Ruiz-Reina Emilio, Carrique Félix
Departamento de Fisica Aplicada II, Universidad de Malaga,Campus de El Ejido, 29071, Malaga, Spain.
J Phys Chem B. 2008 Sep 25;112(38):11960-7. doi: 10.1021/jp8027885. Epub 2008 Sep 3.
We present a model for the theoretical description of the electric double layer of realistic salt-free colloidal suspensions. This kind of systems consist of aqueous suspensions deionized maximally without any electrolyte added during the preparation, in which the only ions present can be (i) the added counterions that counterbalance the surface charge, (ii) the H(+) and OH(-) ions from water dissociation, and (iii) the ions produced by the atmospheric CO2 contamination. Our theory is elaborated in the framework of the classical Poisson-Boltzmann theory, the spherical cell model approach, and the appropriate local equilibrium reactions, and it also includes an efficient mathematical treatment for dealing with the resulting integro-differential equations. We have applied it to the study of the surface electric potential in a wide range of volume fraction and surface charge density values in a variety of cases. The numerical results show that it is necessary to consider the water dissociation influence for volume fractions lower than approximately 10(-2), whereas the atmospheric contamination, if the suspensions are open to the atmosphere, is important in the region of phi<10(-1). The present work sets the basis for theoretical models concerning the equilibrium phase diagram, electrokinetics, and rheology of such systems.
我们提出了一个用于对实际无盐胶体悬浮液的双电层进行理论描述的模型。这类系统由在制备过程中最大限度去离子且未添加任何电解质的水悬浮液组成，其中存在的唯一离子可以是：（i）添加的用于平衡表面电荷的抗衡离子；（ii）水电离产生的H⁺和OH⁻离子；以及（iii）大气中CO₂污染产生的离子。我们的理论是在经典泊松 - 玻尔兹曼理论、球形单元模型方法以及适当的局部平衡反应框架下阐述的，并且还包括对所得积分 - 微分方程的有效数学处理。我们已将其应用于研究各种情况下广泛体积分数和表面电荷密度值范围内的表面电势。数值结果表明，对于体积分数低于约10⁻²的情况，有必要考虑水电离的影响，而如果悬浮液暴露于大气中，在φ < 10⁻¹的区域，大气污染是重要的。本工作为关于此类系统的平衡相图、电动学和流变学的理论模型奠定了基础。
