Rheology modulated high electrochemomechanical energy conversion in soft narrow-fluidic channel

Abstract

We study the influence of viscoelastic fluid on the enhancement of the electrochemomechanical energy conversion efficiency in the polyelectrolyte layer grafted narrow-fluidic channels. We obtain the velocity distribution using the simplified Phan-Thien-Tanner model and calculate the conversion efficiency in the purview of both with and without Debye-Hückel approximations. The analysis unveils that an increment in the fluid velocity obtained with an increment in the shear-thinning nature of the viscoelastic fluid increases the streaming of the counter-ions, which, in turn, increases the conversion efficiency. Also, it is shown that the increased electroviscous effect due to higher rate of streaming potential being developed results in a reduction in the predicted enhancement of the conversion efficiency. This phenomenon is observed for a window of parameters viz. higher polyelectrolyte layer thickness, higher viscoelastic parameter, and lower Debye-Hückel parameter of the electrolyte. We also report that the relatively higher electrostatic potential stemming from the overlapping electrical double layers and the higher wall potential (greater than 25 mV), lead to non-intuitive variation in the conversion efficiency following the pronounced influence of the electroviscous effect. While targeting an increment in the conversion efficiency using viscoelastic fluid and grafted polyelectrolyte layer, we also examine the influence of slip at the walls of the channel and the spatial variation of electrical conductance between the stern layer conductance and that of the walls of the channel. However, the rheology modulated enhancement in the efficiency is found to be effective in case of variation in the stern layer conductance and interfacial slip at the walls of the channel.