Paulo R.G. Fernandes

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.

Viscosity of lyotropic nematic calamitic liquid crystals

Abstract Coneplate viscometry measurements as a function of temperature were made on two lyotropic nematic calamitic liquid crystals involving the potassium laurate/decanol/water and potassium laurate/potassium chloride/water systems. It was observed that whereas, at nematic calamitic phase (system with decanol), the viscosity measurements are smaller than those nematic calamitic phases (systems with potassium chloride). The results are discussed and compared to other liquid crystal sytems.

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.

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.

Caracterização mecânica e estrutural de um dispositivo PDLC baseado em hidrogéis de PAAm e cristal líquido liotrópico LP/DeOH/H2O

MECHANICAL AND STRUCTURAL CHARACTERIZATION OF A PDLC DEVICE BASED ON PAAm HYDROGELS AND KL–DeOH–H2O LYOTROPIC LIQUID CRYSTAL. In this work, a novel device based on polyacrylamide (PAAm) hydrogels and KL–DeOH–H2O lyotropic liquid crystal (LLC), with potential for application as Polymer Dispersed Liquid Crystals (PDLC), was proposed and its properties characterized. The confinement of LLC promoted significant changes in spectroscopic, morphological, optical, hydrophilic, structural and mechanical properties due to the interaction between the LLC-PAAm matrix and entropic parameter changes. The mechanical and structural properties can be controlled by adjusting AAm, temperature and presence of LLC, which can be useful for technological applications of these systems in optical devices.