Procedures
Diluting particles
Polystyrene particles can be diluted with particle-free deionised water or in any other medium as long it does not contain solvents like chloroform, toluene, benzene and methyl chloride. The addition of a surfactant is not necessary when the dilution is less than 500x, because the particle itself a contain already traceable amount of surfactant.
Suspending dry particles
Wet the dry particles with a 1% surfactant solution (anionic or non-ionic, i.e., SDS, Tween 20 or Triton X100) or an alcohol such as ethanol.
Gradually add small amounts of water to the particles in alcohol and mix in between. Finally make up to the desired concentration. Verify the number of particles by determining the wet and dry weight of a certain volume of the suspension or by counting using an appropriate particle count instrument.
Add particle free deionised water to the desired amount. Alternatively, let the resin settle and pour off the suspension into another clean bottle.
Dialysis of suspension
This procedure is recommended for removing surfactants from the particle suspension (not from the particle surface).
Wash the dialysis tubing (i.e., Spectrapor 12,000- 14,000 molecular weight cut-off) thoroughly with deionized water and place it in a container of deionized water (submerged).
Keep refrigerated for storage. When ready to use, cut off the desired length of tubing. Place a clamp on one end or tie it off. Fill about half full with the particle suspension.
Clamp or tie the top end and place in the container of deionized water with at least 10 times the volume of the latex. Roll or stir the contents of the container. Allow to dialyze for at least three hours.
Repeat dialysis three times with fresh water.
Re-suspending wet particles
Polymer microspheres larger than 0,5 µm will easily sink to the bottom of the bottle.
A non-violent manner of shaking the bottle a few times upside down will help the particles to become re-suspended and will minimizes forming bubbles to a minimum.
After shaking it is recommended to use ultrasound to get rid of any air bubbles and resolve temporary agglomeration. To ensure a stable suspension during the experiment it is recommended to use a magnetic stirrer.
