A DEFECTIVE SWELLING LAMELLAR PHASE

The phase equilibria in mixtures of egg lecithin and cetyltrimethylamm onium chloride in brine (100 mM sodium chloride) were studied with par ticular emphasis on the behavior of the lamellar phase. The solvent co rner of this pseudoternary system features an extensive lamellar phase which we have characterized by means of cryo-transmission electron mi croscopy (cryo-TEM), small-angle X-ray diffraction, and H-2 and P-31 N MR. The cryo-TEM micrographs illustrate a smooth transition in aggrega te microstructure between lamellar and micellar structures with a perf orated lamellar structure as an intermediate state. The findings from X-ray diffraction and NMR spectroscopy also indicate a deviation from ordinary bilayer structures in the solvent rich region of the lamellar phase. This is concluded from strongly nonideal swelling and progress ively decreasing H-2 NMR quadrupole splittings of the deuterated cetyl trimethyl-ammonium chloride inside the lamellar region. The correlatio n between the observed aggregate structures and the phase behavior is discussed in terms of a continuous transition from the lamellar to the micellar phase.