A Revolution in Zeta Potential Measurement


The apparatus consists of a few main parts: the motor/rotator, the cell, the voltmeter, the support stage, and the computer that runs it. Click on parts of the picture to learn more about the components.

Variable Speed Rotator (VSR)

The variable speed rotator is used to rotate the submerged sample in the cell. The motor/spindle apparatus used here is supplied by Pine Instruments. A dc input modulates the rotation rate of the ZetaSpin according to a sinewave input between 0 and 4000 rpm. The upper limit is chosen because the flow at the edge of a 25 mm diameter disk becomes turbulent above this value, approximately. Top

VSR Speed Control

The VSR Speed Control is used to moderate the rotational speed of the submerged sample. It is electronically controlled by a dc input from the computer. Top

The Cell

The cell is the center of the ZetaSpin. It comprises a teflon vessel and a machined polycarbonate top that allows insertion of the sample, supports reference electrodes and sensors, and provides baffling of the flow generated by the disk. Click on the picture to learn more. Top
Baffle Support

The baffles damp the strong rotational motion above the plane of the sample, and they support probes and electrodes. Top
Sample Support

The sample support is a pvc cylinder threaded to mate with the spindle. The sample disk is affixed to the end of the pvc support. The sample support is a cylinder to move the opposite lateral surface above the plane of the liquid. Rotational motion induced in the annular space between the samaple support and baffles contributes negligible streaming potential to the measurement. Click on the picture to learn more. Top
Surface sample

  The surface sample is the surface being tested. Mica is shown here. Top
pH Probe

The pH probe measures the pH. Top
Conductivity Probe

The conductivity probe measures the conductivity. Top

The two electrodes measure the potential difference between the center and edge of the sample. Top

The Keithley nanovoltmeter is connected to the two electrodes submerged in the cell. It measures the potential difference between the center of the rotating disc and the radius. Top

The stand moves in the x, y, and z direction so that the sample can be centered over the electrode. Top
LabView Interface

click to enlarge The computer runs the ZetaSpin from a Labview interface. The program varies the rotation speed of the sample and logs the streaming potential. Labview fits the modulated streaming potential to an expected functional form; the zeta potential is the only unknown. The computer reports and records the zeta potential that provides the best fit. A larger version of this image can be seen by clicking on the picture, allowing one to see the inputs and outputs in more detail. Top