Curing of polymer matrix composites. Fluorescence study of dansyl fluorophore labelled to glass fibres and DGEBA-ethyelenediamine epoxy resin

Curing process of diglycidyl ether of bisphenol A/ethylenediamine mixture in the presence of glass fibers was monitored by fluorescence in two ways: first, using dansyl labeled glass fibers and diglycidyl ether of bisphenol A (DGEBA)/ethylenediamine mixture and second, using unlabeled glass fibers and DGBA-dansyl labeled/ethylenediamine mixture. Integral fluorescence intensity was analyzed as a function of time. Results allow comparison between the curing process inside the bulk of the resin and at the glass fiber interface. It was concluded that for the system DGEBA/ethylenediamine the polymer matrix viscosity increases with the curing time faster inside the bulk than at the glass fiber interface.Authors wish to thank CAM (07N/0002/1998) for suppor

Glass transition temperature of low molecular weight poly(3-aminopropyl methyl siloxane). A molecular dynamics study

The average specific volume of the model poly(3-aminopropyl methyl siloxane) as a function of temperature near the glass transition was computed from molecular dynamics simulations. The glass transition temperature was defined as the slop intersection around 210 K, a value similar to that of the experimental result. Globular polymer shaped chains were observed where the chain is closed upon itself. Three amino groups of amino propylene chains were located in the center and the rest of the amino groups were situated outside the main chain. The glass transition temperature of this low molecular weight polymer strongly depends on the binding energies between chains. The intersection of binding energy slopes defines a temperature of 213 K near the glass transition temperature. The most important contributions to the glass transition changes were the electrostatic binding contributions. The Van der Waals contributions in the volume changes were less important. The chain mobility was evaluated by the transition between angles for the states trans, g⁺ and g⁻. The glass transition temperature observed experimentally, 208±2 K, is due to cooperative movements of two different torsion angles, (O–Si) and (Si–C) of the main chain and the lateral chain, respectively, and its rotational mobility. Self-diffusion constant variation for all polymer atoms with the temperature is a probe that the polymer chain cooperative movement had started at temperatures around the glass transition temperature.This work was supported by the CAM through Grant 07N/0002/1998

Tecnologia digital aplicada às restaurações minimamente invasivas

Dissertação para obtenção do grau de Mestre no Instituto Universitário Egas MonizDurante os últimos 30 anos surgiu uma nova abordagem na medicina dentária que promove o desempenho de todos os procedimentos clínicos de forma o mais conservadora possível, a fim de preservar o máximo possível de tecido dentário ou ósseo. Uma das áreas mais envolvida por esta nova tendência é a reabilitação oral. Nesta área da prática clínica diária há 20 ou 30 anos removíamos tecido saudável para assegurar a remoção preventiva e completa da cárie. Durante os últimos anos passamos a tentar remover o mínimo possível de tecido dentário. Esta mudança tem sido possível graças a vários fatores. Por um lado, nos últimos anos temos assistido a grandes avanços nos sistemas adesivos, o que nos permite obter para além de uma retenção mecânica uma retenção química, por outro lado, a contínua evolução tecnológica permite-nos através de imagens digitais planear e realizar tanto preparações como restaurações da forma menos invasiva possível. O sistema que mais tem ajudado nesta mudança é o CAD-CAM (Computer Aided Design/Computer Aided Manufacturing). Através deste sistema e dos seus componentes conseguimos realizar digitalmente todos os processos da odontologia minimamente invasiva, tornando o processo mais fácil e seguro. Graças ainda à tecnologia podemos realizar um diagnóstico precoce das cáries, fazer guias para a preparação dos dentes e desenhar as peças. Isto, juntamente com os avanços acima mencionados relativamente aos sistemas adesivos e materiais, permite-nos realizar um tratamento minimamente invasivo, com boa estética e grande precisão. O objetivo deste trabalho foi avaliar como as novas tecnologias digitais podem influenciar e ajudar na dentisteria minimamente invasiva. Para tal será feita uma pesquisa bibliográfica, assente em artigos disponíveis nas bases de dados Cochrane Library , Medline/Pubmed, Scielo, Google Scholar e B-on, e referentes a artigos dos últimos 10 anos.During the last 30 years a new trend has emerged in dentistry that promotes the performance of all clinical procedures as conservatively as possible in order to preserve as much tooth or bone tissue as possible. One of most affected areas by this new trend is dentistry. In this area of daily clinical practice 20-30 years ago we used to remove healthy tissue to ensure complete removal of caries. During the last few years we have moved on to trying to remove as little tooth tissue as possible. This change was possible thanks to several factors. On the one hand, in the last few years we witnessed great advances in adhesive systems, which allow us to achieve chemical retention. On the other hand, the ongoing technological evolution allows us to design both the preparations and the dental pieces in a minimally invasive way. The system that has helped the most in this change of attitude is CAD-CAM (Computer Aided Design/Computer Aided Manufacturing). Through this system and its components we can carry out all the processes of minimally invasive dentistry digitally, making the process easier and safer. Thanks to this technology, we can carry out an early diagnosis of caries, make preparation guides for the teeth and design the prosthetic pieces. This, together with the aforementioned advances in adhesive systems and materials, allows us to perform a minimally invasive treatment, with good aesthetics and great precision. The aim of this work is to evaluate how new digital technologies can influence and help in minimally invasive dentistry. This evaluation will be made from a bibliographical research, based on articles available in the Cochrane Library, Medline/Pubmed, Scielo, Google Scholar and B-on databases, giving priority to articles referring to the last 10 years.Durante los últimos 30 años ha surgido una nueva tendencia en la odontología que promueve la realización de todos los procedimientos clínicos de la forma más conservadora posible para preservar la mayor cantidad de tejido dental u óseo. Uno de los ámbitos más afectados por esta nueva tendencia es la dentistería. En este ámbito de la práctica clínica diaria, hace 20-30 años eliminábamos el tejido sano para asegurar la eliminación completa de la carie. Durante los últimos años hemos pasado a intentar eliminar el menor tejido dental posible. Este cambio ha sido posible gracias a varios factores. Por un lado, en los últimos años han surgido grandes avances en los sistemas adhesivos, que permiten conseguir una retención química. Por otro lado, la continua evolución tecnológica nos permite diseñar tanto las preparaciones como las piezas dentales de la forma menos invasiva posible. El sistema que más ha ayudado a este cambio de actitud es el CAD-CAM (diseño asistido por ordenador/fabricación asistida por ordenador). A través de este sistema y sus componentes somos capaces de realizar digitalmente todos los procesos de la dentistería mínimamente invasiva, haciendo el proceso más fácil y seguro. Gracias a esta tecnología podemos realizar un diagnóstico precoz de cáries, realizar guías para el tallado de dientes y diseñar las piezas. Esto, junto con los avances ya mencionados en sistemas adhesivos y materiales, nos permite realizar un tratamiento mínimamente invasivo, con buena estética y gran precisión. El objetivo de este trabajo es evaluar cómo las nuevas tecnologías digitales pueden influir y ayudar en la odontología mínimamente invasiva. Esta evaluación se realizará a partir de una investigación bibliográfica, basada en artículos disponibles en las bases de datos Cochrane Library , Medline/Pubmed, Scielo, Google Scholar y B-on, dando prioridad a los artículos publicados en los últimos 10 años

La cinemática introductoria como elemento de identificación e inmersión en el videojuego

Treball Final de Grau en Comunicació Audiovisual. Codi: CA0932. Curs 2013-2014The technological evolution in video games of the last years has brought about an evolution in narrative and storytelling too. This paper analyzes the cultural elements that allow gamers’ immersion in game’s fictions. In order to carry out the reaserch we will analyse Beyond two souls (Quanticdreams, 2013), using a methodology focused on the deconstruction of the game’s plot and the study of the opening cut-scene, the player’s first contact with the fiction of the game. The results and conclusion show that the use of cultural elements helps the immersion in the game. We also see a trend in videogame storytelling that seems to approach the puzzle films’ narrative structures.Junto a la evolución tecnológica de los videojuegos en los últimos años, la narrativa ha evolucionado también. Este trabajo analiza los elementos culturales que facilitan la inmersión del usuario en la ficción del juego. Para ello se construye una metodología centrada en la desestructuración del relato y el estudio de la primera cinemática como primer contacto del jugador con la historia del juego. A través del análisis de Beyond two souls (Quanticdreams, 2013), se concluye que sí se hace uso de elementos culturales para ayudar a la inmersión en la ficción. También observamos una tendencia en el sector a acercase a las estructuras narrativas de los puzzle films

Monitoring of curing process by fluorescence technique. Fluorescence probe and label based on 5-dimethylaminonaphthalene-1-sulfonamide derivatives (DNS)

The curing reaction of glycidyl ether bisphenol A (DGEBA) with n-butyl amine and/or N-methylethylenediamine was monitored by fluorescence spectroscopy. 5-Dimethylaminonaphthalene-1-sulfonamide (DNS) fluorophore was used as a probe and/or label. Fourier transform infrared (FTIR) analysis revealed that the rate constant for the addition reaction of the primary amino group hydrogen of n-butylamine to the epoxide ring is more than four times larger than that arising from a secondary amine. Significant differences have been observed between the fluorescence behavior of the DNS as a probe and label, especially in the system DGEBA-N-butyl amine. Integrated fluorescence intensity for the DNS label, in contrast to the DNS probe, indicates the most important changes in chemical transformations of this reaction mixture (the onset of tertiary amino groups and maximum concentration of secondary amino groups). Similarly, the dependence of the half-bandwidth on the epoxy groups conversion for the DNS label shows these stages of the curing reaction as well. In the system DGEBA-N-methylethylenediamine, the reactivity of the secondary amino group hydrogen is higher than that of the primary amino group. A change in slope of the dependence of integrated fluorescence intensity on epoxy group conversion clearly indicates the gel point and entry of the system into the glassy state. The DNS probe does not sense any of these changes. From the emission spectra of the DNS probe and/or label, the average value = SigmaIF(nu)nu/SigmaIF(nu) of the emission band position has been correlated with the epoxy group conversion determined by FTIR. Smooth dependencies were obtained in all cases. This enables one to monitor on line and in real time the epoxy group conversion.We would like to thank the European Commission for funding through the BRITE-EuRam Project (BE97-4472) and to CAM (07N/0002/98)

Curing of linear and crosslinked epoxy systems: A fluorescence study with dansyl derivatives

The curing of diglycidyl ether of bisphenol A (DGEBA) with N,N′-dimethylethylenediamine (N,N′-DMEDA) or ethylenediamine (EDA) was monitored by fluorescence spectroscopy and Fourier transform infrared (in the near-infrared region). 5-Dimethylamino-naphthalene-1-sulfonamide (DNS) derivatives were used as probes (fluorophores added to the reaction mixture) and labels (fluorophores attached by covalent bonds to diglycidyl reactants). The term containing the ratio of the reaction rate constants for the addition of the secondary and primary amine hydrogens to the epoxide was included in the reduced reaction rate term for the autocatalyzed and catalyzed epoxide curing reactions. The changes in the integrated fluorescence intensities of the labels during the epoxy group conversion indicated, in some cases, the most important changes in the chemical transformations of the reaction mixture: the epoxy group conversion, during which a rapid increase in the tertiary amino group concentration was first observed; the gel point (for EDA); and the entry of the system into the glassy state (for N,N′-DMEDA and EDA). The fluorescence probes monitored neither the gel point nor the threshold of the glassy state. For the DGEBA–N,N′-DMEDA system, a wavy dependence of the integrated fluorescence intensities of the DNS labels on the epoxy group conversion might reflect the molar concentrations of polymer homologues (referred to the initial number of moles in the system) in the reaction mixtures of the diepoxide and secondary diamine.The authors thank the anonymous reviewers for their constructive comments and the European Commission for funding through the BRITE-EuRam project (BE97-4472) and Comunidad Autónoma de Madrid (CAM) (07N/0002/98)

Solvent and Temperature Effects on Polymer-Coated Glass Fibers. Fluorescence of the Dansyl Moiety

E-type glass fibers were coated with poly(γ-aminopropyltriethoxysilane), treating them with a 1% (v/v) monomer aqueous solution. The fibers were labeled with a dansyl-sulfonamide conjugate by reaction of acetonitrile solutions of dansyl chloride with the amine groups immobilized on the glass fiber surface. Interactions of the labeled coating polymer with solvents of different polarities were estimated by measurements of the fluorescence band shifts of the label. It was found that for aprotic solvents, the solvent dipolar coupling relaxation mechanism is dominated by thermodynamic interactions of the solvent with the polymer matrix, while for protic solvents this mechanism is dominated by specific interactions between solvent molecules and the excited state of the chromophore. Different experimental excited-state dipole moments were obtained for nonpolar and polar solvents (μ*ₙₚ = 7.2 ± 1.6 D, μ*ₚ = 11.9 ± 1.5 D). Using the AM1 method, excited-state dipole moments for the first and second singlets were calculated and it was concluded that μ*ₚ ≃ 〈μ*²₁〉½ and μ*ₚ ≃ 〈μ*²₂〉½. Accordingly, neither the glass support nor the coating polar influence the excited-state properties of dansyl. The temperature dependence of dansyl emission allows the determination of the relaxation temperature of the coating polymer, which was estimated as 175 K for the coating used.The authors wish to thank the UE Brite EuRam program (BE97-4472) and CAM (07N/0002/1998) for financial support

Microstructural and wettability study of surface pretreated glass fibres

Commercial glass fibres were calcinated for the removal of organic matter, activated for surface silanol regeneration and silanizated with γ-aminopropyltri-ethoxysilane. Two different activation methods were used: reflux with neutral water and reflux with 10% HCl aqueous solution. Acid treatments hydrolize Si–O bonds, greatly changing the composition of the glass and regenerating silanol groups, some of them being of intraglobular nature. Water treatment does not change appreciably the glass composition, but its surface free energy value is the lowest. The degree of silanization is the greatest for the acid activated samples and the lowest for the water activated one. The polar contribution to the total surface free energy, once the samples are silanizated, is the highest for the fibres activated with boiling water whilst the dispersion component is about the same for all of them. SEM observations indicate that for the greatest degree of coating, debonding of the filaments may induce a peeling-out fractural mechanism.The authors wish to thank CICYT (MAT 930823) for financial support

High porosity scaffold composites of graphene and carbon nanotubes as microwave absorbing materials

The design of microwave absorbing materials requires low reflection and high absorption of radiation simultaneously. Low reflection of electromagnetic waves can be achieved inducing porous faces which minimize the impedance mismatch. High absorption can be obtained by increasing the conductivity of the material. We report the preparation of highly porous scaffolds from a combination of graphene and carbon nanotubes. The bimodal porous structure was controlled making use of the surface properties of graphene oxide that are able to stabilize hexane droplets in aqueous dispersions of graphene oxide and carbon nanotubes. After hydrothermal and two step freeze-drying processes, macro-(220 microns) and mesoporous (10 microns) structures, due to hexane droplets and freeze drying, respectively, were obtained. DC conductivities of 8.2, 14.7, 33.2, and 60.7 S m(-1) were obtained for graphene scaffolds containing 0, 10, 20 and 40% of carbon nanotubes respectively. An electromagnetic characterization was performed on scaffolds infiltrated with epoxy resin; using appropriate models, the electromagnetic properties of the conducting phase have been obtained. Scaffolds with a thickness of 9 mm were able to absorb up to 80% of the incident radiation keeping the reflection as low as 20%.This work was supported by grant NANONARQ (MAT2014-57557-R) from the Spanish Ministerio de Economía y Competitividad

Carbon Nanotube Composites as Electromagnetic Shielding Materials in GHz Range

Following the development of the new electronic systems and communication networks, the levels of electromagnetic contamination have risen dramatically in the recent years. Every day, new studies appear searching for a way to mitigate the electromagnetic interferences (EMI). At the same time, the rapid evolution of technology forces the field to search for lighter and more efficient materials. The composites using carbon allotropes (such as carbon nanotubes) and polymers as reinforcement are gaining importance, due to the many advantages they exhibit in comparison to the materials that were used until now. A great number of applications require absorption to be the main electromagnetic shielding mechanism, thereby making this review necessary as a way to summarize the latest studies on CNT/polymer composites and how to improve the absorption mechanism by changing the morphology and composition of CNTs