The binary phase behavior of 1,3-dimyristoyl-2-stearoyl- sn-glycerol and 1,2-dimyristoyl-3-stearoyl- sn-glycerol

Abstract

The binary phase behavior of pure 1,3-dimyristoyl-2-stearoyl- sn-glycerol (MSM) and 1,2-dimyristoyl-3-stearoyl- sn-glycerol (MMS) was investigated in terms of polymorphism, melting and crystallization behavior, SFC, hardness and microstructure. Samples were crystallized at cooling rates of 3.0 and 0.1 °C/min. The asymmetric TAG demonstrated lower melting and crystallization points at both cooling rates. All samples crystallized in the β′ polymorph when cooled at 0.1 °C/min and in the α polymorph when cooled at 3.0 °C/min. The experimentally determined kinetic phase diagram of MSM–MMS was monotectic for both cooling rates. This data was well described by a thermodynamic model using the Bragg–Williams approximation for non-ideality of mixing and suggested that in both the solid and liquid states, like pair interactions (MSM–MSM and MMS–MMS) were favored over MSM–MMS interaction. A strong tendency to phase separation in the solid phase was also observed. For both cooling rates, the fit of the SFC (%)–time curves to a modified form of the Avrami model indicated that crystallization occurred in two distinct kinetic steps. Depressions seen in SFC did not correspond to depressions in hardness or melting temperatures.