Just out of curiosity: when I filtrate some polymeric nanoparticles, through a millipore membrane (around 0.4 micrometers) the size is reduced. This happened because some polymer that did not form the nanoparticles was left behind? Or why did this change in size happen?
With a high value of PI >0.5 and a particle size of >500nm you will be measuring large/agglomerated particles. These will dominate the scattering over the smaller particles. When you filter these (with your 400nm filter) these will be removed and you will measure the smaller particles. You should always filter before analysis as contaminants will effect the scatter and measurement. Reference: http://nanocomposix.com/sites/default/files/nanoComposix%20Guidelines%20for%20DLS%20Measurements%20and%20Analysis.pdf
off course I evaporate the solvent... after the synthesis, I checked the size with DLS, before and after filtrate the NPs.
How large are your particles before and after filtration? What is the monodispesion of the partcles?
but, after I filtrated the NPs, the suspension kept translucent
With a high value of PI >0.5 and a particle size of >500nm you will be measuring large/agglomerated particles. These will dominate the scattering over the smaller particles. When you filter these (with your 400nm filter) these will be removed and you will measure the smaller particles. You should always filter before analysis as contaminants will effect the scatter and measurement. Reference: http://nanocomposix.com/sites/default/files/nanoComposix%20Guidelines%20for%20DLS%20Measurements%20and%20Analysis.pdf
If your particles have a mean size of 520 nm before filtering, their mean size will obviously drop, because the membrane pore size is 400 nm. The larger particles (which are far away from the mean size of 520 nm) are getting caught on the filter. The smaller particles go through the pores and bring down your mean size.
Sean: Thank you so much for the PDF, now I understand many things and I realized that I got more problems :S I'm using gelatin type A.. so this is like an interference :(
Tatiana, if possible take a SEM of your particles before and after filtration, then you can clearly see the agglomerates before filtration. When you filter them agglomerated particles with size greater than 400 nm will be removed and you are getting smaller particles in the filtrate. If you check the concentration of particles before and after filtration, this can be understood very clearly.
when you filter through 0.4 µm filter you have to expect to remove also particles somewhat smaller 400 nm. The same with sieving, the smaller the mesh size the more the nominal cut will differ from the real one.
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