Article,
Pressure effect on phase behavior of binary mixtures of cis-unsaturated fatty acids
Chemistry and Physics of Lipids, 82 (1): 63--72 (July 1996)
Abstract
The solid-to-liquid phase transition of binary mixtures of cis-monounsaturated fatty acids was investigated as a function of their composition under various pressures up to about 200 MPa by means of a high pressure differential thermal analysis. Two mixture systems were examined; one is the mixture composed of oleic acid (OA; cis-9-octadecenoic acid) and palmitoleic acid (POA; cis-9-hexadecenoic acid), and the other is that composed of asclepic acid (APA; cis-l l-octadecenoic acid) and POA. The components in the former mixture differ in the length of omega-chain (the aliphatic chain segment between the double bond and methyl end group) by two methylene units, whereas those in the latter mixture differ in the length of Delta-chain (the chain segment between double bond and carboxyl group) by two methylene units. In both mixtures, the temperature of solid-liquid phase boundary, i.e. solidus and liquidus lines, was drastically increased by the increase in pressure. On the other hand, the shape of the phase boundary remained almost unaltered regardless of the pressure. The characteristic features in solid phase of these fatty acid mixtures, i.e. the molecular compound formation for OA/POA mixture and the highly restricted mutual miscibility for APA/POA mixture, are retained even under high pressure. This indicates that the intermolecular interaction of cis-monounsaturated fatty acids responsible for determining the phase behavior of binary mixture systems is rather insensitive to pressure, at least in the range up to 200 MPa.
