 PEBBLE Sizes
| 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. |
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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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