Thermo-compression molding of chitosan with a deep eutectic mixture for biofilms development

Supplementary information available at: http://www.rsc.org/suppdata/c5/gc/c5gc02231b/c5gc02231b1.pdf

The Effects of Instrumental Touching on Infant Pain Perception and the Effects of Eutectic Mixture of Local Anesthetics (EMLA) on the Reduction of Pain

Background: Premature infants, who have to spend the first week of their lives in neonatal intensive care units (NICUs), experience pain and stress in numerous cases, and they are exposed to many invasive interventions. The studies have shown that uncontrolled pain experienced during early life has negative and long-term side effects, such as distress, and such experiences negatively affect the development of the central nervous system Objectives: The purpose of the study was to examine the effects of touching on infant pain perception and the effects of eutectic mixture of local anesthetic (EMLA) on the reduction of pain. Patients and Methods: Data for the study were collected between March and August 2012 from the neonatal clinic of a university hospital located in eastern Turkey. The population of the study consisted of premature infants who were undergoing treatment, completed the first month and who were approved for Hepatitis B vaccine. The study consisted of two experimental groups and one control group. Information forms, intervention follow-up forms, and Premature Infant Pain Profile (PIPP) were used to collect the data. EMLA cream was applied on the vastus lateralis muscles of the first experimental group before the vaccination. The second experimental group was vaccinated by imitation (placebo), without a needle tip or medicine. Vaccination was carried out using instrumental touch in this group. A routine vaccination was applied in the control group. Results: Mean pain scores of the group to which EMLA was applied were lower in a statistically significant way (P < 0.05) compared to the pain scores of the other groups. Moreover, it was determined that even though invasive intervention was not applied to the newborns, the touching caused them to feel pain just as in the placebo group (P < 0.005). Conclusions: The results demonstrated that EMLA was an effective method for reducing pain in premature newborns, and the use of instrumental touch for invasive intervention stimulated the pain perception in the newborns.

Liposomal Lidocaine Gel For Topical Use At The Oral Mucosa: Characterization, In Vitro Assays And In Vivo Anesthetic Efficacy In Humans.

To characterize liposomal-lidocaine formulations for topical use on oral mucosa and to compare their in vitro permeation and in vivo anesthetic efficacy with commercially available lidocaine formulations. Large unilamellar liposomes (400 nm) containing lidocaine were prepared using phosphatidylcholine, cholesterol, and α-tocoferol (4:3:0.07, w:w:w) and were characterized in terms of membrane/water partition coefficient, encapsulation efficiency, size, polydispersity, zeta potential, and in vitro release. In vitro permeation across pig palatal mucosa and in vivo topical anesthetic efficacy on the palatal mucosa in healthy volunteers (double-blinded cross-over, placebo controlled study) were performed. The following formulations were tested: liposome-encapsulated 5% lidocaine (Liposome-Lido5); liposome-encapsulated 2.5% lidocaine (Liposome-Lido2.5); 5% lidocaine ointment (Xylocaina®), and eutectic mixture of lidocaine and prilocaine 2.5% (EMLA®). The Liposome-Lido5 and EMLA showed the best in vitro permeation parameters (flux and permeability coefficient) in comparison with Xylocaina and placebo groups, as well as the best in vivo topical anesthetic efficacy. We successfully developed and characterized a liposome encapsulated 5% lidocaine gel. It could be considered an option to other topical anesthetic agents for oral mucosa.

Enhancement of the Nonlinear Optical Absorption of the E7 Liquid Crystal at the Nematic-Isotropic Transition

We present an experimental study of the nonlinear optical absorption of the eutectic mixture E7 at the nematic-isotropic phase transition by the Z-scan technique, under continuous-wave excitation at 532 nm. In the nematic region, the effective nonlinear optical coefficient beta, which vanishes in the isotropic phase, is negative for the extraordinary beam and positive for an ordinary beam. The parameter , whose definition in terms of the nonlinear absorption coefficient follows the definition of the optical-order parameter in terms of the linear dichroic ratio, behaves like an order parameter with critical exponent 0.22 +/- 0.05, in good agreement with the tricritical hypothesis for the nematic-isotropic transition.

Mechanical Characterization of Lead-Free Sn-Ag-Cu Solder Joints by High-Temperature Nanoindentation

The reliability of Pb-free solder joints is controlled by their microstructural constituents. Therefore, knowledge of the solder microconstituents’ mechanical properties as a function of temperature is required. Sn-Ag-Cu lead-free solder alloy contains three phases: a Sn-rich phase, and the intermetallic compounds (IMCs) Cu6Sn5 and Ag3Sn. Typically, the Sn-rich phase is surrounded by a eutectic mixture of β-Sn, Cu6Sn5, and Ag3Sn. In this paper, we report on the Young’s modulus and hardness of the Cu6Sn5 and Cu3Sn IMCs, the β-Sn phase, and the eutectic compound, as measured by nanoindentation at elevated temperatures. For both the β-Sn phase and the eutectic compound, the hardness and Young’s modulus exhibited strong temperature dependence. In the case of the intermetallics, this temperature dependence is observed for Cu6Sn5, but the mechanical properties of Cu3Sn are more stable up to 200°C.

Diseño y síntesis de materiales nanoestructurados basados en aluminatos de estroncio con propiedades fotoluminiscentes

Durante la última década, se han llevado acabo numeroso estudios sobre la síntesis de materiales fotoluminiscentes sub-micrónicos, en gran medida, al amplio número de aplicaciones que demandan este tipo de materiales. En concreto dentro de los materiales fosforescentes o también denominados materiales con una prolongada persistencia de la luminiscencia, los estudios se han enfocado en la matriz de SrAl2O4 dopada con Europio (Eu2+) y Disprosio (Dy3+) dado que tiene mayor estabilidad y persistencia de la fosforescencia con respecto a otras matrices. Estos materiales se emplean mayoritariamente en pinturas luminiscentes, tintas, señalización de seguridad pública, cerámicas, relojes, textiles y juguetes fosforescentes. Dado al amplio campo de aplicación de los SrAl2O4:Eu, Dy, se han investigado múltiples rutas de síntesis como la ruta sol-gel, la síntesis hidrotermal, la síntesis por combustión, la síntesis láser y la síntesis en estado sólido con el fin de desarrollar un método eficiente y que sea fácilmente escalable. Sin embargo, en la actualidad el método que se emplea para el procesamiento a nivel industrial de los materiales basados en aluminato de estroncio es la síntesis por estado sólido, que requiere de temperaturas de entre 1300 a 1900oC y largos tiempos de procesamiento. Además el material obtenido tiene un tamaño de partícula de 20 a 100 μm; siendo este tamaño restrictivo para el empleo de este tipo de material en determinadas aplicaciones. Por tanto, el objetivo de este trabajo es el desarrollo de nuevas estrategias que solventen las actuales limitaciones. Dentro de este marco se plantean una serie de objetivos específicos: Estudio de los parámetros que gobiernan los procesos de reducción del tamaño de partícula mediante molienda y su relación en la respuesta fotoluminiscente. Estudio de la síntesis por combustión de SrAl2O4:Eu, Dy, evaluando el efecto de la temperatura y la cantidad de combustible (urea) en el proceso para la obtención de partículas cristalinas minimizando la presencia de fases secundarias. Desarrollo de nuevas rutas de síntesis de SrAl2O4:Eu, Dy empleando el método de sales fundidas. Determinación de los mecanismos de reacción en presencia de la sal fundida en función de los parámetros de proceso que comprende la relación de sales y reactivos, la naturaleza de la alúmina y su tamaño, la temperatura y atmósfera de tratamiento. Mejora de la eficiencia de los procesos de síntesis para obtener productos con propiedades finales óptimas en procesos factibles industrialmente para su transferencia tecnológica. Es este trabajo han sido evaluados los efectos de diferentes procesos de molienda para la reducción del tamaño de partícula del material de SrAl2O4:Eu, Dy comercial. En el proceso de molienda en medio húmedo por atrición se observa la alteración de la estructura cristalina del material debido a la reacción de hidrólisis generada incluso empleando como medio líquido etanol absoluto. Con el fin de solventar las desventajas de la molienda en medio húmedo se llevo a cabo un estudio de la molturación en seco del material. La molturación en seco de alta energía reduce significativamente el tamaño medio de partícula. Sin embargo, procesos de molienda superiores a una duración de 10 minutos ocasionan un aumento del estado de aglomeración de las partículas y disminuyen drásticamente la respuesta fotoluminiscente del material. Por tanto, se lleva a cabo un proceso de molienda en seco de baja energía. Mediante este método se consigue reducir el tamaño medio de partícula, d50=2.8 μm, y se mejora la homogeneidad de la distribución del tamaño de partícula evitando la amorfización del material. A partir de los resultados obtenidos mediante difracción de rayos X y microscopia electrónica de barrido se infiere que la disminución de la intensidad de la fotoluminiscencia después de la molienda en seco de alta energía con respecto al material inicial se debe principalmente a la reducción del tamaño de cristalito. Se observan menores variaciones en la intensidad de la fotoluminiscencia cuando se emplea un método de molienda de baja de energía ya que en estos procesos se preserva el dominio cristalino y se reduce la amorfización significativamente. Estos resultados corroboran que la intensidad de la fotoluminiscencia y la persistencia de la luminiscencia de los materiales de SrAl2O4:Eu2+, Dy3+ dependen extrínsecamente de la morfología de las partículas, del tamaño de partícula, el tamaño de grano, los defectos superficiales e intrínsecamente del tamaño de cristalito. Siendo las características intrínsecas las que dominan con respecto a las extrínsecas y por tanto tienen mayor relevancia en la respuesta fotoluminiscente. Mediante síntesis por combustión se obtuvieron láminas nanoestructuradas de SrAl2O4:Eu, Dy de ≤1 μm de espesor. La cantidad de combustible, urea, en la reacción influye significativamente en la formación de determinadas fases cristalinas. Para la síntesis del material de SrAl2O4:Eu, Dy es necesario incluir un contenido de urea mayor que el estequiométrico (siendo m=1 la relación estequiométrica). La incorporación de un exceso de urea (m>1) requiere de la presencia de un agente oxidante interno, HNO3, para que la reacción tenga lugar. El empleo de un mayor contenido de urea como combustible permite una quelación efectiva de los cationes en el sistema y la creación de las condiciones reductoras para obtener un material de mayor cristalinidad y con mejores propiedades fotoluminiscentes. El material de SrAl2O4:Eu, Dy sintetizado a una temperatura de ignición de 600oC tiene un tamaño medio 5-25 μm con un espesor de ≤1 μm. Mediante procesos de molturación en seco de baja energía es posible disminuir el tamaño medio de partícula ≈2 μm y homogenizar la distribución del tamaño de partícula pero hay un deterioro asociado de la respuesta luminiscente. Sin embargo, se puede mejorar la respuesta fotoluminiscente empleando un tratamiento térmico posterior a 900oC N2-H2 durante 1 hora que no supone un aumento del tamaño de partícula pero si permite aumentar el tamaño de cristalito y la reducción del Eu3+ a Eu2+. Con respecto a la respuesta fotoluminiscente, se obtiene valores de la intensidad de la fotoluminiscencia entre un 35%-21% con respecto a la intensidad de un material comercial de referencia. Además la intensidad inicial del decaimiento de la fosforescencia es un 20% de la intensidad del material de referencia. Por tanto, teniendo en cuenta estos resultados, es necesario explorar otros métodos de síntesis para la obtención de los materiales bajo estudio. Por esta razón, en este trabajo se desarrollo una ruta de síntesis novedosa para sintetizar SrAl2O4:Eu, Dy mediante el método de sales fundidas para la obtención de materiales de gran cristalinidad con tamaños de cristalito del orden nanométrico. Se empleo como sal fundente la mezcla eutéctica de NaCl y KCl, denominada (NaCl-KCl)e. La principal ventaja de la incorporación de la mezcla es el incremento la reactividad del sistema, reduciendo la temperatura de formación del SrAl2O4 y la duración del tratamiento térmico en comparación con la síntesis en estado sólido. La formación del SrAl2O4 es favorecida ya que se aumenta la difusión de los cationes de Sr2+ en el medio líquido. Se emplearon diferentes tipos de Al2O3 para evaluar el papel del tamaño de partícula y su naturaleza en la reacción asistida por sales fundidas y por tanto en la morfología y propiedades del producto final. Se obtuvieron partículas de morfología pseudo-esférica de tamaño ≤0.5 μm al emplear como alúmina precursora partículas sub-micrónicas ( 0.5 μm Al2O3, 0.1 μm Al2 O3 y γ-Al2O3). El mecanismo de reacción que tiene lugar se asocia a procesos de disolución-precipitación que dominan al emplear partículas de alúmina pequeñas y reactivas. Mientras al emplear una alúmina de 6 μm Al2O3 prevalecen los procesos de crecimiento cristalino siguiendo un patrón o plantilla debido a la menor reactividad del sistema. La nucleación y crecimiento de nanocristales de SrAl2O4:Eu, Dy se genera sobre la superficie de la alúmina que actúa como soporte. De esta forma se desarrolla una estructura del tipo coraza-núcleo («core-shell» en inglés) donde la superficie externa está formada por los cristales fosforescentes de SrAl2O4 y el núcleo está formado por alúmina. Las partículas obtenidas tienen una respuesta fotoluminiscente diferente en función de la morfología final obtenida. La optimización de la relación Al2O3/SrO del material de SrAl2O4:Eu, Dy sintetizado a partir de la alúmina de 6 μm permite reducir las fases secundarias y la concentración de dopantes manteniendo la respuesta fotoluminiscente. Comparativamente con un material comercial de SrAl2O4:Eu, Dy de referencia, se han alcanzado valores de la intensidad de la emisión de hasta el 90% y de la intensidad inicial de las curvas de decaimiento de la luminiscencia de un 60% para el material sintetizado por sales fundidas que tiene un tamaño medio ≤ 10μm. Por otra parte, es necesario tener en cuenta que el SrAl2O4 tiene dos polimorfos, la fase monoclínica que es estable a temperaturas inferiores a 650oC y la fase hexagonal, fase de alta temperatura, estable a temperaturas superiores de 650oC. Se ha determinado que fase monoclínica presenta propiedades luminiscentes, sin embargo existen discordancias a cerca de las propiedades luminiscentes de la fase hexagonal. Mediante la síntesis por sales fundidas es posible estabilizar la fase hexagonal empleando como alúmina precursora γ-Al2O3 y un exceso de Al2O3 (Al2O3/SrO:2). La estabilización de la fase hexagonal a temperatura ambiente se produce cuando el tamaño de los cristales de SrAl2O4 es ≤20 nm. Además se observó que la fase hexagonal presenta respuesta fotoluminiscente. El diseño de materiales de SrAl2O4:Eu,Dy nanoestructurados permite modular la morfología del material y por tanto la intensidad de la de la fotoluminiscencia y la persistencia de la luminiscencia. La disminución de los materiales precursores, la temperatura y el tiempo de tratamiento significa la reducción de los costes económicos del material. De ahí la viabilidad de los materiales de SrAl2O4:Eu,Dy obtenidos mediante los procesos de síntesis propuestos en esta memoria de tesis para su posterior escalado industrial. ABSTRACT The synthesis of sub-micron photoluminescent particles has been widely studied during the past decade because of the promising industrial applications of these materials. A large number of matrices has been developed, being SrAl2O4 host doped with europium (Eu2+) and dysprosium (Dy3+) the most extensively studied, because of its better stability and long-lasting luminescence. These functional inorganic materials have a wide field of application in persistent luminous paints, inks and ceramics. Large attention has been paid to the development of an efficient method of preparation of SrAl2O4 powders, including solgel method, hydrothermal synthesis, laser synthesis, combustion synthesis and solid state reaction. Many of these techniques are not compatible with large-scale production and with the principles of sustainability. Moreover, industrial processing of highly crystalline powders usually requires high synthesis temperatures, typically between 1300 a 1900oC, with long processing times, especially for solid state reaction. As a result, the average particle size is typically within the 20-100 μm range. This large particle size is limiting for current applications that demand sub-micron particles. Therefore, the objective of this work is to develop new approaches to overcome these limitations. Within this frame, it is necessary to undertake the following purposes: To study the parameters that govern the particle size reduction by milling and their relation with the photoluminescence properties. To obtain SrAl2O4:Eu, Dy by combustion synthesis, assessing the effect of the temperature and the amount of fuel (urea) to synthesize highly crystalline particles minimizing the presence of secondary phases. To develop new synthesis methods to obtain SrAl2O4:Eu, Dy powders. The molten salt synthesis has been proposed. As the method is a novel route, the reaction mechanism should be determine as a function of the salt mixture, the ratio of the salt, the kind of Al2O3 and their particle size and the temperature and the atmosphere of the thermal treatment. To improve the efficiency of the synthesis process to obtain SrAl2O4:Eu, Dy powders with optimal final properties and easily scalable. On the basis of decreasing the particle size by using commercial product SrAl2O4:Eu2+, Dy3+ as raw material, the effects of different milling methods have been evaluated. Wet milling can significantly alter the structure of the material through hydrolysis reaction even in ethanol media. For overcoming the drawbacks of wet milling, a dry milling-based processes are studied. High energy dry milling process allows a great reduction of the particle size, however milling times above 10 min produce agglomeration and accelerates the decrease of the photoluminescence feature. To solve these issues the low energy dry milling process proposed effectively reduces the particle size to d50=2.8 μm, and improves the homogeneity avoiding the amorphization in comparison with previous methods. The X-ray diffraction and scanning electron microscope characterization allow to infer that the large variations in PL (Photoluminescence) values by high energy milling process are a consequence mainly of the crystallite size reduction. The lesser variation in PL values by low energy milling proces is related to the coherent crystalline domain preservation and the unnoticeable amorphization. These results corroborate that the photoluminescence intensity and the persistent luminescence of the SrAl2O4:Eu2+, Dy3+ powders depend extrinsically on the morphology of the particles such as particle size, grain size, surface damage and intrinsically on the crystallinity (crystallite size); being the intrinsically effects the ones that have a significant influence on the photoluminescent response. By combustion method, nanostructured SrAl2O4:Eu2+, Dy3+ sheets with a thickness ≤1 μm have been obtained. The amount of fuel (urea) in the reaction has an important influence on the phase composition; urea contents larger than the stoichiometric one require the presence of an oxidant agent such as HNO3 to complete the reaction. A higher amount of urea (excess of urea: denoted m>1, being m=1 the stoichiometric composition) including an oxidizing agent produces SrAl2O4:Eu2+,Dy3+ particles with persistent luminescence due to the effective chelation of the cations and the creation of suitable atmospheric conditions to reduce the Eu3+ to Eu2+. Therefore, optimizing the synthesis parameters in combustion synthesis by using a higher amount of urea and an internal oxidizing agent allows to complete the reaction. The amount of secondary phases can be significantly reduced and the photoluminescence response can be enhanced. This situation is attributed to a higher energy that improves the crystallinity of the powders. The powders obtained have a particle size c.a. 5-25 μm with a thickness ≤1 μm and require relatively low ignition temperatures (600oC). It is possible to reduce the particle size by a low energy dry milling but this process implies the decrease of the photoluminescent response. However, a post-thermal treatment in a reducing atmosphere allows the improvement of the properties due to the increment of crystallinity and the reduction of Eu3+ to Eu2+. Compared with the powder resulted from solid state method (commercial reference: average particle size, 20 μm and heterogeneous particle size distribution) the emission intensity of the powder prepared by combustion method achieve the values between 35% to 21% of the reference powder intensity. Moreover, the initial intensity of the decay curve is 20% of the intensity of the reference powder. Taking in account these results, it is necessary to explore other methods to synthesize the powders For that reason, an original synthetic route has been developed in this study: the molten salt assisted process to obtain highly crystalline SrAl2O4 powders with nanometric sized crystallites. The molten salt was composed of a mixture of NaCl and KCl using a 0.5:0.5 molar ratio (eutectic mixture hereafter abbreviated as (NaCl-KCl)e). The main advantages of salt addition is the increase of the reaction rate, the significant reduction of the synthesis temperature and the duration of the thermal treatment in comparison with classic solid state method. The SrAl2O4 formation is promoted due to the high mobility of the Sr2+ cations in the liquid medium. Different kinds of Al2O3 have been employed to evaluate the role of the size and the nature of this precursor on the kinetics of reaction, on the morphology and the final properties of the product. The SrAl2O4:Eu2+, Dy3+ powders have pseudo-spherical morphology and particle size ≤0.5 μm when a sub-micron Al2O3 ( 0.5 μm Al2O3, 0.1 μm Al2O3 and γ-Al2O3) has been used. This can be attributed to a higher reactivity in the system and the dominance of dissolution-precipitation mechanism. However, the use of larger alumina (6 μm Al2O3) modifies the reaction pathway leading to a different reaction evolution. More specifically, the growth of SrAl2O4 sub-micron particles on the surface of hexagonal platelets of 6μm Al2O3 is promoted. The particles retain the shape of the original Al2O3 and this formation process can be attributed to a «core-shell» mechanism. The particles obtained exhibit different photoluminescent response as a function of the final morphology of the powder. Therefore, through this study, it has been elucidated the reaction mechanisms of SrAl2O4 formation assisted by (NaCl-KCl)e that are governed by the diffusion of SrCO3 and the reactivity of the alumina particles. Optimizing the Al2O3/SrO ratio of the SrAl2O4:Eu, Dy powders synthesized with 6 μm Al2O3 as a precursor, the secondary phases and the concentration of dopant needed can be reduced keeping the photoluminescent response of the synthesized powder. Compared with the commercial reference powder, up to 90% of the emission intensity of the reference powder has been achieved for the powder prepared by molten salt method using 6μm Al2O3 as alumina precursor. Concerning the initial intensity of the decay curve, 60% of the initial intensity of the reference powder has been obtained. Additionally, it is necessary to take into account that SrAl2O4 has two polymorphs: monoclinic symmetry that is stable at temperatures below 650oC and hexagonal symmetry that is stable above this temperature. Monoclinic phase shows luminescent properties. However, there is no clear agreement on the emission of the hexagonal structure. By molten salt, it is possible to stabilize the hexagonal phase of SrAl2O4 employing an excess of Al2O3 (Al2O3/SrO: 2) and γ-Al2O3 as a precursor. The existence of nanometric crystalline domains with lower size (≤20 nm) allows the stabilization of the hexagonal phase. Moreover, it has been evidenced that the hexagonal polymorph exhibits photoluminescent response. To sum up, the design of nanostructured SrAl2O4:Eu2+, Dy3+ materials allows to obtain different morphologies and as consequence different photoluminescent responses. The reduction of temperature, duration of the thermal treatment and the precursors materials needed imply the decrease of the economic cost of the material. Therefore, the viability, suitability and scalability of the synthesis strategy developed in this work to process SrAl2O4:Eu2+, Dy3+ are demonstrated.

Dielectric and electro-optical properties of some cyanobiphenyl liquid-crystals

A variety of methods have been reviewed for obtaining parallel or perpendicular alignment in liquid-crystal cells. Some of these methods have been selected and developed and were used in polarised spectroscopy, dielectric and electro-optic studies. Also, novel dielectric and electro-optic cells were constructed for use over a range of temperature. Dielectric response of thin layers of E7 and E8 (eutectic mixture liquid-crystals) have been measured in the frequency range (12 Hz-100 kHz) and over a range of temperature (183-337K). Dielectric spectra were also obtained for supercooled E7 and E8 in the Hz and kHz range. When the measuring electric field was parallel to the nematic director, one loss peak (low-frequency relaxation process) was observed for E7 and for E8, that exhibits a Debye-type behaviour in the supercooled systems. When the measuring electric field was perpendicular to the nematic director, two resolved dielectric processes have been observed. The phase transitions, effective molecular polarisabilities, anisotropy of polarisabilities and order parameters of three liquid crystal homologs (5CB, 6CB, and 7CB), 60CB and three eutectic nematic mixtures E7, E8, and E607 were calculated using optical and density data measured at several temperatures. The order parameters calculated using the different methods of Vuks, Neugebauer, Saupe-Maier, and Palffy-Muhoray are nearly the same for the liquid crystals considered in the present study. Also, the interrelationship between density and refractive index and the molecular structure of these liquid crystals were established. Accurate dielectric and dipole results of a range of liquid-crystal forming molecules at several temperatures have reported. The role of the cyano-end group, biphenyl core, and flexible tail in molecular association, were investigated using the dielectric method for some molecules which have a structural relationship to the nematogens. Analysis of the dielectric data for solution of the liquid-crystals indicated a high molecular association, comparable to that observed in the nematic or isotropic phases. Electro-optic Kerr effect were investigated for some alkyl cyanobiphenyls, their nematic mixtures and the eutectic mixture liquid-crystals E7 and E8 in the isotropic phase and solution. The Kerr constant of these liquid crystals found to be very high at the nematic-isotropic transition temperatures as the molecules are expected to be highly ordered close to phase transition temperatures. Dynamic Kerr effect behaviour and transient molecular reorientation were also observed in thin layers of some alkyl cyanobiphenyls. Dichroic ratio R and order parameters of solutions containing some azo and anthraquinone dyes in the nematic solvent (E7 and E8), were investigated by the measurement of the intensity of the absorption bands in the visible region of parallel aligned samples. The effective factors on the dichroic ratio of the dyes dissolved in the nematic solvents were determined and discussed.

Membranas compósitas para separação de CO2

O presente trabalho envolveu a produção de membranas compósitas para separação de CO2 a altas temperaturas. Os compósitos habituais são constituídos por duas fases, uma cerâmica, de céria dopada com gadolínio (Ce0.9Gd0.1O0.95 - CGO) condutora de iões óxido, que funciona como suporte da segunda fase composta por uma mistura eutética de carbonatos alcalinos (Li2CO3 e Na2CO3), que assegura o transporte de iões carbonato. O objetivo do trabalho prende-se com o estudo do transporte de iões através destes compósitos, por forma a perceber se os sais destes compósitos apresentam condução iónica singular ou condução mista. Neste sentido a resposta a esta questão teve por base a realização de ensaios de eficiência faradaica com recurso a amostras compósitas envolvendo matrizes de CGO (condutor de iões óxido) e de aluminato de lítio (não condutor de iões óxido). A preparação tanto de esqueletos porosos como de compósitos foi realizada tendo por base métodos e precursores semelhantes aos usados na literatura. Primeiramente efetuou-se o processamento dos esqueletos porosos para posteriormente impregnação com mistura eutética de carbonatos. Obtidos os compósitos estes foram caraterizados por microscopia de impedância e por microscopia eletrónica de varrimento de forma a serem submetidos mais tarde aos ensaios de eficiência faradaica. Os resultados de eficiência faradaica revelaram que na realidade existem processos de condução mista cuja importância depende das condições de operação da membrana.

Novel synthesis of a micro-mesoporous nitrogen-doped nanostructured carbon from polyaniline

Nanostructured carbons with relatively high nitrogen content (3–8%) and different micro and mesoporosity ratio were prepared by activation of polyaniline (PANI) with a ZnCl2–NaCl mixture in the proportion of the eutectic (melting point 270 °C). It was found that the activated carbons consisted of agglomerated nanoparticles. ZnCl2 plays a key role in the development of microporosity and promotes the binding between PANI nanoparticles during heat treatment, whereas NaCl acts as a template for the development of mesoporosity of larger size. Carbons with high micropore and mesopore volumes, above 0.6 and 0.8 cm3/g, respectively, have been obtained. Furthermore, these materials have been tested for CO2 capture and storage at pressures up to 4 MPa. The results indicate that the nitrogen groups present in the surface do not seem to affect to the amount of CO2 adsorbed, not detecting strong interactions between CO2 molecules and nitrogen functional groups of the carbon, which are mainly pyridinic and pyrrolic groups.

Fundamental studies on natural deep eutectic solvents: physico-chemical, thermal and rheological properties

When combined at particular molar fractions, sugars, aminoacids or organic acids a present a high melting point depression, becoming liquids at room temperature. These are called Natural Deep Eutectic Solvents – NADES and are envisaged to play a major role on the chemical engineering processes of the future. Nonetheless, there is a significant lack of knowledge of its fundamental and basic properties, which is hindering their industrial applications. For this reason it is important to extend the knowledge on these systems, boosting their application development [1]. In this work, we have developed and characterized NADES based on choline chloride, organic acids, amino acids and sugars. Their density, thermal behavior, conductivity and polarity were assessed for different compositions. The conductivity was measured from 0 to 40 °C and the temperature effect was well described by the Vogel-Fulcher-Tammann equation. The morphological characterization of the crystallizable materials was done by polarized optical microscopy that provided also evidence of homogeneity/phase separation. Additionally, the rheological and thermodynamic properties of the NADES and the effect of water content were also studied. The results show these systems have Newtonian behavior and present significant viscosity decrease with temperature and water content, due to increase on the molecular mobility. The anhydrous systems present viscosities that range from higher than 1000Pa.s at 20°C to less than 1Pa.s at 70°C. DSC characterization confirms that for water content as high as 1:1:1 molar ratio, the mixture retains its single phase behavior. The results obtained demonstrate that the NADES properties can be finely tunned by careful selection of its constituents. NADES present the necessary properties for use as extraction solvents. They can be prepared from inexpensive raw materials and tailored for the selective extraction of target molecules. The data produced in this work is hereafter importance for the selection of the most promising candidates avoiding a time consuming and expensive trial and error phase providing also data for the development of models able to predict their properties and the mechanisms that allow the formation of the deep eutectic mixtures.

The full Bayesian significance test for mixture models: results in gene expression clustering

Gene clustering is a useful exploratory technique to group together genes with similar expression levels under distinct cell cycle phases or distinct conditions. It helps the biologist to identify potentially meaningful relationships between genes. In this study, we propose a clustering method based on multivariate normal mixture models, where the number of clusters is predicted via sequential hypothesis tests: at each step, the method considers a mixture model of m components (m = 2 in the first step) and tests if in fact it should be m - 1. If the hypothesis is rejected, m is increased and a new test is carried out. The method continues (increasing m) until the hypothesis is accepted. The theoretical core of the method is the full Bayesian significance test, an intuitive Bayesian approach, which needs no model complexity penalization nor positive probabilities for sharp hypotheses. Numerical experiments were based on a cDNA microarray dataset consisting of expression levels of 205 genes belonging to four functional categories, for 10 distinct strains of Saccharomyces cerevisiae. To analyze the method's sensitivity to data dimension, we performed principal components analysis on the original dataset and predicted the number of classes using 2 to 10 principal components. Compared to Mclust (model-based clustering), our method shows more consistent results.

Thermodiffusion in a multicomponent lyotropic mixture in the vicinity of the critical micellar concentration by using the Z-scan technique

Thermodiffusion in a lyotropic mixture of water and potassium laurate is investigated by means of an optical technique (Z scan) distinguishing the index variations due to the temperature gradient and the mass gradients. A phenomenological framework allowing for coupled diffusion is developed in order to analyze thermodiffusion in multicomponent systems. An observable parameter relating to the mass gradients is found to exhibit a sharp change around the critical micellar concentration, and thus may be used to detect it. The change in the slope is due to the markedly different values of the Soret coefficients of the surfactant and the micelles. The difference in the Soret coefficients is due to the fact that the micellization process reduces the energy of interaction of the ball of amphiphilic molecules with the solvent.

Phase diagram of a model for a binary mixture of nematic molecules on a Bethe lattice

We investigate the phase diagram of a discrete version of the Maier-Saupe model with the inclusion of additional degrees of freedom to mimic a distribution of rodlike and disklike molecules. Solutions of this problem on a Bethe lattice come from the analysis of the fixed points of a set of nonlinear recursion relations. Besides the fixed points associated with isotropic and uniaxial nematic structures, there is also a fixed point associated with a biaxial nematic structure. Due to the existence of large overlaps of the stability regions, we resorted to a scheme to calculate the free energy of these structures deep in the interior of a large Cayley tree. Both thermodynamic and dynamic-stability analyses rule out the presence of a biaxial phase, in qualitative agreement with previous mean-field results.

Temperature-driven collapse of a coherent binary mixture of condensates

We present a temperature- dependent Hartree- Fock- Bogoliubov- Popov theory to analyze the properties of the equilibrium states of an homogeneous mixture of bosonic atoms in two different hyperfine states and in the presence of an internal Josephson coupling. In our calculation we show that the bistable structure of the equilibrium states at zero temperature changes when we increase the temperature of the system. We investigate two mechanisms of the disappearance of bistability. In one, near the collapse of one of the equilibrium states, the acoustical branch becomes unstable and the gap of the optical branch goes to zero. In the other, there is no divergent behavior of the system and bistability disappears at a temperature in which the two equilibrium states merge at a zero- population fraction imbalance. When we further increase the temperature, this state remains as a unique equilibrium configuration.

Improvements on ICA mixture models for image pre-processing and segmentation

Today several different unsupervised classification algorithms are commonly used to cluster similar patterns in a data set based only on its statistical properties. Specially in image data applications, self-organizing methods for unsupervised classification have been successfully applied for clustering pixels or group of pixels in order to perform segmentation tasks. The first important contribution of this paper refers to the development of a self-organizing method for data classification, named Enhanced Independent Component Analysis Mixture Model (EICAMM), which was built by proposing some modifications in the Independent Component Analysis Mixture Model (ICAMM). Such improvements were proposed by considering some of the model limitations as well as by analyzing how it should be improved in order to become more efficient. Moreover, a pre-processing methodology was also proposed, which is based on combining the Sparse Code Shrinkage (SCS) for image denoising and the Sobel edge detector. In the experiments of this work, the EICAMM and other self-organizing models were applied for segmenting images in their original and pre-processed versions. A comparative analysis showed satisfactory and competitive image segmentation results obtained by the proposals presented herein. (C) 2008 Published by Elsevier B.V.