Determination of the Zeta Potential of Porous Substrates by Droplet Deflection. I. The Influence of Ionic Strength and pH Value of an Aqueous Electrolyte in Contact with a Borosilicate Surface
Determination of the Zeta Potential of Porous Substrates by Droplet Deflection. I. The Influence of Ionic Strength and pH Value of an Aqueous Electrolyte in Contact with a Borosilicate Surface
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DOI：
10.1021/la802949z
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发表时间：
2009-02-03
期刊：
影响因子：
3.9
通讯作者：
Steen, Paul H.
中科院分区：
文献类型：
--
作者：
Barz, Dominik P. J.;Vogel, Michael J.;Steen, Paul H.
本文提出了一种测定多孔衬底与液体接触的Zeta电位的新方法。电渗作用发生在完全饱和的多孔基质内的固/液边界附近，泵与泵串联放置的液滴的表面张力所产生的毛细压力相反。该方法是基于测量由于外加电势差引起的液/气界面偏转。我们技术的显著特点是精确度、速度和可靠性，通过简单且经济高效的设置即可完成。在这种特殊的设置中，使用了两个相对液滴的双稳态配置。稳定状态之间的能垒定义了毛细阻力的范围，可以通过总液滴体积进行调节。电渗泵被放置在液滴之间。多孔衬底的大表面积与体积比使泵浦强度超过毛细阻力，即使对于足够小的液滴，其形状可以忽略不受重力的影响。利用多孔衬底内流动的相对简单的模型，确定了衬底-液体结合所产生的Zeta电位。对与不同水溶液接触的硼硅酸盐衬底进行了广泛的测量。测量结果阐明了离子强度和pH值对Zeta电位的影响，并给出了一个对工程方法重要的经验关系式。
This paper presents a new method to determine the zeta potential of porous substrates in contact with a liquid. Electroosmosis, arising near the solid/liquid boundaries within a fully saturated porous substrate, pumps against the capillary pressure arising from the surface tension of a droplet placed in series with the pump. The method is based on measuring the liquid/gas interface deflection due to the imposed electric potential difference. The distinguishing features of our technique are accuracy, speed, and reliability, accomplished with a straightforward and cost-effective setup. In this particular setup, a bistable configuration of two opposing droplets is used. The energy barrier between the stable states defines the range of capillary resistance and can be tuned by the total droplet volume. The electroosmotic pump is placed between the droplets. The large surface area-to-volume ratio of the porous substrate enables the pumping strength to exceed the capillary resistance even for droplets small enough that their shapes are negligibly influenced by gravity. Using a relatively simple model for the flow within the porous substrate, the zeta potential resulting from the substrate-liquid combination is determined. Extensive measurements of a borosilicate substrate in contact with different aqueous electrolytes are made. The results of the measurements clarify the influence of the ionic strength and pH value on the zeta potential and yield an empirical relationship important to engineering approaches.