Propriedades ópticas: caracterização e análise de uma fase nemática biaxial negativa

• Autor(a) principal: Braga, Wladimir Sérgio
• Data de Publicação: 2015
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Repositório Institucional da Universidade Estadual de Maringá (RI-UEM)
• Texto Completo: http://repositorio.uem.br:8080/jspui/handle/1/2640
• topic: Conoscopia óptica; Nemática biaxial positiva; Ciências Exatas e da Terra; Física

In this work, the optical conoscopy of polarized light, refractometry and optical birefringence techniques were used to characterize and analyze the negative biaxial nematic phase in lyotropic mixtures. In this sense, samples were prepared from systems containing [potassium laurate (KL), decanol (DeOH), deuterio oxide (D2O)] and [potassium laurate (KL), potassium sulfate (K2SO4), decanol (DeOH), water (H2O)]. In these systems, the phase transitions ND NB - ND and ND - NB - NC were investigated, as well as NC - NB - ND sequence for the second system. For all samples, the conoscopic images of the nematic discotic phase (ND), optically positive, is a well-defined cross (maltese cross). For the nematic calamitic phase (NC), optically negative, the figure is a wide and diffuse cross that occupies practically the entire visual field of the microscope. With a rotation of 45o of the plate, the conoscopic image of a biaxial nematic phase (NB) are two isogires that open toward opposite quadrants. For the phase sequence ND - NB - ND, the biaxial nematic phase is optically positive (N+B). Although already provided in the literature, the study of this phase sequence was presented here for the first time. A complete study was carried out in a ND-NB - NC phase transitions. The optical conoscopy results demonstrate the occurrence of a negative biaxial nematic phase (N-B). The biaxial medium may not only be positive. There is a point on the biaxial medium, where the optical signal changes from N+B to N -B . This study inserted this interesting result in the literature. For the second system, where the sample has the NC - NB - ND transitions phase,it was carried out measurements of refractometry associated associated with optical birefringence. The results showed the behavior of the three indices of refraction in the biaxial medium. Besides the positive biaxial nematic phase N+B, conoscopic images of the system also show the occurrence of the negative biaxial nematic phase N-B.