Hi,
I have a problem in pnipaam nanoparticle synthesis. As it is mentioned in several papers, first i crystallize pnipam and mba. Then mix pnipaam, mba and sometimes sds in a 3necked bottle at 70 C, in nitrogen atmosphere, stirring at 300 rpm. After 1 hour I add APS to the system as an initiator and i see the polymerization. The reaction proceeds for 4 hours, then i filter it with 0.45um filter. I tried centrifugation but it did not work at 10.000 for 45 min.
In DLS i see mostly 2 peaks(480nm and 530nm) Expert advice says that see the result quality report. Even i changed the mixture ratios and concentrations, the results are the same more or less.
Does anybody have an idea about what i am missing during the synthesis?
Hi, the PNIPAm nanoparticles are very soft if you use a little crosslinker (MBA), and when you centrifugation at room temperature the particles are hydrophilic and disperse in the colloids solution, it is difficult to separate. You can increase the crosslinker ratio then the particles will become more stiff and hydrophobic, and they will become easier to separate from the water. @ A.Can Egil
Hi Qifeng Mu,
Actually i tried different mixing ratios between nipaam and mba and aps but the result quality was the same.
The DLS result might be an artefact. I believe you have one rather broad particle size distribution and the algorithm which you use to analyze the data makes to peaks out of it. This a known problem of e.g. numerical Laplace transform algorithms.
This raises the question why you get a broad distribution. Do you purge the reaction mixture with nitrogen before initiation and during heating by bubbling nitrogen through the reactant solution? Else residual O2 might cause problems.
If you really have two discrete size distributions , than you have two different nucleation periods. How do you add the APS? Dissolved or as solid? It should be dissolved.
What is the concentration?
Our procedure is e.g. described in DOI: 10.1021/acsomega.8b03511
and works usually very good.
Egil, I think, the problem is with the filtration you followed after the synthesis. There is no need to filter the particles with a 0.45um filter, you should rather use whatman filter discs or glass wool. The pores are much bigger here and the particles can go through these pores filtering out large aggregates and chunks. Now that you used a 0.45 um filter and say if you had 500nm particles, then definitely you will not obtain proper size in DLS not in centrifugation as 0.45 um filter will allow only particles less than 450nm to go through.
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