场中的动态（或交流电（AC））电泳迁移率。这种悬浮液是一种浓缩悬浮液（在带电荷的固体颗粒中），在制备过程中没有添加任何电解质。溶液中的离子物种只能是：（i）源自颗粒的“添加抗衡离子”（例如，通过颗粒表面可电离基团的电离），（ii）来自水离解的 H(+)和 OH(-)离子，以及（iii）由大气 CO(2)污染产生的离子。在许多直流（DC）电场中感兴趣的实验情况下，与水离解和 CO(2)污染相关的修正已变得非常重要。因此，在更复杂的交流电电泳情况下，必须探索它们的影响。结果证实了在与大气接触的悬浮液中，由水离解产生的离子和由水溶液酸化产生的离子的重要性，对于低至中等颗粒体积分数，添加抗衡离子的作用被其他离子物种屏蔽。值得一提的是，对于高颗粒电荷，在迁移率频率谱中会发展出两个 Maxwell-Wagner 过程，分别与扩散层弛豫和靠近颗粒表面的紧密层抗衡离子的弛豫有关。这就是所谓的高电荷颗粒的离子凝聚效应，已经在文献中描述过，这将是首次在现实的无盐系统中详细研究。在很宽的频率范围内，将数值计算动态电泳迁移率，并将其与纯盐和实际无盐条件的情况进行比较。此外，还将研究与电场在颗粒上诱导的复杂电偶极矩、颗粒惯性以及它们对动态响应的影响相关的不同弛豫过程之间的竞争，针对纯盐和实际情况。
