Phase behavior of the n-decanoic acid plus thallium(I) n-decanoate system

The temperature and enthalpy vs composition diagrams of the binary system [ (1 - x) n-C9H21CO2H + (x) n-C9H21CO2Tl, where x = mole fraction] were deter mined by means of differential scanning calorimetry, differential thermal a nalysis, and optical microscopy. Besides the usual regions of phase separat ion, miscibility was observed in isotropic liquid, liquid crystalline, and solid phases. This binary system displays the formation of: (1) a 1:1 molec ular compound which melts incongruently at T = 322.2 +/- 13.1 K, Delta(fus) H(m) = 50.7 +/- 0.5 kJ.mol(-1); (2) an eutectic at x = 0.125 and T = 302.0 +/- 0.1 K, Delta(fus)H(m) = 28.3 +/- 0.3 kJ.mol(-1); (3) a smectic A lyotro pic mesophase occurring at T = 373.5 +/- 0.1 K over the composition range x > 0.770; (4) a solid solution phase occurring over the composition x > 0.9 13, and 315.3 K < T < 404.2 K.