arXiv subjects

Ramadan Abu-Rjal

Publications and source records attributed to Ramadan Abu-Rjal.

6 recordsLinked to original sources

arXiv2026

The transmembrane potential across a charged nanochannel subjected to asymmetric electrolytes

The transmembrane voltage, $V$, which is the potential drop required to nullify the electrical current ($i=0$), is a key characteristic of water desalination and energy harvesting systems that utilize macroscopically large nanoporous membranes, as well as for physiological ion channels subjected to asymmetric salt concentrations. To date, existing analytical expressions for $V_{i=0}$ have been limited to simple scenarios or under simplifying assumptions. In this work, we derive two expressions for $V_{i=0}$. First, we consider the much simpler scenario of two species. Then, we can consider an electrolyte comprised of an arbitrary number of species. The difference in the models is that the latter solution utilizes an ad-hoc assumption of a linear concentration profile, while the former solution does not require such an ad-hoc assumption. We analyze both models and show how to reduce them to several known models. We also verify both models with numerical simulations of the one-dimensional Poisson-Nernst-Planck equations. We show how the interplay between diffusion coefficients and ionic valencies significantly varies the system response and why it is essential to account for all system parameters. Ultimately, this model can be used to improve experimental interpretation of ion transport measurements

cond-mat.mes-hall↗

arXiv2024

Electrical Response of Nanofluidic Systems Subjected to Viscosity Gradients

It is expected that the introduction of a viscosity gradient across a nanofluidic system will drastically vary its current-voltage response, $i-V$. However, to date, there is no self-consistent theoretical model that can be used to fully characterize such a system. This work provides an internally self-consistent model that details all the key characteristics of ion transport through a nanofluidic system for an arbitrary viscosity field. In particular, this work addresses three separate issues. First, we provide a new expression for the Ohmic conductance, $g_{Ohmic} = i/V$. Second, several previous theoretical studies have suggested that the introduction of a viscosity gradient can result in the shift of the $i-V$ such that it does not cross the origin. This work unequivocally shows that the $i-V$ is expected to always cross the origin. Third, we demonstrate that even without electroosmotic flows, the introduction of a viscosity gradient results in current rectification. Importantly, all theoretical results are verified by non-approximated numerical simulations. This work provides the appropriate framework to analyze and interpret experimental and numerical simulations of nanofluidic systems subject to a viscosity gradient.

cond-mat.mes-hall↗

arXiv2024

Bipolar nanochannels: The effects of an electro-osmotic instability. Part I: Steady-state response

The steady-state current-voltage response of ion-selective systems varies as the number of ion-selective components is varied. For the highly investigated unipolar system, including only one ion-selective component, it has been shown that above a supercritical voltage, an electroosmotic instability is triggered, leading to over-limiting currents. In contrast, the effects of this instability on the current-voltage response of the second most common system of a bipolar system, including two oppositely charged permselective regions, have yet to be reported. Using simulations, we investigate the steady-state electrical response of bipolar systems as we vary the ratio of the charge within the two oppositely charged regions. The responses are divided into those with an internal symmetry related to the surface charge and those without. In contrast to the unipolar systems, bipolar systems with the internal symmetry do not exhibit overlimiting currents, and their steady-state response is identical to the convectionless steady-state response. In contrast, the systems without the internal symmetry exhibit much more complicated behavior. For positive voltages, they have overlimiting currents, while for negative voltages, they do not have over-limiting currents. Our findings contribute to a more profound understanding of the behavior of the current-voltage response in bipolar systems.

cond-mat.mes-hall↗

arXiv2024

Bipolar nanochannels: The effects of an electro-osmotic instability. Part II: Time-transient response

The most common method to characterize the electrical response of a nanofluidic system is through its steady-state current-voltage response. In Part I, we demonstrated that this current-voltage response depends on the geometry, the layout of the surface charge, and the effects of advection. We demonstrated that each configuration has a unique steady-state signature. Here, we will elucidate the behavior of the time-transient response. Similar to the steady-state response, we will show that each configuration has its own unique time-transient signature when subjected to electroosmotic instability. We show that bipolar systems behave differently than unipolar systems. In unipolar systems, the instability appears only at one end of the system. In contrast, in bipolar systems the instability will either appear on both sides of the nanochannel or not at all. If it does appear on both sides, the instability will eventually vanish on one or both sides of the system. In Part I, these phenomena were explained using steady-state considerations of the behavior of the fluxes. Here, we will examine the time-transient behavior to reveal the governing principles that are, on the one hand, not so different from unipolar systems and, on the other hand, remarkably different.

cond-mat.mes-hall↗

arXiv2020

Periodic Concentration-Polarization-Based Formation of a Biomolecule Preconcentrate for Enhanced Biosensing

Ionic concentration-polarization (CP)-based biomolecule preconcentration is an established method for enhancing the detection sensitivity of target biomolecules. However, the formed preconcentrated biomolecule plug rapidly sweeps over the surface-immobilized antibodies, resulting in a short-term overlap between the capture agent and the analyte, and subsequently suboptimal binding. To overcome this, we designed a setup allowing for periodic formation of a preconcentrated biomolecule plug by activating the CP for predetermined on/off intervals. This work demonstrated the feasibility of the cyclic CP actuation and optimized the sweeping conditions required to obtain maximum retention time of a preconcentrated plug over a desired sensing region and enhanced detection sensitivity. The ability of this method to efficiently preconcentrate different analytes and to successfully increase immunoassay sensitivity, underscore its potential in immunoassays serving the clinical and food testing industries.

physics.app-ph↗

arXiv2019

Revisiting, resolving and unifying the nanochannel-microchannel electrical resistance paradigm

Until recently, the accepted paradigm was that the Ohmic electrical response of nanochannel-microchannel systems is determined solely by the nanochannel while the effects of the adjacent microchannels are negligible. Two, almost identical, models were suggested to rationalize experimental observations that appeared to confirm the paradigm. However, recent works have challenged this paradigm and shown that the microchannels contribute in a non-negligible manner, and thus these two models are inadequate in describing realistic nanochannel-microchannel systems. Two newer nanochannel-microchannel models were suggested to replace the nanochannel-dominant models. These models were limited to either very low or very high concentrations. Here, we review these four leading models. The most popular is shown to be incorrect, while the remaining models are unified under a newly derived solution which shows remarkable correspondence to simulations and experiments. The unifying model can be used to improve the design of any nanofluidic based systems as the physics are more transparent, and the need for complicated time-consuming preliminary simulations and experiments has been eliminated.

physics.app-ph↗