ICREA and Department of Chemical Engineering, Universitat Politècnica de Catalunya, Barcelona, Spain.
Langmuir. 2010 Jul 6;26(13):10882-9. doi: 10.1021/la100777z.
It is shown that in tangential electrokinetic measurements with porous films the porous structure makes contribution not only to the cell electric conductance (as demonstrated previously) but also to the observed streaming current. Both of these contributions give rise to dependences of streaming-potential and streaming-current coefficients on the channel height. However, due to the combined contribution of two phenomena, the dependence of streaming-potential coefficient on the channel height may be rather complicated and not allow for simple extrapolation. At the same time, the dependences of streaming-current coefficient and cell electric conductance on the channel height turn out linear and can be easily extrapolated to zero channel heights. This enables one to determine separately the contributions of external surface of porous film and of its porous structure to the streaming current and of the channel and porous structure to the cell electric conductance. This procedure is illustrated by the measurements of tangential electrokinetic phenomena and electric conductance with Millipore mixed-cellulose membrane filters of various average pore sizes (from 0.025 to 5 mum) in the so-called adjustable-gap cell of SurPASS electrokinetic instrument (Anton Paar GmbH). The design of this cell allows for easy and quasi-continuous variation of channel height as well as accurate determination of cell electric conductance, streaming-current coefficient, and channel height (from the cell hydraulic permeability). The quality of linear fits of experimental data has been found to be very good, and thus, the extrapolation procedures were quite reliable and accurate. Zeta-potentials could be determined of both external film and internal pore surfaces. It is demonstrated that the porous structures make considerable contributions to both streaming-current coefficient and cell electric conductance especially in the case of filters with larger pores. It is also found that, rather surprisingly, in filters with smaller pores the reduction in the filter electric conductivity turns out essentially stronger than could be expected proceeding from the filter porosity.
研究表明，在用多孔膜进行切向电动测量时，多孔结构不仅对电池电导（如前所述）有贡献，而且对观察到的流动电流也有贡献。这两种贡献都会导致流动电势和流动电流系数随通道高度的变化。然而，由于两种现象的综合贡献，流动电势系数随通道高度的变化可能相当复杂，无法进行简单的外推。同时，流动电流系数和电池电导随通道高度的变化呈线性关系，很容易外推到零通道高度。这使得可以分别确定多孔膜的外表面和其多孔结构对流动电流的贡献，以及通道和多孔结构对电池电导的贡献。通过在 SurPASS 电动仪器的所谓可调隙池中测量具有各种平均孔径（0.025 至 5 µm）的 Millipore 混合纤维素膜过滤器的切向电动现象和电导，说明了这一过程。该池的设计允许方便且准连续地改变通道高度，以及准确地确定电池电导、流动电流系数和通道高度（从细胞水力渗透率）。实验数据的线性拟合质量非常好，因此，外推程序非常可靠和准确。可以确定外膜和内部孔表面的 Zeta 电位。研究表明，多孔结构对流动电流系数和电池电导都有相当大的贡献，特别是在具有较大孔径的过滤器的情况下。还发现，令人惊讶的是，在具有较小孔径的过滤器中，过滤器电导率的降低实际上比从过滤器孔隙率预计的要强。
