Polymer Wrapping onto Nanoparticles Induces the Formation of Hybrid Colloids

Abstract

Polymers stabilize the nanoparticles onto which they wrap, avoiding coagulation and undesired phase separation processes. Wrapping gives rise to hybrid colloids, and is useful in bio-intended applications. In non-covalent interaction modes, polymers physically adsorb onto the nanoparticles’ surface, NPs, and some of their portions protrude outside. Both their non-interacting parts and the free polymers are in contact with the solvent, and/or are dispersed in it. Wrapping/protruding ratios were forecast with a simple statistical thermodynamic model, and the related energy calculated. The wrapping efficiency is controlled by different contributions, which stabilize polymer/NP adducts. The most relevant ones are ascribed to the NP-polymer, polymer–polymer, and polymer–solvent interaction modes; the related energies are quite different from each other. Changes in the degrees of freedom for surface-bound polymer portions control the stability of adducts they form with the NPs. The links between wrapped, free, and protruding states also account for depletion, and control the system’s properties when the surface adsorption of hosts is undesired. Calculations based on the proposed approach were applied to PEO wrapping onto SiO2, silica, and nanoparticles. The interaction energy, W, and the changes in osmotic pressure associated with PEO binding onto the NPs have been evaluated according to the proposed model.