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Your search keyword '"Palangana, A. J."' showing total 142 results
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142 results on '"Palangana, A. J."'

1. Micellar shape anisotropy and elastic constants in discotic lyotropic liquid crystals

Author

de Castro, P. A., Palangana, A. J., and Evangelista, L. R.

Subjects
Condensed Matter - Statistical Mechanics, Condensed Matter - Other Condensed Matter
Abstract

The elastic constants of a discotic lyotropic nematic liquid crystal are calculated by means of a pseudo-molecular approach as functions of the micellar shape anisotropy. By assuming that the temperature dependence of the ratio of the elastic constants comes from the temperature dependence of the micellar shape anisotropy, the theoretical predictions are connected with experimental measurements for the ratio $K_{33}/K_{11}$. This procedure permits to determine, in a phenomenological way, the temperature dependence for the ratio of elastic constants and for the micellar shape anisotropy near the nematic-isotropic transition in agreement with the experimental data., Comment: 6 pages, 3 figures, published in Physical Review E

Published
2004
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2. Characterisation

Author

Dierking, Ingo, primary, Palangana, Antonio J., additional, Vij, Jagdish K., additional, Kocot, Antoni, additional, Madsen, Louis A., additional, and Davidson, Patrick, additional

Published
2015
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8. Micellar shape anisotropy and optical indicatrix in reentrant isotropic-nematic phase transitions.

Author

Simões, M., Palangana, A. J., Gobato, R., and Santos, O. R.

Subjects
*ANISOTROPY, *PHASE transitions, *NEMATIC liquid crystals, *GENERALIZATION, *REFRACTIVE index, *POTASSIUM, *DEUTERIUM oxide, *PHYSICAL & theoretical chemistry
Abstract

In this work, we will show that the concept of nematic order parameter and a generalization of the concept of optical indicatrix, largely used in optics of anisotropic crystals, can be joined to give a new geometrical representation to the anisotropies found in lyotropic liquid crystals. Our theoretical approach will be illustrated using refractive index data of reentrant isotropic-calamitic (discotic) nematic phase transitions of potassium laurate, decanol, and heavy water mixtures. [ABSTRACT FROM AUTHOR]

Published
2012
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10. Optical signal and optical axes in uniaxial and biaxial nematic phases.

Author

Simões, M., Bertolino, W. H. P., Davincy, T., Braga, W. S., Santos, O. R., Luders, D. D., Sampaio, A. R., Kimura, N. M., and Palangana, A. J.

Subjects
NEMATIC liquid crystals, OPTICAL signal detection, PHASE diagrams, REFRACTIVE index, DATA analysis
Abstract

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]

Published
2019
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11. An image processing study of a reentrant discotic cholesteric – biaxial cholesteric phase transition.

Author

Luders, D. D., Zoner, G. A., Santos, O. R., Braga, W. S., Sampaio, A. R., Kimura, N. M., Palangana, A. J., and Simões, M.

Subjects
PHASE transitions, IMAGE processing, DISCOTIC liquid crystals, CHOLESTERIC liquid crystals, POLARIZATION microscopy
Abstract

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]

Published
2018
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14. Effect of a static non-uniform magnetic field on the surface properties of acrylic resin

Author

Gasparetto, A., Hibler, I., Palangana, A. J., Paula, Claudete Rodrigues, Oliveira, Rosário, and Universidade do Minho

Abstract

INTRODUCTION: The acrylic resin is a polymeric material with several applications in different scientific and technological fields, especially in medicine and biotechnology. Its physical characteristics or their possible modifications can imply new ways of utilization and applicability. OBJECTIVE: To study the effect of a magnetic field on the surface physico-chemical properties usually implied in bacterial adhesion, especially surface hydrophobicity. METHODS: the hydrophobicity of the resin surface was determined by sessile drop contact angle measurements, using van Oss (1994) methodology. Accordingly, a substance (i) is considered hydrophobic when the variation of the free energy of interaction between two entities of substance (i) immersed in water is negative (DGiwi0, substance (i) is hydrophilic. Two types of resin samples were used: hydrated and non-hydrated ones. The hydrated samples were obtained by autoclaving at 121ºC. Before contact angle measurements, the samples submitted to the magnetic field were exposed during 24 hours to a field of 500gauss generated between to parallel magnetite plates. RESULTS AND DISCUSSION: The principal results are summarized in Table 1. As could be expected the hydrated resin is hydrophilic, while the dehydrated is hydrophobic. However, when the hydrated resin is submitted to the magnetic field it becomes even more hydrophobic than when dehydrated. This can be explained by the effect of the magnetic field on the orientation of the water molecules of hydration. Consequently, there is an evident alteration of surface properties promoted by the magnetic field.

Published
2002

16. Unstable periodic structures in nematic liquid crystals

Author

Simòes, M., Palangana, A. J., and Luiz Roberto Evangelista

Abstract

We present a review of our recent progress in the description of the elastic and dynamical properties of the unstable periodic (walls) arising in a nematic liquid crystal sample. The Lonberg criterion for the selection of the period of these walls is analyzed. We present a detailed study of the universal character of these walls, which is the basis for a law of corresponding states of these periodic structures. We show the connection of corresponding states with the constant ratio between the Miesowicz viscosity coefficients. Finally, the collapse of these structures is investigated. We show that it is due to the exponential growth of the fluctuations localized along the lines where the director does not bend at all.

Published
1998

19. Conoscopic image of a biaxial nematic phase in a sodium decyl sulfate – decanol – D2O mixture.

Author

Santos, O. R., Braga, W. S., Luders, D. D., Sampaio, A. R., Kimura, N. M., Simões, M., and Palangana, A. J.

Subjects
DEUTERIUM oxide, NEMATIC liquid crystals, SODIUM dodecyl sulfate, DECANOL, IMAGE processing
Abstract

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]

Published
2016
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27. Uniaxial and Biaxial Nematic Phases in Sodium Dodecyl Sulphate - Decanol - D 2 O Mixtures. An Optical Conoscopy Study.

Author

Santos, O. R., Braga, W. S., Kimura, N. M., Palangana, A. J., and Amaral, L. Q.

Subjects
NEMATIC liquid crystals, SODIUM dodecyl sulfate, MIXTURES, TEMPERATURE effect, DISCOTIC liquid crystals
Abstract

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]

Published
2015
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