Structure of Binary and Ternary Complexes Formed by Sodium Poly(2-acrylamide-2-methyl-1-propanesulfonate) Gel in the Presence of Copper(II) Nitrate and Cetylpyridinium Chloride

Abstract

Binary and ternary interactions of copper(II) nitrate and cetylpyridinium chloride with polyelectrolyte gel of sodium poly(2-acrylamide-2-methyl-1-propanesulfonate) (PAMPS) were studied. In contrast with sodium and calcium chlorides, the addition of copper(II) nitrate to the solution leads to additional shrinking of the gel, while in the presence of the surfactant the gel collapses. In the region of low concentration the composition of the PAMPS−copper(II) complexes is close to stoichiometric. In the highly concentrated solutions of copper(II), the salt concentration becomes the same as in the surrounding solution. ESR study demonstrates two states of the copper(II) ions in the gel phase, namely the ions that are bound to the sulfonate groups of the polymer network, and the free hydrated ions. The competition interaction of cationic surfactant cetylpyridinium chloride with the anionic network results in significant decrease of the fraction of the free copper(II) ions in comparison with bound ions. SAXS study shows that, starting from some critical concentration of cetylpyridinium chloride (ca. 0.005 M) in the solution, an interaction of anionic gel and the cationic surfactant yields a nanocomplex with a complicated structure. Addition of copper nitrate to the complex leads to competition substitution of the surfactant by copper ions from the gel. At the same time the ions of low molecular weight salt can enter the structure of the polyelectrolyte gel−surfactant complex.