López-García J J, Grosse C, Horno J
Departamento de Física, Campus Las Lagunillas, Ed. A3, Universidad de Jaén, 23071 Jaén, Spain.
J Phys Chem B. 2005 Mar 31;109(12):5808-15. doi: 10.1021/jp044585l.
The validity of the hypothesis of electroneutrality outside the double layer of a suspended particle with an applied ac electric field is analyzed. It is shown that the electrolyte solution remains electroneutral for distances greater than a few Debye lengths from the particle surface only when the diffusion coefficients of the two ion species are identical. On the contrary, in the general case, a volume charge density around the particle builds up, which extends to distances that are proportional to the square root of the effective diffusion coefficient value divided by the frequency. These distances can easily attain many particle radii. Numerical results for both uncharged and charged suspended particles are presented, and a correction to existing analytical expressions for the field-induced ion distributions around uncharged particles (J. Phys. Chem. 2004, 108, 8397) is given. While the charge densities far from the particle are usually very weak, it is shown that they strongly contribute to the dipole coefficient value and, therefore, to the calculated values of the permittivity and conductivity increments. The errors that would be committed if these charge densities were ignored, assuming local electroneutrality and determining the dipole coefficient at a few Debye lengths from the particle surface, are analyzed and shown to be substantial.
分析了在施加交流电场的情况下，悬浮颗粒双层外电中性假设的有效性。结果表明，只有当两种离子的扩散系数相同时，在距颗粒表面大于几个德拜长度的距离处，电解质溶液才保持电中性。相反，在一般情况下，颗粒周围会形成体电荷密度，其延伸距离与有效扩散系数值除以频率的平方根成正比。这些距离很容易达到许多颗粒半径。给出了不带电和带电悬浮颗粒的数值结果，并对现有的关于不带电颗粒周围场致离子分布的解析表达式（《物理化学杂志》2004年，108卷，8397页）进行了修正。虽然远离颗粒的电荷密度通常非常弱，但结果表明它们对偶极系数值有很大贡献，因此对介电常数和电导率增量的计算值也有很大贡献。分析了如果忽略这些电荷密度，假设局部电中性并在距颗粒表面几个德拜长度处确定偶极系数时所产生的误差，结果表明这些误差是相当大的。
