Publications by authors named "Jyh-Ping Hsu"

159 Publications

Nanopore-based desalination subject to simultaneously applied pressure gradient and gating potential.

J Colloid Interface Sci 2021 Jul 15;594:737-744. Epub 2021 Mar 15.

Department of Chemical Engineering, National Taiwan University, Taiwan; Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan. Electronic address:

The performance of a dielectric membrane in desalting is assessed by considering a cylindrical nanopore, surface modified by a dielectric layer, subject to simultaneously applied pressure gradient and gating potential. The charged conditions of the nanopore can be tuned by modulating the applied gating potential so that it can be used for rejecting different types of salt. In general, the thinner the dielectric layer and/or the larger its dielectric constant the better the salt rejection performance. For example, if the thickness of the dielectric layer is 10 nm with a relative dielectric constant of 25, applying a pressure difference of 5 MPa and gating potential of 1 V yields 49% rejection. However, it declines to 9% if the relative dielectric constant is lowered to 5 with other parameters fixed, and 23% if that thickness is 50 nm with other parameters fixed. The results of numerical simulation based on various types of single salt and mixture salts with ions of different valences reveal that the type of ions which need be filtrated can be selected effectively through regulating the gating potential.
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http://dx.doi.org/10.1016/j.jcis.2021.03.042DOI Listing
July 2021

Electrokinetic behavior of a pH-regulated dielectric cylindrical nanopore.

J Colloid Interface Sci 2021 Apr 19;588:94-100. Epub 2020 Dec 19.

Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan; Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan. Electronic address:

A continuum model is adopted to describe the electrokinetic behavior of a pH-regulated cylindrical nanopore, the surface of which has charge-regulated carboxyl groups. We focus on the influences of the permittivity of the nanopore material, nanopore size, salt concentration, and solution pH on this behavior, and the underlying mechanisms. The influence of the nanopore permittivity becomes significant when a nanopore is shorter than ca. 50 nm. It is interesting to observe that if it is longer than ca. 100 nm, the nanopore conductance decreases with increasing permittivity. If it is sufficiently short, the conductance increases with increasing permittivity. If the nanopore length takes a medium level, the conductance is insensitive to the variation in the permittivity. For a short nanopore (~20 nm), the conductivity increases with increasing permittivity. However, if pH is sufficiently high, it becomes insensitive to permittivity. Although the larger the permittivity the greater the conductivity, in general, this effect becomes insignificant when the bulk salt concentration is sufficiently high, implying that the effect of membrane polarization is important only if the bulk salt concentration is sufficiently low.
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http://dx.doi.org/10.1016/j.jcis.2020.12.050DOI Listing
April 2021

Amorphous mesoporous matrix from metal-organic framework UiO-66 template with strong nucleophile substitution.

Chemosphere 2021 Apr 30;268:129155. Epub 2020 Nov 30.

Department of Chemical Engineering, National Taiwan University, Taipei, 10617, Taiwan. Electronic address:

The metal-organic framework (MOF) UiO-66 is made of zirconium clusters coordinated with 1,4-benzenedicarboxylate linkers that is stable in water and is highly tolerant to extremely acidic or basic environments. Conversely, the zirconium clusters are affine to nucleophiles so the crystalline structures of UiO-66 can be converted into amorphous derivatives. In a mineral acid solution both protons and coordinating nucleophile are present. This study for the first time revealed that it is the strong nucleophile instead of proton deteriorate the crystalline structures of UiO-66. Also, the so-produced amorphous mesoporous matrix, if not totally dissolved, can be applied as an efficient adsorbent. The noted adsorption capabilities of Cu(II) and nucleophiles by these amorphous mesoporous matrix did not correlate with the structural crystallinity or the internal surface area; conversely, the doped nucleophiles were noted to contribute to the adsorption tendencies towards Cu(II) and phosphate species via electrostatic interactions and hydrogen bonding, respectively. Conversion of sacrificing UiO-66 template to amorphous matrix can be applied as an effective way to fabricate specific adsorbent with resistance to extreme pH and strong nucleophile challenges.
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http://dx.doi.org/10.1016/j.chemosphere.2020.129155DOI Listing
April 2021

Electrokinetic behavior of bullet-shaped nanopores modified by functional groups: Influence of finite thickness of modified layer.

J Colloid Interface Sci 2021 Jan 14;582(Pt B):741-751. Epub 2020 Aug 14.

Department of Chemical Engineering, National Taiwan University, Taiwan; Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan. Electronic address:

We examined theoretically the electrokinetic behavior of a bullet-shaped nanopore modified by a functional layer, focusing on the influence of its thickness. The nanopore contains both fixed surface charge coming from the original bare surface, and space fixed charge from the modified layer. The results of numerical simulation reveal that the presence of this layer is crucial to the electrokinetic behavior of the nanopore. In particular, its softness is capable of influencing ionic profiles through electroosmotic flow (EOF). Unlike a conical nanopore where its surface normal vector is constant, that of the present bullet-shaped nanopore varies along the pore axis, thereby affecting the degree of EOF, which in turn, can make the ionic profile inside the modified layer more uniform. This is crucial to the applications of the nanopore, for example, in mimicking biological membranes and sensing metal ions.
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http://dx.doi.org/10.1016/j.jcis.2020.08.022DOI Listing
January 2021

Estimating the thermodynamic equilibrium constants of metal oxide particles through a general electrophoresis model.

J Colloid Interface Sci 2020 Aug 11;574:293-299. Epub 2020 Apr 11.

Department of Chemical Engineering, National Taiwan University, Taiwan; Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan. Electronic address:

We propose an efficient and convenient procedure for estimating the thermodynamic equilibrium constants of the surface dissociation/association reactions of metal oxide particles through electrophoresis measurements and a general electrophoresis model, which takes account of essentially all the relevant factors. These constants are usually estimated experimentally through a tedious potentiometric acid-base titration procedure. In addition, since several assumptions need be made in applying this procedure, the results obtained can be unreliable, especially when the difference between the equilibrium constant of the dissociation reaction and that of the association reaction is small. Another merit of the procedure proposed is that the site density of the surface dissociation/associations functional groups need not be known in advance so that it becomes much more convenient and efficient than previous procedures. The applicability of the present procedure is examined by applying it to the cases of SiO and TiO nanoparticles dispersed in an aqueous NaCl solution.
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http://dx.doi.org/10.1016/j.jcis.2020.04.044DOI Listing
August 2020

Ion current rectification behavior of a nanochannel having nonuniform cross-section.

Electrophoresis 2020 06 12;41(10-11):802-810. Epub 2020 Mar 12.

Department of Chemical Engineering, National Taiwan University, Taipei, Taiwan.

Due to its versatile applications in biotechnology, ion current rectification (ICR), which arises from the asymmetric nature of the ion transport in a nanochannel, has drawn much attention, recently. Here, the ICR behavior of a pH-regulated nanochannel comprising two series connected cylindrical nanochannels of different radii is examined theoretically, focusing on the influences of the radii ratio, the length ratio, the bulk concentration, and the solution pH. The results of numerical simulation reveal that the rectification factor exhibits a local maximum with respect to both the radii ratio and the length ratio. The values of the radii ratio and the length ratio at which the local maximum in the rectification factor occur depend upon the level of the bulk salt concentration. The rectification factor also shows a local maximum as the solution pH varies. Among the factors examined, the solution pH influences the ICR behavior of the nanochannel most significantly.
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http://dx.doi.org/10.1002/elps.201900396DOI Listing
June 2020

Pressure-driven energy conversion of conical nanochannels: Anomalous dependence of power generated and efficiency on pH.

J Colloid Interface Sci 2020 Mar 30;564:491-498. Epub 2019 Dec 30.

Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan; Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan.

Pressure-driven power generation is one of a simple, green, and promising energy sources. Owing to the overlapping of the electric double layer inside, nanochannel is capable of providing a platform for this power generation approach. Unfortunately, relevant studies, either experimental or theoretical, are very limited in the literature. Here, we present for the first time a comprehensively theoretical study on the pressure-driven energy conversion in a conical nanochannel having carboxyl functional groups, focusing on the influence of its tip size and the solution pH. An anomalous dependence of both the power generated and the efficiency on the latter are observed. Although the charge density on the nanochannel surface increases monotonically with increasing pH, both the power generated and the efficiency exhibit a local maximum as pH varies. This is because the streaming potential has a local maximum as pH varies. Power density (power generated/tip end cross sectional area) also shows a local maximum as the tip radius varies, and the radius at which the local maximum occurs decreases with increasing bulk salt concentration. In addition to explain successfully the behavior reported in the literature, our study also provides desirable and necessary information for designing relevant devices.
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http://dx.doi.org/10.1016/j.jcis.2019.12.103DOI Listing
March 2020

An ultrathin ionomer interphase for high efficiency lithium anode in carbonate based electrolyte.

Nat Commun 2019 12 20;10(1):5824. Epub 2019 Dec 20.

Department of Chemical Engineering, National Taiwan University, Taipei, 10617, Taiwan.

High coulombic efficiency and dendrite suppression in carbonate electrolytes remain challenges to the development of high-energy lithium ion batteries containing lithium metal anodes. Here we demonstrate an ultrathin (≤100 nm) lithium-ion ionomer membrane consisting of lithium-exchanged sulfonated polyether ether ketone embedded with polyhedral oligosilsesquioxane as a coating layer on copper or lithium for achieving efficient and stable lithium plating-stripping cycles in a carbonate-based electrolyte. Operando analyses and theoretical simulation reveal the remarkable ability of the ionomer coating to enable electric field homogenization over a considerably large lithium-plating surface. The membrane coating, serving as an artificial solid-electrolyte interphase filter in minimizing parasitic reactions at the electrolyte-electrode interface, enables dendrite-free lithium plating on copper with outstanding coulombic efficiencies at room and elevated (50 °C) temperatures. The membrane coated copper demonstrates itself as a promising current collector for manufacturing high-quality pre-plated lithium thin-film anode.
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http://dx.doi.org/10.1038/s41467-019-13783-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6925282PMC
December 2019

Tunable Current Rectification and Selectivity Demonstrated in Nanofluidic Diodes through Kinetic Functionalization.

J Phys Chem Lett 2020 Jan 13;11(1):60-66. Epub 2019 Dec 13.

Department of Chemical Engineering , National Taiwan University , Taipei 10617 , Taiwan.

The possibility of tuning the current rectification and selectivity in nanofluidic diodes is demonstrated both experimentally and theoretically through dynamically functionalizing a conical nanopore with poly-l-lysine. We identified an optimum functionalization time equivalent to optimum modification depth that assures the highest rectification degrees. Results showed that the functionalization time-dependent rectification behavior of nanofluidic diodes is dominated by the properties of current at positive voltages that in our electrode configuration indicate the "on" state of the diode and accumulation of ions in the nanopore. The functionalization time also tunes the ion selectivity of the diode. If the functionalization time is sufficiently short, an unusual depletion of counterions near the bipolar interface results in a cation-selective nanopore. However, a further increase in the duration of functionalization renders a nanopore that is an anion-selective nanopore. The dynamic functionalization presented in this Letter enables tuning ion selectivity of nanopores.
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http://dx.doi.org/10.1021/acs.jpclett.9b03344DOI Listing
January 2020

Unraveling the Anomalous Surface-Charge-Dependent Osmotic Power Using a Single Funnel-Shaped Nanochannel.

ACS Nano 2019 Nov 28;13(11):13374-13381. Epub 2019 Oct 28.

Department of Chemical Engineering , National Taiwan University of Science and Technology , Taipei 10607 , Taiwan.

Nanofluidic osmotic power, which converts a difference in salinity between brine and fresh water into electricity with nanoscale channels, has received more and more attention in recent years. It is long believed that to gain high-performance osmotic power, highly charged channel materials should be exploited so as to enhance the ion selectivity. In this paper, we report counterintuitive surface-charge-density-dependent osmotic power in a single funnel-shaped nanochannel (FSN), violating the previous viewpoint. For the highly charged nanochannel, the performance of osmotic power decreases with a further increase in its surface charge density. With increasing pH (surface charge density), the FSN enables a local maximum power density as high as ∼3.5 kW/m in a 500 mM/1 mM KCl gradient. This observation is strongly supported by our rigorous model where the equilibrium chemical reaction between functional carboxylate ion groups on the channel wall and protons is taken into account. The modeling reveals that for a highly charged nanochannel, a significant increase in the surface charge density amplifies the ion concentration polarization effect, thus weakening the effective salinity ratio across the channel and undermining the osmotic power generated.
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http://dx.doi.org/10.1021/acsnano.9b06774DOI Listing
November 2019

Regulating the ionic current rectification behavior of branched nanochannels by filling polyelectrolytes.

J Colloid Interface Sci 2019 Dec 18;557:683-690. Epub 2019 Sep 18.

Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan; Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan. Electronic address:

The overlapping of the electric double layer (EDL) in a nanochannel yields many interesting and significant electrokinetic phenomena such as ionic current rectification (ICR), which occurs only at a relatively low bulk salt concentration (∼1 mM) where the EDL thickness is comparable to the nanochannel size. In an attempt to raise this concentration to higher levels and the ICR performance improved appreciably, a branched nanochannel filled with polyelectrolytes (PEs) is proposed in this study. We show that these objectives can be achieved by choosing appropriate PE. For example, if the stem side of an anodic aluminun oxide nanochannel is filled with polystyrene sulfonate (PSS) an ICR ratio up to 850 can be obtained at 1 mM, which was not reported in previous studies. Taking account of the effect of electroosmotic flow, the underlying mechanisms of the ICR phenomena observed are discussed and the influences of the solution pH, the bulk salt concentration, and how the region(s) of a nanochannel is filled with PE examined. We show that the ICR behavior of a branched nanochannel can be modulated satisfactorily by filling highly charged PE and the solution pH.
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http://dx.doi.org/10.1016/j.jcis.2019.09.062DOI Listing
December 2019

Modulation of Charge Density and Charge Polarity of Nanopore Wall by Salt Gradient and Voltage.

ACS Nano 2019 09 31;13(9):9868-9879. Epub 2019 Jul 31.

Department of Chemical Engineering , National Taiwan University , Taipei 10617 , Taiwan.

Surface charge plays a very important role in biological processes including ionic and molecular transport across a cell membrane. Placement of charges and charge patterns on walls of polymer and solid-state nanopores allowed preparation of ion-selective systems as well as ionic diodes and transistors to be applied in building biological sensors and ionic circuits. In this article, we show that the surface charge of a 10 nm diameter silicon nitride nanopore placed in contact with a salt gradient is not a constant value, but rather it depends on applied voltage and magnitude of the salt gradient. We found that even when a nanopore was in contact with solutions of pH equivalent to the isoelectric point of the pore surface, the pore walls became charged with voltage-dependent charge density. Implications of the charge gating for detection of proteins passing through a nanopore were considered, as well. Experiments performed with single 30 nm long silicon nitride nanopores were described by continuum modeling, which took into account the surface reactions on the nanopore walls and local modulation of the solution pH in the pore and at the pore entrances. The results revealed that manipulation of surface charge can occur without changing pH of the background electrolyte, which is especially important for applications where maintaining pH at a constant and physiological level is necessary. The system presented also offers a possibility to modulate polarity and magnitude of surface charges in a two-electrode setup, which previously was accomplished in more complex multielectrode systems.
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http://dx.doi.org/10.1021/acsnano.9b01357DOI Listing
September 2019

Electrokinetic ion transport in an asymmetric double-gated nanochannel with a pH-tunable zwitterionic surface.

Phys Chem Chem Phys 2019 Apr 28;21(15):7773-7780. Epub 2019 Mar 28.

Department of Chemical Engineering, National Taiwan University, Taipei, 10617, Taiwan.

Bioinspired, artificial functional nanochannels for intelligent molecular and ionic transport control have versatile potential applications in nanofluidics, energy conversion, and controlled drug release. To simulate the gating and rectification functions of biological ion channels, we model the electrokinetic ion transport phenomenon in an asymmetric double-gated nanochannel having a pH-regulated, zwitterionic surface. Taking account of the effect of electroosmotic flow (EOF), the conductance of the nanochannel and its ion current rectification (ICR) behavior are investigated and the associated mechanisms interpreted. In particular, the influences of the solution pH, the bulk salt concentration, and the base opening radius and the surface curvature of the nanochannel on these behaviors are examined. We show that through adjusting the base opening radius and the surface curvature of a nanochannel, its ICR behavior can be tuned effectively. In addition to proposing underlying mechanisms for the phenomena observed, the results gathered in this study also provide necessary information for designing relevant devices.
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http://dx.doi.org/10.1039/c9cp00266aDOI Listing
April 2019

Protection against Neurodegeneration in the Hippocampus Using Sialic Acid- and 5-HT-Moduline-Conjugated Lipopolymer Nanoparticles.

ACS Biomater Sci Eng 2019 Mar 25;5(3):1311-1320. Epub 2019 Feb 25.

Department of Chemical Engineering, National Taiwan University, 1, Sec. 4, Roosevelt Road, Taipei, Taiwan 10617, ROC.

Significant involvement of oxidative stress in the brain can develop Alzheimer's disease (AD); however, a great number of clinical trials explains the limited success of antioxidant therapy in dealing with this neurodegenerative disease. Here, we established a lipopolymer system of poly(lactide--glycolide) (PLGA) nanoparticles (NPs) incorporated with phosphatidic acid (PA) and modified with sialic acid (SA) and 5-hydroxytryptamine-moduline (5HTM) to improve quercetin (QU) activity against oxidative stress induced by amyloid-β (Aβ) deposits. Morphological studies revealed a uniform exterior of QU-SA-5HTM-PA-PLGA NPs with a spherical structure and enhanced aggregation with inclusion of PA in the formulation. A better brain-targeted delivery of the lipopolymeric NPs was verified from the high blood-brain barrier (BBB) permeability of QU through strong interactions of surface SA and 5HTM with O-linked -acetylglucosamine and 5-HT1B receptors, respectively. Immunofluorescence staining images also supported QU-SA-5HTM-PA-PLGA NPs to traverse the microvessels of AD rat brain. Western blot analysis showed that QU-loaded PA-PLGA NPs suppressed caspase-3 expression. The ability of the nanocarriers to recognize Aβ fibrils was demonstrated from the reduced senile plaque formation and the attenuated acetylcholinesterase and malondialdehyde activity in the hippocampus. Hence, the medication of QU-SA-5HTM-PA-PLGA NPs can facilitate the BBB penetration and prevent Aβ accumulation, lipid peroxidation, and neuronal apoptosis for the AD management.
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http://dx.doi.org/10.1021/acsbiomaterials.8b01334DOI Listing
March 2019

Voltage-controlled ion transport and selectivity in a conical nanopore functionalized with pH-tunable polyelectrolyte brushes.

J Colloid Interface Sci 2019 Mar 13;537:496-504. Epub 2018 Nov 13.

Department of Mathematics, Tamkang University, New Taipei City 25137, Taiwan.

Chemically functionalized bioinspired nanopores are widely adopted to control the ionic transport for various purposes. A detailed understanding of the underlying mechanisms is not only desirable but also necessary for device design and experimental data interpretation. Here, the conductance and the ion selectivity of a conical nanopore surface modified by a polyelectrolyte (PE) layer are studied through adjusting the pH, the bulk salt concentration, and the level of the applied potential bias. Possible mechanisms are proposed and discussed in detail. We show that the conductance is sensitive to the variation in the solution pH. The ion selectivity of the nanopore is influenced significantly by both the solution pH and the level of the applied potential bias. In particular, a cation-selective nanopore might become anion-selective through raising the applied potential bias. The ion transport behavior can be tuned easily by adjusting the level of pH, salt concentration, and applied potential bias, thereby providing useful information for the design of nanopore-based sensing devices.
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http://dx.doi.org/10.1016/j.jcis.2018.11.046DOI Listing
March 2019

Ion transport in a pH-regulated conical nanopore filled with a power-law fluid.

J Colloid Interface Sci 2019 Mar 10;537:358-365. Epub 2018 Nov 10.

Department of Mathematics, Tamkang University, New Taipei City 25137, Taiwan. Electronic address:

Extending previous electrokinetic analyses based on a Newtonian fluid to power-law fluids, we investigate the behaviors of the ion current rectification (ICR) and the ion selectivity S of a conical nanopore having a pH-regulated surface. The bulk salt concentration C, the solution pH, and the power-law index n are examined in detail for their influences on these behaviors. We show that the ICR ratio for the case where pH is lower than the isoelectric point (IEP) of the nanopore surface is different both quantitatively and qualitatively from that for the case where pH > IEP. The relative magnitude of the ICR ratio as n varies depends largely on the level of C. In contrast, S (pH < IEP) is qualitatively similar to that for S(pH > IEP), where |S| decreases with increasing C and/or decreasing n. In addition, S is very sensitive to n, for example, a decrease of n from 1.0 (Newtonian fluid) to 0.9 (pseudoplastic fluid) can yield a 245% increase in S at C = 100 mM. Implying that the performance of ion separation can be improved by tuning the fluid viscosity. Mechanisms are proposed for explaining the observed behaviors in the ICR ratio.
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http://dx.doi.org/10.1016/j.jcis.2018.11.020DOI Listing
March 2019

Influence of salt valence on the rectification behavior of nanochannels.

J Colloid Interface Sci 2018 Dec 4;531:483-492. Epub 2018 Jul 4.

Department of Mathematics, Tamkang University, New Taipei City 25137, Taiwan. Electronic address:

Taking account of the influence of electroosmotic flow, the behavior of the ion current rectification of a charged conical nanochannel is studied theoretically focusing on the effect of ionic valence. A continuum-based model comprising coupled Poisson-Nernst-Planck (PNP) equations for the ionic mass transport and Navier-Stokes equations for the hydrodynamic field is adopted. We show that if the bulk salt concentration is fixed, the behavior of the current-voltage curve depends highly on the ionic valence, which arises from the difference in ionic strength and ion diffusivity. As the bulk salt concentration varies, the rectification factor shows a local maximum, and the bulk salt concentration at which it occurs depends upon the salt valence: the higher the valence the lower that concentration. However, regardless of the salt valence, the ionic strength at which that local maximum occurs is essentially the same, implying that the thickness of electric double layer is the key factor. Due to the difference in ionic diffusivity, the magnitude of the rectification factor depends upon the type of salt. For example, the rectification factor of KCl is larger than that of KNO. The qualitative behavior of the ion current rectification of a positively charged conical nanochannel is similar to that of a negatively charged nanochannel.
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http://dx.doi.org/10.1016/j.jcis.2018.07.012DOI Listing
December 2018

Separation of charge-regulated polyelectrolytes by pH-assisted diffusiophoresis.

Phys Chem Chem Phys 2017 Mar;19(13):9059-9063

Department of Mathematics, Tamkang University, New Taipei City, 25137, Taiwan.

The potential of separating colloidal particles through simultaneous application of a salt gradient and a pH gradient, or pH-assisted diffusiophoresis, is evaluated by considering the case of spherical polyelectrolytes (PEs) having different equilibrium dissociation constants in an aqueous solution with KCl as the background salt. The simulation results gathered reveal that the dependence of the particle velocity on pH is more sensitive than that in pH-assisted electrophoresis, where an electric field and a pH gradient are applied simultaneously. This implies that the separation efficiency of pH-assisted diffusiophoresis can be better than that of pH-assisted electrophoresis. In particular, two types of PE having different equilibrium dissociation constants can be separated effectively by applying the former by enhancing/reducing their diffusiophoretic velocities.
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http://dx.doi.org/10.1039/c7cp00030hDOI Listing
March 2017

Ion Current Rectification Behavior of Bioinspired Nanopores Having a pH-Tunable Zwitterionic Surface.

Anal Chem 2017 04 22;89(7):3952-3958. Epub 2017 Mar 22.

Department of Mathematics, Tamkang University , New Taipei City, Taiwan 25137.

The ion current rectification behavior of bioinspired nanopores is modeled by adopting a bullet-shaped nanopore having a pH-tunable zwitterionic surface, focusing on discussing the underlying mechanisms. We show that with its specific geometry, such nanopore is capable of exhibiting several interesting behaviors, including ion concentration polarization and ion current rectification. The influences of the nanopore shape, solution pH, and bulk salt concentration on the associated ion current rectification behavior are examined. We found that if pH exceeds the isoelectric point, the rectification factor has a local maximum as the curvature of the nanopore surface varies, and if it is lower than the isoelectric point, that factor increases (rectification effect decreases) monotonically with increasing surface curvature. In addition to capable of interpreting relevant electrokinetic phenomena, the results gathered also provide necessary information for a sophisticated design of relevant devices.
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http://dx.doi.org/10.1021/acs.analchem.6b04325DOI Listing
April 2017

Importance of polyelectrolyte modification for rectifying the ionic current in conically shaped nanochannels.

Phys Chem Chem Phys 2017 Feb;19(7):5351-5360

Department of Mathematics, Tamkang University, New Taipei City, 25137, Taiwan.

Due to their specific geometry, conical nanochannels/nanopores are capable of exhibiting several interesting electrokinetic phenomena including, for example, ion concentration polarization (ICP) and ion current rectification (ICR). Extending previous analyses, we consider two types of nanochannels: only the inner surface of a nanochannel is functionalized by a polyelectrolyte (PE) layer in a type I nanochannel, and both its outer and inner surfaces are functionalized in a type II nanochannel. The influences of the thickness of a double layer and that of the PE layer on ICR are examined through numerical simulation. We show that the ICP of a type I nanochannel is more significant than that of the corresponding type II nanochannel. The behavior of the rectification factor of the former as the bulk salt concentration varies also differs significantly from that of the latter. In particular, the rectification factor of a type I nanochannel at a low bulk salt concentration shows an inversion.
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http://dx.doi.org/10.1039/c6cp07693aDOI Listing
February 2017

Salt gradient driven ion transport in solid-state nanopores: the crucial role of reservoir geometry and size.

Phys Chem Chem Phys 2016 Nov 25;18(43):30160-30165. Epub 2016 Oct 25.

Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan.

Modern applications of nanotechnology such as salinity gradient power and ionic diodes usually involve the transport of ionic species in a system comprising a nanopore connecting two large reservoirs. The charge properties on the nanopore surface plays a key role, and they need to be estimated by fitting a mathematical model for the system to measurable quantities such as ionic current or conductance. This model can also be used to simulate the system behavior under various conditions. However, the large difference between the linear size of a nanopore and that of a reservoir makes relevant analyses difficult. Considering numerical efforts, the impact of the computational domain for the reservoir geometry and size on the system behavior is almost always overlooked in previous studies, where the computational domain for a reservoir is often assumed to have a relatively small size. Taking salinity gradient ionic current as an example, we show for the first time that the performance of a reservoir-nanopore-reservoir system is influenced appreciably by the computational domain for the reservoir geometry and size, especially when a voltage bias is not applied. Using the reported experimental data for the osmotic current in a single boron nitride nanopore, we show that its surface charge density can be estimated realistically by choosing an appropriate computational domain for reservoir geometry and size. Numerical simulation also reveals that choosing appropriate reservoir geometry and size is necessary; otherwise, the results obtained might be unreliable, or even misleading. To avoid this, we suggest that for the nanopore with the pore length smaller than 1000 nm, the size of the computational domain of a reservoir, (length × radius), with equal length and radius, should exceed 800 × 800 nm.
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http://dx.doi.org/10.1039/c6cp06459kDOI Listing
November 2016

Diffusiophoresis of a pH-regulated toroidal polyelectrolyte in a solution containing multiple ionic species.

J Colloid Interface Sci 2017 Jan 1;486:351-358. Epub 2016 Oct 1.

Institute of Polymer Science and Engineering, National Taiwan University, Taipei 10617, Taiwan; Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan. Electronic address:

Extending previous analysis for the diffusiophoresis of a toroidal PE having a fixed charge density, we consider the case where it is pH-regulated and the liquid phase contains multiple ionic species so that the underlying assumptions are more realistic. The diffusiophoretic behaviors of the toroidal PE considered under various conditions are examined by varying its functional group density, size, and softness, and the solution pH and bulk salt concentration. We show that the behavior of a toroidal PE can be different both quantitatively and qualitatively from the corresponding spherical PE. The effective charge of the present PE is also different both quantitatively and qualitatively from the corresponding PE having fixed charge density. In particular, both the magnitude and the direction of diffusiophoretic velocity depend highly on the conditions assumed, implying that an efficient separation process can be designed. A three-dimensional velocity-pH-Debye length plot is constructed for that purpose.
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http://dx.doi.org/10.1016/j.jcis.2016.09.077DOI Listing
January 2017

Highly Charged Particles Cause a Larger Current Blockage in Micropores Compared to Neutral Particles.

ACS Nano 2016 09 22;10(9):8413-22. Epub 2016 Aug 22.

Department of Chemical Engineering, National Taiwan University , Taipei 10617, Taiwan.

Single pores in the resistive-pulse technique are used as an analytics tool to detect, size, and characterize physical as well as chemical properties of individual objects such as molecules and particles. Each object passing through a pore causes a transient change of the transmembrane current called a resistive pulse. In high salt concentrations when the pore diameter is significantly larger than the screening Debye length, it is assumed that the particle size and surface charge can be determined independently from the same experiment. In this article we challenge this assumption and show that highly charged hard spheres can cause a significant increase of the resistive-pulse amplitude compared to neutral particles of a similar diameter. As a result, resistive pulses overestimate the size of charged particles by even 20%. The observation is explained by the effect of concentration polarization created across particles in a pore, revealed by numerical modeling of ionic concentrations, ion current, and local electric fields. It is notable that in resistive-pulse experiments with cylindrical pores, concentration polarization was previously shown to influence ionic concentrations only at pore entrances; consequently, additional and transient modulation of resistive pulses was observed when a particle entered or left the pore. Here we postulate that concentration polarization can occur across transported particles at any particle position along the pore axis and affect the magnitude of the entire resistive pulse. Consequently, the recorded resistive pulses of highly charged particles reflect not only the particles' volume but also the size of the depletion zone created in front of the moving particle. Moreover, the modeling identified that the effective surface charge density of particles depended not only on the density of functional groups on the particle but also on the capacitance of the Stern layer. The findings are of crucial importance for sizing particles and characterizing their surface charge properties.
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http://dx.doi.org/10.1021/acsnano.6b03280DOI Listing
September 2016

Diffusiophoresis of a charged toroidal polyelectrolyte.

J Colloid Interface Sci 2016 Jun 3;471:14-19. Epub 2016 Mar 3.

Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan. Electronic address:

Considering recent application of concentration driven motion of charged nanoparticles in sensing technology, we model the diffusiophoresis of an isolated toroidal polyelectrolyte (PE) for the first time. Choosing an aqueous KCl solution for illustration, its behavior under various conditions is simulated by varying the double layer thickness, the size of toroid, and its softness and fixed charge density. We show that the behavior of the present PE can be different both quantitatively and qualitatively from that of the corresponding spherical PE. This arises from the competition of the hydrodynamic force and the electric force acting on a PE. The geometry and the nature of a PE can also influence appreciably its behavior, yielding complicated and interesting results.
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http://dx.doi.org/10.1016/j.jcis.2016.03.003DOI Listing
June 2016

Salinity gradient power: influences of temperature and nanopore size.

Nanoscale 2016 Jan;8(4):2350-7

Department of Chemical Engineering, National Taiwan University, Taipei, 10617, Taiwan.

Salinity gradient power is a promising, challenging, and readily available renewable energy. Among various methods for harvesting this clean energy, nanofluidic reverse electrodialysis (NRED) is of great potential. Since ionic transport depends highly on the temperature, so is the efficiency of the associated power generated. Here, we conduct a theoretical analysis on the influences of temperature and nanopore size on NRED, focusing on the temperature and nanopore size. The results gathered reveal that the maximum power increases with increasing temperature, but the conversion efficiency depends weakly on temperature. In general, the smaller the nanopore radius or the longer the nanopore, the better the ion selectivity. These results provide desirable and necessary information for improving the performance of NRED as well as designing relevant units in renewable energy plants.
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http://dx.doi.org/10.1039/c5nr07563gDOI Listing
January 2016

Diffusiophoresis of a charged, rigid sphere in a Carreau fluid.

J Colloid Interface Sci 2016 Mar 22;465:54-7. Epub 2015 Nov 22.

Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan. Electronic address:

Since non-Newtonian fluid behavior are not uncommon in practice, especially in modern applications of colloid and interface science, assessment of how serious is the deviation of the existing results for Newtonian fluids due to fluid nature is highly desirable and necessary. Here, we extend previous analyses for the diffusiophoresis of a particle in a Newtonian fluid to that in a non-Newtonian fluid choosing Carreau fluids as an example. Results gathered reveal that due to the shear-thinning property of the fluid considered, the difference between the particle mobility in a Carreau fluid and that in the corresponding Newtonian fluid can be on the order of 100%. In addition, this difference has a local minimum as the thickness of double layer varies.
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http://dx.doi.org/10.1016/j.jcis.2015.11.049DOI Listing
March 2016

Ionic Current Rectification in a pH-Tunable Polyelectrolyte Brushes Functionalized Conical Nanopore: Effect of Salt Gradient.

Anal Chem 2016 Jan 23;88(2):1176-87. Epub 2015 Dec 23.

Department of Mathematics, Tamkang University , Tamsui, New Taipei City, Taiwan 25137.

The behavior of ionic current rectification (ICR) in a conical nanopore with its surface modified by pH-tunable polyelectrolyte (PE) brushes connecting two large reservoirs subject to an applied electric field and a salt gradient is investigated. Parameters including the solution pH, types of ionic species, strength of applied salt gradient, and applied potential bias are examined for their influences on the ionic current and rectification factor, and the mechanisms involved are investigated comprehensively. The ICR behavior depends highly on the charged conditions of the PE layer, the level of pH, the geometry of nanopore, and the thickness of the double layer. In particular, the distribution of ionic species and the local electric field near the nanopore openings play a key role, yielding profound and interesting results that are informative to device design as well as experimental data interpretation.
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http://dx.doi.org/10.1021/acs.analchem.5b03074DOI Listing
January 2016

Effect of eccentricity on the electroosmotic flow in an elliptic channel.

J Colloid Interface Sci 2015 Dec 21;460:81-6. Epub 2015 Aug 21.

Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan.

The electroosmotic flow in an elliptic channel having constant surface potential (CSP) or charge density (CSCD) is considered at low potential and arbitrary double layer thickness. Analytical expressions for the flow velocity and the corresponding asymptotic results for thick double layers that are readily applicable to experimentalists are recovered. For the range of salt concentration usually encountered in practice, the mean flow velocity for the case of CSP differs both quantitatively and qualitatively from that for the case of CSCD. Using an equivalent circular channel to simulate an elliptic one is inappropriate, in general, neither is assuming electroneutrality on the channel axis even when double layer is ca. 1/3 of the equivalent channel radius.
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http://dx.doi.org/10.1016/j.jcis.2015.08.038DOI Listing
December 2015

Diffusiophoresis of polyelectrolytes: Effects of temperature, pH, type of ionic species and bulk concentration.

J Colloid Interface Sci 2015 Dec 6;459:167-174. Epub 2015 Aug 6.

Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan. Electronic address:

Extending previous analyses on rigid particles to non-rigid ones, we model the diffusiophoresis of a pH-regulated polyelectrolyte (PE) in a solution containing multiple ionic species. For the first time, the effects of temperature, pH, type of ionic species and bulk concentration are taken into account, and therefore, the conditions considered are more comprehensive and closer to reality than those of the available results in the literature. Numerical simulation is conducted to examine the diffusiophoretic behaviors of a PE under various conditions, and empirical relationships are developed for the dependence of its mobility on the factors mentioned above. We show that temperature and pH influence appreciably the charged conditions of a PE, the ionic diffusivities, and the fluid viscosity, yielding complicated and interesting behaviors that are informative to device design.
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http://dx.doi.org/10.1016/j.jcis.2015.08.014DOI Listing
December 2015

Influence of electroosmotic flow on the ionic current rectification in a pH-regulated, conical nanopore.

Nanoscale 2015 Sep 4;7(33):14023-31. Epub 2015 Aug 4.

Institute of Polymer Science and Engineering, National Taiwan University, Taipei, Taiwan 10617.

The ionic current rectification (ICR) is studied theoretically by considering a pH-regulated, conical nanopore. In particular, the effect of electroosmotic flow (EOF), which was often neglected in previous studies, is investigated by solving a set of coupled Poisson, Nernst-Planck, and Navier-Stokes equations. The behaviors of ICR under various conditions are examined by varying solution pH, bulk ionic concentration, and applied electric potential bias. We show that the EOF effect is significant when the bulk ionic concentration is medium high, the pH is far away from the iso-electric point, and the electric potential bias is high. The percentage deviation in the current rectification ratio arising from neglecting the EOF effect can be on the order of 100%. In addition, the behavior of the current rectification ratio at a high pH taking account of EOF is different both qualitatively and quantitatively from that without taking account of EOF.
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http://dx.doi.org/10.1039/c5nr03433gDOI Listing
September 2015