Kirby Brian J, Hasselbrink Ernest F
Microfluidics Department, Sandia National Laboratories, Livermore, CA 94551, USA.
Electrophoresis. 2004 Jan;25(2):187-202. doi: 10.1002/elps.200305754.
This paper summarizes theory, experimental techniques, and the reported data pertaining to the zeta potential of silica and silicon with attention to use as microfluidic substrate materials, particularly for microchip chemical separations. Dependence on cation concentration, buffer and cation type, pH, cation valency, and temperature are discussed. The Debye-Hückel limit, which is often correctly treated as a good approximation for describing the ion concentration in the double layer, can lead to serious errors if it is extended to predict the dependence of zeta potential on the counterion concentration. For indifferent univalent electrolytes (e.g., sodium and potassium), two simple scalings for the dependence of zeta potential on counterion concentration can be derived in high- and low-zeta limits of the nonlinear Poisson-Boltzman equation solution in the double layer. It is shown that for most situations relevant to microchip separations, the high-zeta limit is most applicable, leading to the conclusion that the zeta potential on silica substrates is approximately proportional to the logarithm of the molar counterion concentration. The zeta vs. pH dependence measurements from several experiments are compared by normalizing the zeta based on concentration.
本文总结了与二氧化硅和硅的zeta电位相关的理论、实验技术及已报道的数据，重点关注其作为微流控基底材料的应用，特别是在微芯片化学分离方面的应用。文中讨论了zeta电位对阳离子浓度、缓冲液和阳离子类型、pH值、阳离子价态及温度的依赖性。德拜-休克尔极限通常被正确地视为描述双电层中离子浓度的良好近似，但如果将其扩展用于预测zeta电位对反离子浓度的依赖性，可能会导致严重误差。对于惰性单价电解质（如钠和钾），在双电层中非线性泊松-玻尔兹曼方程解的高zeta和低zeta极限情况下，可以推导出zeta电位对反离子浓度依赖性的两种简单标度关系。结果表明，在与微芯片分离相关的大多数情况下，高zeta极限最为适用，由此得出结论：二氧化硅基底上的zeta电位近似与摩尔反离子浓度的对数成正比。通过基于浓度对zeta进行归一化，比较了多个实验中zeta与pH依赖性的测量结果。
