Brief Summary of the Landau-de Gennes Model

The simplest and best known description of the thermodynamic behavior in the vicinity of the N-I transition was given by de Gennes many years ago [1]. This phenomenological description of the pretransi-tional effects in the isotropic phase is based on the expansion of the excess free energy as a function of the order parameter 5 in the 

In the vicinity of the transition, it is expected that A varies as A=a(T-T ), where T is the second order transition temperature (B=0). As T lies below T, the effective transition temperature, we have (T -T )= (2B)/(9aC). When the transition is weakly first order, which is generally the case with calamitic liquid crystals, B is small and the quantity T -T ) is expected to be small too. 

Short range effects are of importance just above the transition temperature T, and are responsible for the formation of small domains already exhibiting a nematic order. These effects lead to some specific physical properties [1-3] below are reported two examples of static pretransitional effects observed experimentally. 

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