ALPHA-MELT-MEDIATED CRYSTALLIZATION OF 1-PALMITOYL-2-OLEOYL-3-STEAROYL-SN-GLYCEROL

The alpha-melt-mediated crystallization of 1-palmitoyl-2-oleoyl-3-stea royl-sn-glycerol (POS) has been investigated by differential scanning calorimetry (DSC), combined with polarized-light microscopy. Starting from a completely liquid state, the melt was first cooled down and mai ntained at a temperature, T-1, during a time, t(1), where the alpha-ph ase formed. Then it was heated to a temperature, T-2, above the meltin g point of alpha for isothermal solidification into a solid phase, whi ch was identified as delta. Based upon DSC solidification peaks, the t ime-temperature-transformation (TTT) diagram of POS was constructed fo r these solidification conditions and was compared with the TTT diagra m of direct crystallization from the melt. The alpha-melt-mediated sol idification showed accelerated kinetics of the delta-phase. The effect s of T-1 and t(1) were also studied: at short t(1), crystallization wa s faster with a decreasing value of T-1, whereas the opposite trend wa s observed for a longer plateau at T-1. These tendencies were interpre ted in terms of three competing phenomena: the density of delta-nuclei that can form during the plateau at T-1, alpha-delta solid-state tran sformation, and memory effects of molecule arrangements in the alpha-r emelted phase.