Molecular dynamics investigation of polymer-decorated nanoparticles with co-nonsolvent: Structural transitions from isotropic layers to heterogeneous patches

With the assistance of molecular dynamics simulations, we systematically investigate the conformations of polymer-decorated nanoparticles (PDNP), making use of the co-nonsolvency effect, which dramatically alters the effective solvent quality through minor variations of co-nonsolvent (CNS) concentrations. In response, surface-grafted polymers undergo a transition from an isotropic brush-layer in a good solvent to heterogeneous patches in CNS. To quantitatively describe this transition, we use the surface coverage θ as an additional order parameter and develop a theoretical model for its calculation, which is compared with the simulations. By further examining θ as a function of CNS concentration, we observe that PDNPs exhibit a collapse-reentry process similar to planar brushes, but with richer details of the two-step reentry behavior: angular isotropy recovery followed by radial expansion. We investigate how this CNS-induced collapse transition influences the reversible adsorption/exclusion of cargo nanoparticles on PDNPs, depending on the size of the cargo and the concentration of the cosolvent.