Testing the Curie de-Gennes conjecture

Orateur : Soutenance de Thèse de Fatima RIDA

Mirror symmetry breaking is an ever-fascinating topic that plays a crucial role in physics, chemistry, and biology. The ultimate goal of this study is to demonstrate experimentally the so-called Curie de-Gennes conjecture. It was proposed for the first time by P. Curie (1894) and later developed by de-Gennes to generate dissymmetry (enantiomeric excess (e.e.)) by submitting a racemic mixture to the combined influence of collinear magnetic and electric fields. Such influence modifies the kinetics of the system : one of the enantiomers is being formed faster with respect to the other because of a lower activation energy (Ea), depending on the orientation between magnetic and electric fields ((anti)parallel). This influence was later named by Barron as a « falsely chiral influence ». To achieve that goal two different experiments were developed : 1) The enantioselective crystallization of a chiral metal-organic framework under external physical influence (magnetic field or rotation force) by slow diffusion. The small e.e. is expected to be created and amplified by crystal growth at the interface (aqueous solution / ethanol-saturated vapors). In this experiment, we have found that the Curie de-Gennes conjecture demonstration is difficult to achieve due to high dispersion of the average of the observed e.e. and the weakness of the expected effect. 2) Creating an enantiomeric excess in a racemic atropisomeric biphenyl based liquid crystal (LC) by applying (anti)parallel magnetic and electric fields. The helical twisting power of biphenyls molecules in the nematic phase will enhance the e.e. signal to a measurable level. The second experiment gave us more convincing results regarding a Curie de-Gennes conjecture demonstration. We have experimentally observed for the first time e.e of biphenyl-based Nematic Liquid Crystals (NLCs) derivatives induced by (anti)parallel combination of magnetic and electric fields. This excess was linearly dependent on the product of magnetic and electric fields and within one order of magnitude of the theoretical estimates. Based on the above results, Curie de Gennes conjecture is tentatively confirmed.

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