Mini-Encyclopedia of Papermaking Wet-End
Part Two: Definitions and Concepts
The stationary level is a plane of focus within the capillary cell of a microelectrophoresis instrument. In the case of a cylindrical capillary this location is about 14.6% of the distance from one inner wall to the opposite inner wall. In the case of a rectangular cell the stationary level is located about 20% for the distance from one wall to the other. At the stationary level there is zero contribution to particle velocity from electro-osmosis. Instead, any observed particle motion can be attributed to either (a) electrophoretic mobility, or (b) Brownian motion. Electro-osmosis occurs because the capillary walls can have an electrical charge. When an electrical field is applied along the axis of the capillary it tends to pull some of the counter-ions adjacent to the wall. Associated fluid is moved along with the ions, creating a flow of solution. Because the chambers of a microelectrophoresis instrument are closed during use, a parabolic return flow occurs in the middle part of the capillary. Brownian motion can be defined as random movement of small particles in suspension due to chance collisions with adjacent molecules; Brownian motion is a consequence of thermal energy.
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