TY - JOUR
T1 - Solution Rheology of Poly(acrylic acid)-Grafted Silica Nanoparticles
AU - Zhang, Chongfeng
AU - Yang, Siyang
AU - Padmanabhan, Venkat
AU - Akcora, Pinar
N1 - Publisher Copyright:
© 2019 American Chemical Society.
PY - 2019/12/24
Y1 - 2019/12/24
N2 - Network 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.
AB - Network 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.
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U2 - 10.1021/acs.macromol.9b01309
DO - 10.1021/acs.macromol.9b01309
M3 - Article
AN - SCOPUS:85076630114
SN - 0024-9297
VL - 52
SP - 9594
EP - 9603
JO - Macromolecules
JF - Macromolecules
IS - 24
ER -