Effect of solution chemistry on the surface charge of polymeric reverse osmosis and nanofiltration membranes

A streaming potential analyzer has been used to investigate the effect of solution chemistry on the surface charge of four commercial reverse osmosis and nanofiltration membranes. Zeta potentials of these membranes were analyzed for aqueous solutions of various chemical compositions over a pH range of 2 to 9. In the presence of an indifferent electrolyte (NaCl), the isoelectric points of these membranes range from 3.0 to 5.2. The curves of zeta potential versus solution pH for all membranes display a shape characteristic of amphoteric surfaces with acidic and basic functional groups. Results with salts containing divalent ions (CaCl₂, Na₂SO₄, and MgSO₄) indicate that divalent cations more readily adsorb to the membrane surface than divalent anions, especially in the higher pH range. Three sources of humic acid, Suwannee River humic acid, peat humic acid, and Aldrich humic acid, were used to investigate the effect of dissolved natural organic matter on membrane surface charge. Other solution chemistries involved in this investigation include an anionic surfactant (sodium dodecyl sulfate) and a cationic surfactant (dodecyltrimethylammonium bromide). Results show that humic substances and surfactants readily adsorb to the membrane surface and markedly influence the membrane surface charge.     

Zeta-potentials of self-assembled surface micelles of ionic surfactants adsorbed at hydrophobic graphite surfaces

The zeta-potentials of the self-assembled surface ionic surfactants (sodium dodecyl sulfate—SDS and hexadecyltrimethyl ammonium bromide—CTAB) on graphite surfaces were determined both from streaming potential and electrophoretic mobility measurements. The adsorption of the surfactants at graphite–liquid interfaces has been studied using atomic force microscopy (AFM) soft-contact imaging which shows the formation of linear, parallel hemicylinders with headgroups oriented towards the solution. The magnitude of the zeta-potential increased with an increase in surfactant concentration, reaching a constant value at a concentration corresponding to the point of surface micelle formation as confirmed from AFM imaging. The streaming potential and electrophoretic mobility measurements showed that the zeta-potentials of SDS and CTAB surface micelles adsorbed at the graphite surface were about −75 and +70 mV, respectively, well in agreement with the values reported for bulk phase micelles in the literature.     

Vergleichende Messungen des Zeta-Potentials von Faserstoffen durch Elektroosmose und Strömungsstrom/Strömungspotential

An apparatus for the determination of zetapotential is described, which allows measurement of both streaming potential and streaming current as well as electroosmosis with one and the same fiber diaphragm with various electrodes (calomel, Ag/AgCl, palladium). Measurements with glass fibers, fibers of polyacrylonitrile and of polyester, and with cellulose pulp show that identical values for the electrokinetic parameters are obtained independent of voltage applied during electroosmosis resp. pressure difference during streaming measurements. This allows the conclusion that the zetapotential in dilute electrolyte solution is here an unequivocally determinable figure.

Herrn Prof. Dr.R. C. Schulz mit den herzlichsten Glückwünschen zum 65. Geburtstag gewidmet.     

Digital flow control of electroosmotic pump: Onsager coefficients and interfacial parameters determination

Electroosmosis and streaming potential are two complementary electrokinetic processes related by the Onsager relation. In particular, an electroosmotic pump (EOP) is potentially useful for a variety of engineering and bio-related applications. By fabricating samples consisting of dry-etched cylindrical pores (50 μm in length and 3.5 μm in diameter) on silicon wafers, we demonstrate that the use of digital control via voltage pulses can resolve the flow regulation and stability issues associated with the EOP, so that the intrinsic characteristics of the porous sample medium may be revealed. Through the consistency of the measured electroosmosis (EO) and the streaming potential (SP) coefficients as required by the Onsager relation, we deduce the zeta potential and the surface conductivity, both physical parameters pertaining to the liquid-solid interface.     

流动电位/胶体滴定法测定聚电解质电荷密度的研究

探讨了应用粒子电荷测定仪的流动电位判定胶体滴定终点的可行性。结果表明流动电位曲线能在样品浓度大于 0 .6× 1 0 - 5mol· L- 1的溶液中准确指示胶体滴定的终点 ,较常用指示剂邻甲胺兰的使用极限浓度低一个数量级。观察到由阳离子聚电质滴定阴离子聚电质能减少盐干扰的现象。叔胺型阳离子淀粉应在酸性下滴定     

Electrokinetic flow in an elliptic microchannel covered by ion-penetrable membrane

The electrokinetic flow of an electrolyte solution in an elliptical microchannel covered by an ion-penetrable, charged membrane layer is examined theoretically. The present analysis extends previous results in that a two-dimensional problem is considered, and the system under consideration simulates the flow of a fluid, for example, in a microchannel of biological nature such as vein. The electroosmostic volumetric flow rate, the total electric current, the streaming potential, and the electroviscous effect of the system under consideration are evaluated. We show that, for a constant hydraulic diameter, the variations of these quantities as a function of the aspect ratio of a microchannel may have a local minimum or a local maximum at a medium level of ionic strength, which depends on the thickness of the membrane layer. For a constant cross-sectional area, the electroosmostic volumetric flow rate, the total electric current, and the streaming potential increase monotonically with the increase in the aspect ratio, but the reverse is true for the electroviscous effect.     

Measurement of currents and floating potential in multilayer sensor due to oil-flow electrification

This paper presents floating potential and current measurements due to oil-flow electrification inside a multilayer sensor incorporated in a closed loop filled with fresh transformer oil. All leakage currents at the sensor inlet and outlet, the capacitive current and the streaming current are measured. The waveforms of these currents, floating potential as well as the oil temperature at the sensor inlet are simultaneously recorded for laminar flow and at controlled operating conditions. The measured floating potentials are compared with the calculated ones under different oil-flow velocities and good agreement has been found.     

Streaming potential analysis on the hydrodynamic transport of pressure-driven flow through a rotational microchannel

In this study, the streaming potential and electrokinetic energy conversion efficiency are discussed under the low zeta potential approximation through a microparallel channel with consideration of rotational effect. By solving Poisson-Boltzmann equation and modified Navier–Stokes equation, the analytical expressions of the streaming potential and electrokinetic energy conversion efficiency in the electrolyte solution are obtained. Combining with the numerical calculation, the influences of the dimensionless electrokinetic width K and the rotational angular velocity ω on streaming potential and the electrokinetic energy conversion efficiency are discussed. The results show that the streaming potential fields decrease both in mainstream and secondary directions with the electrokinetic width K, it decreases with the non-dimensional rotational angular velocity in the mainstream direction and it shows a first increasing then decreasing trend in the secondary flow direction. In addition, the influences of related non-dimensional parameters, including electrokinetic width, wall electric potential and rotational angular velocity, on the electrokinetic energy conversion efficiency are also discussed in detail. The rotating effect can enhance conversion efficiency comparing to the case of no rotation. The increase of wall electric potential gives rise to an augment in electrokinetic energy conversion efficiency. These theoretical results make sense to the energy harvesting in the rotating microfluidic systems.     

Developing Systems for Real-Time Streaming Analysis

Sources of streaming data are proliferating and so are the demands to analyze and mine such data in real time. Statistical methods frequently form the core of real-time analysis, and therefore, statisticians increasingly encounter the challenges and implicit requirements of real-time systems. This work recommends a comprehensive strategy for development and implementation of streaming algorithms, beginning with exploratory data analysis in a flexible computing environment, leading to specification of a computational algorithm for the streaming setting and its initial implementation, and culminating in successive improvements to computational efficiency and throughput. This sequential development relies on a collaboration between statisticians, domain scientists, and the computer engineers developing the real-time system. This article illustrates the process in the context of a radio astronomy challenge to mitigate adverse impacts of radio frequency interference (noise) in searches for high-energy impulses from distant sources. The radio astronomy application motivates discussion of system design, code optimization, and the use of hardware accelerators such as graphics processing units, field-programmable gate arrays, and IBM Cell processors. Supplementary materials, available online, detail the computing systems typically used for streaming systems with real-time constraints and the process of optimizing code for high efficiency and throughput.