Apparatus and method for determining the zeta potential of surfaces for the measurement of streaming metrics related thereto

1. An apparatus for measuring a streaming potential or streaming current corresponding to a rotating surface, wherein the surface has a radius and wherein the surface rotates around an axis of rotation, comprising:

a working electrode located within one radius from the axis of rotation and within three radii from the surface, and wherein the working electrode does not contact the surface;

a counter electrode, wherein the counter electrode is cylindrical in shape, has a radius greater than that of the surface, and wherein the surface is located within the counter electrode;

a meter connected to the working electrode and the counter electrode;

a rotatable spindle on which the surface is mounted; and

a container for holding electrolyte, wherein the working electrode, counter electrode, and surface are located within the container.

2. The apparatus of claim 1 , wherein the working electrode is located on the axis of rotation.

3. The apparatus of claim 1 , wherein the working electrode is located at least ten Debye lengths from the surface.

4. The apparatus of claim 1 , wherein the working electrode is within 5% of the radius from the surface.

5. The apparatus of claim 1 , wherein the meter measures electrical current passing through the electrodes and the meter.

6. The apparatus of claim 1 , wherein the meter measures electrical voltage at the working electrode relative to the counter electrode.

7. The apparatus of claim 1 , wherein the surface is not a disk centered on the axis of rotation, and wherein the radius includes at least two different radial distances between the axis of rotation and at least two edges of the surface.

8. A method for measuring a streaming potential or streaming current corresponding to a rotating surface, wherein the surface has a radius, comprising:

rotating the surface around an axis of rotation; and

measuring the streaming potential or streaming current at a location within one radius from the axis of rotation and within three radii from the surface, wherein the location does not contact the surface.

9. The method of claim 8 , wherein measuring the streaming potential or streaming current includes measuring the streaming potential or streaming current relative to a location which does not rotate with the surface.

10. The method of claim 8 , wherein measuring a streaming potential or streaming current includes measuring streaming potential.

11. The method of claim 8 , wherein measuring a streaming potential or streaming current includes measuring streaming current.

12. The method of claim 8 , wherein rotating includes rotating the disk in one direction around the axis of rotation.

13. The method of claim 8 , wherein rotating includes oscillating the surface in different directions around the axis of rotation.

14. The method of claim 8 , wherein measuring a streaming potential or streaming current includes measuring a streaming potential or streaming current at least ten Debye lengths from the surface.

15. The method of claim 8 , wherein measuring a streaming potential or streaming current is done with reference to a location at least ten radii from a point at which the axis intersects the surface.

16. The method of claim 11 , further comprising determining a current collection efficiency.

17. The method of claim 16 , wherein determining current collection efficiency includes determining:

Eff=I meas /( i z πa 2 )

wherein I meas is measured current;

i z is current density flowing from the surface; and

a is the radius of the surface.