Heat of dilution of aqueous solutions of polyacrylates

Abstract

The heats of dilution (ΔH) of aqueous solutions of polyacrylates having various gegenions, i.e., sodium and tetra-alkylammonium (alkyl = methyl, ethyl, n-propyl and n-butyl), were measured. The (ΔH) value of the sodium polyacrylate was negative in the investigated concentration range (0.005–0.17 mol dm^–3), whereas those of organic salts were positive. With the addition of urea, the endothermicity was lessened. These results are discussed in terms of hydrophobic interactions between solute and solvent. The observed (ΔH) values were found to be in agreement with the values calculated by the theory of Lifson and Katchalsky, when an appropriate value of d ln a/d ln T is assumed (a is the ionic radius of rodlike macroion and T the temperature). However, the assumed value for this parameter was in disagreement with that obtained directly from the partial molal volume measurements (by a factor of ∼10²).