基礎講座 電気泳動(Electrophoresis)

The development of novel materials is a fundamental focal point of chemical research; and this interest is mandated by advancements in all areas of industry and technology. A good example of the synergism between scientific discovery and technological development is the electronics industry, where discoveries of new semiconducting materials resulted in the evolution from vacuum tubes to diodes and transistors, and eventually to miniature chips. The progression of this technology led to the development * To whom correspondence should be addressed. B.L.C.: (504) 2801385 (phone); (504) 280-3185 (fax); bcushing@uno.edu (e-mail). C.J.O.: (504)280-6846(phone);(504)280-3185(fax);coconnor@uno.edu (e-mail). 3893 Chem. Rev. 2004, 104, 3893−3946

http://depa.fquim.unam.mx/amyd//archivero/FidelmarLechugaSanabria_4940.pdf

Recent advances in the liquid-phase syntheses of inorganic nanoparticles.

1: Magnetic Particles: Preparation, Properties and Applications: M. Ozaki. 2: Maghemite (gamma-Fe2O3): A Versatile Magnetic Colloidal Material C.J. Serna, M.P. Morales. 3: Dynamics of Adsorption and Oxidation of Organic Molecules on Illuminated Titanium Dioxide Particles Immersed in Water M.A. Blesa, R.J. Candal, S.A. Bilmes. 4: Colloidal Aggregation in Two-Dimensions A. Moncho-Jorda, F. Martinez-Lopez, M.A. Cabrerizo-Vilchez, R. Hidalgo Alvarez, M. Quesada-PMerez. 5: Kinetics of Particle and Protein Adsorption Z. Adamczyk.

Surface and Colloid Science

This chapter introduces the finite element method (FEM) as a tool for solution of classical electromagnetic problems. Although we discuss the main points in the application of the finite element method to electromagnetic design, including formulation and implementation, those who seek deeper understanding of the finite element method should consult some of the works listed in the bibliography section.

Introduction to the Finite Element Method

Applied Numerical Analysis. By C.F. Gerald. Pp. xii, 340. £3·60. 1970. (Addison-Wesley.)

The influences of the boundary effect and the charged conditions of a particle on its diffusiophoretic behavior are studied by considering the diffusiophoresis of a nonuniformly charged sphere along the axis of a narrow cylindrical pore. We show that the surface charge distribution of the particle is capable of yielding the complicated phenomenon of double-layer polarization and, together with the presence of the pore, leads to profound and interesting diffusiophoretic behaviors. For example, if the electrophoresis effect coming from the difference in the ionic diffusivities is absent, then the diffusiophoretic velocity of a particle with the sign of the surface charge on its middle part different from that on its left- and right-hand parts has both a local maximum and a local minimum as the fraction of the middle varies; that velocity has only a local minimum if the whole particle is charged with the same sign. If the electrophoresis effect is significant, then the diffusiophoretic behavior of the particle depends mainly on its averaged surface charge density.

Diffusiophoresis of a Nonuniformly Charged Sphere in a Narrow Cylindrical Pore

The electrical interaction between two planar, parallel dissimilar surfaces, which may have different charged conditions arising from different ion-adsorption mechanisms, in an arbitrary electrolytic solution is investigated theoretically. The electrical interaction force and the interaction energy between these surfaces are evaluated, and analytical expressions for various charged conditions under the Debye-Huckel condition are derived. In general, assuming constant surface potential and assuming constant surface charge density lead respectively to the lower and the upper bounds in the electrical interaction energy between two surfaces. We show that assuming a linear relation between surface potential and surface charge density under the Debye-Huckel condition, as is often done in the literature, is appropriate for two planar parallel surfaces only but becomes inadequate for other orientations or nonplanar surfaces. The present approach does not have this limitation.

Electrical interaction between two planar, parallel dissimilar surfaces in a general electrolytic solution

The electrophoresis of a rigid, positively charged ellipsoidal particle at the center of a spherical cavity is investigated theoretically under the conditions where the effects of double-layer polarization and the presence of an electroosmotic flow can be important. The equations governing the problem under consideration and the associated boundary conditions are solved numerically, and the influences of the key parameters on the electrophoretic mobility of the particle are discussed. We show that if the cavity is uncharged, the effect of double-layer polarization yields a local minimum in the electrophoretic mobility as the thickness of the double layer varies. This local minimum disappears if the cavity is also positively charged. In addition to reducing the scaled mobility of an ellipsoid, the presence of the boundary is also capable of influencing the relative magnitudes of the scaled mobility for particles of various shapes. For instance, if the volume of an ellipsoid is fixed, the scaled mobility ranks as prolate > sphere > oblate if the boundary effect is unimportant, but that order is reversed if the boundary effect is important.

Effects of double-layer polarization and electroosmotic flow on the electrophoresis of an ellipsoid in a spherical cavity.

The deposition of charge-regulated particles to a rigid, planar charged surface is modeled theoretically, taking the effects of the excluded area arising from deposited particles and finite ionic sizes into account. Here, a particle comprises a rigid core and an ion-penetrable charged membrane layer, which represents a general type of particle. If the membrane layer has a negligible thickness, the particle simulates a regular inorganic particle, and if the membrane layer has a finite thickness, it simulates biocolloids such as cells. The results of numerical simulation reveal that the rate of particle deposition is faster under the following conditions: (1) lower potential of the planar surface, (2) thicker membrane, (3) higher counterion valance, (4) lower fixed charge density, (5) smaller counterions, (6) larger co-ions, (7) larger functional group, and (8) lower pH. Neglecting the sizes of ionic species may lead to an appreciable deviation in both the electrical repulsive force between particle and surface and the rate of deposition. Typical deviation for the former is approximately 20%, and that for the latter is approximately -75%.

Effect of ionic size on the deposition of charge-regulated particles to a charged surface.

The feasibility of detecting a trace concentration of multivalent ions based on the ionic current rectification (ICR) of a nanopore when impurity ions might present is assessed. Adopting a bullet-shaped nanopore surface modified with tannic acid as an example, the detection of trace concentrations of Cu2+ (target ion) when Fe3+ (impurity) is present with K+ as background ions under various conditions is simulated. In particular, the influence of the reaction order of the association of target ions and tannic acid on the nanopore performance is examined. We show that the lower the background concentration the better the detection performance. For the examined background concentrations of 1, 10, 100, and 1000 mM, the optimal detection ranges are [0.5, 1000 μM] and [1, 1000 nM] for Cu2+ and Fe3+, respectively. The detection limits, 0.5 μM for Cu2+ and 1 nM for Fe3+, are lower than those that can be obtained from conventional instruments, suggesting the potential of applying the present nanopore-based approach. In addition, we also consider the presence of multiple ions, which can occur, for example, in detecting Cu2+ (target ion) when Fe3+ (impurity) might present or vice versa with K+ as background ions. The competitive adsorption of these three kinds of ions can yield complicated ICR behaviors.

Jyh-Ping Hsu

Papers

Diffusiophoresis of a Nonuniformly Charged Sphere in a Narrow Cylindrical Pore

Electrical interaction between two planar, parallel dissimilar surfaces in a general electrolytic solution

Effects of double-layer polarization and electroosmotic flow on the electrophoresis of an ellipsoid in a spherical cavity.

Effect of ionic size on the deposition of charge-regulated particles to a charged surface.

Nanopore-Based Detection of Trace Concentrations of Multivalent Ions When Impurity Ions Are Present.