Influence of ionic surfactant on the anchoring energy of liquid crystal with a surface investigated using magnetic threshold fields of freedericksz transition

Abstract

The coupling of nematic liquid crystal 5CB and 5CB doped with ionic surfactant CTAB in the cells with plane-parallel interfaces was studied. For the cells with the varied nematic layer thickness at different temperatures, the dependencies of the passed laser radiation intensity on the magnetic field were obtained. From the threshold fields of Freedericksz transition, the polar anchoring energy of the liquid crystal to the surface was determined. The effect of the ionic surfactant on the anchoring energy was studied and it was found that the addition of the ionic surfactant to liquid crystal weakens the anchoring energy. The analysis of the accuracy of the anchoring energy determination based on the expression following from the Rapini - Popular relation was carried out. It was shown that the best experimental resolution of the anchoring energy is achieved when the thin nematic layers, stronger magnetic fields and weak anchoring of the liquid crystal molecules with the surface are used.