BOUNDARY EFFECTS ON OSMOPHORESIS - MOTION OF A VESICLE IN AN ARBITRARY DIRECTION WITH RESPECT TO A PLANE WALL

Authors
Citation
Hj. Keh et Fr. Yang, BOUNDARY EFFECTS ON OSMOPHORESIS - MOTION OF A VESICLE IN AN ARBITRARY DIRECTION WITH RESPECT TO A PLANE WALL, Chemical Engineering Science, 48(20), 1993, pp. 3555-3563
Citations number
13
Categorie Soggetti
Engineering, Chemical
ISSN journal
00092509
Volume
48
Issue
20
Year of publication
1993
Pages
3555 - 3563
Database
ISI
SICI code
0009-2509(1993)48:20<3555:BEOO-M>2.0.ZU;2-X
Abstract
The problem of the osmophoretic motion of a spherical vesicle in the p resence of a nearby plane wall is analyzed in the quasi-steady limit o f negligible Reynolds and Peclet numbers. The solute concentration gra dient in the surrounding fluid is uniform in the undisturbed state and is oriented at an arbitrary angle relative to the plane wall. The sol ution of conservative equations for the solute species and fluid momen tum applicable to the system is constructed by superposing solutions o f the corresponding problems of motion normal to the plane and motion parallel to it. Using the spherical bipolar coordinate system, the tra nslational and angular velocities of the osmophoretic vesicle are solv ed for various cases. Interestingly, the osmophoretic mobility of the vesicle increases monotonically as it approaches the wall. The interac tion between the boundary and the vesicle can be very strong when the gap thickness gets close to zero. The direction of motion of the vesic le is, in general, different from that of the solute concentration gra dient. The plane wall exerts the greatest influence on the vesicle in the case of parallel osmophoresis, and the weakest in the case of moti on normal to it. In addition to the translational migration, the osmop horetic vesicle rotates at the same time in the direction opposite to that which would occur if the spherical particle sedimented parallel t o a plane wall. The ratio of rotational-to-translational speeds of the sphere is, in general, much larger for osmophoresis than for sediment ation.