Spanos N, Koutsoukos PG
Department of Chemical Engineering, University of Patras, Patras, GR 265 00, Greece
J Colloid Interface Sci. 1999 Jun 1;214(1):85-90. doi: 10.1006/jcis.1999.6169.
The O'Brien theory developed for the electrical conductivity and electro-osmosis in porous plugs consisting of nonconducting particles has been applied for the calculation of zeta-potentials from conductivity and streaming potential measurements at two pH values, 3.3 and 6.5 or 5.8, on plugs composed of titania (undoped and doped with W6+ and Li+ ions) particles. The particles have been prepared both by precipitation (continuous crystallization at constant supersaturation) and by the sol-gel method. It was found that O'Brien's theory is also applicable in n-type semiconductor particles, such as titania (doped and undoped). Specifically, for the correct determination of zeta-potentials measured in solutions of relatively low ionic strength, it is necessary to take into account surface conduction behind the shear plane, for all samples measured at pH 3.3, a value considerably lower than the isoelectric point (i.e.p.) of titania. Under these conditions the surface charge of the suspended titania particles is high, and consequently the contribution of surface conductance to the conductivity of the plug is significant. The effect of surface conduction behind the shear plane on the calculation of zeta-potential is enhanced for the Li+-doped preparations due to the increase of surface conductivity caused by doping with Li+. Measurements of the streaming potential for the samples prepared with the sol-gel method were made at pH 6.5 (5.8 for the undoped titania); i.e., near the pH corresponding to the i.e.p., correct values of zeta-potential may be obtained in suspensions even at low ionic strength without taking into account the polarization of the double layer due to surface conduction, by applying the primitive Smoluchowski theory. This treatment is valid because at pH values near the i.e.p. the surface charge of the particles is very low, and consequently surface conductance is negligible compared with the conductivity of the plug. Copyright 1999 Academic Press.
奥布赖恩理论是针对由非导电颗粒组成的多孔塞中的电导率和电渗现象而提出的，现已应用于通过在两个pH值（3.3和6.5或5.8）下对由二氧化钛（未掺杂以及掺杂W6+和Li+离子）颗粒组成的多孔塞进行电导率和流动电势测量来计算ζ电位。颗粒通过沉淀法（在恒定过饱和度下连续结晶）和溶胶 - 凝胶法制备。结果发现，奥布赖恩理论也适用于n型半导体颗粒，如二氧化钛（掺杂和未掺杂的）。具体而言，为了正确测定在相对低离子强度溶液中测量的ζ电位，对于所有在pH 3.3下测量的样品，有必要考虑剪切面后的表面传导，该值远低于二氧化钛的等电点（i.e.p.）。在这些条件下，悬浮的二氧化钛颗粒的表面电荷很高，因此表面传导对多孔塞电导率的贡献很大。由于Li+掺杂导致表面电导率增加，对于Li+掺杂制剂，剪切面后的表面传导对ζ电位计算的影响增强。对于用溶胶 - 凝胶法制备的样品，在pH 6.5（未掺杂二氧化钛为5.8）下测量流动电势；即在对应于i.e.p.的pH附近，通过应用原始的斯莫卢霍夫斯基理论，即使在低离子强度下，在不考虑由于表面传导引起的双层极化的情况下，也可在悬浮液中获得ζ电位的正确值。这种处理是有效的，因为在接近i.e.p.的pH值下，颗粒的表面电荷非常低，因此与多孔塞的电导率相比，表面传导可以忽略不计。版权所有1999年学术出版社。
