Acrylic polymers (Butyl acrylate, MMA, Methacrylic acid), modified nanosilica,
Hm, this is interesting. Regarding gel content I presume you refer to soluble polymer content and residue - considered to be "gel". It is well known in rubber chemistry that carbon black and silica aerogels (sometimes denotes ad "white soot") adsorb polymer molecules so strongly that this strongly bound layer cannot be removed even by good solvents of the polymer. This is probably what you call "gel". To a certain point probably this insoluble part increases with the filler content. It has been shown by sevaral authors that nanoparticles influence the polymer structure (including mobility) at far distances even at low concentration.
The second part of the statement (lower water absorption) is somewhat puzzling for me. So far in all of my earlier studies (which were normal micro-filler in various polymers) the addition of the filler increased rather than decreased the water absorption and this was well detectable by dielecric spectroscopy. This water adsorption at the filler/polymer interface proved to be fairly reversible.
It would be interesting to see your results on decreasing water absorption on filler addition. If thsi proves to be true, it would eb inetrestting to study the mobility of water in these sysems by NMR or by dielectric methods.
Totally agree with Dr. Banhegyi.. decreasing water absorption is interesting indeed.. but you used "modified silica".. what's the modifier? If the modifier is hydrophobic, then its pretty obvious..
Sridhar Vadahanambi;
yes, its almost hydrophobic (glycidyl methacrylate), but modification has been not complete (30 %wt).
Gyorgy Banhegyi;
see this article (water uptake): http://www.sciencedirect.com/science/article/pii/S002197970800163X
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