ma8b00432_si_001.pdf (2.82 MB)
Do Very Small POSS Nanoparticles Perturb s‑PMMA Chain Conformations?
journal contribution
posted on 2018-07-11, 00:00 authored by Nicolas Jouault, Sanat K. Kumar, Robert J. Smalley, Changzai Chi, Robert Moneta, Barbara Wood, Holly Salerno, Yuri B. Melnichenko, Lilin He, William E. Guise, Boualem Hammouda, Michael K. CrawfordSmall-angle neutron
scattering (SANS) measurements of syndiotactic
s-PMMA polymers mixed with weakly attractive 1.0 nm diameter polyhedral
oligomeric silsesquioxane (POSS) nanoparticles (NPs) show no observable
changes in the chain radius of gyration Rg, regardless of the polymer molecular weights, the amount of residual
solvent, or the POSS NP loading and dispersion (from 0 to 20 vol %).
In retrospect, these results are not surprising since scaling arguments
imply that chain size in the concentrated region of the phase diagram
of a polymer solution is ideal and independent of the polymer volume
fraction ϕ, and only as the semidilute region is entered with
decreasing concentration does the chain size for a good solvent begin
to increase due to polymer excluded volume and then scales with concentration
as ϕ–1/8. For typical polymer nanocomposites
the NP concentrations are less than 50% v/v, so the polymers are still
generally within the concentrated regions of their phase diagrams,
where ideal chain conformations are observed for small molecule solvents.
By combining the present results with previous results from the literature,
we conclude that spherical NPs apparently have little effect on the
conformations of polymer chains, especially in typical polymer nanocomposites
that only incorporate moderate amounts of NPs.