I have analyzed metal oxide nanoparticles using Dynamic Light Scattering measurement. I got the particle size in the range of 300-500 nm (due to hydrodynamic radii).
DLS is a first principles method, but it cannot ignore the impact of any attached solvent. If you know the solvent viscosity and the sample is reasonably monodisperse, your DLS result is likely very good. To check if solvent attached to surface is yielding a value that is too big, you need to use TEM. SInce your particles are in the range of 300-500 nm, you also could use optical microscopy to check your results.
..I would suggest you to do SAED ( using HRTEM) and EDX studies also .They would provide not only the size but also specific locations .Xray Magnetic Circular Dichroism studies can reveal very reliable information even about energetics
HRTEM is reliable because it rotates the incident beam on the specimen and hence can give a better result.
The biggest weakness of DLS is that it heavily skews its result towards the size of any large size impurities in the sample. These impurities may be aggregates of your primary particles, or they could be dust particles in your solvent. I would examine the TEM data to look for evidence of aggregates. Also, you may want to run a known size standard, such as a monodisperse latex to make sure your DLS and associated software are operating properly. If you get correct results for known standards, then do a concentration series with your sample. Particle-particle interactions can be attractive and repulsive. Keep diluting your sample by a factor of 3 or 4 until you no longer get enough scattering to get a reliable result in five minutes. Then plot the sizes as a function of concentration. The extrapolated size in the limit of zero concentration is probably the best result you can get by DLS. If your software has a "dust filter," turn it on and see what effect it has the result; look at the correlation function to see if it is decaying to zero nicely, or if the longtime behavior is skewed. Also, before doing the concentration series, prepare your measurement dilution, and filter it through a 1 um to 5 um filter to remove any large impurities, and see how this impacts your result. I think the most probable causes of your problem are intrinsic (aggregates) or accidental (dust) impurities. Next, I would suspect particle-particle interactions (need to do concentration series). Particle-particle correlations superimposes collective particle motions on your apparent size. Good luck!
- Badges
- Science topic
- Similar topics
- Chemistry
- Nanotechnology
- Nanostructured Materials
- Nanoparticles