Hybrid Colloids Made with Polymers

Abstract

Polymers adsorb onto nanoparticles, NPs, by different mechanisms. Thus, they reduce coagulation, avoid undesired phase separation or clustering, and give rise to hybrid colloids. These find uses in many applications. In cases of noncovalent interactions, polymers adsorb onto nanoparticles, which protrude from their surface; the polymer in excess remains in the medium. In covalent mode, conversely, polymers form permanent links with functional groups facing outward from the NPs’ surface. Polymers in contact with the solvent minimize attractive interactions among the NPs. Many contributions stabilize such adducts: the NP–polymer, polymer–polymer, and polymer–solvent interaction modes are the most relevant. Changes in the degrees of freedom of surface-bound polymer portions control the stability of the adducts they form with NPs. Wrapped, free, and protruding polymer parts favor depletion and control the adducts’ properties if surface adsorption is undesired. The binding of surfactants onto NPs takes place too, but their stabilizing effect is much less effective than the one due to polymers. The underlying reason for this is that surfactants easily adsorb onto surfaces, but they desorb if the resulting adducts are not properly stabilized. Polymers interact with surfactants, both when the latter are in molecular or associated forms. The interactions occur between polymers and ionic surfactants or amphiphiles associated with vesicular entities. Hybrids obtained in these ways differ each from each other. The mechanisms governing hybrid formation are manifold and span from being purely electrostatic to other modes. The adducts that do form are quite diverse in their sizes, shapes, and features, and depend significantly on composition and mole ratios. Simple approaches clarify the interactions among different particle types that yield hybrids.

Keywords

• nanoparticles
• polymers
• surfactants
• covalent interactions
• noncovalent interactions
• interaction energy