Synthesis and characteristics of cross-linked polymer hydrogels with embedded CdS nanocrystals

Abstract

Structural combining of polymer hydrogel network with mineral nanoparticles (metals, oxides, salts) is a very promising approach to create new functional materials with the specific properties. In this study, the cross-linked polymer hydrogels with embedded cadmium sulphide nanocrystals have been synthesized via radical copolymerization of acryl amide with acrylic acid or 2-(dimethylamino)ethyl methacrylate and N,N′-methylenebis(acrylamide) as cross-linker in aqueous media in the presence of nanoparticle precursor-cadmium salt, followed by subjecting the hydrogel obtained to gaseous hydrogen sulphide; this provides the in situ formation of CdS nanocrystals in pores of the hydrogel polymeric network. The effect of the Cd 2+ cation concentration on the copolymerization kinetics, as well as on the gel-fraction content has been studied. The formation of CdS nanocrystals with the size of 3-6 nm has been proved by UV-vis spectroscopy and X-Ray diffractometry. Importantly, the nanocrystal size is largely determined by the density of the hydrogel polymer network. The compressive strain of hydrogels with CdS nanoparticles is significantly larger than that for the initial hydrogels containing Cd 2+ cations only, apparently owing to the breaking of ionic and coordination bonds between metal cations and polar functional groups of matrix copolymer, which provide additional cross-linking of the hydrogel matrix. The obtained nanocomposite hydrogels are highly elastic materials characterized by a sufficiently high strength.