Showing papers by "Jyh-Ping Hsu published in 2013"
01 Oct 2013
TL;DR: It is concluded that the zeta potential measurements for the tested NPs are reliable only if their concentration exceeds a certain level, and this also applies to other metal oxides or hydroxides, the surface of which reacts appreciably with dissolved CO2.
Abstract: In an attempt to estimate the zeta potential of various metal oxide nanoparticles (NPs) dispersed in water, it is interesting to observe that both the magnitude and the sign of this property depend highly upon their concentration. For example, in the case of naked TiO2 at pH 6, the zeta potential increased from -6.7 to 8.2 mV as the particle concentration varied from 0.5 to 5 mg L(-1). As a result, the isoelectric points of naked TiO2, Fe3O4, Fe(OH)3, and Al2O3-coated TiO2 could deviate ca. one, one, two, and three pH units, respectively, depending upon the particle concentration. We showed that these behaviors arise mainly from that the dissolved ambient CO2 reacts with the particle surface functional groups to form M-OCO2(-), which neutralizes or even overcompensates the particle surface charge. The surface density of M-OCO2(-), [M-OCO2(-)](s) depends upon the particle concentration; if it is sufficiently high, [M-OCO2(-)](s) becomes negligible, so is its influence on the zeta potential. We concluded that the zeta potential measurements for the tested NPs are reliable only if their concentration exceeds a certain level. This also applies to other metal oxides or hydroxides, the surface of which reacts appreciably with dissolved CO2. The results gathered are of practical significance in estimating the surface properties of unknown and/or newly synthesized NPs since conventional measurements are usually made at dilute particle concentrations.
115 citations
TL;DR: Capillary osmotic flow is from the high salt concentration reservoir to the low salt concentration one, and its magnitude has a maximum as the reservoir salt concentrations vary, thereby being capable of improving the performance of electrophoresis-based biosensors.
Abstract: Experimental evidence revealed that the performance of nanopore-based biosensing devices can be improved by applying a salt concentration gradient. To provide a theoretical explanation for this observation and explore the mechanisms involved, we model the capillary osmosis (or diffusioosmosis) in a charged solid-state nanopore connecting two large reservoirs. The effects of nanopore geometry and the reservoir salt concentrations are examined. We show that the capillary osmotic flow is from the high salt concentration reservoir to the low salt concentration one, and its magnitude has a maximum as the reservoir salt concentrations vary. In general, the shorter the nanopore and/or the smaller its radius, the faster the osmotic flow. This flow enhances the current recognition, and the ion concentration polarization across nanopore openings raises the entity capture rate, thereby being capable of improving the performance of electrophoresis-based biosensors. The results gathered provide necessary information for designing nanopore-based biosensor devices.
20 citations
TL;DR: In this paper, the authors model the flow of an electrolyte solution containing multiple ionic species in a charge-regulated cylindrical nanochannel and show that if the density of the functional groups on the channel surface increases (decreases), it approaches a constant potential (charge density) surface; if that density is low, the channel behavior is similar to that of a constant charge density channel at high salt concentration and large channel radius.
Abstract: Considering the wide applications of the electrokinetic flow regulated by pH, we model the flow of an electrolyte solution containing multiple ionic species in a charge-regulated cylindrical nanochannel. This extends previous analyses, where only two kinds of ionic species are usually considered, and a charged surface assumed to maintain at either constant potential or constant charge density, to a case closer to reality. Adopting a fused silica channel containing an aqueous NaCl background salt solution with its pH adjusted by HCl and NaOH as an example, we show that if the density of the functional groups on the channel surface increases (decreases), it approaches a constant potential (charge density) surface; if that density is low, the channel behavior is similar to that of a constant charge density channel at high salt concentration and large channel radius. Several interesting results are observed, for example, the volumetric flow rate of a small channel has a local maximum as salt concentration varies, which is not seen in a constant potential or charge density channel.
15 citations
TL;DR: The maximum mobility occurs at the center of a throat, and the higher the charge density of the throat the larger the ratio of maximum mobility/mobility far away from the throat.
Abstract: The influence of boundary shape on electrophoresis is modeled by considering a soft spherical particle comprising a positively charged rigid core and an uncharged membrane layer on the axis of a necked cylindrical pore with its throat positively charged. The presence of the throat makes the associated flow and electric fields nonuniform, yielding several interesting behaviors. In general, the reduction in the cross-section area of the pore intensifies the local electric field and, therefore, accelerates the particle. It also makes the ionic distribution nonuniform, and the electric field induced accelerates the particle. The maximum mobility occurs at the center of a throat, and the higher the charge density of the throat the larger the ratio of maximum mobility/mobility far away from the throat. This result is informative for the design of separation devices having variable cross sectional area.
14 citations
TL;DR: Adopting a Brinkman fluid model, the electrophoresis of a charged‐regulated, bi‐functional particle containing both acidic and basic functional groups in a gel solution is analyzed, yielding interesting and significant results.
Abstract: Adopting a Brinkman fluid model, we analyzed the electrophoresis of a charged-regulated, bi-functional particle containing both acidic and basic functional groups in a gel solution Both the long-range hydrodynamic effect arising from the liquid drag and the short-range steric effect from particle-polymer interaction are considered The type of particle considered is capable of simulating both biocolloids such as microorganisms and cells, and particles with adsorbed polyelectrolyte or membrane layer Our model describes successfully the experimental data in the literature The presence of gel has the effect of reducing the particle mobility and alleviating double-layer polarization so that the particle behavior is less complicated than that in the case where gel is absent On the other hand, both the quantitative and qualitative behaviors of a particle depend highly on solution pH and background salt concentration, yielding interesting and significant results These results provide valuable information for both experimental data interpretation and electrophoresis devices design
14 citations
TL;DR: The influence of the shape of a polyelectrolyte (PE) on its electrophoretic behavior in a nanofluidic channel is investigated by considering the translocation of a deformable ellipsoidal PE along the axis of a cylindrical nanochannel.
Abstract: The influence of the shape of a polyelectrolyte (PE) on its electrophoretic behavior in a nanofluidic channel is investigated by considering the translocation of a deformable ellipsoidal PE along the axis of a cylindrical nanochannel. A continuum model comprising a Poisson equation for the electric potential, Nernst–Planck equations for the ionic concentrations, and modified Stokes equations for the flow field is adopted. The effects of the PE shape, boundary, bulk ionic concentration, counterion condensation, electroosmotic retardation flow, and electroosmotic flow (EOF) on the PE mobility are discussed. Several interesting behaviors are observed. For example, if the nanochannel is uncharged and the double layer is thick, then the PE mobility increases (decreases) with increasing double-layer thickness for a smaller (larger) boundary, which has not been reported previously. If the nanochannel is negatively charged and the double layer is thick, then a negatively charged PE moves in the direction of the a...
11 citations
TL;DR: In this article, the diffusiophoresis of a particle along the axis of a charged, necked nanopore and the mechanisms involved were studied theoretically for improving the performance of single-molecule nanopore-based biosensors.
Abstract: In an attempt to improve the performance of single-molecule nanopore based biosensors, we study theoretically the diffusiophoresis of a particle along the axis of a charged, necked nanopore, and the mechanisms involved. Numerical simulation is conducted by varying the geometry of the nanopore and its charged status, the particle position, and the background salt concentration to examine the particle behavior under various conditions and to gather necessary information for future device design. We show that the strength of the local concentration gradient, the charge density of the nanopore, and the presence of the nanopore wall yield complicated and interesting diffusiophoretic behaviors, which are informative to potential applications.
9 citations
TL;DR: The influence of temperature on the electrophoretic behavior of a charge-regulated zwitterionic particle is investigated by considering a spherical SiO(2) particle in a relatively dilute aqueous NaCl solution of concentration C(NaCl) with its pH adjusted by NaOH and HCl as an example.
Abstract: The influence of temperature on the electrophoretic behavior of a charge-regulated zwitterionic particle is investigated by considering a spherical SiO2 particle in a relatively dilute aqueous NaCl...
7 citations
TL;DR: A thorough theoretical analysis is performed for the first time on the diffusiophoresis of a polyelectrolyte (PE) in the presence of two representative types of boundaries, finding that due to the effects of double-layer polarization, counterion condensation, polarization of condensed counterions, and diffusion of co-ions across a PE, its diffus iophoretic behavior can be influenced both quantitatively and qualitatively by a boundary.
Abstract: Considering the potential applications of diffusiophoresis conducted in nanodevices, a thorough theoretical analysis is performed for the first time on the diffusiophoresis of a polyelectrolyte (PE) in the presence of two representative types of boundaries: the direction of diffusiophoresis is either normal (type I) or parallel (type II) to a boundary, using two large parallel disks and a cylindrical pore as an example, respectively. It is interesting to observe that due to the effects of double-layer polarization, counterion condensation, polarization of condensed counterions, and diffusion of co-ions across a PE, its diffusiophoretic behavior can be influenced both quantitatively (magnitude of mobility) and qualitatively (direction of diffusiophoresis) by a boundary. In general, type I (II) boundary raises the diffusiophoretic mobility of a PE toward the high (low) salt concentration side. The results gathered provide necessary information for applications in, for example, designing catalytic swimmers a...
7 citations
TL;DR: A thorough numerical simulation is conducted to examine the behavior of a charge-regulated, zwitterionic particle subject to an applied salt concentration gradient under various conditions, and empirical relationships that correlate the scaled particle mobility with key parameters are developed for that purpose.
Abstract: Previous theoretical diffusiophoresis analyses were usually based on a fixed temperature, and its influence on the diffusiophoresis behavior of a particle was seldom discussed. Because both the physicochemical properties of the liquid phase and the charged conditions of a particle can be influenced appreciably by the temperature, so is diffusiophoresis behavior. This effect is taken into account in the present study for the first time, along with the possible presence of multiple ionic species in the liquid phase, a factor of practical significance if reactions occur on the particle surface and/or the solution pH is adjusted. Taking an aqueous dispersion of SiO2 particles as an example, a thorough numerical simulation is conducted to examine the behavior of a charge-regulated, zwitterionic particle subject to an applied salt concentration gradient under various conditions. Considering the potential applications of diffusiophoresis, the results gathered provide necessary information for the design of diffusiophoresis devices, and empirical relationships that correlate the scaled particle mobility with key parameters are developed for that purpose.
6 citations
TL;DR: The importance of the effective membrane charge on the electrophoretic behavior of a soft spherical particle comprising a rigid core and a charge-regulated membrane layer, mimicking both inorganic and biological colloids, is investigated.
TL;DR: This work considers the electrophoresis of a rigid sphere along the axis of a narrow cylindrical capillary; both are pH-regulated and zwitterionic and the presence of four kinds of ionic species should be considered if NaCl is the background electrolyte.
Abstract: We consider the electrophoresis of a rigid sphere along the axis of a narrow cylindrical capillary; both are pH-regulated and zwitterionic. This extends available analyses in the literature to a more general and realistic case. Adopting a titanium oxide (TiO2) particle in a silicon dioxide (SiO2) capillary as an example, we examine the capillary radius, the solution pH, and the electrolyte concentration (or double-layer thickness) for their influences on the electrophoretic behavior of a particle. Because the pH solution is adjusted by HCl and NaOH, the presence of four kinds of ionic species, namely, H+, OH–, Na+, and Cl–, should be considered if NaCl is the background electrolyte. This also extends conventional electrophoresis analyses to the case of multiple ionic species. The interactions of the electroosmotic flow, the properties of the particle and the solution, and the capillary wall yield complicated electrophoretic behavior that can be regulated by the solution pH and the background electrolyte c...
TL;DR: In this paper, the influence of temperature on the mobility of a particle having dissociable/associable functional groups is assessed, taking the temperature dependence of the permittivity and viscosity of the liquid medium, the diffusivity of ionic species, and the equilibrium constant of the surface reactions into account, and therefore, is more general and realistic than available models in the literature.
Abstract: The gel electrophoresis of a pH-regulated, zwitterionic sphere is investigated based on a Brinkman model taking account of the steric effects coming from the presence of polymer structure. In particular, the influence of temperature on the mobility of a particle having dissociable/associable functional groups is assessed. The model proposed takes the temperature dependence of the permittivity and viscosity of the liquid medium, the diffusivity of ionic species, and the equilibrium constant of the surface reactions into account, and therefore, is more general and realistic than available models in the literature. A thorough numerical simulation is conducted for temperature and pH ranging from 283 K to 323 K and 5 to 8.5, respectively, to illustrate the electrophoretic behavior of the particle mobility in various conditions.
TL;DR: This work considers the electrophoresis of a soft nanocylinder comprising a rigid core and a pH-regulated, zwitterionic polyelectrolyte layer along the axis of a rigid cylindrical nanopore to simulate the electrokinetic behavior of a particle.
TL;DR: In this article, differential scanning calorimetry (DSC) was employed to determine the thermal hazard such as heat of decomposition (ΔHd), exothermic onset temperature (T0), etc., in various acids.
Abstract: This article covers the incompatible properties of nitric acid (HNO3) with formic acid (CH2O2), and more generally with various acids such as sulfuric acid (H2SO4), hydrochloric acid (HCl), and acetic acid (C2H4O2). Differential scanning calorimetry (DSC) was employed to determine the thermal hazard such as heat of decomposition (ΔHd), exothermic onset temperature (T0), etc., in various acids. T0 of HNO3 and CH2O2 were determined as 50 °C using DSC. Thus it has been observed that HNO3 mixed with CH2O2 should be prohibited during transportation, storage, and use. And more generally, process safety engineers and operator must take care to handle tanker and storage tank of typical acids in the transportation, storage, and manufacturing process. It is clear that there exists a need to follow and enforce in the chemical industries safety data sheets, globally harmonized system of classification and labeling of chemicals of United Nations (UN), education of safety and health, emergency response system, and process safety management. It is the aim of the present study concerning HNO3 with various acids.