Nematic phase

The nematic phase has orientational order, but no positional order.

Discotic nematic phase

In the uniaxial nematic phase, defining the z-axis to be parallel to the nematic axis, one has

\epsilon _{\alpha \beta }={\begin{pmatrix}\epsilon _{\bot }&0&0\\0&\epsilon _{\bot }&0\\0&0&\epsilon _{\|}\end{pmatrix}}

The anisotropy is defined as

\Delta \epsilon =\epsilon _{\|}-\epsilon _{\bot }

.

The response of a nematic liquid crystal to an external electric field depends on both the sign and the magnitude of $\Delta \epsilon$ .