I am measuring the particle size of nanoparticles by Malvern Zetasizer Ultra Particle Analyzer but I am not sure I would get a better size with TEM or not. Because I read in a paper that there is some difference in particle size with those two methods.
Dipti Debnath
How is the sample prepared for TEM? This is crucial and an attached picture may tell you why...
There are plenty of prior discussions on RG on the topic, so a little bit of prior research, on you part, would have been beneficial. The differences depend on the width of the distribution. If every particle was the same monodisperse system) then the intensity (proportional to r^6) and number (proportional to r^1) means would be the same. Small quantities of large particles weight toward the intensity mean, so the ensemble route of measuring the entire system may be beneficial as opposed to observing a few particles under electron microscopy. Also one has to judge the effects of aggregates, agglomerates, as well as sample 'preparation' (which alters the starting system).
Dipti Debnath It depends on the nature of the nanoparticles but there are always some differences in the size between these two techniques. This is because, in DLS, you are measuring the hydrodynamic diameter i.e. the diameter of the particles with an extra layer of solvent around it in the dispersed phase. For TEM/SEM, the samples are dried, which might lead to a smaller size or aggregation of the particles unless it's a monodispersed sample. So, do not worry if there's a size difference of 5-10% between the two techniques.
The Malvern Zetasizer provides the hydrodynamic radius (diameter) defined by Stokes Eintein equation in, which can be larger than the particle diameter due to a number of factors.
Hi Dipti Debnath , in addition to the valid points above, differences can also be due to the type of representation, i.e. number (for TEM/SEM) or intensity (typical for DLS) distribution. For more details, you might like these two blogs
- https://www.materials-talks.com/blog/2017/01/23/intensity-volume-number-which-size-is-correct/
- https://www.materials-talks.com/blog/2018/05/31/polydispersity-from-a-gold-standard/
Dipti Debnath
How is the sample prepared for TEM? This is crucial and an attached picture may tell you why...
There are plenty of prior discussions on RG on the topic, so a little bit of prior research, on you part, would have been beneficial. The differences depend on the width of the distribution. If every particle was the same monodisperse system) then the intensity (proportional to r^6) and number (proportional to r^1) means would be the same. Small quantities of large particles weight toward the intensity mean, so the ensemble route of measuring the entire system may be beneficial as opposed to observing a few particles under electron microscopy. Also one has to judge the effects of aggregates, agglomerates, as well as sample 'preparation' (which alters the starting system).
Dipti Debnath, For the same particle, the size in TEM would be smaller than in DLS. Aa Nabodita Sinha mentioned in DLS, the hydrodynamic diameter is measured.
Additional reading in these discussions might help!
https://www.researchgate.net/post/Hydrodynamics_size_of_nanoparticles
https://www.researchgate.net/post/Why_does_the_particle_size_differ_in_TEM_and_DLS_measurements
https://www.researchgate.net/post/Why_am_I_getting_different_measurements_of_particle_size_by_dynamic_light_scattering_laser_diffractometry_and_TEM
Thank you everyone for your expert answers to my question. It's really helped me to understand the facts about nanoparticle size. I am grateful to all of you.
The difference mostly depends on the size of the capping agent. TEM gives particle core size whereas DLS gives the particle hydrodynamic diameter which includes the core size and the stabilizer as well.
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