By DLS technique we can measure the approximate range (Z-avg) of nanosized droplets dispersed in continuous medium by using Zetasizer. But can we go for TEM for getting exact size of the droplets suspended in the continuous phase.
Both DLS and TEM provide 'exact sizes' and both can be verified with appropriate standards. One technique provides a hydrodynamic diameter (so includes the protective/stabilizing surfactant layer) based on intensity (z-average) and one provides the number distribution of the electron-dense rich core of the particulate system. You'd need cryo-EM or freeze-fracture for an emulsion and sufficient numbers of particles (> 10000) measured for a mean to 1% standard error in electron microscopy. Obviously the low-resolution DLS technique measures many millions of particles simultaneously and get results within 30 seconds or so. Sample preparation and measurement is much longer on electron microscopy. Both techniques are essential and provide complementary (not competitive) information.
Good summary by Alan,
here are two links that may also be of interest
primarily for dynamic light scattering...
There's no such thing as exact size unless every particle were perfectly identical. You have to qualify the size with the name of the technique.
You have to be very careful when comparing "sizes" from different techniques. e.g., one technique may measure according to the length (or diameter) whereas another measures according to the volume. Mathematically, you can "convert" a distribution of sizes from one type (length) to another (volume) but it is a very risky thing to do.
Dear sir (@john Francis MIller) thanks for answering the question. your explanation related to exact size of nanoparticle is absolutely correct. But by writing exact size i mean the technique that could show the images of the nanodrops.
Hermat. Remember that images are a 2-D representation of a 3-D object - and shape is a 3-dimensional issue....
To add to John's answer, the killer word in particle size distribution is the last one...And distribution is the bane of all particle size analysis techniques. We can only define 'exact size' for monodispersed spheres. Even for cubes (say of unit length) the volume or surface equivalent diameters are different from the edge length. Further information along those lines in the attached.
Dear sir (@ Alan F Rawle). Thanks for your detailed description about particle size analysis and valuable pdf.
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