Role of Casting Solvent
on Nanoparticle Dispersion
in Polymer Nanocomposites
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Abstract
We investigate the influence of casting
solvent on the final spatial
dispersion of nanoparticles (NPs) in polymer nanocomposites (PNCs).
We prepared nanocomposites of bare silica NPs and poly(2-vinylpyridine)
(P2VP) by casting from two different solventsmethyl ethyl
ketone (MEK) and pyridinewhich are theta/good solvents, respectively,
for both the polymer and the NPs. In MEK, we show that P2VP strongly
adsorbs onto the silica surface to create a temporally stable bound
polymer layer. The resulting “hairy” particles are sterically
stabilized against agglomeration, and thus good NP dispersion in PNCs
is always achieved, independent of P2VP molecular weight, concentration,
or NP loading. On the contrary, in pyridine, P2VP does not adsorb
on the silica NPs. The phase behavior in this case is thus governed
by a subtle balance among electrostatic repulsion, polymer-induced
depletion attraction, and the kinetic slowdown of diffusion-limited
NP aggregation. While there is little remnant solvent in the dry PNC,
and since these dispersion states are hardly altered on annealing,
these results serve to emphasize the crucial role played by the casting
solvent in the spatial dispersion state of NPs in a polymer matrix