Specific Interactions of Ag+ Ions with Anionic Polyacrylate Chains in Dilute Solution
2014
Ezhova, A. | Huber, K.
A detailed light scattering investigation is presented on dilute solutions of two long-chain sodium polyacrylates (NaPA) in the presence of monovalent Ag⁺ ions in 0.01 M NaNO₃ aqueous solution at a pH of 9. The relevance for the investigation is based on two features: (i) despite its monovalency, Ag⁺ is expected to exhibit a much more complex interaction pattern with NaPA than salts based on alkaline cations do; (ii) aqueous solutions of AgNO₃ nucleate Ag–nanoparticle formation in the presence of NaPA under UV light, which may be modulated by the solution behavior. Our study revealed the following results. Addition of a low amount of Ag⁺ ions leads to an aggregation of PA-chains without considerable coil shrinking. At a ratio of silver ions per monomer of 0.001 ≤ [Ag⁺]/[COO–] ≤ 0.05, combined static and dynamic light scattering (SLS/DLS) suggests formation of homogeneous low density aggregates. Further increase of the Ag⁺ ion concentration results in a formation of dense unstable aggregates. At ratios of [Ag⁺]/[COO–] > 0.3 with variable NaPA concentrations aggregation occurs within a few seconds, resulting in small but stable aggregates with a high density of Ag⁺–PA aggregates. A structure-sensitive factor ρ close to 0.5 obtained from combined SLS/DLS identifies a corona of dangling chains enclosing the stable dense Ag⁺–PA aggregates which have a size of 25–50 nm. Finally, a 3-fold excess of Ag⁺ to COO– in the systems induces precipitation of Ag⁺–PA.
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