A hexagonal phase of
lyotropic liquid crystal is formed by some amphiphilic molecules when they are mixed with water or another polar solvent. In this phase, the
amphiphile
An amphiphile (from the Greek αμφις amphis, both, and φιλíα philia, love, friendship), or amphipath, is a chemical compound possessing both hydrophilic (''water-loving'', polar) and lipophilic (''fat-loving'') properties. Such a compou ...
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 hexagonal phases, which are formed by
type I amphiphiles
Type may refer to:
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, the hydrocarbon chains are contained within the cylindrical aggregates such that the polar-apolar interface has a positive
mean curvature In mathematics, the mean curvature H of a surface S is an ''extrinsic'' measure of curvature that comes from differential geometry and that locally describes the curvature of an embedded surface in some ambient space such as Euclidean space.
T ...
.
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
I while inverse topology hexagonal phases are denoted by H
II. When viewed by
polarization microscopy, thin films of both normal and inverse topology hexagonal phases exhibit
birefringence
Birefringence is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light. These optically anisotropic materials are said to be birefringent (or birefractive). The birefrin ...
, 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 and mixed
lipid polymorphism in aqueous dispersions can be easily identified and characterized by
negative staining transmission electron microscopy too.
[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]
File:Hexagonal1a.jpg, smokey 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
See also
*
Lamellar phase Lamellar phase refers generally to packing of polar-headed long chain nonpolar-tail molecules in an environment of bulk polar liquid, as sheets of bilayers separated by bulk liquid. In biophysics, polar lipids (mostly, phospholipids, and rarely, gl ...
*
Lipid polymorphism
*
Micelle
A micelle () or micella () (plural micelles or micellae, respectively) is an aggregate (or supramolecular assembly) of surfactant amphipathic lipid molecules dispersed in a liquid, forming a colloidal suspension (also known as associated col ...
References
Surfactants
Liquid crystals
Colloidal chemistry
Biophysics
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