Induced-Charge Electro-Osmosis

We describe the general phenomenon of `induced-charge electro-osmosis' (ICEO) -- the nonlinear electro-osmotic slip that occurs when an applied field acts on the ionic charge it {\sl induces} around a polarizable surface. Motivated by a simple physical picture, we calculate ICEO flows around conducting cylinders in steady (DC), oscillatory (AC), and suddenly-applied electric fields. This picture, and these systems, represent perhaps the clearest example of nonlinear electrokinetic phenomena. We complement and verify this physically-motivated approach using a matched asymptotic expansion to the electrokinetic equations in the thin double-layer and low potential limits. ICEO slip velocities vary like $u_s \propto E_0^2 L$, where $E_0$ is the field strength and $L$ is a geometric length scale, and are set up on a time scale $\tau_c = \lambda_D L/D$, where $\lambda_D$ is the screening length and $D$ is the ionic diffusion constant. We propose and analyze ICEO microfluidic pumps and mixers that operate without moving parts under low applied potentials. Similar flows around metallic colloids with fixed total charge have been described in the Russian literature (largely unnoticed in the West). ICEO flows around conductors with fixed potential, on the other hand, have no colloidal analog and offer further possibilities for microfluidic applications.Comment: 36 pages, 8 figures, to appear in J. Fluid Mec

Study of pulsatile pressure-driven electroosmotic flows through an elliptic cylindrical microchannel with the Navier slip condition

This paper aims to study an unsteady electric field-driven and pulsatile pressure-driven flow of a Newtonian fluid in an elliptic cylindrical microchannel with Navier boundary wall slip. The governing equations of the slip flow and distributions of electric potential and charge densities are the modified Navier-Stokes equations, the Poisson equation and the Nernst-Planck equations, respectively. Analytical and numerical analyses based on the Mathieu and modified Mathieu equations are performed to investigate the interplaying effects of pulsatile pressure gradients and the slip lengths on the electroosmotic flow

Modelling Advection and Diffusion in Microchannels

This project will investigate mixing in microchannels. Specifically, the advection and diffusion of a passive scalar, using a split step Monte Carlo method. Numerically the implementation of this method is well understood. The current experimental geometry is a rectangular pipe with grooves on one wall. Mixing results with straight walls agree closely with experiment. The velocity field over grooves is also studied

Niosomal 5-Flourouracil gel for effective treatment of skin cancer; In-vitro and In-vivo evaluation

This study was designated to form core-enriched 5-flourouracil (5-FU) niosomes and apply it to skin as a niosomal gel for topical treatment of skin cancer. Different molar ratios of the two surfactants used namely; sorbitan monostearate (Span 60), sorbitan monolaurate (Span 20) to cholesterol were employed, in addition; sodium deoxycholate was used a co-surfactant. The drug was successfully entrapped in niosomes with entrapment efficiency reached up to 67.08 ± 2.53 mg % (w/w). The produced niosomes had particle size below 300 nm, zeta potential values between -15 ± -1.6 and -37.73 ± -2.53 mV and polydispersity index between 0.09 ± 0.06 and 0.20 ± 0.02. Transmission electron microscopy showed the formation of spherical niosomes with closed bilayer structure. Formula N8 had more than two fold increase in amount permeated compared to free drug in in-vitro permeation study. The niosomal gel formulae had better permeation parameters compared to formulae containing free drug. Niosomal gel formula composed of sodium carboxymethyle cellulose (Na CMC) had the best permeation parameters among the produced gel formulae. Histopathological studies showed that niosomal 5-FU gel was able to penetrate more readily into deep layers of skin to treat tumor as indicated by the reduction in inflammatory reaction and hemorrhage signs observed in animals treated by niosomal 5-FU gel.

Electrokinetics of Polar Liquids in Contact with Nonpolar Surfaces

Surface science is widely applied in different engineering/scientific fields by exploiting the various physical and chemical properties of interfaces. Here, we explore the electrical properties at hydrophobe/liquid interfaces and the mechanical properties of hydrogels.Most solid surfaces become charged when placed in contact with liquids. This interfacial charge is critical in practical applications such as colloidal suspensions and microfluidic devices. In order to study the charge at the hydrophobe/liquid interface, we developed a simple method to determine the zeta potential (an indication of surface charge strength) of planar hydrophobic surfaces by combining electroosmosis and capillarity. We showed that the measurement of the centerline velocity of the liquid inside the channel is enough to deduce the zeta potential of the surface. This method was further utilized to investigate the basic physics of the charge origin at the hydrophobe/liquid interface. Negative zeta potentials were observed on apparently passive nonpolar hydrocarbon and fluorocarbon surfaces when they are in contact with polar liquids (water, ethylene glycol, formamide, and dimethyl sulfoxide). The current models of charging via the adsorption of hydroxide ions on the interface or the dissociation of pre-existing moieties are not sufficient to illustrate the experimental observations. We hope that these results will inspire further experimental and theoretical studies in this important area of research that has potential practical implications.On the other hand, mechanical properties of surfaces are also important from an adhesion perspective. A side project focuses on investigating the adhesion between thin hydrogel films and flat-end rigid studs. We designed a composite material that was composed of a polyvinyl alcohol (PVA) hydrogel coating covalently bonded to a thin polydimethylsiloxane (PDMS) film. This PVA coating passed a stability test and was characterized by high resolution x-ray photoelectron spectroscopy (XPS) and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). This hydrogel layer was found to lower the removal shear stress of a silanized glass cube by ~60% (compared to a thin unmodified PDMS film). This reduction of the adhesive shear stress was presumably due to the lubrication of water kept in the swollen PVA gel

Integrated solar electrokinetic remediation of soil contaminated with copper

Electrokinetic remediation is an emerging in-situ technology for cleaning contaminated soil. The contaminants are mobilized by passing a low-level direct current between a row of positively charged electrodes (anode) and negatively charged electrodes (cathode). Due to the low electric current required by the technology, solar power can be an excellent option for providing the electric field. Along with the environmental benefits of solar power, solar cells can provide electricity in remote sites with no access to power lines. The electrolysis reactions in electrokinetic process generate an acid front at the anode and a base front near the cathode. The acid front travels by electroosmosis and electromigration towards the cathode, while the base front moves by electromigration to the anode. The base front reacts with the cations in the soil pore fluid causing premature precipitation of the cations as heavy metal hydroxides at a distance from the cathode equal 0.3 to 0.5 times the distance between the electrodes

Sewage Sludge Electro-Dewatering

Original sludge from wastewater treatment plants (WWTPs) usually has a poor dewaterability. Conventionally, mechanical dewatering methods are used to increase the dry solids (DS) content of the sludge. However, sludge dewatering is an important economic factor in the operation of WWTPs, high water content in the final sludge cake is commonly related to an increase in transport and disposal costs. Electro‐dewatering could be a potential technique to reduce the water content of the final sludge cake, but the parameters affecting the performance of electro‐dewatering and the quality of the resulting sludge cake, as well as removed water, are not sufficiently well known. In this research, non‐pressure and pressure‐driven experiments were set up to investigate the effect of various parameters and experimental strategies on electro‐dewatering. Migration behaviour of organic compounds and metals was also studied. Application of electrical field significantly improved the dewatering performance in comparison to experiments without electric field. Electro‐dewatering increased the DS content of the sludge from 15% to 40 % in non‐pressure applications and from 8% to 41% in pressure‐driven applications. DS contents were significantly higher than typically obtained with mechanical dewatering techniques in wastewater treatment plant. The better performance of the pressure‐driven dewatering was associated to a higher current density at the beginning and higher electric field strength later on in the experiments. The applied voltage was one of the major parameters affecting dewatering time, water removal rate and DS content of the sludge cake. By decreasing the sludge loading rate, higher electrical field strength was established between the electrodes, which has a positive effect on an increase in DS content of the final sludge cake. However interrupted voltage application had anegative impact on dewatering in this study, probably because the off‐times were too long. Other factors affecting dewatering performance were associated to the original sludge characteristics and sludge conditioning. Anaerobic digestion of the sludge with high pH buffering capacity, polymer addition and freeze/thaw conditioning had a positive impact on dewatering. The impact of pH on electro‐dewatering was related to the surface charge of the particles measured as zeta‐potential. One of the differences between electro‐dewatering and mechanical dewatering technologies is that electro‐dewatering actively removes ionic compounds from the sludge. In this study, dissolution and migration of organic compounds (such as shortchain fatty acids), macro metals (Na, K, Ca, Mg, Fe) and trace metals (Ni, Mn, Zn, Cr) was investigated. The migration of the metals depended on the fractionation and electrical field strength. These compounds may have both negative and positive impacts on the reuse and recycling of the sludge and removed water. Based on the experimental results of this study, electro‐dewatering process can be optimized in terms of dewatering time, desired DS content, power consumption and chemical usage