Local non-randomness and excess second-order thermodynamic quantities

Abstract

Systems exhibiting large H E and G E and within ~100 K of the UCST show a W-shape concentration dependence in C p E which is ascribed to two contributions: a “normal”, random C p E of negative sign and a positive non-random C p E. Approaching the LCST, the W-shape should be found when the LCST is due to a large free volume difference between the components but not for an aqueous system LCST. As with C p , other second-order quantities such as α p and K T tend to infinity at T C. It appears that a W-shape d V E d P would be discernible only for T less than a degree from T C. Both random and non-random contributions to d V E d T have the same sign and hence the W-shape should not be found. Experimental d V E d T results were discussed in terms of the Flory theory. The discrepancy observed between experimental and predicted values near the UCST is associated with non-random contributions to d V E d T .