Early steps of formation of silver/polyacrylate complexed oligomer clusters. A pulse radiolysis study

Abstract

Pulse radiolysis has been carried out on aqueous solutions of silver ions complexed with polycrylate (PA). Over the time scale 10⁻⁸−10 s, only a few kinetic steps have been observed which have been identified through spectroscopic and kinetic analysis. The reaction rate of e^-_aq with Ag⁺ is lowered in the presence of PA (3.6×10⁹lmol⁻¹s⁻¹ when [PA]/[Ag⁺]=100). The first products (Ag⁰ λ_max≈360 nm, Ag⁺₂ λ_max=310 nm) are similar to those obtained in the absence of PA, except for an additional absorption band (350–450 nm) which indicates that Ag⁺₂ is itself complexed. Then through dimerization (2k=3×10⁹lmol⁻¹s⁻¹) and reaction with the alcoholic radical (in the presence of 2-PrOH, 1.5×10⁹lmol⁻¹s⁻¹), Ag⁺₂ leads to an “Ag₂” species peaking at 300, 320 and 360 nm, noticeably different from the reported Ag²⁺₄ species. Two further steps are observed which are assigned to a ligand reorganization of “Ag₂” in the millisecond range (10³s⁻¹), followed by a coalescence to “Ag₄” in the range of seconds (10⁵lmol⁻¹s⁻¹). This last product is thought to be the stable Ag_a cluster known to be formed by γ-radiolysis. A kinetic simulation accounts for the whole mechanism which is much lower than in the absence of PA.