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Multi-angle light scattering results for four different PEBBLE samples (two sol gel and two polyacrylamide) showing some of the possible sizes.
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There are a few different ways of finding out the size of the PEBBLEs. We have already shown some TEM micrographs. TEM works best for the more dense sol gel particles, or for polyacrylamide stained with heavy atoms (which scatter electrons better). We also use SEM (scanning electron microscopy) of dried particles covered in a light coating of gold (so their surface conducts electricity for the imaging). You can see an example of this in the Decyl Methacrylate section. This method works best for particles which are 100 nm or larger. For the smaller particles, like the polyacrylamide PEBBLEs, we use light scattering to determine the sizes. Some people use dynamic light scattering (sometimes called quasi-elastic light scattering) for this type of application, but that technique has a bit of trouble with complicated particle distributions (as when there is aggregation, etc.). We have chosen a Wyatt Technologies multi-angle static light scattering apparatus connected to a liquid separation channel (AFFF - asymmetric field flow fractionation). In this technique, the particles are separated according to size before these sizes are determined, and a distribution of sizes is obtained without any assumptions made about that distribution beforehand. |
