Caracterização eletro-óptica de cristais líquidos dispersos em matriz polimérica

• Ano de defesa: 2005
• Autor(a) principal: Jesus, Manoel Messias Alvino de
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Estadual de Maringá; Brasil; Programa de Pós-Graduação em Física; UEM; Maringá, PR; Departamento de Física
• Palavras-chave em Português: Cristal líquido polimérico; Caracterização eletro-óptica; Cristal líquido liotrópicos; Matriz dispersa; Permissividade elétrica; Fotosensibilidade.; Ciências Exatas e da Terra; Física
• Link de acesso: http://repositorio.uem.br:8080/jspui/handle/1/2652

Throughout decades, liquid crystals come almost being used exclusively in electro-optic devices such as displays of information and sensors. The characterization of such devices becomes possible, over all in function of its anisotropic physical properties. Although research in lyotropics liquid crystals (LLC) presents intriguing peculiarities of the scientific point of view, the interest in this liquid crystal class has a focus in the study of biological systems, in view of the fact of they present similar structure to many organic components as the blood, cellular membranes and mitochondria. The application of LLC in devices does not constitute, necessarily, an insurmountable barrier but a rewarding challenge for the researchers of the area, taking in consideration, over all, the fact of that LLCs possess an very inferior cost and characterization and production relatively simple if compare to TLC (thermotropic liquid crystals). The CLL are formed by amphiphilic molecules dispersed in water forming aggregates called "micelles", with an anisotropy of form. In liquid crystalline mesophases, show a long-range orientational order, being uniaxial or biaxial, to the step that TLC are formed by "rigid" molecules with anisotropy of form. In the second half of the decade of eighty was developed a new material to the based on LC (liquid crystal) and polymer; this material was called PDLC (Polymer-Dispersed Liquid Crystal). In these systems, the liquid crystal is confined in a polymeric matrix in small spherical (or curvilinear) drops. The size changes in accordance with the concentration of mixture LC- Polymer. The objective of this work is to study the electro - optic properties such as electric permissivity and transmittance of LCs and PDLCs. The electric permissivity of these materials (in function of the frequency) is determined through the technique of dielectric spectroscopy, where the material is placed enters the plates of a capacitor. The dynamic answer of the material must be basically mechanisms of dielectric relaxation, or either, orientation of permanent dipoles or induction of dipoles. In the measures carried out, we use CLT (E7), CLL, PDLC (CLL + NOA65 and CLT + NOA65). We basically produce PDLC with only one photo sensible polymer, the NOA65 (Norland Optical Adhesive 65). Different concentrations of LC have been used and cells with different thickness had been characterized. We observe that the measures of electric permissivity of the sample depend strongly on geometry and area of the capacitor. Our results show that best geometry for dielectric characterization is circular geometry, with relatively great area. The investigation of the electro-optical properties is was made basically through three techniques: dielectric spectroscopy, optic refractometry, and optic transmittance; we use also optical microscopy with polarized light. We determined the electric permissivity in function of the frequency and amplitude of the applied electric field. Through these techniques we can observe the process of the dielectric relaxation of PDLC, formed from TLC and LLC, and verify the changes suffered in function of the confinement and the geometry of the system. We prove also that the results of dielectric spectroscopy obtained with a Lock-In are the same that the results obtained using a commercial impedance bridge (Solartron 1260).