# Hexagonal phase

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{{for|the sixth series of The Hitchhiker's Guide to the Galaxy|The Hitchhiker's Guide to the Galaxy Tertiary to Hexagonal Phases}}

{{Refimprove|date=September 2014}}
thumb|right|Schematic of the molecular organisation in a type I hexagonal lyotropic liquid crystalline phase.
A '''hexagonal phase''' of [lyotropic liquid crystal](/source/lyotropic_liquid_crystal) is formed by some amphiphilic molecules when they are mixed with water or another polar solvent. In this phase, the [amphiphile](/source/amphiphile) molecules are aggregated into cylindrical structures of indefinite length and these cylindrical aggregates are disposed on a hexagonal lattice, giving the phase long-range orientational order.

In [normal topology](/source/normal_topology) hexagonal phases, which are formed by [type I amphiphiles](/source/type_I_amphiphiles), the hydrocarbon chains are contained within the cylindrical aggregates such that the polar-apolar interface has a positive [mean curvature](/source/mean_curvature). [Inverse topology](/source/Inverse_topology) hexagonal phases have water within the cylindrical aggregates and the hydrocarbon chains fill the voids between the hexagonally packed cylinders. Normal topology hexagonal phases are denoted by H<sub>I</sub> while inverse topology hexagonal phases are denoted by H<sub>II</sub>. When viewed by [polarization microscopy](/source/polarization_microscopy), thin films of both normal and inverse topology hexagonal phases exhibit [birefringence](/source/birefringence), giving rise to characteristic optical textures. Typically, these textures are smoke-like, fan-like or mosaic in appearance. The phases are highly viscous and small air bubbles trapped within the preparation have highly distorted shapes. Size and shapes of lamellar, micellar and hexagonal phases of [lipid bilayer phase behavior](/source/lipid_bilayer_phase_behavior) and mixed [lipid polymorphism](/source/lipid_polymorphism) in aqueous dispersions can be easily identified and characterized by [negative staining](/source/negative_staining) transmission electron microscopy too.<ref>YashRoy R.C. (1990) Lamellar dispersion and phase separation of chloroplast membrane lipids by negative staining electron microscopy. Journal of Biosciences, vol.15(2), pp. 93-98. http://www.ias.ac.in/jarch/jbiosci/15/93-98.pdf</ref>

<gallery>
File:Hexagonal1a.jpg|Smoky optical texture of type I hexagonal phase
File:Hexagonal2a.jpg|Mosaic optical texture of type I hexagonal phase
File:Hexagonal3a.jpg|Mosaic/focal conic optical texture of type I hexagonal phase
</gallery>

==See also==
*[Lamellar phase](/source/Lamellar_phase)
*[Lipid polymorphism](/source/Lipid_polymorphism)
*[Micelle](/source/Micelle)

== References ==
<references />

Category:Surfactants
Category:Liquid crystals
Category:Colloidal chemistry
Category:Biophysics

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Adapted from the Wikipedia article [Hexagonal phase](https://en.wikipedia.org/wiki/Hexagonal_phase) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Hexagonal_phase?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.