Characterization of poled and non-poled β-PVDF films using thermal analysis techniques

ß-poly(vinylidene fluoride)—ß-PVDF—exhibits ferroelectric properties due to the special arrangement of the chain units in the crystalline phase. The ferroelectric phase can be optimised by poling the original stretched film, that tends to align the randomly organised crystallites against the applied field. In this work, polarised and non-polarised ß-PVDF from the same batch are characterised by mechanical tests and a series of thermal analysis techniques, including DMA, TMA and DSC. The films exhibit mechanical anisotropy, and in the longitudinal direction the poled film presents larger mechanical properties, due to the higher structural organisation. Poled and non-poled show similar crystallinity levels but the melting temperature probed by DSC is higher for the non-poled film; for both films the melting peak exhibits a complex shape, indicating a heterogeneous crystalline organization. Two relaxation processes were found (ß and alpha_c) by dynamic mechanical analysis (DMA). The ß process, attributed to segmental motions in the amorphous phase, appears at the same temperature in both directions, but its intensity was found to be higher for the films tested in the longitudinal direction. For a given direction, the poled films exhibit lower peaks, due to the more organised amorphous structure. At higher temperature, the alpha_c-relaxationwas related to the contraction of the films in the longitudinal direction during heating, recorded by thermal mechanical analysis (TMA). The onset of molecular mobility within the crystalline phase allows for cooperative diffusion processes in the amorphous phase, generating the randomisation of the initially oriented structure.Fundação para a Ciência e Tecnologia (FCT) - Programa Operacional "Ciência, Tecnologia, Inovação" (POCTI) - POCTI/CTM/33501/99

CMOS x-rays detector array based on scintillating light guides

This paper describes a pixel imaging array consisting in 400µm x 400µm photodiodes fabricated in CMOS technology. An array of scintillating CsI:Tl crystals is placed above the photodiodes. These crystals are encapsulated in aluminum walls, forming a light path that guides the visible light produced by the scintillating crystal into the photodiodes. In This way, the x-ray energy is first converted into visible light which is then detected by the photodiode at the end of each light guide. The scintillator is 800 µm thick, absorbing almost all 20keV x-ray photons. Usually, the spatial resolution of the scintillating x-ray detectors is identical to the scintillator thickness. By using the light guides, the scintillator thickness can be increased without decreasing the spatial resolution. The increase of the scintillator thickness is desirable in order to increase the x-rays absorption efficiency. Tests carried out on the system show very promising results near 20keV

Modeling and simulation of the mixing process of fluids in microchannels promoted by acoustic streaming

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.This work describes a study on the acoustic streaming phenomenon, for promoting mixing in microfluidic channels. Acoustic microagitation is a solution to overcome the slow molecular diffusion and accelerate chemical reactions, which is essential to the success of microfluidic devices. A preliminary study has been performed on the piezoelectric effect generated by an electroactive polymer and on the compressible flow Navier-Stokes equations. The simulations were based on finite elements numerical methods. It was concluded that the positioning of the transducer influences the pressure distribution over the fluid domain. It was also seen that the Navier-Stokes equations can be expanded as a sum of equilibrium, first and second order values, that describe the damped propagation of acoustic waves and the global flow, respectively. The time average of the first order results corresponds to a force and can be applied as a source term in the second order equations to determine the mean global flow into the microcuvette.Programa Operacional Factores de Competitividade – COMPETE and FCT- Fundação para a Ciência e a Tecnologia project reference PTDC/BIO/70017/2006 and SFRH/BD/61767/200

Magnetoelectric CoFe2O4/polyvinylidene fluoride electrospun nanofibres.

Magnetoelectric 0-1 composites comprising CoFe2O4 (CFO) nanoparticles in a polyvinylidene fluoride (PVDF) polymer-fibre matrix have been prepared by electrospinning. The average diameter of the electrospun composite fibres is ∼325 nm, independent of the nanoparticle content, and the amount of the crystalline polar β phase is strongly enhanced when compared to pure PVDF polymer fibres. The piezoelectric response of these electroactive nanofibres is modified by an applied magnetic field, thus evidencing the magnetoelectric character of the CFO/PVDF 0-1 composites.This work was supported by FEDER through the COMPETE Program and by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Project PEST C/FIS/UI607/2014 and PTDC/CTM NAN/112574/2009. R. G., P. M., V. S., G. B. and S. L. M. acknowledge support from “Matepro – Optimizing Materials and Processes” (ref. NORTE-07-0124-FEDER-000037), co funded by “Programa Operacional Regional do Norte” (ON.2 – O Novo Norte, QREN, FEDER). P. M. and R. Gonçalves acknowledges also support from FCT (SFRH/BPD/96227/2013 and SFRH/BD/88397/2012 grants respectively). X. M. acknowledges support from the Ramón y Cajal (RYC) Programme (Spanish MEC) and the Royal Society.This is the accepted manuscript. The final version is available at http://pubs.rsc.org/en/Content/ArticleLanding/2015/NR/c5nr00453e#!divAbstract

Kinetic study of thermal degradation of chitosan as a function of deacetylation degree

[EN] Thermal degradation of chitosan with varying deacetylation degree (DD) ranging between 50 and 85% was analyzed by dynamic thermogravimetric analysis at different heating rates. The present study focused on the temperature range between 500 and 800 K, above water evaporation. Thermal degradation showed a main degradation stage in this temperature interval with a second stage that appeared in the weight derivative curves as a shoulder in the high temperature side of the main peak with increasing intensity as the DD decreased. The Kissinger and isoconversional Ozawa-Flynn-Wall models were employed to evaluate the Ea of both thermal degradation processes. Different kinetic models were tested to computer simulate the thermogravimetric traces calculating the model parameters with a non-linear least squares fitting routine. The Sestack-Berggren model allowed reproducing accurately the overlapping of the two degradation mechanisms and calculating the mass fraction lost in each of them revealing the coupling between the two degradation mechanisms.Thermal degradation of chitosan with varying deacetylation degree (DD) ranging between 50 and 85% was analyzed by dynamic thermogravimetric analysis at different heating rates. The present study focused on the temperature range between 500 and 800 K, above water evaporation. Thermal degradation showed a main degradation stage in this temperature interval with a second stage that appeared in the weight derivative curves as a shoulder in the high temperature side of the main peak with increasing intensity as the DD decreased. The Kissinger and isoconversional Ozawa-Flynn-Wall models were employed to evaluate the Ea of both thermal degradation processes. Different kinetic models were tested to computer simulate the thermogravimetric traces calculating the model parameters with a non-linear least squares fitting routine. The Sestack-Berggren model allowed reproducing accurately the overlapping of the two degradation mechanisms and calculating the mass fraction lost in each of them revealing the coupling between the two degradation mechanisms.Gamiz-Gonzalez, MA.; Correia, D.; Lanceros-Mendez, S.; Sencadas, V.; Gómez Ribelles, JL.; Vidaurre, A. (2017). Kinetic study of thermal degradation of chitosan as a function of deacetylation degree. Carbohydrate Polymers. 167:52-58. https://doi.org/10.1016/j.carbpol.2017.03.020S525816

Enhanced proliferation of pre-osteoblastic cells by dynamic piezoelectric stimulation

[EN] This work reports on the influence of the polarization of electroactive poly(vinylidene fluoride), PVDF, on the biological response of cells cultivated under static and dynamic conditions. Non-poled and "poled +" beta-PVDF with and without a titanium layer were thus prepared. A thin titanium layer was deposited on PVDF films in order to obtain a more homogeneous surface charge. The MC3T3-E1 osteoblast cell culture exhibited different responses in the presence of PVDF films. The positively charged beta-PVDF films promote higher osteoblast adhesion and proliferation, which is higher under dynamic conditions on poled samples, showing that the surface charge under mechanical stimulation improves the osteoblast growth. Therefore, electroactive membranes and scaffolds can provide the necessary electrical stimuli for the growth and proliferation of specific cells.JLGR acknowledge the support of the Spanish Ministry of Education through project No. MAT2010-21611-C03-01 (including the FEDER financial support) and project EUI2008-00126.Ribeiro, C.; Moreira, S.; Correia, V.; Sencadas, V.; Rocha, JG.; Gama, FM.; Gómez Ribelles, JL.... (2012). Enhanced proliferation of pre-osteoblastic cells by dynamic piezoelectric stimulation. RSC Advances. 2(30):11504-11509. https://doi.org/10.1039/c2ra21841k115041150923

Environmentally friendly carrageenan-based ionic-liquid driven soft actuators

UID/FIS/04650/2020 UID/QUI/0686/2020 LA/P/0008/2020 PID2019-106099RB-C43/AEI/10.13039/501100011033A naturally derived polymer based on iota carrageenan and different ammonium and imidazolium based ionic liquids (ILs) are used for the development of environmentally friendly soft actuators. The influence of IL content and type and solvent evaporation temperature on the morphological and physico-chemical properties of the materials was evaluated, together with the effect on actuator functional response. Independently of the IL content and type, and the solvent evaporation temperature, a non-porous structure is obtained. The incorporation of the IL within the polymer matrix does not affect the thermal stability but leads to a decrease in the Young modulus for the different IL/carrageenan samples. The highest influence was observed by using the [Ch][DHP] IL at a filler content of 40% w/w with a decrease in the Young modulus from 748 MPa for the neat polymer to 145 MPa for the [Ch][DHP]/carrageenan sample. Furthermore, the ionic conductivity of the samples increases with increasing IL content, with the highest values being 2.9 × 10-6 S cm-1 and 1.2 × 10-6 S cm-1 for the samples with 40% w/w of [Bmim][FeCl4] and [Ch][DHP], respectively. Regarding the soft actuator performance, the maximum displacement was obtained for the [Ch][DHP]/carrageenan sample with an IL content of 40% w/w, showing a maximum displacement of 5.8 mm at a DC applied voltage of 9 V.publishersversionpublishe

Indirect X-ray detectors based on inkjet-printed photodetectors with a screen-printed scintillator layer

Organic photodetectors (PDs) based on printing technologies will allow to expand the current field of PD applications toward large-area and flexible applications in areas such as medical imaging, security, and quality control, among others. Inkjet printing is a powerful digital tool for the deposition of smart and functional materials on various substrates, allowing the development of electronic devices such as PDs on various substrates. In this work, inkjet-printed PD arrays, based on the organic thin-film transistor architecture, have been developed and applied for the indirect detection of X-ray radiation using a scintillator ink as an X-ray absorber. The >90% increase of the photocurrent of the PDs under X-ray radiation, from about 53 nA without the scintillator film to about 102 nA with the scintillator located on top of the PD, proves the suitability of the developed printed device for X-ray detection applicationsThe authors thank FEDER funds through the COMPETE 2020 Programme and National Funds through FCT-Portuguese Foundation for Science and Technology under Strategic Funding UID/FIS/04650/2013 and projects PTDC/EEI-SII/5582/2014, PTDC/CTM-ENE/5387/2014 and in the framework of EuroNanoMed 2016 call, Project LungChek ENMed/0049/2016. J.O. and V.C. thank the FCT for the SFRH/BD/98219/2013 and SFRH/BPD/97739/2013 grants, respectively. The authors acknowledge funding by the Spanish Ministry of Economy and Competitiveness (MINECO) through the project MAT2016-76039-C4-3-R. Financial support from the Basque Government Industry Department under the ELKARTEK program is also acknowledged. The authors thank Iain McCulloch and Martin Heeney from Flexink for providing the OSC. Dirk Rittrich (Department Layer Deposition at Fraunhofer ENAS) is acknowledged for the FIB/SEM analysis and the sample preparation. R.D.R acknowledges the DFG Unit FOR1317 SMINT, the Cluster of Excellence, and the Tomsk Polytechnic University Competitiveness Enhancement Program grant TPU CEP_IHTP_73\2017. This work was performed in the context of the European COST Action MP1302 Nanospectroscopy.info:eu-repo/semantics/publishedVersio

Nucleation of the electroactive γ phase and enhancement of the optical transparency in low filler content poly(vinylidene)/clay nanocomposites

Poly(vinylidene fluoride), PVDF, based nanocomposites with different clays structures have been processed by solvent casting and melt crystallisation. Depending on the melting temperature of the polymer, the nanocomposite recrystalises in the electroactive or non electroactive β-phase of the polymer. This fact is related to the thermal behaviour of the clay. For montmorillonite clay, the full crystallisation of the electroactiveγ-phase occurs for clay contents lower than 0.5 wt%, allowing the nanocomposites to maintain the mechanical properties of the polymer matrix. The electroactivity of the material has been proven by measuring the piezoelectric d33 response of the material. The obtained value of d33 is -7 pC/N, lower than in β-PVDF obtained by mechanical stretching, but still among the largest coefficients obtained for polymers. Further, the optical transmittance in the visible range is strongly enhanced with respect to the transmittance of the pure polymer. Finally, it is demonstrated that the nucleation of the β-phase can be also obtained in other clays, such as in kaolinite and laponite.Fundação para a Ciência e a Tecnologia (FCT) - NANO/NMed-SD/0156/2007, PTDC/CTM/69316/2006, PTDC/CTM-NAN/112574/2009, SFRH/BD/62507/2009.FEDER funds through the "Programa Operacional Factores de Competitividade – COMPETECOST Action MP1003, the ‘European Scientific Network for Artificial Muscles’ (ESNAM)

Multilayer passive radiative selective cooling coating based on Al/SiO2/SiNx/SiO2/TiO2/SiO2 prepared by dc magnetron sputtering

A multilayer passive radiative selective cooling coating based on Al/SiO2/SiNx/SiO2/TiO2/SiO2 prepared by dc magnetron sputtering is presented. The design was first theoretically optimized using the optical constants, refractive index and extinction coefficient, of thin single layers. The spectral optical constants in the wavelength range from 0.3 to 27 µm were calculated from the transmittance and reflectance data of thin single layers deposited on silicon and glass substrates. The samples were characterized by Scanning Electron Microscopy, X-ray diffraction, Fourier-transform Infrared Spectroscopy and UV–VIS–NIR spectroscopy. It is shown that the TiO2 layer presents a partially rutile phase polycrystalline structure and a higher refractive index than amorphous SiO2 and SiNx layers in the spectral range from 0.3 to 2.5 μm. The cooling device was deposited on copper substrates and a thin low-density polyethylene foil with high transmittance in the 8 to 13 µm spectral range was used as convection cover material. The device is characterized by both low reflectance (high emittance) in the sky atmospheric window (wavelength range from 8 to 13 µm) and high hemispherical reflectance elsewhere, allowing for temperature drops of average 7.4 °C at night-time in winter, which corresponds to a net cooling power of ~43 W m−2. Further, a temperature drop of 2.5 °C was obtained during winter daytime.FCT in the framework of the Strategic Funding UID/FIS/04650/2013 and the financial support of FCT, POCI and PORL operational programs through the project POCI-01-0145-FEDER-016907 (PTDC/CTM-ENE/2892/2014), co-financed by European community fund FEDE