Santa’s Christmas dispersant list
Written by: Steve Ward-Smith
For wet laser diffraction measurements it can be useful to have a variety of different types of dispersant available so you can measure any compound that gets presented to you.
Of course water is always the best starting point, but unfortunately many compounds dissolve in water.
At this time of year we thought we’d cover what every well equipped solvent cabinet wants for Christmas.
Alcohols – ethanol can be useful for materials like gypsum, but the best all round alcohol is Isopropyl alcohol. Cement disperses well in it, and so does chocolate.
Something with an “ane” in it – mid range saturated organics work in many cases. The most flexible is iso-octane, but hexane is a good back up. It is many a Malvern applications specialist first dispersant to try for pharmaceutical materials.
A few paraffinic solvents – they are often good candidates when the material seems to dissolve in everything. They are often not as viscous as silicone oils or vegetable oils. Kerosene is very useful, Isopar G is as well. If you do have to use a more viscous oil such as sunflower or silicone oil always fill it with the dispersion unit stirrer off otherwise bubbles may be ingested which are hard to remove.
These are the good solvents, what’s on the naughty list?
Well, saturated solutions are sometimes the only option, but a great deal of experimentation should occur before they are selected as they really are the dispersant of last resort. The change in temperature between sites can influence the degree of saturation, and if an experimental preparation needs ultrasound, the heat created can drastically change the degree of saturation. They are sometimes the only thing that works, but should be left as a final option.
May I take this opportunity to wish all the readers here a very Merry Xmas and a happy and prosperous 2013.