In
liquid crystals, homeotropic alignment is one of the ways of alignment of liquid crystalline molecules. Homeotropic alignment is the state in which a rod-like liquid crystalline molecule aligns perpendicularly to the substrate. In the polydomain state, the parts also are called homeotropic domains. In contrast, the state in which the molecule aligns to a substance in parallel is called
homogeneous alignment
In liquid crystals homogeneous alignment, sometimes called planar alignment, is the state of alignment where molecules align in parallel to a substrate. The opposite method is homeotropic alignment
In liquid crystals
Liquid crystal (LC) is ...
.
There are various other ways of alignment in liquid crystals. Because homeotropic alignment is not anisotropic optically, a dark field is observed between crossed polarizers in
polarizing optical microscopy
Polarized light microscopy can mean any of a number of optical microscopy techniques involving polarized light. Simple techniques include illumination of the sample with polarized light. Directly transmitted light can, optionally, be blocked wit ...
.
By conoscope observation, however, a cross image is observed in the homeotropic alignments. Homeotropic alignment often appears in the
smectic A phase
Liquid crystal (LC) is a state of matter whose properties are between those of conventional liquids and those of solid crystals. For example, a liquid crystal may flow like a liquid, but its molecules may be oriented in a crystal-like way. T ...
(S
A).
In
discotic liquid crystals homeotropic alignment is defined as the state in which an axis of the column structure, which is formed by
disc-like liquid crystalline molecules, aligns perpendicularly to a substance. In other words, this alignment looks like a state in which columns formed by piled-up coins are arranged in an orderly way on a table.
In practice, the homeotropic alignment is usually achieved by surfactants and detergent for example lecithin, some esilanes or some special polyimide (PI 1211). Generally liquid crystals align homeotropically at an air or glass interface.
Crystallography
Liquid crystals
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