Thermal Behavior of Anhydrous Ascorbic Acid 6‐Palmitate with Trace of Decomposition

Abstract

AbstractAscorbic acid 6‐palmitate (AsP) is an industrially utilized antioxidant and amphiphilic lipid, which forms a liquid crystalline (LC) phase. Herein, we describe the basic thermal behavior of AsP under anhydrous condition. Grazing‐incidence wide‐angle X‐ray‐diffraction (GI‐WAXD) measurements using a two‐dimensional detector (2D‐GI‐WAXD) and perpendicularly aligned AsP films, together with thermal analysis, showed that the AsP forms only a lamellar LC phase above its melting point (Tm); however, when the LC phase was cooled to facilitate annealing and recrystallization, crystals (Cr) formed with a low degree of crystallinity. Furthermore, a composite system, consisting of the Cr phase and LC phase of AsP, was obtained upon reheating. These anomalous phenomena were likely caused by trace dimerization and decomposition of AsP at a temperature just above Tm, although thermal decomposition accompanied by weight reduction occurred at a much higher temperature in the isotropic phase (IL). Thus, the basic thermal behavior of AsP, which is essential for its use, was unveiled.