Phase equilibria and thermodynamics of liquid and solid crystal phases: formation of transition metal dodecyl benzenesulfonates

Abstract

The precipitation solubility equilibria in detergent-metal ion aqueous solutions were characterized by the solubility constants (pK ⁰_so ) of manganese, cobalt, nickel, and copper dodecyl benzenesulfonate as follows: Mn (DBS)²:10.78±0.10 Co (DBS)²:11.17±0.19 Ni (DBS)²:11.01±0.12 Cu (DBS)²:11.33±0.29

The formation of solid and liquid crystal phases, as well as their mixtures due to the mutual nucleation of crystals (usually very fast) and the formation of smectic (slower processes) were characterized by reaction enthalpies.

The precipitation experiments were performed by the light scattering method (20°–90°C); reaction calorimetry was used for the heat exchange measurements, and the characterization of phases was done by polarization microscopy and x-ray diffraction.

The precipitation enthalpies (ΔH ⁰_prec ), as well as the reaction enthalpies (ΔH _SC), showed almost the same values for some of the examined dodecyl benzenesulfonates. The formation of liquid or solid crystal phases exhibited endothermic or exothermic behavior, respectively. Several periodicities exhibited in the smectics of the samples examined point to a different structural organization in smectic bilayers.