1,721,028 research outputs found
Orientation distribution and electrophoretic motions of rod-like particles in a capillary
No full textWe consider motions of charged rod-like particles in a capillary under the action of externally applied electric field as a model problem for the electrophoresis through a capillary. Since the electrophoretic velocity through the capillary is dependent upon the particle orientation relative to the electric field, the probability distribution function for the particle orientation is determined from the Smoluchowski equation. In the statistical equation considered here, the random rotary Brownian potential is balanced with the potentials from both electrical and hydrodynamic origins. First, the dipole moment associated with the asymmetrical distribution of particle surface charges and that induced by the external electric field are calculated by utilizing slender body theory. The results are strictly valid under the conditions that the contribution from double-layer distortion is negligible, which is typical of charged macromolecules in aqueous media. The dipole moments are expressed in terms of the particle charge (or zeta potential) distribution, external field strength, and aspect ratio of the particle. The two distinct dipole moments incorporate into the Smoluchowski equation for the particle orientation distribution which in turn determines the electrophoretic mobility. Finally, the particle velocity in a capillary is simply given as superposition of the electrophoretic velocity and the electroosmotic velocity which is driven by the surface charges on the capillary wall. (C) 1996 Academic Press, Inc.This work has been supported partly by a grant from Korea Research
Foundation. The authors also appreciate financial support from Bioprocess
Engineering Research Center at KAIST
Electrokinetic effects on fractionation of colloidal particles by capillary flow
No full textAn analytical separation of submicron colloidal polystyrene latex particles of different sizes has been carried out by capillary hydrodynamic fractionation, We examined various factors which affect separation of the colloidal particles such as the ratio of particle to tube diameter, the average eluant velocity, the ionic strength, and the surfactant concentration, In particular, the electrokinetic interaction between the capillary wall and the particle was studied intensively by measuring the zeta-potentials of the capillary wall and the colloidal particles using capillary electrophoresis, The results showed that the increase in the eluant ionic strength, especially of positive ions, reduced the velocity enhancement factor by the screening effect of positive ions, In addition, we confirmed that sodium dodecyl sulphate molecules, which dissociate in aqueous medium into positive sodium ions and hydrocarbon chains with negative charges, modify the electrokinetic properties of the particles in different way from the case for the capillary wall. For the particles, adsorption of the hydrocarbon chains with negative charges changes the zeta-potential. On the other hand, the screening effect by the dissociated sodium ions is dominant on the electrokinetic properties of the capillary wall
CAPTURE OF SMALL PARTICLES ON A BUBBLE COLLECTOR BY BROWNIAN DIFFUSION AND INTERCEPTION
No full textThis paper considers capture of small particles on the surface of a much larger bubble by Brownian diffusion and interception induced by flow. The bubble is assumed to rise under the action of gravity, and the terminal rising velocity is determined for the bubble size typical of bubble flotation processes. The mechanism of particle transport to the surface of bubble is controlled by the ratio of particle (a) to bubble radius (A). The dominant transport mechanism changes from diffusion to interception as the size ratio delta(=a/A) increases above a certain critical value. Although the Marangoni effect caused by the adsorbed particles reduces the collection efficiency, the general features of transport mechanism are preserved when the tangential velocity is nonzero on the bubble surface. Specifically, the analysis shows that for a bubble collector with slip boundary the critical value follows delta(cr) proportional to A(-4/3), in contrast to the result delta(cr) proportional to A(-1) for a no-slip collector. In the diffusion-control region, the collection efficiency of a col lector with slip boundary decreases with increasing collector radius as A(-3/2), which is much slower than A(-2) for the case of a no-slip collector. On the other hand, in the interception-control region, the collection efficiency increases in proportion to the size ratio delta. In this limit, the efficiency of a collector with slip boundary is very large compared to the result for the case of a no-slip collector where the efficiency is only O(delta(2)). (C) 1995 Academic Press, Inc
Epipristis roseus Exposito & Han, sp. nov.
No full textEpipristis roseus Expósito & Han sp. nov. Figs. 3–4Published as part of Hermosa, Expósito, 2009, A taxonomic study of Epipristis Meyrick, 1888 from China, with descriptions of two new species (Lepidoptera: Geometridae, Geometrinae), pp. 31-41 in Zootaxa 2263 on page 35, DOI: 10.5281/zenodo.27524
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