Fase azul : um estudo de parâmetros ópticos e termodinâmico

Abstract

In this work, we study the phases transitions of liquid-crystalline composite around the transitions temperatures N*-BP-I (cholesteric, "blue-phase", isotropic). The characterization techniques used were: densimetry, refractometry, optic microscopy of polarized light, interferometry and Z-scan experiment. We studied the optic and thermodynamic parameters using the Lorentz-Lorenz equation, to investigate the transitions nature N*-BP-I. The studied composites were the C46H80O3, COC, (cholesteryl oleyl carbonate) and the C9H18O2 (n-Propyl hexanoate, Propyl caproate or n-hexanoate). The composite cholesteryl oleyl carbonate presents the transitions N*-BPII-BPI-I, cholesteric-"blue-phase"II-"blue-phase"I-isotropic. Transition BPI-I of composite COC occurs at 36ºC, and the transitions interval between BPII-BPI and BPI-I is 0,33ºC. The composite n-hexanoate presents transitions N*-BPII-BPI-I. Transition BPI-I of the composite n-hexanoate occurs at 100ºC, and the transition interval between BPII-BPI and BPI-I is 0,55ºC. Both the composites, COC and n-hexanoate, are thermotropic. Using interferometry technique, we measured the thermal coefficient of the refractive index on a nematic composite K-15, that presents transition N-I, nematic-isotropic, at 35,3ºC, to compare the results obtained by means of this technique of composites nematics and cholesterics.