Hexagonal phases initial formation

Proposed more than 20 years ago, the stalk intermediate—a highly curved lipid stmcture— provides the most plausible description of the initial fusion stage currently available. The related stalk-pore mechanism (23-25) of fusion is viewed favorably by most researchers. It shows the close relation between fusion and the transition from lamellar into bilayer cubic and hexagonal phases (see Fig. 4 in the section entitled Formation of nonlamellar phases in membrane lipids ). Studies on the rhombohedral phase formed in partially dehydrated lipids provide another insight into the possible structure of fusion stalks (26). 

Tricalcium aluminate hydrates to form, initially, hexagonal phases identifiable by endothermal effects in DTA at 150-200°C and 200-280°C. These are converted to a cubic phase of formula C3AHg which exhibits endothermal effects at 300-350°C and 450-500°C. The addition of ligno-sulfonate influences the rate of formation of these phases and their interconversions to the cubic phase. Depending on the amount of lignosulfonate, the hexagonal phase may be stabihzed even up to fourteen days or more with lignosulfonate, but in that hydrated without the admixture, the cubic form may appear at six hours or earlier (Fig. 1). ... 

Although most of the initial polymers and copolymers are no longer available, these systems should help us to investigate the details and structural consequences of a pre-ordering of the polymer melt, or the formation of a precursor crystal in polymer crystallization. From the present and as yet still sketchy results, it appears however that (a) if a crystal phase results from the transformation of a liquid crystal phase (usually of hexagonal symmetry), different orientations of the crystal unit cell are likely, which is not observed in conventional polymer crystallization (for example, in polyethy-... 

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