Using the Surface Zeta Potential Cell Kit
Note: Malvern has a video that goes through all of these steps in detail. There is a link on the NBTC Zetasizer information page and it is bookmarked on the Zetasizer computer.
Requirements:
To take a surface zeta potential measurement, you will need a sample holder. These can be purchased directly from Malvern—10 for about $600, or they can be purchased directly from the NBTC—1 for $75. The sample holder is reusable if you are careful not to damage it in the process of attaching and removing your sample.
The sample needs to be relatively flat and uniform, between ~ 4x3mm and 7x4 mm, and can be up to 1.5 mm thick. It needs to be able to be glued or taped, and should be stable in aqueous solutions.
A negatively-charged tracer particle needs to be used for negatively-charged surfaces, and a positively-charged tracer particle needs to be used for positively-charged surfaces. The zeta potential standard solution provides a negatively-charged particle.
Parts:
Surface Zeta potential cell. Note the alignment groove in the front and the cell cap, which adjusts the height of the surface.
Set up computer
• Activate the instrument computer by logging in to the central login system in the service corridor. If needed, log in to the local instrument computer – Username: zetasizer. Password: zetasizer.
• Start the Zetasizer software by clicking the DTS desktop icon:
• If measurement data from the previous user shows up, close it: From the File menu select close until all the measurement data is removed from the window OR Click the lower “X” in the right corner of the data window until all measurement data is removed from the window.
Prepare and mount sample.
• Put the sample gluing tool into a well of the 12-well plate for stability and insert a sample holder with the flat face up, as in the picture.
• Attach the material to the sample holder. Double-sided tape was sufficient in our tests, but epoxy glue has also been used with good results.
• Remove the sample holder from the gluing tool and insert it into the surface zeta potential cell as shown below with a gold surface:
Align surface zeta potential cell and cuvette
• Perform a coarse alignment using the height alignment tool. Put the cell into the height alignment tool, with the alignment groove on the cell aligned with the alignment dot on the height alignment tool. The surface can be raised and lowered by turning the cap of the cell. Adjust the height of the surface until it lines up with the reticules in the height alignment tool.
The surface is aligned and ready to be inserted into the cuvette.
• Fill a quartz cuvette with about 1mL of tracer solution and insert the surface zeta cell at a 45 degree angle to minimize bubbles. The level of the liquid should be completely above the screw of the cell, and there should be no bubbles on the surface to be measured or on the electrodes in the cuvette.
• Open the lid to the zetasizer by pressing the metallic button, and insert the cell and cuvette into the instrument. The alignment groove on the cell should face forward.
Fine alignment
• Now a fine alignment of the surface relative to the laser is needed. Go to toolsCount Rate Meter. Select the “forward measurement angle”, select “ZEN 1020 plate cell”, and set the attenuation to 11. If the surface is in the way of the laser, the signal will be very low. If the surface is not in the way of the laser, the signal will be higher. The surface will need to be precisely adjusted such that the signal is high, but the surface is still very close to the laser.
Fine adjustment of the cell. In this image, the signal drops off between the fourth and fifth adjustments. The cell is moved back to the fourth position before taking a measurement. • Turning the cap counterclockwise lowers the surface (eventually blocking the laser
light). Turning the cap counterclockwise raises the surface (and thereby increases a very low signal). Adjustments are generally made about 45 degrees at a time.
When performing the measurement, you will be rotating the cell cap several times. • Once you have decided on a starting position, make a note of the orientation of the cell
cap for future reference.
Set up the experimental parameters
• Go to Measure Manual, and change each parameter tab as needed. a. Measurement type:
• Select “Surface Zeta Potential” b. Sample
• Label the sample. The data for this measurement will contain this label. c. General Options
d. Tracer Material
• Select the tracer particle material from the list.
• If the material has not been listed, you will need to find the refractive index and absorption for that material.
e. Dispersant
• Select the liquid in the cuvette from the list.
• If the dispersant you are using has not been listed, you will need to find the viscosity, refractive index, and dielectric constant for that material at your measuring temperature. The NBTC has a viscometer and refractometer to assist with these measurements. Contact staff if you need help taking these measurements.
f. Temperature
• Temperature limits for cuvettes are listed on page 1 of these instructions. • Give the sample at least 2 minutes to equilibrate.=
g. SZP Measurement
• The number of sub-runs per measurement should not be more than 15 due to possible sample heating.
• Recommended parameters: 5 measurements at 5 different locations, with a 60 second wait between measurements to allow the sample to
re-equilibrate. h. Tracer measurement:
These values are identical to those that would be used in a typical zeta potential measurement. 100 as a maximum number of sub-runs is appropriate, and 5 measurements with 20 seconds between is an appropriate number of measurements.
i. Cell: At this time, there is only one cuvette available for this type of measurement.
j. Advanced: These settings should be at the default and do not need to be changed. Please contact staff if you have a reason to change these settings. k. Report/Export
When all the parameters have been set, click OK.
Taking a measurement
will pop up several times depending on the number of data points you chose. The “Multi-View” and “Zeta Potential versus Displacement” tabs will give you some information on the quality of the measurement in progress.
Cleaning up
Remove the cell from the cuvette and rinse the entire area in contact with fluid thoroughly with DI water. Rinse the cuvette thoroughly with DI water. Remove your surface using the same screw you used to insert it. Dry the cuvette with the nitrogen gun and replace all of the parts in the surface cell kit box. You may reuse your sample holder if it is not damaged in the process of removing your surface.
