|
The Distortion free energy density is a quantity that describes the increase in the free energy density of a liquid crystal caused by distortions from its uniformly aligned configuration. It also commonly goes by the name Frank free energy density named after Frederick Charles Frank. ==Nematic Liquid Crystal== The Distortion free energy density in a nematic liquid crystal is a measure of the increase in the Helmholtz free energy per unit volume due to deviations in the orientational ordering away from a uniformly aligned nematic director configuration. The total free energy density for a nematic is therefore given by: : where is the total free energy density of a liquid crystal, is the free energy density associated with a uniformly aligned nematic, and is the contribution to the free energy density due to distortions in this order. For a non-chiral nematic liquid crystals is commonly taken to consist of three terms given by: : The unit vector , which describes the nature of the distortion. The three constants are known as the Frank constants and are dependent on the particular liquid crystal being described. They are usually of the order of dyn. Each of the three terms represent a type of distortion of a nematic. The first term represents pure splay, the second term pure twist, and the third term pure bend. A combination of these terms can be used to represent an arbitrary deformation in a liquid crystal. It is often the case that all three Frank constants are of the same order of magnitude and so it is commonly approximated that . This approximation is commonly referred to as the one-constant approximation and is used predominantly because the free energy simplifies when used to the much more computationally compact form: : A fourth term is also commonly added to the Frank free energy density called the saddle-splay energy that describes the surface interaction. It is often ignored when calculating director field configurations since the energies in the bulk of the liquid crystal are often greater than those due to the surface. It is given by: : The anchoring energy is given by and the unit vector is normal to the particles surface. 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Distortion free energy density」の詳細全文を読む スポンサード リンク
|