3. Physical characteristics and structure-properties correlation

3.1 Elastic constants

In the absence of any external intervention, the nematic liquid crystal chooses a uniform molecular orientation. To change this orientation, energy must be expended, just as to deform a solid. The elastic constants used in Frank's elastic theory are a measure of this energy. The greater the constants, the more difficult it is to deform the structure. In the case of liquid crystals, this involves a change of orientation, which is why the word "distortion" replaces "deformation".

In the presence of external actions (mechanical, electrical or magnetic), the liquid crystal chooses a texture that ensures the minimum of its total energy. If the molecular orientation of the nematic liquid crystal is described by the local director