In trying to store and analyze some iron oxide nanoparticles I find that they agglomerate and so I cannot measure them by DLS.
My particles are coated with a polypyrrole polymer shell. Should I run DLS in a solution of this polymer?
For details
http://www.princeton.edu/cbe/people/faculty/sundaresan/group/publications/pdf/To-et-al.pdf
http://www.nseresearch.org/2006/NewFiles/41Dave%2005006722%20NIRT%202005%20overview.pdf
You can stabilize the suspension either sterically or via charge (electrostatic). Dilute in the mother liquor - the same continuous phase that the iron oxide began in. Carry out a Stokes' law calculation - iron oxide in dense and I suspect there'll be appreciable settling above 50 nm or so. Magnetic forces overcome van der Waals so only steric stabilization is normally feasible. See (registration required):
May 28th, 2019 Dispersion and nanotechnology
https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W190528DispNanoMat
November 3rd, 2015 Adhesion and cohesion
https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W180725AdhesionCohesion
For details
http://www.princeton.edu/cbe/people/faculty/sundaresan/group/publications/pdf/To-et-al.pdf
http://www.nseresearch.org/2006/NewFiles/41Dave%2005006722%20NIRT%202005%20overview.pdf
Have you used an ultrasonic probe to deagglomerate them before your DLS measurement? Using ultrasound might give you some short term stability and allow you to record a DLS measurement. A 20 kHz tapered horn usually gives the best results.
Sonication might work, different dispersion, or additives. There are some publications on these systems, for example Article Characterization of magnetic nanoparticle by dynamic light scattering
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