Polysiloxane Side-Chain Azobenzene-Containing Liquid Single Crystal Elastomers for Photo-Active Artificial Muscle-Like Actuators

Liquid crystals (LCs) are unique materials with amazing properties and uses. Since their discovery in 1889 by F. Reinitzer1, they have experienced an explosive growth because of their successful application in a wide variety of areas such as information displays2, cosmetics and health care3, thermography4-5, artificial muscle-like actuators6-7 and enantioselective synthesis8, among others. Thus, liquid crystals play an important role in modern technology and they are present in the most common devices used in our daily live. Research into this field is growing day by day and new promising applications for such materials are discovered and developed continuously..

Estudi de Viabilitat de l'Aprofitament Hidroelèctric d'un Canal Artitifial de Reg

El present projecte pretén demostrar la viabilitat tècnica de l’aprofitament hidroelèctric dels salts existents en un canal artificial de reg. Per les característiques d’aquests, desnivell de 7 metres i cabal variable entre 1,5 i 3 m3/s durant sis mesos l’any, fan que aquests pertanyin a la categoria de microcentrals hidroelèctriques, amb una potència elèctrica al voltant dels 150 kW. La metodologia emprada en el desenvolupament de l’estudi consisteix en la justificació tècnica dels elements mes rellevant de la instal·lació, essent aquest: la turbina hidràulica, l’acoblament mecànic, el generador elèctric, el transformador elèctric i l’energia elèctrica venuda a la xarxa. A partir d’aquesta última es pot valorar la seva viabilitat econòmica

Photochromic heteroarylethenes with fast thermal isomerization kinetics

Stilbenes (diphenylethenes) are fully examined organic chromophores for very diverse applications. However, these molecules might show poor stability under irradiation because several simultaneous reactions (oxidative photocyclization and dimerization) can take place during the photochemical isomerization of their Cdouble bondC bond. In this context, heteroarylethenes emerge as powerful counterparts thanks to their improved stability. In addition, the chosen heterocycles and their functionalization allows to fine tune and increase the speed at which the thermal back reaction occurs, broadening the scope of application of the resulting chromophores. Here we report on the thermal Z-to-E isomerization kinetics of a series of rationally designed heteroarylethenes and how the chemical architecture of the chromophore modulates the speed of the process. Specifically, the metastable Z isomers display relaxation times covering a wide time window, from a few hours to hundreds of microseconds. In fact, one of the studied dyes is the fastest photochromic switch based on heteroarylethenes. It should be also noticed that the described heteroarylethenes exhibit great photochemical stability, it being possible to switch them back and forth many times without degradation

Fast isomerizing methyl iodide azopyridinium salts for molecular switches

The usefulness of azopyridinium methyl iodide salts for designing new promising light-controlled molecular switches is presented. Large absorbance changes have been produced in the samples by irradiation with light at λ ) 355 nm. The thermal recovery of the initial state took place completely within 130-450 ms, which is much faster than that reported previously for other push-pull azobenzene-doped nematic mixtures.Fil: Garcia Amorós, Jaume. Centro de Investigación en Nanociencia y Nanotecnología (CIN2); España. Universidad de Barcelona. Facultad de Química; EspañaFil: Massad, Walter Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina. Universitat Ramon Llull; EspañaFil: Nonell, Santi. Universitat Ramon Llull; EspañaFil: Velasco, Dolores. Centro de Investigación en Nanociencia y Nanotecnología (CIN2); España. Universidad de Barcelona. Facultad de Química; Españ

Influence of design parameters in the optimization of linear switched reluctance motor under thermal constraints

The objective of this paper is to present an original study for optimizing the size of the LongitudinalFlux Double-Sided Linear Switched Reluctance Motor (LSRM) under thermal and weight constraints. The performance is evaluated taken into account duty cycle operating conditions and thermal restrictions. The proposed approach couples Finite Element Analysis for magnetic propulsion force computation and Lumped Parameter Thermal Network for thermal transient analysis. The LSRMs design parameters are characterized by the number of phases and by their size denoted by the pole stroke. The operating conditions are the current density, the duty cycle and the admissible temperature rise of the insulation system. The grid search algorithm is used for solving the optimization problem. From the results, with the help of a novel multivariable optimization chart, a set of optimal configurations regarding to miniaturizations and downsizing of LSRMs is provided.Peer ReviewedPreprin

Thermal performance analysis of the double sided-linear switched reluctance motor

This paper presents an exhaustive study about the propulsion force and the thermal performance of the double-sided flat Linear Switched Reluctance Motor (LSRM) according to the number of phases (m) and the pole stroke (PS). The analysis is performed by means of the Finite Element Method (FEM) for electromagnetic computations and a lumped parameter for thermal model (LPT) both linked to an optimization algorithm based on the Response Surface Methodology (RSM) in order to reduce the computing time. The results show the optimal design of LSRM from the point of view of the thermo-mechanical performance for a given insulation class and a duty cycle operating conditions

Photochromic heteroarylethenes with fast thermal isomerization kinetics

Supplementary data to this article can be found online at https://doi.org/10.1016/j.dyepig.2022.111000Stilbenes (diphenylethenes) are fully examined organic chromophores for very diverse applications. However, these molecules might show poor stability under irradiation because several simultaneous reactions (oxidative photocyclization and dimerization) can take place during the photochemical isomerization of their C=C bond. In this context, heteroarylethenes emerge as powerful counterparts thanks to their improved stability. In addition, the chosen heterocycles and their functionalization allows to fine tune and increase the speed at which the thermal back reaction occurs, broadening the scope of application of the resulting chromophores. Here we report on the thermal Z-to-E isomerization kinetics of a series of rationally designed heteroarylethenes and how the chemical architecture of the chromophore modulates the speed of the process. Specifically, the metastable Z isomers display relaxation times covering a wide time window, from a few hours to hundreds of microseconds. In fact, one of the studied dyes is the fastest heteroarylethene known to date. It should be also noticed that the described heteroarylethenes exhibit great photochemical stability, it being possible to switch them back and forth many times without degradation.This research was funded by the Ministerio de Ciencia, Innovacion y Universidades (Spain)/Agencia Estatal de Investigacion (Spain)/Fondo Europeo de Dearrollo Regional (FEDER, European Union), grant number PGC2018-095477-B-I00. Thanks are also due to Fundação para a Ciência e Tecnologia (FCT) and to FEDER-COMPETE for financial support through the research center CQUM (UID/QUI/0686/2016) and (UID/ QUI/0686/2020). The NMR spectrometers are part of the National NMR Network (PTNMR) and are partially supported by Infrastructure Project Nº 022161 (co-financed by FEDER through COMPETE 2020, POCI and PORL and FCT through PIDDAC). Authors also thank Prof. Santi Nonell for granting access to the nanosecond laser flash photolysis setup

Kinetic study of the fast thermal cis-to-trans isomerisation of para-, ortho- and polyhydroxyazobenzenes

The thermal cis-to-trans isomerisation process has been studied for a series of para-, ortho- and polyhydroxy-substituted azobenzenes in different solvents. The kinetics of the thermal back reaction for the p-hydroxy-substituted azobenzenes depend strongly on the nature of the solvent used, with relaxation times ranging from 200-300 milliseconds in ethanol to half an hour in toluene. Otherwise, the process rate is mainly independent of the solvent nature for the ortho substituted analogues. Polyhydroxy-substituted azobenzenes show very much faster kinetics than the para- and ortho- monohydroxyazoderivatives. With relaxation times of 6-12 milliseconds in ethanol, they are optimal molecules for designing fast optical switching devices. All the hydroxyazoderivatives thermally isomerise from the metastable cis form to the thermodynamically stable trans isomer through a rotational mechanism.Fil: Garcia Amorós, Jaume. Universidad de Barcelona; EspañaFil: Sánchez Ferrer, Antoni. Universidad de Barcelona; EspañaFil: Massad, Walter Alfredo. Universitat Ramon Llull; España. Universidad Nacional de Río Cuarto. Instituto para el Desarrollo Agroindustrial y de la Salud. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto para el Desarrollo Agroindustrial y de la Salud; ArgentinaFil: Nonell, Santi. Universitat Ramon Llull; España. Universidad Nacional de Río Cuarto. Instituto para el Desarrollo Agroindustrial y de la Salud. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto para el Desarrollo Agroindustrial y de la Salud; ArgentinaFil: Velasco, Dolores. Universidad de Barcelona; Españ

Simple environmentally-friendly reduction of 4-nitrophenol

Abstract: 4-nitrophenol is a low molecular-mass organic compound involved in many chemical processes and commonly present in soils and in surface and ground waters, thereby causing severe environmental impact and health risk. Several methods have been proposed for its transformation (bio and chemical degradation). However, these strategies not only produce equally or more toxic aromatic species but also require harsh operating conditions and/or time-consuming treatments. In this context, we report a comprehensive and systematic study of the electrochemical reduction of 4-nitrophenol as a viable alternative. We have explored the electrochemical reduction of this pollutant over different metallic and carbonaceous substrata. Specifically, we have focused on the use of gold and silver working electrodes since they combine a high electrocatalytic activity for 4-nitrophenol reduction and a low electrocatalytic capacity for hydrogen evolution. The influence of the pH, temperature, and applied potential have also been considered as crucial parameters in the overall optimization of the process. While acidic media and high temperatures favor the clean reduction of 4-nitrophenol to 4-aminophenol, simultaneous hydrogen evolution results pernicious for this purpose. As a whole, a simple and effective electrochemical method for the transformation of 4-nitrophenol into 4-aminophenolis proposed with virtually no undesired by-products

Fastest non-ionic azo dyes and transfer of their thermal isomerisation kinetics into liquid-crystalline materials

Push-pull bithienylpyrrole-based azo dyes exhibit thermal isomerisation rates as fast as 1.4 μs in acetonitrile at 298 K becoming, thus, the fastest neutral azo dyes reported so far. These remarkably low relaxation times can be transferred into liquid-crystalline matrixes enabling light-triggered oscillations in the optical density of the final material up to 11 kHz under ambient conditions.Financial support for this research was obtained from the Ministerio de Economía y Competitividad (Spain, CTQ2012-36074 and CTQ2015-65770-P). The authors thank Prof. Santi Nonell for his help with the flash photolysis measurements. Thanks are also due to: Fundação para a Ciência e Tecnologia (FCT) for a PhD grant to M. C. R. Castro (SFRH/BD/78037/2011); FEDERCOMPETE for financial support through the Centro de Quı ´mica – UM, PEst-C/QUI/UI0686/2013 (FCOMP-01-0124-FEDER-037302). The NMR spectrometer Bruker Avance III 400 is part of the National NMR Network and was purchased within the framework of the National Program for Scientific Re-equipment, contract REDE/1517/RMN/2005 with funds from POCI 2010 (FEDER) and FCT