Highly Efficient Conversion of Salinity Difference to Electricity in Nanofluidic Channels Boosted by Variable Thickness Polyelectrolyte Coating.

The inherent limits of the current produced by imposing salinity gradients along a nanofluidic channel having "hard" boundary walls heavily constrain the resulting energy harvesting efficacy, acting as major hindrances against the practicability of harnessing high power density from the mixing of water having different salinities. In this work, the infusion of variable-thickness polyelectrolyte layer of a conical shape is projected to augment salinity gradient power generation in nanochannels. Such a progressive thickening of a charged interfacial layer on account of axially declining ion concentration facilitates the shedding of enhanced numbers of mobile ions, bearing a net charge of equal and opposite to the surface-bound ions, into the mainstream current flow.

Improved ionic current rectification utilizing cylindrical nanochannels coated with polyelectrolyte layers of non-uniform thickness.

Conical nanochannels employed to create ionic current rectification (ICR) in nanofluidic devices are prone to clogging due to the contraction at one end. As an alternative approach for creating ICR, a cylindrical nanochannel covered with a polyelectrolyte layer (PEL) of variable thickness is proposed in the present study. The efficacy of the proposed design is studied by numerically solving the governing equations including the Poisson, Nernst-Planck, and Stokes-Brinkman equations.

Slip-Coupled Electroosmosis and Electrophoresis Dictate DNA Translocation Speed in Solid-State Nanopores.

Controlling the DNA translocation speed is critical in nanopore sequencing, but remains rather challenging in practice, as attributable to a complex coupling between nanoscale fluidics and electrically mediated migration of DNA in a dynamically evolving manner. One important factor influencing the translocation speed is the DNA-liquid slippage stemming from the hydrophobic nature of the oligonucleotide, an aspect that has been widely ignored in the reported literature. In an effort to circumvent this conceptual deficit, here we first develop an analytical model to bring out the slip-mediated coupling between the electroosmosis and DNA-electrophoresis in a solid-state nanopore at low surface charge limits, ignoring the end effects.

Creating lifting force in liquids via thermal gradients.

In this paper, we explore a concept and present the first experimental evidence to show that it is possible to form a stable liquid film and create lifting force at the interface via thermal gradient to minimize interfacial rubbing of surfaces and the associated wear. The approach is based on manipulating the flow behavior via thermocapillary, which describes how a liquid can be made to flow from warm to cold regions purely by inducing a thermal gradient. We show that liquid bridges between two parallel plates can be manipulated and stabilized under a combined effect of the thermocapillary flow and the Couette flow, which describes the motion of a viscous fluid between two parallel plates in a relative sliding motion.

Tripling the reverse electrodialysis power generation in conical nanochannels utilizing soft surfaces.

We theoretically investigate the feasibility of enhancing the reverse electrodialysis power generation in nanochannels by covering the surface with a polyelectrolyte layer (PEL). Along these lines, two conical nanochannels are considered that differ in the extent of the covering. Each nanochannel connects two large reservoirs filled with KCl electrolytes of different ionic concentrations.

Covering the conical nanochannels with dense polyelectrolyte layers significantly improves the ionic current rectification.

Because of their asymmetry, conical nanochannels/nanopores exhibit various attractive electrokinetic features, including ion selectivity, ionic concentration polarization, and ionic current rectification. The polyelectrolyte layer (PEL)-covered (soft) conical nanochannels have recently attracted significant attention because of their unique rectification characteristics. In the modeling of soft nanochannels, it is usually assumed that the properties of the PEL and the electrolyte are the same, an assumption that is not true, especially for dense PELs.

Electrophoresis of spherical soft particles in electrolyte solutions: A review.

Theories on the electrophoresis of spherical soft particles suspended in an electrolyte solution are thoroughly reviewed. The review predominantly covers studies on the electrophoresis in dilute and concentrated suspensions as well as bounded media, carried out mainly during the past two decades. Moreover, studies on the electrostatics of soft particles are also surveyed.

Significant alteration in DNA electrophoretic translocation velocity through soft nanopores by ion partitioning.

The application of nanopores for DNA sequencing faces some challenges. The main challenge is controlling the electrophoretic translocation velocity of DNA and one remedy is covering the inner wall of the nanopore with a polyelectrolyte layer (PEL). In this study, a more realistic analytical model is presented for DNA translocation in PEL-grafted nanopores that improves the available models by considering different values for permittivity and viscosity inside and outside the PEL, taking the wall charge effects into account, and relaxing the assumption of a linear hydrodynamic drag profile inside the PEL.

Effect of ion partitioning on electrostatics of soft particles with volumetrically charged inner core coated with pH-regulated polyelectrolyte layer.

The effect of ion partitioning on the electrostatics of a soft particle with a volumetrically charged core and a pH-dependent polyelectrolyte layer (PEL) is numerically investigated. It is observed that, whenever the ion partitioning is noticeable, the soft layer can be fully charged in a broader range of pH. Besides, a higher number density of the PEL functional groups and a lower charge density of the core result in a sharper dependence of the electric potential on the electrolyte pH.

Reduction of production rate in Y-shaped microreactors in the presence of viscoelasticity.

The viscoelasticity effects on the reaction-diffusion rates in a Y-shaped microreactor are studied utilizing the PTT rheological model. The flow is assumed to be fully developed and considered to be created under a combined action of electroosmotic and pressure forces. In general, finite-volume-based numerical simulations are conducted to handle the problem; however, analytical solutions based on the depthwise averaging approach are also obtained for the case for which there is no reaction between the inlet components.

Diffusioosmotic flow in rectangular microchannels.

The diffusioosmosis of an electrolyte solution inside a uniformly charged rectangular channel at steady locally developed conditions is the subject of this study. Utilizing a finite element based numerical procedure, we try to estimate the errors incurred by modeling the actual rectangular geometry of typical microchannels as a slit. We demonstrate that the flow pattern and direction are generally dependent upon the width-to-height ratio of the channel.

Drastic alteration of diffusioosmosis due to steric effects.

The inclusion of the ionic size (steric) effects into the steady and locally developed diffusioosmotic flow inside a uniformly charged slit microchannel through a theoretical analysis is the subject of this study. The results indicate essential quantitative and qualitative distinctions between the steric effects on classical electrokinetic phenomena like electroosmosis and on diffusioosmosis. For example, although the steric effect on electroosmotic flow is always unfavorable, it may have a positive influence on diffusioosmosis and even double the mean velocity under certain conditions.

Electrokinetic mixing at high zeta potentials: ionic size effects on cross stream diffusion.

The electrokinetic phenomena at high zeta potentials may show several unique features which are not normally observed. One of these features is the ionic size (steric) effect associated with the solutions of high ionic concentration. In the present work, attention is given to the influences of finite ionic size on the cross stream diffusion process in an electrokinetically actuated Y-shaped micromixer.

Numerical modeling of surface reaction kinetics in electrokinetically actuated microfluidic devices.

We outline a comprehensive numerical procedure for modeling of species transport and surface reaction kinetics in electrokinetically actuated microfluidic devices of rectangular cross section. Our results confirm the findings of previous simplified approaches that a concentration wave is created for sufficiently long microreactors. An analytical solution, developed for the wave propagation speed, shows that, when normalizing with the fluid mean velocity, it becomes a function of three parameters comprising the channel aspect ratio, the relative adsorption capacity, and the kinetic equilibrium constant.