Modeling of Electroosmotic Nanoflows With Overlapped Double Layer

2011 ◽  
Author(s):  
Reza Nosrati ◽  
Mehrdad Raisee ◽  
Ahmad Nourbakhsh
Keyword(s):  
Zeta Potential ◽  
Double Layer ◽  
Electric Double Layer ◽  
Potential Distribution ◽  
Present Model ◽  
Ionic Concentration ◽  
Channel Height ◽  
Parabolic Profile ◽  
Poisson Boltzmann ◽  
Volume Method

In the present paper a new model is proposed for electric double layer (EDL) overlapped in nanochannels. The model aimed to obtain a deeper insight of transport phenomena in nanoscale. Two-dimensional Nernst and ionic conservation equations are used to obtain electroosmotic potential distribution in flow field. In the proposed study, transport equations for flow, ionic concentration and electroosmotic potential are solved numerically via finite volume method. Moreover, Debye-Hu¨ckle (DH) approximation and symmetry condition, which limit the application, are avoided. Thus, the present model is suitable for prediction of electroosmotic flows through nanochannels as well as complicated asymmetric geometries with large nonuniform zeta potential distribution. For homogeneous zeta potential distribution, it has been shown that by reduction of channel height to values comparable with EDL thickness, Poisson-Boltzmann model produces inaccurate results and must be avoided. Furthermore, for overlapped electric double layer in nanochannels with heterogeneous zeta potential distribution it has been found that the present model returns modified ionic concentration and electroosmotic potential distribution compare to previous EDL overlapped models due to 2D solution of ionic concentration distribution. Finally, velocity profiles in EDL overlapped nanochannels are investigated and it has been showed that for pure electroosmotic flow the velocity profile deviates from the expected plug-like profile towards a parabolic profile.

Effects of Externally Applied Electric Field on the Electric Double Layer Formed in an Electrolyte Layer and its Contribution Towards Joule Heating

2011 ◽  
Author(s):  
Neeraj Sharma ◽  
Gerardo Diaz ◽  
Edbertho Leal-Quiros
Keyword(s):  
Electric Field ◽  
Double Layer ◽  
Joule Heating ◽  
Electric Potential ◽  
Applied Electric Field ◽  
Electric Double Layer ◽  
Potential Distribution ◽  
Electrolyte Layer ◽  
Poisson Boltzmann ◽  
Poisson Boltzmann Equation

Joule heating of liquid films in the presence of an externally applied electric field is influenced by the formation of the electric double layer. The thickness and charge distribution inside the electric double layer determine the extent of interaction of the charge in the electric double layer with the externally applied electric field and the Joule heating of the electrolyte layer. For this reason, the effects of externally applied electric field (both parallel and along the normal to the surface) on the electric double layer are being studied in the present paper. In the absence of the externally applied electric field, the distribution of the electric potential in the double layer is given by Poisson equation. Assuming Boltzmann distribution for the ionic concentration in the double layer, one arrives at Poisson-Boltzmann equation for the electric potential distribution. The externally applied electric field changes this electric potential distribution. Hence, the contribution of the externally applied electric field is studied by including it in the Poisson-Boltzmann equation.

scholarly journals Debye-Hückel Free Energy of an Electric Double Layer with Discrete Charges Located at a Dielectric Interface

Membranes ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 129
Author(s):  
Guilherme Volpe Bossa ◽  
Sylvio May
Keyword(s):  
Free Energy ◽  
Double Layer ◽  
Electric Double Layer ◽  
Low Dielectric Constant ◽  
Surface Charges ◽  
Dielectric Interface ◽  
Charge Densities ◽  
Low Dielectric ◽  
Poisson Boltzmann ◽  
The Continuum

Poisson–Boltzmann theory provides an established framework to calculate properties and free energies of an electric double layer, especially for simple geometries and interfaces that carry continuous charge densities. At sufficiently small length scales, however, the discreteness of the surface charges cannot be neglected. We consider a planar dielectric interface that separates a salt-containing aqueous phase from a medium of low dielectric constant and carries discrete surface charges of fixed density. Within the linear Debye-Hückel limit of Poisson–Boltzmann theory, we calculate the surface potential inside a Wigner–Seitz cell that is produced by all surface charges outside the cell using a Fourier-Bessel series and a Hankel transformation. From the surface potential, we obtain the Debye-Hückel free energy of the electric double layer, which we compare with the corresponding expression in the continuum limit. Differences arise for sufficiently small charge densities, where we show that the dominating interaction is dipolar, arising from the dipoles formed by the surface charges and associated counterions. This interaction propagates through the medium of a low dielectric constant and alters the continuum power of two dependence of the free energy on the surface charge density to a power of 2.5 law.

scholarly journals INFLUENCE OF THE ELECTRIC DOUBLE LAYER ON INDUCED PRESSURE FIELDS AND DEVELOPMENT LENGTHS IN ELECTRO-OSMOTIC FLOWS

2005 ◽  
Vol 19 (28n29) ◽  
pp. 1655-1658
Author(s):  
YONGHAO ZHANG ◽  
XIAO-JUN GU ◽  
ROBERT W. BARBER ◽  
DAVID R. EMERSON
Keyword(s):  
Double Layer ◽  
Electric Double Layer ◽  
Pressure Field ◽  
Volumetric Flow Rate ◽  
Channel Height ◽  
Fluid Viscosity ◽  
Development Length ◽  
Pressure Fields ◽  
Flow Development ◽  
Electro Osmotic Flow

Electro-osmotic flow can be used as an efficient pumping mechanism in microfluidic devices. For this type of flow, frictional losses at the entrance and exit can induce an adverse longitudinal pressure distribution that can lead to dispersive effects. The present study describes a numerical investigation of the influence of the electric double layer on the induced pressure field and the flow development length. The induced pressure gradient is affected by the volumetric flow rate, fluid viscosity and the channel height. When the electric double layer is small, the development length remains constant at 0.57 of the channel height but decreases as the double layer grows in thickness.

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