Softness Induced Enhancement in Net Throughput of Non-Linear Bio-Fluids in Nanofluidic Channel under EDL Phenomenon

Harshad Sanjay Gaikwad,Pranab Kumar Mondal,Somchai Wongwises

doi:10.1038/s41598-018-26056-6

Abstract

In this article, we describe the electro-hydrodynamics of non-Newtonian fluid in narrow fluidic channel with solvent permeable and ion-penetrable polyelectrolyte layer (PEL) grafted on channel surface with an interaction of non-overlapping electric double layer (EDL) phenomenon. In this analysis, we integrate power-law model in the momentum equation for describing the non-Newtonian rheology. The complex interplay between the non-Newtonian rheology and interfacial electrochemistry in presence of PEL on the walls leads to non-intuitive variations in the underlying flow dynamics in the channels. As such, we bring out the variations in flow dynamics and their implications on the net throughput in the channel in terms of different parameters like power-law index (n), drag parameter (α), PEL thickness (d) and Debye length ratio (κ/κPEL) are discussed. We show, in this analysis, a relative enhancement in the net throughput through a soft nanofluidic channel for both the shear-thinning and shear-thickening fluids, attributed to the stronger electrical body forces stemming from ionic interactions between polyelectrolyte layer and electrolyte layer. Also, we illustrate that higher apparent viscosity inherent with the class of shear-thickening fluid weakens the softness induced enhancement in the volumetric flow rate for the shear-thickening fluids, since the viscous drag offered to the f low f ield becomes higher for the transport of shear-thickening fluid.

Highlights

Emulsions show a shear-thinning nature, while W-O has higher apparent viscosity than the O-W emulsion[18]
Attention has been paid by the researchers on the flow dynamics of a Jeffrey fluid, which belongs to the category of non-Newtonian fluid as well, through a soft narrow fluidic channel[28], the rheology driven modifications in viscous force under electro-kinetic influences and its interaction with the soft substrate together with a few pertinent aspects like the consideration of the finite thickness of polyelectrolyte layer (PEL) and the interaction of Electrical Double layer (EDL) formed near the walls of square/rectangular channels may bring in new flow physics, which are remaining still untouched in the literature till date
Due to a comparatively higher thickness of EDL in soft narrow fluidic channels than that of the rigid channels, we here assume a channel with square cross section essentially to consider the interactive effects of the EDLs being formed at two perpendicular walls of the channel on the underlying flow dynamics, which is yet to be considered in the literature

Summary

Introduction

Emulsions show a shear-thinning nature, while W-O has higher apparent viscosity than the O-W emulsion[18]. Considering all above pertinent issues involved with different bio-medical/biochemical applications, a thorough understanding of the underlying transport of non-Newtonian fluids through a soft narrow fluidic channel appears to be an important aspect for the modifications in the micro-electro-mechanical circuitry, primarily attributed to the complex interplay among different forcings associated with the underlying transport process Accounting this aspect, a few studies as reported in the literature have delineated the physico-chemical interaction of electromechanics at small scales and fluid dynamics such as charge regulated surface, ion-partitioning effect, higher surface charge (relaxation effect) and surface potential, pH dependent charge density, Field Effect Transistor (FET) regulated surface potential, diffusion effect of ions, specific ion interaction, grafting of end charged polyelectrolyte brushes and their influential impacts on streaming current, streaming potential as well as electro-viscous effect[10,13,20,21,22,23,24,25,26]. It should be mentioned here that the potential at the walls of the channel is assumed to be less than |25 mV|, leading to the validity of applicability of ( ( ) ) Debye-Huckel approximation sinh z eeψ kBT

Methods

Results

Conclusion