Phase behavior and rheological properties of lecithin/TTAOH/H2O mixtures

Abstract

The phase behavior, structures, and rheological properties of lecithin/tetradecyltrimethylammonium hydroxide (TTAOH)/water system were investigated by cryogenic transmission electron microscopy (cryo-TEM), polarization optical microscope, 1H and 31P nuclear magnetic resonance (NMR) spectra, surface tension, and rheological measurements. With the variation of mixing molar ratios and concentrations of lecithin and TTAOH, the system exhibits the phase transition from micelles (L1 phase) to vesicles (Lα phase) through a phase separation region. The rod-like micelles, uni- and multilamellar vesicles were determined by means of cryo-TEM observations. The surface tension and rheological measurements were performed to follow the phase transition. The samples of L1 phase region behave as Newton fluids at low concentration of lecithin. With the increase of the lecithin concentration, a shear-thinning L1 phase at the shearing rate 100 s−1 was found. The samples of \( {{\text{L}}_{\alpha }} \) phase region show viscoelastic properties of the typical vesicles. The interactions between lecithin and TTAOH were monitored by 1H and 31P NMR spectra. These results could contribute towards the understanding of the basic function of lecithin in biological membranes and membranous organelles.