Viscosity of polyelectrolyte-grafted nanoparticle solutions.

The effect of charges and hydrogen bonding on viscosity in solutions containing polyelectrolyte-grafted nanoparticles (PENP) has been investigated using molecular dynamics (MD) simulations. The electrostatic interaction between the charged monomers on the grafted chains, which increases with the degree of ionization, causes the grafted polymers to stretch and increases the hydrodynamic size of the nanoparticles. The viscosity of the solution is partially governed by the balance between the entanglement of grafted chains and the electrostatic repulsion. Moreover, the charge-assisted hydrogen bonds between the monomers of different particles further enhance the viscosity of the solution. For shorter grafted chains, a majority of hydrogen bonds are formed within the same particle and thus show no significant enhancement in viscosity. The addition of polymer chains with hydrogen bonding sites has been shown to bridge multiple nanoparticles, creating a network structure, that increases viscosity. The chain stiffness has been shown to have a direct correlation with bridging and thus the viscosity of the solution.