Influence of Temperature on the Phase Behavior of 1,2-Diol Derivatives

• Published in: The journal of physical chemistry. B Vol. 102; no. 17; pp. 3238 - 3242
• Main Authors: DeWolf, C, Brezesinski, G, Weidemann, G, Möhwald, H, Kjaer, K, Howes, P. B
• Format: Journal Article
• Language: English
• Published: American Chemical Society 23-04-1998
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp9802174

Monolayers of the racemic 1-palmitoylglycerol (1) and 1-hexadecylglycerol (2) were investigated by grazing incidence X-ray diffraction (GIXD) and Brewster angle microscopy (BAM) at temperatures from 5 to 33 °C. Above 13 °C a liquid-expanded phase was found for 1 and 2, and both compounds show a transition to a condensed phase with a NN tilted centered rectangular structure. This transition pressure increases with increasing temperature. A second transition to a NNN tilted phase was observed using GIXD. In the case of 1 this transition pressure has a stronger temperature dependence than for 2. The NN−NNN transition pressures were additionally found to be much higher for 1 than 2. The surface pressure at which upright oriented molecules should be found was extrapolated from GIXD measurements. The transition was visualized for 1 using Brewster angle microscopy. A nonzero lattice distortion at zero tilt angle was obtained for both compounds, indicating an ordering of chain backbones, possibly herringbone packing. Phase diagrams have been constructed for 1 and 2.