K. Endoh et al., Thermally-induced transition in aqueous solution of cationic surfactant containing aromatic ring, J THERM ANA, 57(3), 1999, pp. 669-678
Heat capacities of aqueous solutions of cetyltrimethylammonium (CTA) salicy
late, of CTA m-hydroxybenzoate and of CTA p-hydroxybenzoate were measured u
sing a scanning microcalorimeter. Only the salicylate solution exhibited he
at-capacity anomaly around 330 K, depending on the heating rate. The transi
tion enthalpy was 3.5+/-0.2 kJmol(-1), which was similar to that observed i
n solution of 1:1 intermolecular compound between CTA bromide (CTAB) and o-
iodophenol (OIPh). The enthalpy of formation Delta H-f of the 1:1 intermole
cular compound from CTAB and OIPh was determined by measuring the enthalpie
s ofsolution of the relevant crystals into ethanol. Positive value Delta(f)
H=3.0+/-0.3 kJmol(-1) was explained from a large difference between the he
at capacities of the 1:1 compound and 1:1 mixture of the component crystals
.