Coil-Collapse and Coil-Aggregation due to the Interaction of Cu²⁺ and Ca²⁺ Ions with Anionic Polyacylate Chains in Dilute Solution

Abstract

A detailed light scattering investigation is presented on dilute solutions of long chain sodium polyacrylate in the presence of Cu 2þ ions under conditions which are close to the precipitation threshold of the respective Cu 2þ -PA chains. The results are compared with literature data ( Eur. Phys. J E 2001, 5, 117-126) from the corresponding system in the presence of Ca 2þ ions. In all cases the solvent is a 0.1 M NaCl solution in water. The PA coils shrink considerably with increasing Cu 2þ concentration as the conditions approach the precipitation threshold. Yet, the extent of shrinking can not be driven as far as for the respective Ca 2þ -PA system, where fully collapsed sphere-like polymers had been observed at the threshold. Analysis of the aggregation process with time-resolved static light scattering reveals loose coil-like aggregate structures for Cu 2þ -PA aggregates and compact sphere-like aggregates for Ca 2þ -PA in accordance with the limiting shape of the respective shrunken single chains. The onset of Ca 2þ or Cu 2þ induced aggregation of PA chains at the precipitation threshold borders an intramolecular coil shrinking process. The transition of shrinking into aggregation occurs more readily with Cu 2þ -PA as it does with Ca 2þ -PA.

Molecular Insights in the Structure and Layered Assembly of Polyelectrolytes at the Oil/Water Interface

“…This long time dependence is in part attributed to adsorption of highly disordered, coiled chain structures 92,93,[96][97][98][99] to the interface that subsequently spread at the interface due to favorable interactions between the polymer hydrophilic groups and the water and the hydrophobic groups with the oil. As clarified by previous bulk studies, these coiled chain structures increase in stability with increasing the number of interactions between the Ca 2+ ions and the carboxylate groups, 95 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 As with PAA, monovalent cations are also shown to induce the adsorption of iPMA to oilwater interface, and the interactions with the carboxylate groups are also found to be weaker than with divalent cations. 29 This is seen in the VSF spectra of iPMA with 10 mM ionic strength KCl compared to with 10 mM ionic strength CaCl 2 , as shown in Figure 15.…”

Kinetic and Structural Features of a Dyestuff Coaggregation Studied by Time-Resolved Static Light Scattering

“…It was demonstrated in preceding works 6,11,25 that this approximation holds up to q 2 ⟨R g 2 ⟩ z = 4 for the scattering patterns of semiflexible chains. Its application makes the apparent weight-averaged molar mass M w and the z-averaged square radius of gyration ⟨R g 2 ⟩ z of the solute accessible from fitting Kc/R(q) by a quadratic polynomial if the scattering contrast and the concentration are known.…”

Formation of Nanoparticles and Nanostructures—An Industrial Perspective on CaCO3, Cement, and Polymers

“…[82] 2) The interaction of, for example, polycarboxylates with divalent cations is complex and may involve the non-adjacent binding of ions to carboxylate groups for entropic reasons, [83,84] ion-induced polymer aggregation, [83,85] as well as ion-specific non-equilibrium effects. [86] 3) Polymers may bind to CaCO 3 ion pairs [87] or larger clusters [88] instead of simply sequestering calcium ions. 4) Polymer-ion, polymer-ion pairs, or polymer-cluster complexes may act as nucleating centers.…”