Transformation relationships among monomers, micelles, metastable solid, and stable solid in aqueous cetylpyridinium...

Kinetic studies on metamorphoses among monomer, micelle, metastable solid, and stable solid during the Krafft transition of cetylpyridinium chloride (CPC) in the aqueous solution were carried out. The Krafft transition accompanied a decrease of the electric conductance with a large increment of the dielectric permittivity Delta epsilon, which vanished after finishing the transition. The observing duration of large Delta epsilon in transforming to the metastable solid was much shorter than the duration in transforming to the stable solid. From the observing duration of Delta epsilon, a formation boundary between the metastable and the stable solids was determined as a function of the temperature and the CPC concentration. It was found from the boundary that the metastable solid forms in the micelle solution. A change in the electric conductivity kappa of metastable solid suspensions during metastable-stable transformation suggests the solid dissolution-limited metamorphosis of metastable solid into the stable solid in the solution. Arrhenius plots of the metastable-stable transformation durations obtained from the time courses of kappa changes gave the high activation energy of 290 kJ/mol for the metastable solid dissolution-limited metastable-stable transition.