We have an issue with 20nm silica nanoparticle powder not dispersing well in a gel and forming large soft agglomerates instead of separating into primary particles. Is there a known method for maintaining silica colloids as monodisperse primary particles without adsorbing something on its surface, then calcining it so that it converts into dry powder but remains easily dispersible? There is a Stober synthesis process using ammonium salts to add greater charges than when using regular ammonium hydroxide, with the end result of producing smaller primary particles. Will that aid the dispersion to some appreciable degree? Thanks everyone!
There is no route forward other then making your material in a bottom-up process. A dry powder ('nanopowder' is an oxymoron as there are no free independent discrete particles of 20 nm in a powder even if the primary particles are 20 nm) is a fused collection of sub- and post-micron particles. The are aggregates not agglomerates. See:
Nov 11th, 2008. Dispersion and nanotechnology http://tinyurl.com/hpywsge
November 3rd, 2015 Adhesion and cohesion http://tinyurl.com/zwb2wlh
“If the particles are agglomerated and sub-micron it may be impossible to adequately disperse the particles……The energy barrier to redispersion is greater if the particles have been dried. Therefore the primary particles must remain dispersed in water….”
J H Adair, E. Suvaci, J Sindel, “Surface and Colloid Chemistry” Encyclopedia of materials: Science and Technology pp 8996 - 9006 Elsevier Science Ltd. 2001 ISBN 0-08-0431526
Buy 20 nm Ludox if you want 20 nm silica in colloidal suspension.
I agree with Alan, I observed the same: when we synthesised nanoparticles and dried them it was very difficult to re-dispers them (sometimes immposible) but when we synthesised them and left in a solvent (in our case water) later on it was much easier to re-disperse them or transfer to another solvent
Thanks everyone! I'll try to remove the majority of the remnant monomers and solvent after mixing then.
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