REPULSIVE PRESSURE BETWEEN MONOGLYCERIDE BILAYERS IN THE LAMELLAR AND GEL STATES

The swelling pressure of two different monoglycerides, monoolein and monopalmitin, has been investigated at different temperatures through the analysis of water vapor pressure data obtained by head-space gas chromatography. The structural characteristics of the lamellar and gel phases of monoglyceride-water mixtures were determined by low-angle X-ray diffraction. In the lamellar phase, a strong repulsive force is observed, which is not very dependent on the type of monoglyceride or on the temperature. In the gel phase, the repulsive pressure is significantly lower. The range of the swelling pressure is less than for phospholipids (about 10 Å for monoglycerides and 20-30 Å for phospholipids), demonstrating the decisive rule of the polar head-group. A comparison with the forces acting between monoglyceride layers deposited on solid surfaces, measured by a surface force apparatus, reveals a qualitative agreement between the two techniques. The most significant difference is that the repulsive force at short separations (<5 Å) is lower between deposited layers than between free bilayers. © 1990 American Chemical Society.