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Resolving Anomalies in Predicting Electrokinetic Energy Conversion Efficiencies of Nanofluidic Devices.

Majumder S, Dhar J, Chakraborty S - Sci Rep (2015)

Bottom Line: We devise a new approach for capturing complex interfacial interactions over reduced length scales, towards predicting electrokinetic energy conversion efficiencies of nanofluidic devices.By embedding several aspects of intermolecular interactions in continuum based formalism, we show that our simple theory becomes capable of representing complex interconnections between electro-mechanics and hydrodynamics over reduced length scales.The present model, thus, may be employed to rationalize the discrepancies between low energy conversion efficiencies of nanofluidic channels that have been realized from experiments, and the impractically high energy conversion efficiencies that have been routinely predicted by the existing theories.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical Engineering, Indian Institute of Technology Kharagpur Kharagpur 721302, INDIA.

ABSTRACT
We devise a new approach for capturing complex interfacial interactions over reduced length scales, towards predicting electrokinetic energy conversion efficiencies of nanofluidic devices. By embedding several aspects of intermolecular interactions in continuum based formalism, we show that our simple theory becomes capable of representing complex interconnections between electro-mechanics and hydrodynamics over reduced length scales. The predictions from our model are supported by reported experimental data, and are in excellent quantitative agreement with molecular dynamics simulations. The present model, thus, may be employed to rationalize the discrepancies between low energy conversion efficiencies of nanofluidic channels that have been realized from experiments, and the impractically high energy conversion efficiencies that have been routinely predicted by the existing theories.

No MeSH data available.


Variation of the ratio  (inset: conversion efficiency η) as a function of dimensionless wall potential , for different values of the non-electrostatic strength α over (a) hydrophilic and (b) hydrophobic surfaces.Other values considered are: the dimensionless Debye length  and steric factor v = 10−4.  is the dimensionless streaming potential field obtained from the classical PB description. Credited authors: S. Majumder, J. Dhar and S. Chakraborty.
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f4: Variation of the ratio (inset: conversion efficiency η) as a function of dimensionless wall potential , for different values of the non-electrostatic strength α over (a) hydrophilic and (b) hydrophobic surfaces.Other values considered are: the dimensionless Debye length and steric factor v = 10−4. is the dimensionless streaming potential field obtained from the classical PB description. Credited authors: S. Majumder, J. Dhar and S. Chakraborty.

Mentions: We next attempt to assess the implication of the parameter α. Fig. 4 describes the ratio as a function of for different values of α, corresponding to: a) a hydrophilic surface (with typical contact angle of 80°), and b) a hydrophobic surface (with typical contact angle of 140°)36, where is the streaming potential field from the solution of the classical PB equation with no existence of sublayers assumed. The inset of Fig. 4 shows the corresponding variations in the conversion efficiency. We observe that the induced streaming potential and the resulting conversion efficiency are slightly less for hydrophobic surfaces in comparison to that corresponding to hydrophilic surfaces for similar values of α. This observation has also been shown in other studies depicting two types of surfaces63. Although, in reality, the presence of hydrophobic surface does enhance the efficiency to some extent as it corresponds to the case of α > 0 (which points to a higher efficiency compared to the hydrophilic cases characterized by α < 0), our model does not predict giant augmentations in efficiency in such scenarios as previously predicted in some theoretical studies2731. For α < 0, we see that the induced streaming potential is less. This may be attributed to the fact that a negative non-electrostatic potential attracts the ionic species (here the counterions) towards the wall, leading to a lower streaming field. On the contrary, when α > 0, the induced streaming field is higher since the counterions are generally repelled away from the wall more effectively and get distributed towards the bulk region. Consequently, a higher conversion efficiency is achieved when compared to the previously calculated reference of . One more observation pertaining to the current figure corresponds to the case when is less. In this situation, the effect of the non-electrostatic interaction among the ions is not so pronounced, as compared to the effects due to the presence of the wall-adjacent sublayers. Thus, a ratio lower than unity is obtained.


Resolving Anomalies in Predicting Electrokinetic Energy Conversion Efficiencies of Nanofluidic Devices.

Majumder S, Dhar J, Chakraborty S - Sci Rep (2015)

Variation of the ratio  (inset: conversion efficiency η) as a function of dimensionless wall potential , for different values of the non-electrostatic strength α over (a) hydrophilic and (b) hydrophobic surfaces.Other values considered are: the dimensionless Debye length  and steric factor v = 10−4.  is the dimensionless streaming potential field obtained from the classical PB description. Credited authors: S. Majumder, J. Dhar and S. Chakraborty.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4593964&req=5

f4: Variation of the ratio (inset: conversion efficiency η) as a function of dimensionless wall potential , for different values of the non-electrostatic strength α over (a) hydrophilic and (b) hydrophobic surfaces.Other values considered are: the dimensionless Debye length and steric factor v = 10−4. is the dimensionless streaming potential field obtained from the classical PB description. Credited authors: S. Majumder, J. Dhar and S. Chakraborty.
Mentions: We next attempt to assess the implication of the parameter α. Fig. 4 describes the ratio as a function of for different values of α, corresponding to: a) a hydrophilic surface (with typical contact angle of 80°), and b) a hydrophobic surface (with typical contact angle of 140°)36, where is the streaming potential field from the solution of the classical PB equation with no existence of sublayers assumed. The inset of Fig. 4 shows the corresponding variations in the conversion efficiency. We observe that the induced streaming potential and the resulting conversion efficiency are slightly less for hydrophobic surfaces in comparison to that corresponding to hydrophilic surfaces for similar values of α. This observation has also been shown in other studies depicting two types of surfaces63. Although, in reality, the presence of hydrophobic surface does enhance the efficiency to some extent as it corresponds to the case of α > 0 (which points to a higher efficiency compared to the hydrophilic cases characterized by α < 0), our model does not predict giant augmentations in efficiency in such scenarios as previously predicted in some theoretical studies2731. For α < 0, we see that the induced streaming potential is less. This may be attributed to the fact that a negative non-electrostatic potential attracts the ionic species (here the counterions) towards the wall, leading to a lower streaming field. On the contrary, when α > 0, the induced streaming field is higher since the counterions are generally repelled away from the wall more effectively and get distributed towards the bulk region. Consequently, a higher conversion efficiency is achieved when compared to the previously calculated reference of . One more observation pertaining to the current figure corresponds to the case when is less. In this situation, the effect of the non-electrostatic interaction among the ions is not so pronounced, as compared to the effects due to the presence of the wall-adjacent sublayers. Thus, a ratio lower than unity is obtained.

Bottom Line: We devise a new approach for capturing complex interfacial interactions over reduced length scales, towards predicting electrokinetic energy conversion efficiencies of nanofluidic devices.By embedding several aspects of intermolecular interactions in continuum based formalism, we show that our simple theory becomes capable of representing complex interconnections between electro-mechanics and hydrodynamics over reduced length scales.The present model, thus, may be employed to rationalize the discrepancies between low energy conversion efficiencies of nanofluidic channels that have been realized from experiments, and the impractically high energy conversion efficiencies that have been routinely predicted by the existing theories.

View Article: PubMed Central - PubMed

Affiliation: Department of Mechanical Engineering, Indian Institute of Technology Kharagpur Kharagpur 721302, INDIA.

ABSTRACT
We devise a new approach for capturing complex interfacial interactions over reduced length scales, towards predicting electrokinetic energy conversion efficiencies of nanofluidic devices. By embedding several aspects of intermolecular interactions in continuum based formalism, we show that our simple theory becomes capable of representing complex interconnections between electro-mechanics and hydrodynamics over reduced length scales. The predictions from our model are supported by reported experimental data, and are in excellent quantitative agreement with molecular dynamics simulations. The present model, thus, may be employed to rationalize the discrepancies between low energy conversion efficiencies of nanofluidic channels that have been realized from experiments, and the impractically high energy conversion efficiencies that have been routinely predicted by the existing theories.

No MeSH data available.