DOCSLIB.ORG

Charge-Related Measurements – a Reappraisal. Part 1. Streaming

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Charge-Related Measurements – a Reappraisal. Part 1. Streaming Martin A. Hubbe and Junhua Chen Charge-Related Measurements – A North Carolina State University, Reappraisal. Dept. of Wood and Paper Science Part 1. Streaming Current In a 1995 article in this journal Jaycock(1) (a) various factors can interfere with the A 1995 article in this maga- expressed concerns about the accuracy and analyses, and zine raised concerns about interpretation of two types of charge-related (b) one should not stray too far outside of the use and interpretation of measurements that have become increasingly the ranges of conditions under which the two kinds of measurements common in papermaking applications, methods can be expected to give reliable that are being carried out in namely, the streaming current (SC) and the answers. paper mills to evaluate the SP (c) In addition to these two reasons, there electrical charges at sur- streaming potential ( ) methods. faces in fibre slurries. In the intervening years there does not are concerns about the interpretation of SC This article relates to the appear to have been any attempt either to data obtained in paper mills. streaming current method, support or to refute those cautionary state- To start, it is worth quoting Jaycock’s which is widely used for ments. Rather, there has been increasing use statements about the SC method in the Con- (1) endpoint detection when in the paper industry of the test methods that clusions section of the article: (2-10) testing the charge demand of Jaycock cautioned us about. The present “The piston type streaming current detec- whitewater or filtrate sam- article deals with SC measurements. A tor has no established theoretical basis! It is ples from fibre stock. companion article will deal with a second assumed that the measured potential is related Although there is still type of measurement discussed in the same to the zeta potential, and that the adsorbed (11) some truth in the statement article. layers responsible for the generation of this that the “streaming current It seems that there are two ways in which potential are characteristic of the papermak- detector has no established one could view the set of circumstances ing system as a whole, being in equilibrium theoretical basis,” subse- described in the first paragraph. with it. There are doubts about the validity of quent work has helped to i) On the one hand, maybe the increased both of these assumptions.” define ranges of experimen- use of SC devices – even without considering In addition, Jaycock advocated use of tal conditions within which other factors – is sufficient proof that the microelectrophoresis(10,21) as the best way to the test gives reliable results. method must be providing practical value to obtain zeta potential data for a papermaking Also, some specific sources the users. Otherwise, the thinking goes, cost furnish. of interference have become conscious managers of paper companies and To address Jaycock’s concerns, it is first better understood. chemical supply companies would not con- necessary to describe the main equipment and tinue to invest in that technology. a little bit about the procedure of analysis ii) Another way to view the situation is to used in a typical papermaking application. assume that Jaycock’s worst fears were cor- rect, and that much of the data obtained by SC The streaming current (SC) method measurements in paper mills over the inter- Figure 1 (next page) is a schematic diagram vening years have been either inaccurate or of a typical SC device. It is worth bearing in misleading. mind that different brands of equipment can Fortunately, due to some ongoing research be quite different in appearance, despite their during the period between 1995 and now, we sharing the same basic operating principles. are now in a better position to answer some of Suppliers of SC equipment, in different forms, the concerns raised by in the 1995 article.(1) include Rank Brothers, Mütek, Chemtrac, and Some of that continued work was conducted Milton-Roy companies. by us North Carolina State University(12-14) and As noted by others,(1,22-24) the main wetted some was done by others.(15-20) parts of the SC device consist of a plastic pis- The purpose of this review article is to re- ton that moves in a sinusoidal manner back examine the main concerns raised by Jaycock and forth within a dead-ended plastic cylin- and to give qualified support for continued der, usually at a frequency of about 4 Hz. efforts to implement SC measurements, both Because the gap between the piston and cylin- in the laboratory and online in paper machine der is narrow (often less than 1 mm) systems. The reason that the support needs to compared to the diameter of the piston (often be “qualified” is that about 12 mm), the motion of the piston gives 17 PAPER TECHNOLOGY OCTOBER 2004 STREAMING CURRENT MEASUREMENTS rise to a more rapid movement of aqueous These “extra” ionic charges will exist very fluid back and forth within the annulus. near to the surface in a region that is often Also, there are two metal electrodes built called the “double layer.” The average distri- into the cylinder wall at different axial posi- bution of counter-ion charges in the double tions. The probes are connected to an layer depends on electronic system capable of rectifying and (a) attraction to the surface smoothing any electrical signal that results (b) random diffusion of the ions in all direc- from the reciprocating motion. tions, and Except in some unusual cases,(25) the origin (c) screening of the electrostatic effects by of most of the electrical signal that is salt ions.(26-28) observed with SC devices arises due to the electrically charged nature of the plastic sur- The movement of aqueous solution past the faces, with the understanding that the word charged surface causes net movement of the “surface” includes anything that becomes counter-ions, especially in the “tail” of the adsorbed onto the plastic itself. counter-ion distribution lying farthest from Many SC devices are made with the charged surface. poly-tetrafluoroethylene (PTFE), a contamina- The most common use of SC devices in the tion-resistant substance which, if absolutely paper mill has been to determine the cationic pure, would have no surface charge of its demand or anionic demand of samples of own. Practical use of the SC method, espe- process water, usually in the absence of cially in the case of paper machine fibres.(5-8,12,17) In other words, the device is used applications, requires that the plastic becomes as the means of detecting the endpoint of a charged due to the adsorption of polyelec- titration. trolytes and colloidal materials from the A solution of charged polymer is gradually sample. added to a stirred aliquot of process water, The user makes an implicit assumption and a “zero” reading on the SC device is taken that any excess of charged materials existing as evidence that a sufficient amount of poly- in the sample will determine the sign of the mer solution has been added to the mixture to electrical current signal that is generated. just neutralize any excess of electrical charge. Setting aside, for the moment, the question This excess is understood to exist at the about whether the water-loving, charged surfaces of particles, very finely divided materials present in paper mill water samples materials (i.e. “colloidal matter”), dissolved actually adsorb to a significant extent onto the polyelectrolytes, and various surface-active low-energy plastic surfaces, the reciprocating molecules in the mixture, such as salts of flow of aqueous solution past a charged sur- resin acid molecules from the wood.(29) face gives rise to an electrical signal due to (15-20) the presence of counter-ions. Theoretical limitations to the SC method For example, if the net charge of the PTFE, Before considering practical uses of SC with its covering of colloidal materials, is tests, let’s consider what Jaycock meant by negative, then there needs to be an equal and saying that the SC method has “no theoretical opposite excess of positively charged ions in basis”.(1) To help justify these strong words, it the solution phase adjacent to the surface. is worth noting that typical raw output of an SC device does not have a simple, quantitative relationship to zeta potential. The inventor of the SC method used only a rudimentary theo- retical approach to rationalize the observed output signals in terms of a zeta potential at the plastic surfaces of the piston and cylinder in the SC device.(22) Though there has been important progress more recently in quantifying the SC signal in ideal cases,(16-20) the calculation depends criti- cally on the annular distance between the piston and cylinder. That distance is subject to change due to wear, a “ribbed” pattern of some SC pistons, and possible changes in alignment of the piston within the device. Further support of the words “no theoreti- cal basis” involves the fact that one is measuring an electronic quantity related to a coated PTFE surface, despite the fact that PTFE has a completely different surface character Figure 1 Schematic diagram of wetted parts of a common type of streaming compared to that of the fibres, fine particles, current detector or colloidal materials in a sample of process 18 PAPER TECHNOLOGY OCTOBER 2004 STREAMING CURRENT MEASUREMENTS water from a paper mill. After all, it takes a Streaming current – the range of reliability brave individual to place their trust in that the For purposes of process control, it is often PTFE (i.e. Teflon® ) surface becomes uni- more important that a measurement be repro- formly and consistently coated by the ducible, regardless of whether the results can colloidal materials in the sample.
Load more

Recommended publications
  • Lab on a Chip PAPER
    View Online / Journal Homepage / Table of Contents for this issue Lab on a Chip Dynamic Article LinksC< Cite this: Lab Chip, 2011, 11, 4006 www.rsc.org/loc PAPER Strong enhancement of streaming current power by application of two phase flow Yanbo Xie,a John D. Sherwood,b Lingling Shui,a Albert van den Berga and Jan C. T. Eijkela Received 17th May 2011, Accepted 30th September 2011 DOI: 10.1039/c1lc20423h We show that the performance of a streaming-potential based microfluidic energy conversion system can be strongly enhanced by the use of two phase flow. Injection of gas bubbles into a liquid-filled channel increases both the maximum output power and the energy conversion efficiency. In single- phase systems the internal conduction current induced by the streaming potential limits the output power, whereas in a two-phase system the bubbles reduce this current and increase the power. In our system the addition of bubbles enhanced the maximum output power of the system by a factor of 74 and the efficiency of the system by a factor of 163 compared with single phase flow. Introduction overlap, and efficiency has reached about 3 to 5% in single nano- channels5 and nanopores6 respectively. Recently, Duffin and Say- Energy has become an important topic in scientific research. In kally7,8 used microjets to enhance the energy conversion efficiency particular, novel environmentally-friendly energy conversion to above 10%. systems are required. The developing ‘‘lab on a chip’’ technology Streaming currents or potentials generated by multiphase flow provides new opportunities to convert fluidic mechanical energy 1 have been studied for geophysical, mineral and petroleum to electrical energy.
    [Show full text]
  • Polyelectrolyte Assisted Charge Titration Spectrometry: Applications to Latex and Oxide Nanoparticles
    Polyelectrolyte assisted charge titration spectrometry: applications to latex and oxide nanoparticles F. Mousseau1*, L. Vitorazi1, L. Herrmann1, S. Mornet2 and J.-F. Berret1* 1Matière et Systèmes Complexes, UMR 7057 CNRS Université Denis Diderot Paris-VII, Bâtiment Condorcet, 10 rue Alice Domon et Léonie Duquet, 75205 Paris, France. 2Institut de Chimie de la Matière Condensée de Bordeaux, UPR CNRS 9048, Université Bordeaux 1, 87 Avenue du Docteur A. Schweitzer, Pessac cedex F-33608, France. Abstract: The electrostatic charge density of particles is of paramount importance for the control of the dispersion stability. Conventional methods use potentiometric, conductometric or turbidity titration but require large amount of samples. Here we report a simple and cost-effective method called polyelectrolyte assisted charge titration spectrometry or PACTS. The technique takes advantage of the propensity of oppositely charged polymers and particles to assemble upon mixing, leading to aggregation or phase separation. The mixed dispersions exhibit a maximum in light scattering as a function of the volumetric ratio �, and the peak position �!"# is linked to the particle charge density according to � ~ �!�!"# where �! is the particle diameter. The PACTS is successfully applied to organic latex, aluminum and silicon oxide particles of positive or negative charge using poly(diallyldimethylammonium chloride) and poly(sodium 4-styrenesulfonate). The protocol is also optimized with respect to important parameters such as pH and concentration, and to the polyelectrolyte molecular weight. The advantages of the PACTS technique are that it requires minute amounts of sample and that it is suitable to a broad variety of charged nano-objects. Keywords: charge density – nanoparticles - light scattering – polyelectrolyte complex Corresponding authors: [email protected] [email protected] To appear in Journal of Colloid and Interface Science leading to their condensation and to the formation of the electrical double layer [1].
    [Show full text]
  • Influence of Polyelectrolyte Multilayer Properties on Bacterial Adhesion
    polymers Article Influence of Polyelectrolyte Multilayer Properties on Bacterial Adhesion Capacity Davor Kovaˇcevi´c 1, Rok Pratnekar 2, Karmen GodiˇcTorkar 2, Jasmina Salopek 1, Goran Draži´c 3,4,5, Anže Abram 3,4,5 and Klemen Bohinc 2,* 1 Department of Chemistry, Faculty of Science, University of Zagreb, Zagreb 10000, Croatia; [email protected] (D.K.); [email protected] (J.S.) 2 Faculty of Health Sciences, Ljubljana 1000, Slovenia; [email protected] (R.P.); [email protected] (K.G.T.) 3 Jožef Stefan Institute, Ljubljana 1000, Slovenia; [email protected] (G.D.); [email protected] (A.A.) 4 National Institute of Chemistry, Ljubljana 1000, Slovenia 5 Jožef Stefan International Postgraduate School, Ljubljana 1000, Slovenia * Correspondence: [email protected]; Tel.: +386-1300-1170 Academic Editor: Christine Wandrey Received: 16 August 2016; Accepted: 14 September 2016; Published: 26 September 2016 Abstract: Bacterial adhesion can be controlled by different material surface properties, such as surface charge, on which we concentrate in our study. We use a silica surface on which poly(allylamine hydrochloride)/sodium poly(4-styrenesulfonate) (PAH/PSS) polyelectrolyte multilayers were formed. The corresponding surface roughness and hydrophobicity were determined by atomic force microscopy and tensiometry. The surface charge was examined by the zeta potential measurements of silica particles covered with polyelectrolyte multilayers, whereby ionic strength and polyelectrolyte concentrations significantly influenced the build-up process. For adhesion experiments, we used the bacterium Pseudomonas aeruginosa. The extent of adhered bacteria on the surface was determined by scanning electron microscopy. The results showed that the extent of adhered bacteria mostly depends on the type of terminating polyelectrolyte layer, since relatively low differences in surface roughness and hydrophobicity were obtained.
    [Show full text]
  • Surface Polarization Effects in Confined Polyelectrolyte Solutions
    Surface polarization effects in confined polyelectrolyte solutions Debarshee Bagchia , Trung Dac Nguyenb , and Monica Olvera de la Cruza,b,c,1 aDepartment of Materials Science and Engineering, Northwestern University, Evanston, IL 60208; bDepartment of Chemical and Biological Engineering, Northwestern University, Evanston, IL 60208; and cDepartment of Physics and Astronomy, Northwestern University, Evanston, IL 60208 Contributed by Monica Olvera de la Cruz, June 24, 2020 (sent for review April 21, 2020; reviewed by Rene Messina and Jian Qin) Understanding nanoscale interactions at the interface between ary conditions (18, 19). However, for many biological settings two media with different dielectric constants is crucial for con- as well as in supercapacitor applications, molecular electrolytes trolling many environmental and biological processes, and for confined by dielectric materials, such as graphene, are of interest. improving the efficiency of energy storage devices. In this Recent studies on dielectric confinement of polyelectrolyte by a contributed paper, we show that polarization effects due to spherical cavity showed that dielectric mismatch leads to unex- such dielectric mismatch remarkably influence the double-layer pected symmetry-breaking conformations, as the surface charge structure of a polyelectrolyte solution confined between two density increases (20). The focus of the present study is the col- charged surfaces. Surprisingly, the electrostatic potential across lective effects of spatial confinement by two parallel surfaces
    [Show full text]
  • Semester II, 2015-16 Department of Physics, IIT Kanpur PHY103A: Lecture # 5 Anand Kumar
    Semester II, 2017-18 Department of Physics, IIT Kanpur PHY103A: Lecture # 8 (Text Book: Intro to Electrodynamics by Griffiths, 3rd Ed.) Anand Kumar Jha 19-Jan-2018 Summary of Lecture # 7: • Electrostatic Boundary Conditions E E = Electric Field: = above below E − E = 00 above− below � 0 above − below Electric Potential: V V = 0 above − below • Basic Properties of Conductors (1) The electric field = 0 inside a conductor, always. = 0 = = 0 (2) The charge density inside a conductor. This is because . (3) Any net charge resides on the surface. Why? To minimize the energy. 0 ⋅ (4) A conductor is an equipotential. (5) is perpendicular to the surface, just outside the conductor. 2 Summary of Lecture # 7: Prob. 2.36 (Griffiths, 3rd Ed. ): - Surface charge ? = = − 2 - Surface charge ? 4 + - Surface charge ? = − 2 4 1 2 - ( ) ? = 4 out 2 1 0 � - ( ) ? = 4 out 2 10 �+ - ( ) ? =4 out out 2 � - Force on ? 0 40 - Force on ? 0 3 Summary of Lecture # 7: Prob. 2.36 (Griffiths, 3rd Ed. ): - Surface charge ? = Same ª = − 2 Same - Surface charge ? 4 ª + - Surface charge ? = − 2 Changes � 4 1 2 = - ( ) ? 4 Same ª out 2 1 0 � = 4 - ( ) ? Same ª out 2 � 10 + Changes � - ( ) ? =4 out out 2 - Force on ? 0 0 � 4 Same ª Bring in a third - Force on ? 0 Same ª charge 4 Surface Charge and the Force on a Conductor: What is the electrostatic force on the patch? Force per unit area on the patch is: = (? ) = other = + , above other patch above = + 2 other 0 � = + , below other patch below 1 = = + 2 2 other − � other above below 0 But, inside a metal, = , so = 0 below = = + = 2 2 other � above other � � 5 0 0 0 Surface Charge and the Force on a Conductor: What is the electrostatic force on the patch? Force per unit area on the patch is: = (? ) = other = = 2 other � above � Force per unit0 area on the patch is: 0 = = 2 2 other � Force per unit area is pressure.0 So, the electrostatic pressure is: = = 2 2 20 2 6 0 Capacitor: Two conductors with charge and .
    [Show full text]
  • Ion Current Rectification in Extra-Long Nanofunnels
    applied sciences Article Ion Current Rectification in Extra-Long Nanofunnels Diego Repetto, Elena Angeli * , Denise Pezzuoli, Patrizia Guida, Giuseppe Firpo and Luca Repetto Department of Physics, University of Genoa, via Dodecaneso 33, 16146 Genoa, Italy; [email protected] (D.R.); [email protected] (D.P.); [email protected] (P.G.); giuseppe.fi[email protected] (G.F.); [email protected] (L.R.) * Correspondence: [email protected] Received: 29 April 2020; Accepted: 25 May 2020; Published: 28 May 2020 Abstract: Nanofluidic systems offer new functionalities for the development of high sensitivity biosensors, but many of the interesting electrokinetic phenomena taking place inside or in the proximity of nanostructures are still not fully characterized. Here, to better understand the accumulation phenomena observed in fluidic systems with asymmetric nanostructures, we study the distribution of the ion concentration inside a long (more than 90 µm) micrometric funnel terminating with a nanochannel. We show numerical simulations, based on the finite element method, and analyze how the ion distribution changes depending on the average concentration of the working solutions. We also report on the effect of surface charge on the ion distribution inside a long funnel and analyze how the phenomena of ion current rectification depend on the applied voltage and on the working solution concentration. Our results can be used in the design and implementation of high-performance concentrators, which, if combined with high sensitivity detectors, could drive the development of a new class of miniaturized biosensors characterized by an improved sensitivity. Keywords: nanofunnel; FEM simulation; ionic current rectification; micro-nano structure interface 1.
    [Show full text]
  • Beryllium Desorption from Minerals and Organic Ligands Over Time
    Chemical Geology 439 (2016) 52–58 Contents lists available at ScienceDirect Chemical Geology journal homepage: www.elsevier.com/locate/chemgeo Beryllium desorption from minerals and organic ligands over time Vanessa Boschi ⁎,JaneK.Willenbring Department of Earth and Environmental Science, University of Pennsylvania, 251 Hayden Hall, 240 South 33rd Street, Philadelphia, PA 19104, USA article info abstract Article history: Beryllium isotopes sorbed to sediments have provided useful tools in the field of geochronology and geomor- Received 13 April 2016 phology over the last few decades. The use of beryllium isotopes relies on the premise that beryllium sorbed to Received in revised form 3 June 2016 sediments is unaltered over large timescales. Changes in the environmental chemistry, either in-situ or en Accepted 10 June 2016 route from soil to fluvial system, to the ocean, can cause beryllium desorption and may preclude some beryllium Available online 11 June 2016 isotopic applications. Keywords: Four mechanisms were tested to determine the relative desorption potential of beryllium including a reduction Beryllium in pH, an increase in ionic strength (NaCl) and complexation by soluble organic (malonic acid) and inorganic spe- Desorption cies (NaF). To assess the relative effect of each mechanism on beryllium desorption from both organic and min- Minerals eral fractions, we prepared separate solutions of beryllium bound to minerals and organic compounds and Organic ligands measured beryllium concentrations in solution before and after each chemical perturbation. We conclude a re- Inner and outer sphere complexation duction in pH resulted in the greatest amount of desorption among the four treatments, removing 97% and 75% of sorbed beryllium from illite and montmorillonite, respectively, and none from the organic ligands tested.
    [Show full text]
  • 6.007 Lecture 5: Electrostatics (Gauss's Law and Boundary
    Electrostatics (Free Space With Charges & Conductors) Reading - Shen and Kong – Ch. 9 Outline Maxwell’s Equations (In Free Space) Gauss’ Law & Faraday’s Law Applications of Gauss’ Law Electrostatic Boundary Conditions Electrostatic Energy Storage 1 Maxwell’s Equations (in Free Space with Electric Charges present) DIFFERENTIAL FORM INTEGRAL FORM E-Gauss: Faraday: H-Gauss: Ampere: Static arise when , and Maxwell’s Equations split into decoupled electrostatic and magnetostatic eqns. Electro-quasistatic and magneto-quasitatic systems arise when one (but not both) time derivative becomes important. Note that the Differential and Integral forms of Maxwell’s Equations are related through ’ ’ Stoke s Theorem and2 Gauss Theorem Charges and Currents Charge conservation and KCL for ideal nodes There can be a nonzero charge density in the absence of a current density . There can be a nonzero current density in the absence of a charge density . 3 Gauss’ Law Flux of through closed surface S = net charge inside V 4 Point Charge Example Apply Gauss’ Law in integral form making use of symmetry to find • Assume that the image charge is uniformly distributed at . Why is this important ? • Symmetry 5 Gauss’ Law Tells Us … … the electric charge can reside only on the surface of the conductor. [If charge was present inside a conductor, we can draw a Gaussian surface around that charge and the electric field in vicinity of that charge would be non-zero ! A non-zero field implies current flow through the conductor, which will transport the charge to the surface.] … there is no charge at all on the inner surface of a hollow conductor.
    [Show full text]
  • Streaming Potential Analysis
    ABSTRACT WANG, YUN. Colloidal Behavior of Polyampholytes. (Under the direction of Dr. M. A. Hubbe). Polyampholytes are polymers that have both positively and negatively charged groups in the same chain. In recent years polyampholytes have started to be used in papermaking applications, as well as in sludge treatment processes. Benefits, in the case of papermaking, have included increased dry-strength and faster removal of water. But the molecular mechanisms by which such benefits are achieved have not been fully understood. This thesis project focused on effects related to polyampholyte charge density. A series of polyampholytes with a fixed charge ratio but different charge density was used for the experiments. Analysis methods included pH titrations, streaming current titrations, and adsorption isotherms. From pH titrations the charge density of cationic and anionic groups under different pH were calculated. From streaming current tests the net apparent charge density under different pH was calculated. And from adsorption tests it was found that the highest adsorbed amounts were achieved in certain cases corresponding to the highest content of ionic groups on the polyampholytes. Adsorption depended strongly on pH. Substantial differences were observed when comparing results obtained with polyampholyte samples versus ordinary polyelectrolyte samples with same charge density of cationic or anionic groups. Colloidal Behavior of Polyampholytes by YUN WANG A thesis submitted to the Graduate Faculty of North Carolina State University in partial fulfillment of the requirements for the Degree of Master of Science PULP AND PAPER SCIENCE Raleigh 2006 APPROVED BY: ________________________ _________________________ _________________________ Chair of Advisory Committee BIOGRAPHY The author was born on November 10, 1981 in Changzhou, Jiangsu province, People’s Republic of China.
    [Show full text]
  • Analysis of Streaming Potential Flow and Electroviscous Effect in a Shear
    www.nature.com/scientificreports OPEN Analysis of streaming potential fow and electroviscous efect in a shear‑driven charged slit microchannel Adham Riad, Behnam Khorshidi & Mohtada Sadrzadeh* Investigating the fow behavior in microfuidic systems has become of interest due to the need for precise control of the mass and momentum transport in microfuidic devices. In multilayered‑fows, precise control of the fow behavior requires a more thorough understanding as it depends on multiple parameters. The following paper proposes a microfuidic system consisting of an aqueous solution between a moving plate and a stationary wall, where the moving plate mimics a charged oil–water interface. Analytical expressions are derived by solving the nonlinear Poisson–Boltzmann equation along with the simplifed Navier–Stokes equation to describe the electrokinetic efects on the shear‑ driven fow of the aqueous electrolyte solution. The Debye–Huckel approximation is not employed in the derivation extending its compatibility to high interfacial zeta potential. Additionally, a numerical model is developed to predict the streaming potential fow created due to the shear‑driven motion of the charged upper wall along with its associated electric double layer efect. The model utilizes the extended Nernst–Planck equations instead of the linearized Poisson–Boltzmann equation to accurately predict the axial variation in ion concentration along the microchannel. Results show that the interfacial zeta potential of the moving interface greatly impacts the velocity profle of the fow and can reverse its overall direction. The numerical results are validated by the analytical expressions, where both models predicted that fow could reverse its overall direction when the interfacial zeta potential of the oil–water is above a certain threshold value.
    [Show full text]
  • Chapter 5 Capacitance and Dielectrics
    Chapter 5 Capacitance and Dielectrics 5.1 Introduction...........................................................................................................5-3 5.2 Calculation of Capacitance ...................................................................................5-4 Example 5.1: Parallel-Plate Capacitor ....................................................................5-4 Interactive Simulation 5.1: Parallel-Plate Capacitor ...........................................5-6 Example 5.2: Cylindrical Capacitor........................................................................5-6 Example 5.3: Spherical Capacitor...........................................................................5-8 5.3 Capacitors in Electric Circuits ..............................................................................5-9 5.3.1 Parallel Connection......................................................................................5-10 5.3.2 Series Connection ........................................................................................5-11 Example 5.4: Equivalent Capacitance ..................................................................5-12 5.4 Storing Energy in a Capacitor.............................................................................5-13 5.4.1 Energy Density of the Electric Field............................................................5-14 Interactive Simulation 5.2: Charge Placed between Capacitor Plates..............5-14 Example 5.5: Electric Energy Density of Dry Air................................................5-15
    [Show full text]
  • Electrical Double Layer Interactions with Surface Charge Heterogeneities
    Electrical double layer interactions with surface charge heterogeneities by Christian Pick A dissertation submitted to Johns Hopkins University in conformity with the requirements for the degree of Doctor of Philosophy Baltimore, Maryland October 2015 © 2015 Christian Pick All rights reserved Abstract Particle deposition at solid-liquid interfaces is a critical process in a diverse number of technological systems. The surface forces governing particle deposition are typically treated within the framework of the well-known DLVO (Derjaguin-Landau- Verwey-Overbeek) theory. DLVO theory assumes of a uniform surface charge density but real surfaces often contain chemical heterogeneities that can introduce variations in surface charge density. While numerous studies have revealed a great deal on the role of charge heterogeneities in particle deposition, direct force measurement of heterogeneously charged surfaces has remained a largely unexplored area of research. Force measurements would allow for systematic investigation into the effects of charge heterogeneities on surface forces. A significant challenge with employing force measurements of heterogeneously charged surfaces is the size of the interaction area, referred to in literature as the electrostatic zone of influence. For microparticles, the size of the zone of influence is, at most, a few hundred nanometers across. Creating a surface with well-defined patterned heterogeneities within this area is out of reach of most conventional photolithographic techniques. Here, we present a means of simultaneously scaling up the electrostatic zone of influence and performing direct force measurements with micropatterned heterogeneously charged surfaces by employing the surface forces apparatus (SFA). A technique is developed here based on the vapor deposition of an aminosilane (3- aminopropyltriethoxysilane, APTES) through elastomeric membranes to create surfaces for force measurement experiments.
    [Show full text]