N.M. Kimura

Biaxial phase and coexistence of the two uniaxial nematic phases in the system sodium dodecyl sulphate–decanol–D2O

The system sodium dodecyl sulphate (SDS)/decanol (DeOH)/water presents, with temperature increase, an unusual phase transition between a stable biaxial phase and a coexistence region of the two uniaxial nematic phases (discotic ND + cylindrical NC). This has been detected previously by several methods for a sample with water/SDS molar ratio Mw = 36. Here, this system is investigated changing the ratio Mw to 32, where previously the coexistence region was reported after a discotic ND phase, without the biaxial phase. We report now the existence of a biaxial NB in the temperature range of ~2°C, defining for both values of Mw and the phase sequence as NB – (ND + NC) – NC. The change in temperature is followed by conoscopic and orthoscopic optical techniques and also analysed through the curve obtained by the technique of digital image processing of the textures, which reveals a continuous transition ND – NB – (ND + NC). While the biaxial phase is stable for at least 10 hours, in a reproducible way, the coexistence region evolves with time, and drops of the discotic phase grow immersed in a NC matrix. Results are explained in terms of recent theories dealing with stabilisation of mixtures of cylinders and discs.

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.

Reentrant isotropic – discotic nematic phase transition: a critical exponent study

In this work the critical exponents associated with the behavior of the macroscopic orientational order parameter are determined near the reentrant isotropic (IRE)–discotic nematic (ND) and ND–isotropic (I) phase transitions in a lyotropic mixture of potassium laurate, decanol and D2O by measurement of optical birefringence. The critical exponents found indicate that the low temperature ND–IRE phase transition is quasi‐continuous, having a critical exponent, β1∼0.17, which is markedly different from that found at the classical ND–I phase transition, β2∼0.38. The results are discussed and compared with others obtained with different lyotropic mixtures.

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.

Uniaxial and Biaxial Nematic Phases in Sodium Dodecyl Sulphate - Decanol - D2O Mixtures. An Optical Conoscopy Study

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 NC matrix. Results are explained in terms of recent theories dealing with stabilization of mixtures of cylinders and discs.

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.

Mechano-Optical Effect in Isotropic Phase of a Lyotropic Liquid Crystal

In this work we show experimental results reporting the induced order in isotropic phase of a lyotropic liquid cxzrystal(KL/DeOH/water)when it is submitted to a mechanical vibration. We have been found five resonance frequencies for all isotropic domains surrounded by lamellar phases and two principal frequencies in both isotropic regions with nematic phase between them. In order to make a comparison with others isotropic fluids the optical transmittance of the lyotropic has been found of about four thousand when compared with DeOH and, at least three hundred in comparison to water. We are exploring this effect to produce a mechanical vibration sensor able to detect small mechanical perturbations at room temperature. As far we know this appears to be one of the first real technological application of a device based upon lyotropic liquid crystals.

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.

Corresponding states in the smectic-A phase

ABSTRACT In the last few years, experimental data of many different sources has been gathered to show that order parameter curves of essentially all nematic liquid crystals (NLCs) compounds can be reduced to a single and universal curve of the corresponding states; experimental data of an impressive number of different nematic compounds has been linearly rescaled in such a way that all them coalesced in a single curve. The surprising novelty observed on NLCs is that this universal behaviour is not restricted to the neighbourhoods of a critical region, as is usually expected from critical phenomena, but it covers the entire domain of the nematic phase, from the nematic isotropic temperature to the nematic crystalline temperature. The aim of this paper is to study the statistical mechanics fundamentals of this behaviour and show that it is a consequence of the universality of the angular part of the potential of the interaction between the particles composing the liquid crystal (LC). We will illustrate this behaviour presenting evidences that it can be found on the smectic-A phase. GRAPHICAL ABSTRACT