Comutação eletro-óptica em amostras nemáticas torcidas dopadas com nanobastões de ouro

Abstract

In the last decades, interest in improving the physical properties of liquid-crystalline systems using noble metal nanoparticles has grown significantly. These materials have unique optical and electrical properties associated to the phenomenon of surface Plasmon resonance, some studies show that the addition and geometry of gold nanoparticles can alter the electrical reactions of liquid crystals. This study is dedicated to the investigation of reorientation properties in liquid crystal samples 4-octyl-4-cyanobiphenyl (8CB), under helical confinement conditions, doped with gold nanobonds varying the average length of the nanobonds. For this, an optical experimental configuration is used to investigate the electro-optical response of twisted cells, associated with the effects of the aspect ratio on the viscoelastic properties of nematic cells when subjected to an AC electric field. We found a reduction in the Freedericksz threshold voltage and in the reorientation times, in samples containing gold nanobonds, compared to the pure sample, the effects are more pronounced in the system containing the longer elongated nanoparticles. The band longitudinal plasmon extinction is excited in order to evaluate the contributions of surface plasmon resonance to the times of reorientation induced by the metallic particles. Gooch-Tarry conditions and Mauguin minimums are explored in order to evaluate the thermal dependence of nematic birefringence in both samples: pure and doped, observing in the doped materials a reduction of the discontinuity of the nematic parameter. We studied the effects associated with anisotropy dielectric of doped and pure samples in a helical configuration. Our results show that the electro-optical and thermal parameters of twisted nematic cells are strongly affected by the addition of gold nanobars. A discussion is made of the relationship between the introduction of gold nanobonds and the liquid-crystalline order, revealing the possibility of improvements in technological applications using these systems.