Polymeric chains are grown on the surface of nanoparticle using free radical polymerization
Dear Neetish Maurya
In general, adding a salt to the solution changes its properties. I would suggest that the reason for the increase in viscosity you observed is that the grafted polymer chains have a more expanded conformation in the solution with the salt.
To completely clarify: more expanded conformation means that the chains will occupy more space around the nanoparticle (larger hydrodynamic radius) and thus influence the solution viscosity similarly as if they had a larger Mw.
Regards
Josef
Josef Chmelar ,
Thanks for your reply. I had somewhat thought the same and the DLS data does show the increase in hydrodynamic radius. But in general, I have seen the presence of salt always leads to decrease in viscosity of the polymer. Have you seen any research paper where it has been discussed?
What is the salt (type and conc.) polymer and nanoparticle concentration?
It could be what is suggested above, but could be the opposite and could be that the salt has caused a decrease in the ads polymer layer thickness (by dehydrating the polymer) so that the particles aggregate thru van der Waals forces.
Paul
Dear Paul F,
Thanks for your reply.
The nanoparticle is silica(SiO2). Polyacrylamide is grafted on the surface of nanoparticle through free radical polymerization. I have tested the NaCl and CaCl2 in concentration from 2000 pm to 20,000 ppm. Across all the salt concentration result have been the same
In that case I suspect the polymer layer is contacting
This paper might help understand what is going on a bit more,.
I know its for a gel but the linear polymer would behave in a similar way
Interactions between inorganic salts and polyacrylamide in aqueous solutions and gels
Journal of Polymer Science Part B Polymer Physics 41(5):508 - 519 · March 2003
DOI: 10.1002/polb.10406
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