Reversible Electrically Modulated Electroosmotic Flow Via Carbon Nanotube Membrane

Electroosmotic flow (EOF) is widely used to manipulate solutions in capillaries and microfluidic devices, and more recently in the nanotubes of a carbon nanotube membrane. In all of these applications it is important to control both the rate and direction of EOF through the system, independently of the electric field that drives EOF. For this reason, there has been considerable recent effort devoted to developing ways of modulating the rate and direction of EOF. We describe here a new method, and we use the carbon nanotube membrane (CNM) system to demonstrate this method. This new method entails coating the inside walls of the carbon nanotubes within the CNM with redox-active polymer films. The redox polymer, poly(vinylferrocene), can be reversibly electrochemically switched between an electrical neutral and a polycationic form. This provides a way for controlling both the magnitude and the sign of the surface charge on the nanotube walls, which in turn allows for control of both the rate and direction of EOF through the CNM.

Amide functionalized DWCNT nanocomposite membranes for chiral separation of the racemic DOPA

The global water shortage has become a serious threat for the world and the most promising solution for the water issue is the desalination of seawater or brackish water. In this work, direct contact membrane distillation (DCMD) as one of thermal desalination technologies was numerically and exprimentally analyzed to study its performance. A large DCMD system with multiple membrane modules in a parallel arrangement running on the waste heat from a diesel power generator was numerically analyzed using a thermo-fluid network model to study the technical feasibility of the use of the low-grade engine waste heat and simulate the distillation performance of the DCMD system. Next, a small DCMD experimental apparatus was fabricated to test for the distillation performance for various operating conditions (inlet temperatures, flow rates of feed and permeate streams and NaCl concentration) and design variables (filament spacing of a screen spacer in the flow channels and flow configuration). In the DCMD, two different regimes were observed in the water flux behavior regarding the salinity of feed water. In the first regime, from low NaCl concentration to 90% saturated NaCl concentration, there was a gradual decrease in the water flux due to the suppression of vapor pressure at the feed water which is simulated by a CFD model. In the second regime, at higher 90% saturated NaCl concentration, there was a sharp drop in the water flux due to the deposition of NaCl crystals on the membrane surface which is simulated by an analytical model using the adjusting parameter from the experiment. Finally, a nanoscale DCMD using Carbon Nanotube (CNT) membrane was numerically analyzed using non-equilibrium molecular dynamics (NEMD) simulation for different diameters and lengths of the CNT and operating conditions such as system temperature, temperature difference between the feed (hot) and permeate (cold) reservoirs, and sodium chloride (NaCl) concentration in the feed reservoir. The distillation performance of the DCMD systems is enhanced by increasing system temperature, temperature difference between feed and permeate streams, and decreasing the NaCl concentration. The permeability of the CNT membrane (1.8 x 10-5 liter/m2-s-Pa) was found two orders-of-magnitudes higher than a Polytetrafluoroethylene (PTFE) membrane (1.7 x 10-7 liter/m2-s-Pa ) used in our experimental work.

In this study, we propose a novel technique to measure electric fields and electrokinetic phenomena in microchannels using two kinds of tracer particles with different electrophoretic mobilities. In the present technique, electric fields, whose precise measurement is quite difficult, is obtained from the velocity differences between two kinds of tracer particles. The principle of electric field measurement is based on the flow visualization and the mathematical analysis of the flow fields of different particles. Each tracer particle with different mobilities due to surface charge densities is mixed in a buffer solution to analyze the flow by particle image velocimetry (PIV). Experimental demonstrations are successfully conducted both in straight and T-shaped microchannels with rectangular cross sections. The experimental results of the electric field are compared with the roughly estimated values based on the numerical analysis of the Laplace equation. The comparison indicates the applicability of the proposed technique because they are in reasonable agreement. Moreover, the detailed electrokinetic phenomena, e.g., the electrophoresis and electro osmosis flow, are successfully investigated using the electric field obtained here. These results lead us to conclude that the proposed method can be used as a practical tool to access the details of electrokinetic phenomena in microchannels.

HypothesisElectronic paper displays rely on electrokinetic effects in nonpolar solvents to drive the displacement of colloidal particles within a fluidic cell. While Electrophoresis (EP) is a well-established and frequently employed phenomenon, electro-osmosis (EO), which drives fluid flow along charged solid surfaces, has not been studied as extensively. We hypothesize that by exploiting the interplay between these effects, an enhanced particle transport can be achieved. ExperimentsIn this study, we experimentally investigate the combined effects of EP and EO for colloidal particles in non-polar solvents, driven by an electric field. We use astigmatism micro-particle tracking velocimetry (A-μPTV) to measure the motion of charged particles within model fluidic cells. Using a simple approach that relies on basic fluid flow properties we extract the contributions due to EP and EO, finding that EO contributes significantly to particle transport. The validity of our approach is confirmed by measurements on particles with different magnitudes of charge, and by comparison to numerical simulations. FindingsWe find that EO flows can play a dominant role in the transport of particles in electrokinetic display devices. This can be exploited to speed up particle transport, potentially yielding displays with significantly faster switching times.

Chapter 5 - Electrophoretic Motion of a Rigid Spherical Particle in a Cylindrical Pore

Chapter 17 - Diffusiophoresis of Liquid Droplets and Gas Bubbles

We studied the surface properties of eruptive material from Deception Island (South Shetland Islands, Antarctica). The surface free energy and zeta potential were analyzed in obsidian and pumice stones immersed in different electrolytes (NaCl, BaCl2, AlCl3, VCl2, PbCl2, CdCl2, FeCl3, and CrCl3). The results show that obsidian has a monopolar character. The value of the obsidian electron-donor component increased in the presence of heavy metals, reaching 61.0 mJ/m2 in the case of CrCl3. This means that the heavy metals transform the surface of obsidian into a hydrophilic material in almost all cases, except in the case of FeCl3, which makes the obsidian surface hydrophobic. The pH variation of the liquid phase has a significant influence on the zeta potential, not only changing its value, but also the sign of the surface electric charge. A significant result is that a variation of two in pH (between 5 and 7) changes the sign of the charge from positive to negative or vice versa, depending on the electrolyte used. In general, the presence of electrolytes changes the surface properties of solid materials and consequently the adhesion and growth of microorganisms on coastal rocks.

To address the global challenge of water pollution, membrane-based technologies are being used as a dignified separation technology. However, designing low-cost, reusable, freestanding and flexible membranes for wastewater treatment with tunable pore size, good mechanical strength, and high separation efficiency is still a major challenge. Herein, we report the development of a scalable, reusable, freestanding, flexible and functionalized multiwalled carbon nanotube (FMWCNT) membrane filter with tunable pore size for wastewater treatment, which has attractive attributes such as high separation efficiency (>99% for organic dyes and ∼80% for salts), permeance (∼225 L h−1 m−2 bar−1), tensile strength (∼6 MPa), and reusability of both the membrane as well as contaminants separately. This FMWCNTs membrane filter has been developed by a simple vacuum-assisted filtration technique followed by the synthesis of MWCNTs using a cost-effective spray pyrolysis assisted chemical vapor deposition (CVD) technique and chemical functionalization. This study deals with understanding the rejection, retrieval, and reusability of both the membranes as well as waterborne contaminants separately. The developed membrane filter has potential utility in many applications such as wastewater treatment, food industry, and life sciences due to its robust mechanical and separation performance characteristics.

Insights into the remediation of cadmium-pyrene co-contaminated soil by electrokinetic and the influence factors

Introduction High pressure polymer electrolyte membrane water electrolyzer (PEMWE) is expected to efficiently produce high pressure hydrogen gas in direct manner. Couple of companies and research institutes continues to develop PEMWEs. PEMWEs can be utilized to fuel the hydrogen gas to FCV[1]. Also, PEMWEs with PEMFC can be a good candidate for load leveling of electricity between consumer demand and renewable energy.[2] However, high pressure PEMWEs, as disadvantage, have large concern on its current efficiency. Produced hydrogen gas crossovers PEM from cathode to anode, and the amount of crossover hydrogen gas directly corresponds to reduction of the current efficiency. An estimation based on the permeability suggests that current efficiency decreases up to 10 % under 40 MPa [3]. Experimental result shows 23 % reduction of current efficiency [4]. Authors have succeeded to decrease the crossover and increase the current efficiency with convection effect, where water is intentionally fed to cathode channel. This additional feeding of water promotes the drainage of hydrogen gas, leading to the 4% increase of current efficiency. However, this method suggests additional cost for a pump to feed water to cathode, although the power consumption of the pump is negligible. A further simple method is expected. This study proposes a current supplier, whose wettability is controlled so that it has hydrophobic or hydrophilic property. Carbon paper is built in a PEMWE as cathode current supplier, and experimentally evaluated if it can suppress the hydrogen gas crossover and increase the current efficiency. Also, this study conducts visualization, where the window placed in cathode separator can visualize the impact of the wettability on hydrogen gas bubble behavior. Experimental Method Experimental apparatus is shown in Fig. 1. In anode side, water is circulated, and the produce oxygen gas drains through gas/liquid separator. The water flow rate is adjusted so that electrolytic rate becomes 70 ppm. Anode side is operated at atmospheric pressure. Cathode piping has two cases, where water is circulated or not. The water flow rate in cathode is adjusted to be the same as anode case, and the operation pressure is controlled up to 2 MPa with back pressure valve. The flow meter located in the downstream of the valve measures the practically produced hydrogen gas amount, which is converted to current efficiency. The cell consists of cathode separator, cathode current supplier, CCM, anode current supplier, anode separator. Two type of the current supplier in cathode are prepared. One is carbon paper (SGL, 35AA), which has hydrophobicity with the contact angle of 135. The other one is the carbon paper, which shows the hydrophilic characteristic so that a water droplet is completely absorbed. This hydrophilic carbon paper is fabricated by the impregnation of titanium oxide into carbon paper. As anode current supplier, titanium sintered compact with Pt coating is used. CCM has Iridium oxide layer as for anode and Pt/C layer for cathode sprayed and hot-pressed on Nafion membrane. Results and discussion Figure 2 is the wettability impact of current supplier in the case of feeding water in cathode channel. Fig (a), (b) are hydrogen current efficiency and detachment frequency of the bubble, respectively. As expected, the case of hydrophilic current supplier has slightly higher current efficiency (approximately 1%). In the hydrophilic case, the current supplier actively absorbs water and may be fully saturated. This situation enhances to detach the hydrogen gas bubble from the supplier (Fig. 2 (c)), and increase the efficiency. Figure 3 is the wettability impact of current supplier without feeding water in cathode channel. Because of not feeding water, only the current efficiency is shown. Contrary to expectation, the hydrophobic supplier indicated higher efficiency (2%). In the case of not feeding water into cathode channel, the cathode current supplier is still impregnated with water, which is transported from anode by electro-osmosis flow. In this situation, gas path is thought to be formed in current supplier if it has hydrophobicity, and the path contributes to drain the produced hydrogen from catalyst layer to channel in cathode. Whereas, hydrophilic current supplier tend to saturate water, and the saturated water disturb the drainage of hydrogen gas from catalyst layer to channel. Thus, the hydrophobic current supplier indicated the higher efficiency.

An experimental setup is developed to emulate a wind turbine-generator system. The configuration of the wind energy conversion system is elaborated using OPAL-RT real-time simulator and electrical modules from Lab-Volt. In order to operate such system, a control scheme is designed for the generator side and grid side converters. The experiment can be reconfigured for conducting research and teaching various control concepts to both undergraduate and graduate students in wind energy systems.

Determination of the magnitude of the topological charge of a partially coherent vortex beam has been reported both theoretically and experimentally recently, while how to determine the sign of the topological charge of such beam remains unsolved. In this paper, we propose a simple method for simultaneous determination of the sign and the magnitude of the topological charge of a partially coherent vortex beam. This method is based on the measurement of the complex degree of coherence (CDOC) of a partially coherent vortex beam after propagating through a couple of cylindrical lenses. We find that the number of the bright fringes and the orientation of the distribution of the CDOC correspond to the magnitude and the sign of the topological charge, respectively. This phenomenon is confirmed by our experimental results.

Parameterization has been applied to extended Monte Carlo simulations of the electric charge modulation of aerosol scavenging by droplets, both for particle charges of the same sign as droplets and of opposite sign. Separate parameterizations are given for electro‐antiscavenging for small aerosol particles with same‐sign charges; electroscavenging for larger particles with same‐sign charges; and electroscavenging for opposite‐sign particles. A wide range of sizes and charges is treated, together with altitude and humidity variations. The simulations of particle trajectories take Brownian diffusion into account by Monte Carlo perturbations and include the full conducting‐sphere electrical force, and phoretic and gravitational forces. For larger particles with larger droplets, the image force causes increases in collision rate coefficients irrespective of the sign of the particle charge, or the amount and sign of the droplet charge, or the degree to which space charge in the cloud is unipolar. Thus, even with little space charge in a cloud, the atmospheric ion production increases the scavenging of larger aerosol particles. With the presence of space charge, the scavenging rate for small particles with high mobility decreases or increases depending on the unipolarity of the space charge. The results are applicable to a wide range of electrical environments associated with clouds and stratified aerosol layers, and are relevant to precipitation and ice‐nucleation processes and cloud albedo effects.

There is a growing interest in the development of nanomechanical oscillators operating in the gigahertz range and beyond. This paper introduces a novel nano-oscillator based on a chloride ion inside an open carbon nanocone decorated by functional groups at both small and wide ends. Assuming that the carbon atoms and the electric charges of functional groups are evenly distributed over the surface and the two ends of nanocone, respectively, a continuum-based model is presented through which potential energy and interaction force are evaluated analytically. The van der Waals interactions between ion and nanocone are modeled by the 6–12 Lennard–Jones potential, while the electrostatic interactions between ion and two functional groups are modeled by the Coulomb potential. With respect to the proposed formulations, potential energy and interaction force distribution are presented by varying sign and magnitude of functional groups charge and geometrical parameters (size of small and wide ends of nanocone and its vertex angle). Using the fourth-order Runge–Kutta numerical integration scheme, the equation of motion is also solved to arrive at the time histories of separation distance and velocity of ion. An extensive study is performed to investigate the effects of sign and magnitude of functional groups charge, geometrical parameters, and initial conditions (initial separation distance and initial velocity) on the oscillatory behavior of ion-electrically charged open carbon nanocone oscillator. Numerical results demonstrate that the oscillation frequency of chloride ion inside an uncharged nanocone is respectively lower and higher than those generated inside a nanocone whose small end is decorated by positively and negatively charged functional groups. It is further shown that oscillation frequency is highly affected by the sign of electric charges distributed at the small end of nanocone.