ma9b01309_si_001.pdf (10.1 MB)
Solution Rheology of Poly(acrylic acid)-Grafted Silica Nanoparticles
journal contribution
posted on 2019-12-11, 21:45 authored by Chongfeng Zhang, Siyang Yang, Venkat Padmanabhan, Pinar AkcoraNetwork formation of polymer-grafted nanoparticles in
aqueous solutions
is an unexplored area in polymer science. In this study, nanoparticles
grafted with poly(acrylic acid) (PAA) chains with different grafting
densities and similar graft chain lengths at semidilute concentrations
are investigated using small-angle neutron scattering (SANS) and rheology
experiments. We found that at a low graft density and fully ionized
state, stretching of grafted chains accommodates a thick lubricating
water layer, which lowers the viscosity. At low graft density and
50% ionization, grafts are in extended conformations as observed from
the broad PAA volume fraction profile around the particles in SANS
data. This is attributed to the hydrogen bonding between ionized and
unionized carboxylic acid groups. The highest viscosity measured at
this pH confirms the intraparticle bonding between the grafted chains.
Viscosity adjustment with the addition of short poly(N-vinylpyrrolidone)
chains suggests that hydrogen bonding is possible within the grafted
chains of individual particles at low graft density, whereas interchain
networking occurs at high graft density. Molecular dynamics simulation
results of model systems confirmed the interparticle bridging at high
grafting density. These results demonstrate that hydrogen bonding
between polymer-grafted nanoparticles using small molecules can be
used to modulate the viscosity of the physical networks in solution.