Grandjean terraces

The textures in homeotropic lamellar phases of lecithin are studied in lecithin-water phases by polarizing microscopy and in dried phases by electron microscopy. In the former, we observe the La phase (the chains are liquid, the polar heads disordered)—the texture displays classical FriedeVs oily streaks, which we interpret as clusters of parallel dislocations whose core is split in two disclinations of opposite sign, with a transversal instability of the confocal domain type. In the latter case, the nature of the lamellar phase is less understood. However, the elementary defects (negative staining) are quenched from the La phase they are dislocations or Grandjean terraces, where the same transversal instability can occur. We also observed dislocations with an extended core these defects seem typical of the phase in the electron microscope. 

More interesting are the specimens obtained by drying on filter paper. In the best parts are beautiful homeotropic areas approximately 2000 A thick which can be observed without any structural change for hours, except for a slight recrystallization of Pb which has no effect on observations. There is no indication whatever of ordering in the layers. We classify the observed defects as (a) Grandjean terraces, (b) dislocation lines, (c) extended disolcation lines, and (d) other objects (see Ref. 19). 

Figure 13. Grandjean terrace (arrow indicates the axis of tilt)...

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