The ascorbyl palmitate–polyethyleneglycol 400–water system phase behavior

Ascorbyl palmitate (Asc16) in polyethyleneglycol 400 (PEG 400)–water mixtures at weight fractions (w/w) between 0.05 and 1.0 were studied by differential scanning calorimetry (DSC) and polarizing microscopy (PM) at different temperatures. The employed PEG 400–water proportions were: 0–25–50% and 75% of polymer. A complete phase diagram was determined for each PEG 400–water mixture. c mesophase and two (probably three) lamellar mesophases were detected in different regions of the phase diagrams. The addition of PEG 400 to the Asc16–water system shifts the limits of the liquid crystalline domains to lower temperature and surfactant concentration. At weight fraction of PEG 400 ≥ 50%, the limits of the domain of existence of cubic mesophase shift to low surfactant concentration compared with water-rich systems. The hydrated crystals are Asc16.2·6H2O. If the proportion of water is lower than that value, a mixture of hydrated and anhydrous crystals appears. Heating these crystals produce waxy crystals having melted hydrocarbon bilayers retaining their crystalline structure because the polar bilayers are still rigid.