Solubilization of Trilaurin in Surfactant Solutions

We have studied the process of solubilization of dispersions of trilaurin by ethoxylated nonionic surfactants using optical microscopy and differential scanning calorimetry (DSC). The equilibrium solubility of the oil in the nonionic surfactant solution increases with increasing temperature and decreasing ethoxylate length, as would be expected for a system below the phase inversion temperature. The DSC data show that the nonionic surfactant partitions into the oil, producing a number of new structures that are not polymorphs of trilaurin. One of these new structures may be a mesophase that melts about 1−1.5 °C below that of pure trilaurin. Upon cooling this structure, which increases the affinity of the ethoxylate headgroup for water, further crystallizing and melting of the structure is prevented, possibly because it transforms into micellized trilaurin or into small droplets that are unable to nucleate. Creaming of the dispersion of trilaurin in the calorimeter cell complicates the results, though the heat changes measured are reproducible and not affected by creaming. Addition of poly(acrylic acid) to the trilaurin/surfactant dispersion slightly reduces the amount of oil solubilized and retards the distribution of the surfactant into the oil.