Copolymers of Maleic Acid and Their Amphiphilic Derivatives as Stabilizers of Silver Nanoparticles

Silver nanoparticles were prepared by reduction of the corresponding metal salt with NaBH 4 in the presence of appropriate dispersing agents, namely, copolymers of maleic acid: poly(N-vinyl-2-pyrrolidone-alt-maleic acid), poly(ethylene-alt-maleic acid), poly(styrene-alt-maleic acid) or their amphyphilic derivatives. A thorough study of the whole process of silver nanoparticles production including formation of polymeric silver salt and stabilization of nanoparticles has been carried out. The degree of cooperativity of copolymer silver ions binding process and binding capacity of copolymers with respect to silver ions was calculated. To estimate the effect of silver binding on dimension of copolymers particles in solutions viscometric method and atomic force microscopy were used. The most stable and highly silver-"loaded" colloids, identified with optical absorption spectroscopy and transmission electron microscopy, were prepared at biphilic copolymers concentrations lower than their critical aggregation concentrations and copolymer/Ag + molar ratio was equal to unity. Under optimal reduction conditions, the final morphology of Ag nanoparticles is governed by structural similarity (strict alternation of monomer units) and similar polymer chains length of all copolymers; hydrophobic ligands only assist in stabilization of nanoparticles. A simple method for evaluating the thickness of polymer protective layer based on atomic force microscopy and transmission electron microscopy data is proposed.