Heats of dilution of polyacrylic acid at various degrees of ionization

The heats of dilution of polyacrylic acid at four constant degrees of ionization (α = 0, 0.25, 0.50, and 1.00) have been measured in the concentration range 0.6-0.002 monomolal. The heat of dilution for pure acid (α = 0) is positive in the investigated concentration range, whereas it is negative for partially neutralized acid (α = 0.25 and 0.50). For completely neutralized add, for sodium polyacrylate (α = 1), the measured heat effects are exothermic at concentrations above about 0.05 monomolal. while below 0.05 M they become endothermic. The experimental results have been evaluated with the help of a previously developed theoretical treatment based on the cell model.