Capacité calorifique de polyélectrolytes en solution

Heat capacities of polyelectrolytes in aqueous solutions have been measured at 25 °C using a Picker-type dynamic micro-calorimeter. The precision of the apparatus is such that it is possible to calculate the apparent molar heat capacity of the solute, even at high dilution. The polymers that were studied include polymethacrylic acid (PMAH) and polyacrylic acid (PAH), as well as its sodium salt and the sodium salt of the polystyrenesulfonate. For the salts, the results show that the value of decreases rapidly with dilution to low concentrations; this result is in perfect concordance with a relation derived from the theory of Lifson and Katchalsky. A study of the variation of at a constant concentration, with the extent of the neutralization of the acids PMAH and PAH has also been conducted. As has been shown previously, the chain of the PMAH undergoes a conformational transformation when the level of neutralization gets close to 25%. This transformation implies an increase of the value of [Journal translation]