Chemistry: electrical and wave energy – Processes and products – Electrophoresis or electro-osmosis processes and electrolyte...
Reexamination Certificate
1999-06-18
2001-09-11
Gorgos, Kathryn (Department: 1741)
Chemistry: electrical and wave energy
Processes and products
Electrophoresis or electro-osmosis processes and electrolyte...
C204S601000
Reexamination Certificate
active
06287440
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains generally to a method for improving the performance of electrokinetic pumps that produce high pressures by converting electric potential to hydrodynamic force. More particularly, by manipulating the surface charge or zeta potential of a porous dielectric material used in these electrokinetic pumps, this invention provides a method for eliminating gas bubble induced blocking of current flow, and consequent pump failure, caused by electrolytic decomposition of the electrolyte.
2. Description of the Related Art
It has been demonstrated that it is possible, by means of a process called electrokinetic pumping, to produce hydraulic pressures in excess of 5000 psi by the application of a voltage gradient along a porous dielectric in contact with a conductive electrolyte material using at least two spaced electrodes, as shown in
FIG. 1. A
detailed discussion of the electrokinetic pumping process can be found in prior co-pending U.S. Pat. No. 6,013,164 and entitled ELECTROKINETIC HIGH PRESSURE HYDRAULIC SYSTEM, assigned to the same assignee. In electrokinetic pumping, an electric potential on the order of hundreds to thousands of volts, well above the potential required for electrolytic decomposition of any electrolyte, is required to develop the desired high pressures. Electrolytic decomposition of the electrolyte results in gas generation and the gas generated at the high pressure side of an electrokinetic pump can form bubbles that can block the current flow required for pressure generation, causing pump failure. This condition is particularly troublesome in miniaturized applications, such as in capillary tubes or microchannels, an area where the use of hydraulic pressure for manipulation of liquids holds great promise, but where current flow can be easily blocked. What is needed is a means for eliminating blocking current flow by bubble formation in electrokinetic pumping applications or providing for any gas generated to be removed from the system before operational complications are created.
SUMMARY OF THE INVENTION
The present invention provides a method and an apparatus for eliminating electrokinetic pump failure caused by gas bubbles formed by electrolytic decomposition of an electrolyte thereby blocking current flow through the electrokinetic pump.
By controlling the surface charge or effective zeta potential of the porous dielectric medium used in electrokinetic pumps it is possible to control the direction of electroosmotic flow and thus the direction in which hydraulic pressure is applied by an electrokinetic pump. When a common junction is formed between the outlets of two or more electrokinetic pumps, having dielectric media that provide different effective zeta potentials, the difference in the direction of electroosmotic flow created when voltages are applied to these pumps generates a hydrostatic pressure at the common junction that can create pressure-driven flow from this junction. Moreover, since the flow is purely pressure-driven there is no electric field associated with these flows in contrast to conventional electroosmotically driven flows. By taking advantage of this phenomenon, the present invention provides a novel electrokinetic pump configuration that allows placement of electrodes away from the pressurized region of the pump, thereby eliminating blocking of capillary channels by gas bubbles that can interrupt current flow and lead to pump failure. Further, the novel electrokinetic pump configuration described herein provides for other unique applications of electrokinetic pumping, in particular, an apparatus and a method for controlled blending of different fluids and for producing layered or “sheath” flow of fluids.
In one aspect of the present invention, the inventive device employs a porous dielectric pump medium that has a negative surface charge to form one segment of a pump configuration and a second porous dielectric pump medium that has a positive surface charge to form the second segment. By arranging these pump segments in an opposing configuration it is possible to generate very high pressures at the intersection of the pump outlets. Moreover, by placing the electrodes at the low-pressure side of the pump, bubble formation that could lead to current interruption and pump failure is eliminated. In another aspect of the invention disclosed here, one or more of the porous dielectric pump media can support ionic conduction but minimal or no electroosmotic or pressure-driven flow (e.g., a salt bridge). Voltages can be applied in series or parallel, or both, in order to create various combinations of electroosmotic flow, pressure-driven flow, or both.
REFERENCES:
patent: 5942093 (1999-08-01), Rakestraw et al.
patent: WO 99/16162 (1999-04-01), None
Weigl, B. and Yager, P., “Microfluidic Diffusion-based SeparatIon and Detection”,Science, 283, 346-7, Jan. 15,1999.
Arnold Don W.
Paul Phillip H.
Schoeniger Joseph S.
Gorgos Kathryn
Parsons Thomas H
Sandia Corporation
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