A correspondence between the Flory–Rehner theory for microgels and the Daoud–Cotton model for polymer-grafted nanoparticles

Abstract

Poly(N-isopropyl acrylamide) (PNIPAM) is a commonly investigated thermoresponsive polymer that exhibits a number of interesting physical behaviors. Here, we use small-angle neutron scattering (SANS) measurements to determine the conformation of PNIPAM in two regions of the chain when it is grafted at moderate grafting densities to the surface of SiO2 nanoparticles (rNP ≈ 10 nm). At these grafting densities, polymer chains may adopt two primary conformations, depending on the specific value of the second virial coefficient, the molecular weight of the chains, and other properties. The nanoparticles are studied in D2O and ethanol-d6 to ascertain the effect of solvent quality on the chain conformation in both the inner and outer regions of the brush. The SANS measurements are interpreted using a modified Daoud–Cotton model that connects the Flory–Rehner theory of microgel thermodynamics to the structure of polymer-grafted nanoparticles.