CALCIUM-INDUCED SHRINKING OF POLYACRYLATE CHAINS IN AQUEOUS-SOLUTION

Conformational changes of polyacrylate chains induced by Ca2+ ions have been studied by means of static light scattering and viscosity measurements with two different sodium polyacrylate samples. The reference system was sodium polyacrylate in an aqueous solution of 0.1 N NaCl at a pH of 9. Replacement of different amounts of the Na+ ions from the added NaCl by Ca2+ ions led to different Ca2+ fractions at constant ionic strength of the low molecular weight salt. At each Ca2+ ion fraction, the size of the polyelectrolyte coils was recorded as a function of polyacrylate concentration. The results were discussed in terms of a coil collapse which precedes precipitation of the calcium polyacrylate when lowering the polyacrylate concentration. The polyacrylate concentration where this coil collapse occurs correlates with the content of calcium ions in solution.