A.R. Sampaio

Digital Image Processing Study of a Reentrant Isotropic-Discotic Nematic Phase Transition

The structural change in the discotic nematic textures is investigated, by means of digital image processing, near the reentrant isotropic(IRE)–discotic nematic(ND)–isotropic(I)phase transitions in a lyotropic mixture of potassium laurate, decanol and D2O. The NDphase is characterized by extraordinary and ordinary refractive index measurements and discussed in terms of the mean square deviation parameter determined through a statistical method for the image data detected by the CCD camera.

Utilização de máquina fotográfica digital (multi-burst) para aulas experimentais de cinemática - queda livre

In this work we used a digital camera, with multi-burst function (photos taken in sequence) to analise the free fall motion and with the data obtained calculate the value of the local acceleration of gravity. To evaluate the experiment, was also calculated a theoretical value for the local acceleration of gravity. By comparing with that obtained experimentally, it was possible to observe a small deviation. That showed that the digital camera can be a good tool to aid pedagogical in the teaching of physics.

An image processing study of a reentrant discotic cholesteric – biaxial cholesteric phase transition

ABSTRACT In this work, we study and characterize the cholesteric sequence of phases (ChDr − ChB − ChD), where the first ChDr is the reentrant cholesteric discotic phase, ChB is the cholesteric biaxial phase and the second ChD is 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.

Studies of Image Processing and Refractive Index in Blue Phase

The isotropic - blue phases - cholesteric phase transitions are studied in a thermotropic (COC) by image processing and refractive index measurements. Textures of blue phases are optically characterized as well as their transition points. The experimental investigation employed here is sensitive to detect changes in the structural configuration of blue phases as a consequence of our refractive index data. In this context the experimental results are presented and discussed.

Refractive index measurements in a reentrant discotic nematic–biaxial nematic phase transition

ABSTRACT The optical characterization of uniaxial (reentrant discotic – and discotic – ) and biaxial nematic ( phases requires the measurements of two and three refractive indices, respectively. These optical parameters were determined near the reentrant isotropic -isotropic (I) phase transitions in a lyotropic mixture of potassium laurate, decanol and . Biaxial positive ( nematic phase is optically characterized between two uniaxial discotic nematic phases from refractive index data and confirmed via conoscopic images. The micellar configuration of uniaxial and biaxial nematic phases is discussed as a consequence of our experimental data.

Decanol effect on viscoelasticity and rheology in lamellar mesophases

ABSTRACT The lyotropic lamellar mesophase consists of amphiphilic molecules arranged in bilayer sheets separated by layers of water . Among its various rheological properties, two are worth mentioning: yield-point and viscoelasticity. In this work, we studied lamellar samples of lauryl sulfate /Decanol /water system, as described in the phase diagram proposed by Quist and colleagues. (molar ratio fixed in ). We have investigated the changes in and viscoelasticity properties as a function of the molar ratio . The lamellar mesophases are characterized by using polarized light microscopy and conoscopy. All the rheological measurements were performed using rotational and oscillatory rheometry. The results show that the lamellar phase exhibits gel-like behavior. The increase of molar ratio weakens the microstructure of the lamellar network, affecting the elastic properties and the yield stress values.

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

ABSTRACT The nematic phases of a lyotropic system NadS/ 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. The NB phase observed here is discussed as part of the nature of the micellar configuration of lyotropic materials which exhibit uniaxial nematic phases.

Shear viscosity and rheology of ternary and quaternary lyotropic liquid crystals in discotic and calamitic nematic phases

We report rheological studies of micellar nematic phases of potassium laurate/ decanol/ water mixtures with and without addition of salt (K2SO4) at a fixed temperature of 20 ∘C. Using a cone-plate rheometer, we verified that the ternary mixture (i.e., without salt) exhibiting the discotic (ND) nematic phase showed only a slight pseudo-plastic (or shear-thinning) behavior. In contrast, a pronounced pseudo-plastic effect was observed in the ND phase of the quaternary samples. On the other hand, all the NC samples (salted or unsalted) showed a quasi-Newtonian behavior. In addition, we have made viscosity measurements using a (variation of a) rotating Couette flow viscometer. Finally, we also performed density measurements, using a density cell attached to the viscometer. Our results showed a contrasting behavior between the two types of nematic phases in two aspects. Firstly, regarding the ternary samples only, the apparent viscosity η at moderate shear rates was lower in the NC than in the ND phase. The second aspect, regarding both ternary and quaternary samples, is that η in the ND phase dramatically increased as the salt concentration increased, while in the NC phase η was quite insensitive to the addition of salt. In order to analyse the results, we have used two different theoretical frameworks, namely the nematodynamics in the first aspect and the classical theory of electrolyte solutions in the second one.

Modelo dinâmico do Sistema Solar em actionscript com controle de escalas para ensino de astronomia

This paper presents a dynamic software simulation of the solar system, where the relative scales between the size of the Sun, the planets and their orbits can be adjusted to improve the visibility and understanding of their movements. It was developed using Actionscript (Flash Professional 8) that can be ported to different hardware platforms. The program is explained in detail to encourage those who want to learn the language. Besides arousing a great interest in students, this software allows a better visualization of the greatness of the Solar System and its main constituents than the models that are usually present in schools and textbooks.

The 2:1 cycloadducts from [3+2] 1,3-dipolar cycloaddition of nitrile oxide and vinylacetic acid. Synthesis and liquid crystal behaviour

Four liquid crystals (LC) 3,7a-bis(4-alkyloxyphenyl)-7,7a-dihydro-6H-isoxazolo[2,3-d][1,2,4]oxadiazol-6-yl)acetic acid (7a–d) were synthesised and the mesomorphic behaviour reported. The LCs were characterised as 2:1 bisadducts, which were obtained from a double [3 + 2] 1,3-dipolar cycloaddition. In the first step, the cycloaddition of 4-alkyloxyphenylnitrile oxide (4a–d) and vinylacetic acid (5) gave the initial unobserved 1:1 cycloadducts 2-[3-(4-alkyloxyphenyl)-4,5-dihydroisoxazol-5-yl]acetic acid (6a–d). In the second step, the addition of a second equivalent of 4 to 6 yielded the 2:1 bisadducts 7a–d without any traces of 6. All compounds 7a–d were unstable during the transition from the mesophase to the isotropic state upon first heating as evidenced by the large peaks in the differential scanning calorimetry traces. Due to the chemical instability of the compounds upon heating, the transition temperature related to the smectic C to smectic A transitions was acquired by means of an image processing method. X-Ray diffraction experiments were also used to analyse the liquid-crystalline phases. A theoretical calculation was performed using density functional theory (DFT) methods at the PBE1PBE/6-311+G(2d,p) level (with solvent effect) in order to get information about the energetic profile of the 2:1 cycloaddition. DFT studies revealed that the cycloaddition process is controlled by the HOMO(dipolarophile) – LUMO(1,3-dipole), and that the double [3 + 2] 1,3-dipolar cycloaddition reaction is quite possible.