Properties of molten carboxylates

Data are presented for the heats of phase changes and specific heats for the even chain length lead(II) carboxylates from hexanoate to octadecanoate. Structures are proposed by analogy to the properties of “fused” aqueous ampiphilic mesophases. Optical examination under a polarising microscope suggests the phase sequence

for the dodecanoate and lower chain length soaps. For tetradecanoate, and above, the V₂ phase is absent and the G phase melts directly to the liquid. The chain length dependence of the entropies of the crystal→G and G→V₂ or G→liquid transitions demonstrates that disordering of the hydrocarbon chain is a stepwise process. The entropy of the V₂→liquid transition is consistent with the melting of a globular solid and may indicate an average micelle size of 4 carboxylate molecules. This leads to a model of the isotropic liquid consistent with the viscosity data previously presented².