Carbon nanotubes as reinforcement of cellulose liquid crystalline responsive networks

The incorporation of small amount of highly anisotropic nanoparticles into liquid crystalline hydroxypropylcellulose (LC-HPC) matrix improves its response when is exposed to humidity gradients due to an anisotropic increment of order in the structure. Dispersed nanoparticles give rise to faster order/disorder transitions when exposed to moisture as it is qualitatively observed and quantified by stress-time measurements. The presence of carbon nanotubes derives in a improvement of the mechanical properties of LC-HPC thin films.

Liquid-vapor interfaces of patchy colloids

We investigate the liquid-vapor interface of a model of patchy colloids. This model consists of hard spheres decorated with short-ranged attractive sites ("patches") of different types on their surfaces. We focus on a one-component fluid with two patches of type A and nine patches of type B (2A9B colloids), which has been found to exhibit reentrant liquid-vapor coexistence curves and very low-density liquid phases. We have used the density-functional theory form of Wertheim's first-order perturbation theory of association, as implemented by Yu and Wu [J. Chem. Phys. 116, 7094 (2002)], to calculate the surface tension, and the density and degree of association profiles, at the liquid-vapor interface of our model. In reentrant systems, where AB bonds dominate, an unusual thickening of the interface is observed at low temperatures. Furthermore, the surface tension versus temperature curve reaches a maximum, in agreement with Bernardino and Telo da Gama's mesoscopic Landau-Safran theory [Phys. Rev. Lett. 109, 116103 (2012)]. If BB attractions are also present, competition between AB and BB bonds gradually restores the monotonic temperature dependence of the surface tension. Lastly, the interface is "hairy," i.e., it contains a region where the average chain length is close to that in the bulk liquid, but where the density is that of the vapor. Sufficiently strong BB attractions remove these features, and the system reverts to the behavior seen in atomic fluids.

Viscosity measurements of compressed liquid dipropyl and dibutyl adipates

The paper reports viscosity measurements of compressed liquid dipropyl (DPA) and dibutyl (DBA) adipates obtained with two vibrating wire sensors developed in our group. The vibrating wire instruments were operated in the forced oscillation, or steady-state mode. The viscosity measurements of DPA were carried out in a range of pressures up to 18. MPa and temperatures from (303 to 333). K, and DBA up to 65. MPa and temperature from (303 to 373). K, covering a total range of viscosities from (1.3 to 8.3). mPa. s. The required density data of the liquid samples were obtained in our laboratory using an Anton Paar vibrating tube densimeter and were reported in a previous paper. The viscosity results were correlated with density, using a modified hard-spheres scheme. The root mean square deviation of the data from the correlation is less than (0.21 and 0.32)% and the maximum absolute relative deviations are within (0.43 and 0.81)%, for DPA and DBA respectively. No data for the viscosity of both adipates could be found in the literature. Independent viscosity measurements were also performed, at atmospheric pressure, using an Ubbelohde capillary in order to compare with the vibrating wire results. The expanded uncertainty of these results is estimated as ±1.5% at a 95% confidence level. The two data sets agree within the uncertainty of both methods. © 2015 Published by Elsevier B.V.

Liquid crystal mobility and PDLC memory effects

Dissertation presented at Faculdade de Ciências e Tecnologia of Universidade Nova de Lisboa to obtain the Degree of Master in Chemical and Biochemical Engineering

Cochineal, a precious source of red: cochineal dyes characterization by high performance liquid chromatography with diode array detection and principal component analysis

Presented at Faculdade de Ciências e Tecnologias, Universidade de Lisboa, to obtain the Master Degree in Conservation and Restoration of Textiles

Development of new biomaterials based on liquid crystalline phases of cellulose derivatives

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para obtenção do Grau de Mestre em Engenharia Biomédica

Novel optical PVC probes for on-site detection/determination of fluoroquinolones in a solid/liquid interface: Application to the determination of Norfloxacin in aquaculture water

A novel optical disposable probe for screening fluoroquinolones in fish farming waters is presented, having Norfloxacin (NFX) as target compound. The colorimetric reaction takes place in the solid/liquid interface consisting of a plasticized PVC layer carrying the colorimetric reagent and the sample solution. NFX solutions dropped on top of this solid-sensory surface provided a colour change from light yellow to dark orange. Several metals were tested as colorimetric reagents and Fe(III) was selected. The main parameters affecting the obtained colour were assessed and optimised in both liquid and solid phases. The corresponding studies were conducted by visible spectrophotometry and digital image acquisition. The three coordinates of the HSL model system of the collected image (Hue, Saturation and Lightness) were obtained by simple image management (enabled in any computer). The analytical response of the optimised solid-state optical probe against concentration was tested for several mathematical transformations of the colour coordinates. Linear behaviour was observed for logarithm NFX concentration against Hue+Lightness. Under this condition, the sensor exhibited a limit of detection below 50 μM (corresponding to about 16 mg/mL). Visual inspection also enabled semi-quantitative information. The selectivity was ensured against drugs from other chemical groups than fluoroquinolones. Finally, similar procedure was used to prepare an array of sensors for NFX, consisting on different metal species. Cu(II), Mn(II) and aluminon were selected for this purpose. The sensor array was used to detect NFX in aquaculture water, without any prior sample manipulation.

Dielectric study of triton X100: a glass-forming liquid

Dissertação para obtenção do grau de mestre em Engenharia de Materiais

Advanced instrumentation for superheated liquid detectors in dark matter searches

Dissertação para obtenção do Grau de Doutor em Engenharia Física

Towards cryogenic liquid –vapor energy storage units for space applications

Dissertation to obtain the Doctoral degree in Physics Engineering

The additive effects in matrix dispersed liquid crystals

Dissertation presented at Faculdade de Ciências e Tecnologia from Universidade Nova de Lisboa to obtain the degree of Master in Chemical and Biochemical Engineering

Development of suberin films driven by an ionic liquid-based depolymerisation process

Dissertation presented to obtain the Ph.D degree in Chemistry

Cellulose micro/nano fibers conformational effects probed by nematic liquid crystal droplets

Probing micro-/nano-sized surface conformations, which are ubiquitous in biological systems, by using liquid crystal droplets, which change their ordering and optical appearance in response to the presence of more than ten times smaller cellulose based micro/nano fibers, might find new uses in a range of biological environments and sensors. Previous studies indicate that electrospun micro/nano cellulosic fibers produced from liquid crystalline solutions could present a twisted form [1]. In this work, we study the structures of nematic liquid crystal droplets threaded by cellulose fibers prepared from liquid crystalline and isotropic solutions as well as droplets pierced by spider-made fibers [2]. Planar anchoring at the fibers and planar and homeotropic at the drop surfaces allowed probing cellulose fibers different helical structures as well as aligned filaments.

Cellulose nanorods in liquid crystalline elastomers for improved actuators

Nanotechnology plays a central role in ‘tailoring’ materials’ properties and thus improving its performances for a wide range of applications. Coupling nature nano-objects with nanotechnology results in materials with enhanced functionalities. The main objective of this master thesis was the synthesis of nanocrystalline cellulose (NCCs) and its further incorporation in a cellulosic matrix, in order to produce a stimuli-responsive material to moisture. The induced behaviour (bending/unbending) of the samples was deeply investigated, in order to determine relationships between structure/properties. Using microcrystalline cellulose as a starting material, acid hydrolysis was performed and the NCC was obtained. Anisotropic aqueous solutions of HPC and NCC were prepared and films with thicknesses ranging from 22μm to 61μm were achieved, by using a shear casting technique. Microscopic and spectroscopic techniques as well as mechanical and rheological essays were used to characterize the transparent and flexible films produced. Upon the application of a stimulus (moisture), the bending/unbending response times were measured. The use of NCC allowed obtaining films with response times in the order of 6 seconds for the bending and 5 seconds for the unbending, improving the results previously reported. These promising results open new horizons for building up improved soft steam engines.

Development of new membranes based on ionic liquid materials for gas separation

In the field of energy, natural gas is an essential bridge to a clean, low carbon, renewable energy era. However, natural gas processing and transportation regulation require the removal of contaminant compounds such as carbon dioxide (CO2). Regarding clean air, the increasing atmospheric concentrations of greenhouse gases, specifically CO2, is of particular concern. Therefore, new costeffective, high performance technologies for carbon capture have been researched and the design of materials with the ability to efficiently separate CO2 from other gases is of vital importance.(...)