Abstract
AbstractThe phase separation of polycarboxylates in the presence of high concentrations of 1:1 and 1:2 electrolytes has been studied. Sodium polyacrylate remained in one phase at concentrations as high as 5 mol dm−3 sodium chloride whereas the fully ionised copolymer of acrylic acid and maleic anhydride (PAMA) phase separated at less than 1.0 mol dm−3. PAMA phase separated at polymer and electrolyte concentrations that had constant sodium ion activity, showing that the separation was essentially due to the common ion effect. Potassium salts did not produce any separation. In contrast to the 1:1 electrolytes, addition of 1:2 electrolytes (Na2SO4 and Na2CO3) produced no separation, indeed caused a two‐phase system, to revert to one phase. This initially surprising result was attributed to the increasing negative adsorption of the SO4−2 or CO3−2 from the polyion as the latter's concentration increased. This negative adsorption was expected to be greater for divalent than monovalent anions.
Published Version
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