Landau—de Gennes Model for the Isotropic Phase of Nematogens: The Experimental Evidence Challenge

The Landau–de Gennes model is one of the most fundamental frameworks in the Physics of Liquid Crystals and Soft Matter Physics. It is based on the universal parameterisation of the Cotton–Mouton effect, the Kerr effect, and light scattering in the isotropic phase of nematogens. However, it was not until 1974 that de Gennes identified the first two problems of this model. Over the following decades, this list expanded. This report presents the first comprehensive analysis of these issues and demonstrates a coherent model explanation. Significant for reasoning are experimental results for the dielectric constant and its extension in a strong electric field, the nonlinear dielectric effect (NDE), where unusual features in the isotropic phase are particularly pronounced. Notably, NDE belongs to the mentioned group of properties, directly detecting the impact of pretransitional fluctuations. Essential role plays prenematic fluctuation, the structure of liquid crystalline molecules, and the scanning time-scale introduced by experimental methods. However, the question arises as to whether the proposed model explanation falls within or beyond the framework of the Landau–de Gennes model.