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In this work we will study the behavior of the optical signal and optical axes along the continuous transition of a lyotropic system from a nematic discotic () phase to a nematic calamitic () phase; we will study in detail the case in which there is a biaxial nematic () phase at the interstice between these two uniaxial phases. It will be shown that the optical signal and optical axes change simultaneously in order to agree with the optical signals of the uniaxial phases at their borders: the optical signal is positive at the frontiers with the phase and it turns to be negative at the frontiers with the phase. Concomitantly, the optical axes rotates from the direction to the direction. We will illustrate these findings with experimental data that confirm our results. [ABSTRACT FROM AUTHOR]

In this work, we study and characterize the cholesteric sequence of phases (ChDr−ChB−ChD), where the firstChDris the reentrant cholesteric discotic phase,ChBis the cholesteric biaxial phase and the secondChDis the cholesteric discotic phase. This sequence of phases is studied through polarized light microscopy and image processing technique, where, for the first time, the domains and borders of these transitions are established and characterized. They are also investigated and optically characterized throughout their textures. [ABSTRACT FROM AUTHOR]

The nematic phases of a lyotropic systemNadS/ decanol/ heavy water are investigated using optical conoscopy and image processing. The phase diagram obtained from these lyotropic materials predicts the occurrence of a direct phase transition, which does not present the biaxial nematic phase, between the discotic (ND) and calamitic (NC) nematic phases. A biaxial nematic (NB) phase is optically characterized and confirmed through conoscopic image, inside the biaxial range, between the two uniaxial nematic phases. Also, their respective transition points are determined by means of image processing. TheNBphase observed here is discussed as part of the nature of the micellar configuration of lyotropic materials which exhibit uniaxial nematic phases. [ABSTRACT FROM AUTHOR]

The system SDS/decanol/water is investigated by polarized optical microscopy. A reported biaxial island is here confirmed by conoscopy, in the temperature interval 20°C to 26°C. Coexistence regions of the two uniaxial nematic phases (discotic ND+ cylindrical NC) are also confirmed, in different temperature intervals. While the biaxial phase is stable for at least 10 hours, in a reproducible way, along the same time the coexistence region evolves with time, and drops of the discotic phase grow immersed in a NCmatrix. Results are explained in terms of recent theories dealing with stabilization of mixtures of cylinders and discs. [ABSTRACT FROM AUTHOR]

The phase diagram is an interesting field of research, particulary in lyotropic liquid crystals (LLC). In this way, one of the most important phase diagrams of this LLC system was reported by Yu and Saupe. Two uniaxial (calamitic --NC and discotic --ND) and one biaxial nematic (NB) phases were determined by these authors. Furthermore, in this phase diagram the classical isotropic phase ( I was observed at high temperature as well as a reentrant isotropic phase (IRE) which takes place at lower temperature. Later, this phase diagram was also studied by several authors and in all cases the IRE-NC- I phase transitions were not observed. In this work, we present a study of this phase diagram through digital image processing and refractometry optical techniques. The occurrence of these phase transitions is investigated and characterized. In addition, the order parameter is obtained based on the Vuks hypothesis from a particular point, in the range of the NC phase, where the absolute value of the optical birefringence (Δ n is maximum. [ABSTRACT FROM AUTHOR]

The calamitic nematic (NC)-biaxial nematic (NB)-discotic nematic (ND) phase transitions are studied in a potassium laurate-decanol-potassium sulfate and water mixture by optical conoscopy. The NC-(ND+) phase is uniaxially negative (positive) as expected. A biaxial negative (NB-) nematic phase is optically characterized and confirmed through conoscopic image, inside the biaxial range, beyond the known biaxial positive (NB+) nematic phase. Conoscopic image of a biaxial nematic induced by material flow from ND+ phase is investigated and discussed in this work. [ABSTRACT FROM AUTHOR]