At the nanoscale, finite ion size and channel diameter strongly affect electric double layer (EDL) overlap, making Bikerman’s model more accurate than classical theory.
Author
Rajni, Associate Professor,Jindal Global Business School, O.P. Jindal Global University, Sonipat, Haryana, India
Summary
With an overlapped electric double layer formed in a nanochannel, the electrolyte is subjected to two kind of interactions, the van der Waals interactions and the electric double layer (EDL) electrostatic interactions. The operating scale is different for these interactions. The electrostatic interaction formed near the interface is of significant interest in several applications from electrochemistry to nanofluidics. The classical Poisson-Boltzmann (PB) theory explains the EDL potential in detail, but this theory fails at smaller separation distances. Electric Double Layer (EDL) has great influence on fluid flows in nanochannels. Most of the nanochannels have circular or rectangular cross-section. Hence, there is a need to undertake thorough investigation of EDL effect in two dimensional nanochannels. In nanoconfinements electrolytes form an overlapped EDL. At this scale, the ion size and the nanochannel gap size becomes comparable. The steric effects become significant and thus, ion size cannot be neglected.
In the present work, an analysis is performed to observe the steric effects on the electric potential distribution in a nanochannel. Then the analysis is moved on to the effects of the hydraulic diameter on electric potential distribution. The Modified Poisson- Boltzmann equation proposed originally by Bikerman (Philos. Mag. 1942, 33, 384) is solved numerically with the constant surface potential condition. This equation is highly nonlinear and thus numerical techniques have been used for its solution. In this paper, Bikerman’s model equation is solved through numerical method to analyze the steric effects of ions on the electric potential distribution and ionic concentration in a nanochannel with variation in hydraulic diameter for a rectangular nanochannel. The electrokinetic phenomena is investigated in terms of the nanochannel electric potential, the steric factor and the nanochannel gap size. Investigations reveal the relation between EDL overlap phenomenon and finite size effects.
Published in: AIP Conference Proceedings
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