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Thermal studies on the phase transitions of the binary systems of water and surface active compounds such as (C18H37)N(CH3)3X(X=Cl, Br), (C18H37)2N(CH3)2X(X=Cl, Br) and C17H35COOK were performed and revealed that all the so-called Tc curves go down stepwise with an increase of the water content. At a temperature below the Tc curve, new, two phase transitions of Tgel (stable coagel-to-stable gel) and Tc* (metastable gel-to-supercooled liquid crystal/micellar solution) were discovered with detailed annealing treatments. In connection with this, thermodynamic stability of the gel phases was discussed on the basis of the schematic diagram of Gibbs energy vs. temperature. Furthermore, the "intermediate water" named by the authors, which is newly incorporated between the polar-layers of the surface active molecules at the elevated Tgel transition, was discovered, referring to the ice-melting thermogram below 0°C, and the predominent role of the bulk free water coexisting with the coagel phase for the appearance of the Tgel transition was stressed. In the extremely dilute aqueous solution at the neighborhood of c. m. c., thermodynamical data obtained by the adiabatic calorimeter provided new informations regarding the dissolution process of the surface active compound in the "Krafft temperature region", in the place of the so-called "Krafft point".
日本熱測定学会の論文