Abstract
The effect of hydrostatic Pressure on the polymorphic transformation and melting of cis-unsaturated fatty acids, palmitoleic acid (POA), oleic acid (OA), asclepic acid (APA), petroselinic acid (PSA) and erucic acid (EA), were investigated by means of a high-pressure differential thermal analysis. The temperature range of α form of OA and POA becomes wider as the pressure is increased, which is the same tendency as the high pressure phase of polyethylene. On the contrary, those of α1 form of EA and high pressure crystallized αp form of APA are narrowed by increasing pressure. This is similar trend to the hexagonal (rotator) phase of n-alkane. The values of ΔV on melting and conformational order-disorder transitions of ω chain were estimated from the Clausius-Clapeyron equation. The ΔV on γ-α transitions for POA, OA, and APA are almost the same (5.6-5.9cm3/mol), but that on γ1-α1 transition for EA is larger than those for the former acids. New polymorphs were formed for APA by the melt-crystallizatoin under high pressure above about 110MPa.
