Department of Applied Physics, Faculty of Science, University of Extremadura, Avda de Elvas s/n, 06006 Badajoz, Spain.
Phys Chem Chem Phys. 2012 Jul 21;14(27):9758-67. doi: 10.1039/c2cp40743d. Epub 2012 Jun 8.
The electrical characterization of surfaces in terms of the zeta potential (ζ), i.e., the electric potential contributing to the interaction potential energy, is of major importance in a wide variety of industrial, environmental and biomedical applications in which the integration of any material with the surrounding media is initially mediated by the physico-chemical properties of its outer surface layer. Among the different existing electrokinetic techniques for obtaining ζ, streaming potential (V(str)) and streaming current (I(str)) are important when dealing with flat-extended samples. Mostly dielectric materials have been subjected to this type of analysis and only a few papers can be found in the literature regarding the electrokinetic characterization of conducting materials. Nevertheless, a standardized procedure is typically followed to calculate ζ from the measured data and, importantly, it is shown in this paper that such a procedure leads to incorrect zeta potential values when conductors are investigated. In any case, assessment of a reliable numerical value of ζ requires careful consideration of the origin of the input data and the characteristics of the experimental setup. In particular, it is shown that the cell resistance (R) typically obtained through a.c. signals (R(a.c.)), and needed for the calculations of ζ, always underestimates the zeta potential values obtained from streaming potential measurements. The consideration of R(EK), derived from the V(str)/I(str) ratio, leads to reliable values of ζ when dielectrics are investigated. For metals, the contribution of conductivity of the sample to the cell resistance provokes an underestimation of R(EK), which leads to unrealistic values of ζ. For the electrical characterization of conducting samples I(str) measurements constitute a better choice. In general, the findings gathered in this manuscript establish a measurement protocol for obtaining reliable zeta potentials of dielectrics and conductors based on the intrinsic electrokinetic behavior of both types of samples.
表面的电学特性可以用 ζ 电位来描述，即对相互作用位能有贡献的电动势能。在各种工业、环境和生物医学应用中，这一点非常重要，因为任何材料与周围介质的初始结合都是由其外层表面的物理化学特性介导的。在获得 ζ 电位的各种现有电动技术中，对于平面扩展样品，流动电位 (V(str)) 和流动电流 (I(str)) 非常重要。大多数介电材料都经过了这种分析，只有少数文献中提到了对导电材料的电动特性进行分析。然而，通常会遵循标准化程序来根据测量数据计算 ζ，并且重要的是，本文表明，当研究导体时，该程序会导致不正确的 ζ 电位值。无论如何，评估 ζ 的可靠数值需要仔细考虑输入数据的来源和实验装置的特性。特别是，本文表明，通常通过交流信号获得的电池电阻 (R) (R(a.c.)) 对于 ζ 的计算，总是低估了从流动电位测量获得的 ζ 电位值。考虑从 V(str)/I(str) 比得出的 R(EK)，当研究电介质时，会得出可靠的 ζ 值。对于金属，样品的导电性对电池电阻的贡献会导致 R(EK) 的低估，从而导致 ζ 的不切实际的值。对于导电样品的电特性研究，I(str) 测量是更好的选择。总的来说，本文中的研究结果为基于两种类型样品的固有电动行为，获得介电材料和导体的可靠 ζ 电位建立了一个测量协议。
