Streaming potential and streaming current measurements at planar solid/liquid interfaces for simultaneous determination of zeta potential and surface conductivity
ABSTRACT Strongly encouraged and supported by Stanislav S. Dukhin the authors of this article recently designed, built and tested a new device for the simultaneous determination of zeta potential and surface conductivity from streaming potential and streaming current measurements across rectangular slit channels formed between two planar samples. In this Microslit Electrokinetic Set-up (MES) the planar samples are adjusted in parallel to form a channel of variable height which can become as narrow as about 1 μm. Due to this key feature of the device electrokinetic measurements can be performed at conditions where surface conductivity can be neglected and at conditions where surface conductivity provides a substantial part of the total channel conductivity. Utilizing the novel set-up, zeta potential and surface conductivity data can be obtained for a wide variety of materials which can be prepared as thin films on top of planar, macroscopic glass carriers. In order to demonstrate the potentialities of the advanced experimental technique of electrokinetic surface characterization we discuss three examples reflecting different levels of complexity of the analysed solid/liquid interface: (1) The charge formation at unpolar polymers without dissociating surface functions is studied referring to an inert, plasma-deposited fluoropolymer layer (PDFP) in simple electrolyte solutions. An extended evaluation of the experimental data of zeta potential and surface conductivity is given; (2) Further, grafted polypetide chains bearing dissociating side groups (polyglutamic acid and polylysine) were characterized with regard to the pH-depended variation of zeta potential and surface conductivity to provide new insights into the interrelation of charge density and conformation; (3) Finally, adsorbed fibrinogen on top of plasma-deposited fluoropolymer was studied by zeta potential and surface conductivity measurements as an example for highly hydrated macromolecular adsorption layers.
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ABSTRACT: We report that a droplet dispensed from a micropipette almost always has a considerable electrical charge of a magnitude dependent on the constituents of the droplet, on atmospheric humidity and on the coating material of pipette tip. We show that this natural electrification of a droplet originates from the charge separation between a droplet and pipette tip surface by contact with water due to the ionization of surface chemical groups. Charge on a droplet can make it difficult to detach the droplet from the pipette tip, can decrease its surface tension, can affect the chemical characteristics of solutions due to interactions with charged molecules, and can influence the combination and localization of charged bio-molecules; in all cases, the charge may affect results of experiments in which any of these factors is important. Thus, these findings reveal experimental parameters that should be controlled in experiments that use micropipettes.Scientific Reports 06/2013; 3:2037. · 5.08 Impact Factor
- Journal of The American College of Cardiology - J AMER COLL CARDIOL. 01/2011; 57(14).
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ABSTRACT: Pollutant migration in dense clay barriers appears to be strongly influenced by the electric double layer of colloidal surfaces. Osmosis that is resulted from chemical potential or electric potential difference across the clay membrane has been successively described in a number of theoretical works. Streaming potential (SP) which is present in charged porous medium under hydraulic gradient has been recognized as a significant factor governing the mass migration in compacted clays. However, few studies have been carried out in geo-environmental area with regard to this physical phenomenon. A coupled model was proposed to account for the effects of electrical, chemical and fluidic fields on solute transport in porous medium in this study. The electrical field deals with both the streaming potential and the externally applied electrical potential. The coupled nonlinear partial differential equations are numerically simulated by finite element method. Both the steady state solution and the time-dependent solution were investigated with the consideration of a series of influential factors. The streaming potential coefficient and the electro-osmotic coefficient were found to control the solute transport process. The potential application of the materials with tendency of producing SP was discussed. With appropriate selection of materials and parameters, optimum barring effect could be obtained for soil barriers in waste containment applications.Applied Clay Science 10/2014; · 2.34 Impact Factor