Experiencias de cátedra en las clases de física de primer curso de Escuelas Técnicas

We have performed a set of lecture room experiences in a Physics course at the Escuela Universitaria de Informática, of the Universidad Politécnica de Valencia; we have studied the effects produced on the students. This paper shows that we can prepare and perform this method easily, and also its low cost. On the other hand, the general assessment of the students is positive, and it is particularly helpful to improve the motivation and the understanding of the concepts

Conformational mobility in a polymer with mesogenic side groups- dielectric and DSC studies

The relaxation times of the conformational rearrangements of the main-chain segments of a liquid crystalline side-chain polymer was determined from differential scanning calorimetry experiments in the temperature interval around and below its glass transition. Phenomenological models with fitting parameters were used to evaluate the temperature dependence of the relaxation times and the form parameter of the relaxation times distribution. These parameters were compared with its counterparts in the dielectric a relaxation process which appear in the temperature interval immediately above the calorimetric glass transition. For the temperature interval below the calorimetric glass transition the differential scanning calorimetry (DSC) results were compared with the dielectric results obtained by the thermally stimulated depolarisation technique

Relaxation in non-Markovian models: From static to dynamic heterogeneity

[EN] Glass transition processes have often been explained in terms of wide distributions of relaxation times. By means of a simple stochastic model we here show how dynamic heterogeneity is the key to the emergence of the glass transition. A non-Markovian model representing a small open region of the amorphous material was previously shown to reproduce the time and thermal characteristic behavior of supercooled liquids and glasses. Due to the interaction of the open regions with their environment, the temperature dependence of the equilibrium relaxation times differs from the featureless behavior of the relaxation times of closed regions, whose static disorder does not lead to a glass transition, even with wider distributions of equilibrium relaxation times. The dynamic heterogeneity of the open region produces a glass transition between two different regimes: a faster-thanArrhenius and non-diverging growth of the supercooled liquid relaxation times and an average Arrhenius behavior of the ideal glass. The Kovacs' expansion gap was studied by evaluating the nonequilibrium distribution of relaxation times after the temperature quenches.Funding for open access charge: CRUE-Universitat Polit`ecnica de Val`encia. RSS and JMM acknowledge the Spanish Ministry of Science, Innovations and Universities through the RTI2018-097862-B-C21 Project (including the FEDER financial support). CIBER-BBN is an initiative funded by the VI National R&D&I Plan 2008-2011, Iniciativa Ingenio 2010, Consolider Program. CIBER Actions are financed by the Instituto de Salud Carlos III with assistance from the European Regional Development Fund.Torregrosa Cabanilles, C.; Molina Mateo, J.; Sabater I Serra, R.; Meseguer Dueñas, JM.; Gómez Ribelles, JL. (2022). Relaxation in non-Markovian models: From static to dynamic heterogeneity. Journal of Non-Crystalline Solids. 576. https://doi.org/10.1016/j.jnoncrysol.2021.12124512124557

Solid polymer electrolytes based on lithium bis(trifluoromethanesulfonyl)imide/poly(vinylidene fluoride -co-hexafluoropropylene) for safer rechargeable lithium-ion batteries

The increasing use of electronic portable systems and the consequent energy demand, leads to the need to improve energy storage systems. According to that and due to safety issues, high-performance non-flammable electrolytes and solid polymer electrolytes (SPE) are needed.SPE containing different amounts of lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) into a poly(vinylidene fluoride-co-hexafluoropropylene), PVDF-HFP, polymer matrix have been prepared by solvent casting. The addition of LiTFSI into PVDF-HFP allows to tailor thermal, mechanical and electrical properties of the composite.In particular, the ionic conductivity of the composites increases with LiTFSI content, the best ionic conductivities of 0.0011 mS/cmat 25 degrees C and 0.23 mS/cmat 90 degrees C were obtained for the PVDF-HFP/LiTFSI composites with 80 wt % of LiTFSI.This solid electrolyte allows the fabrication of Li metallic/SPE/C-LiFePO4 half-cells with a discharge capacity of 51.2 mAh/ g at C/20. Further, theoretical simulations show that the discharge capacity value depends on the lithium concentration and percentage of free ions and is independent of the solid polymer electrolyte thickness. On the other hand, the voltage plateau depends on the SPE thickness. Thus, a solid electrolyte is presented for the next generation of safer solid-state batteries.The authors thank the FCT (Fundação para a Ciência e Tecnologia) for financial support under the framework of Strategic Funding grants UID/FIS/04650/2013, UID/EEA/04436/2013 and UID/QUI/0686/2016; and project no. PTDC/FIS-MAC/28157/2017. The authors also thank the FCT for financial support under grant SFRH/BPD/112547/2015 (C.M.C.). Financial support from the Basque Government Industry Department under the ELKARTEK and HAZITEK programs is also acknowledged. JMMD and JLGR acknowledge funding by the Spanish Ministry of Economy and Competitiveness (MINECO) through the project MAT2016-76039-C4-1 and 3-R (including the FEDER financial support) CIBER-BBN is an initiative funded by the VI National R&D&i Plan 2008–2011, Iniciativa Ingenio 2010, Consolider Program, CIBER Actions and financed by the Instituto de Salud Carlos III with assistance from the European Regional Development Fund

Results of a university experience, comparing face-toface, online and hybrid teaching in a context of Sarscov19

[EN] The irruption of sarscov19 in the spring of 2020 was a challenge for everyone, particularly university teaching, where solutions had to be improvised urgently. Technological resources and online teaching played a fundamental role, and the involvement of students, teachers and administration led to an acceptable outcome. After the first impact of the pandemic, new alternatives compatible with the protocols of social distancing and health security were proposed in the planning for the academic year 2020-2021. As in many other universities, a synchronous hybrid learning (SHL) model was offered at the Universitat Politècnica de València (UPV), combining online learning and face-to-face (F2F) activities. In the SHL model, some students attended classes in-person (the room capacity limited the number according to the minimum distances between people required) and stream for the rest of the students, who followed the class simultaneously. In addition, the classes were recorded to enable their asynchronous use. SHL was only used when the conditions were favourable. Vulnerable teachers were teaching entirely online in their groups. When the number of students in a group was small enough, teaching was fully F2F, maintaining the online option only for vulnerable or confined students. The laboratory practices followed a similar hybrid scheme. The tutorials were attended by email or videoconference, and the exams were preferably in-person, with ad hoc solutions in the cases of confined or vulnerable students. Between February and June 2021, a pilot experience was carried out in the Electricity course of the degree in Electronic Engineering and Industrial Automation at the UPV. Three groups were taught with a different methodology: online, SHL and F2F teaching. Planning, academic resources, and evaluation were the same in the three groups. All three followed active flipped classroom methods. In this paper, the student's academic outcomes and the results of opinion surveys conducted on the activities are presented. Results are analysed in terms of the three groups/methodologies showing reasonable doubts about the SHL model where, the academic results and the student's opinions are significantly lower than the other two methodologies. These results could help to decide the best methodological solution if we had a similar situation in the future.Authors would like to thank the Institute of Education Sciences of the Universitat Politècnica de València (Spain) for supporting the Teaching Innovation Group e-MACAFI and for the financial support through PIME Project PIME 20-21/220 and PIME Project PIME/2018/B25.Tort-Ausina, I.; Gómez-Tejedor, J.; Molina Mateo, J.; Riera Guasp, J.; Meseguer Dueñas, JM.; Martín-Cabezuelo, R.; Vidaurre, A. (2022). Results of a university experience, comparing face-toface, online and hybrid teaching in a context of Sarscov19. IATED. 896-905. https://doi.org/10.21125/edulearn.2022.025889690

Bond fluctuation model to describe physical aging in polymeric materials

International audienc

Bond fluctuation model to describe physical aging in polymeric materials

International audienc

Glass transition and structural relaxation in semi-crystalline poly(ethylene terephthalate): a DSC study

The aim of this work is to determine the relaxation times of the cooperative conformational rearrangements of the amorphous phase in semi-crystalline poly(ethylene terephthalate) (PET) and compare them with those calculated in amorphous PET. Samples of nearly amorphous polymer were prepared by quenching and samples with different crystallinity fractions were prepared from the amorphous one using cold crystallisation to different temperatures. The differential scanning calorimetry (DSC) thermograms measured on samples rapidly cooled from temperatures immediately above the glass transition show a single glass transition which is much broader in the case of high-crystallinity samples than in the amorphous or low-crystallinity PET. To clarify this behaviour, the samples were subjected to annealing at different temperatures and for different periods prior to the DSC measuring heating scan. The thermograms measured in samples with low crystallinity clearly show the existence of two amorphous phases with different conformational mobility, these are called Phases I and II. Phase I contains polymer chains with a mobility similar to that in the purely amorphous polymer, while Phase II shows a much more restricted mobility, probably corresponding to conformational changes within the intraspherulitic regions. The model simulation allows to determine the temperature dependence of Phase II relaxation times, which are independent from the crystallinity fraction in the sample and around two decades longer than those of the amorphous polymer at the same temperature

Crystallization kinetics of poly(ethylene oxide) confined in semicrystalline poly(vinylidene) fluoride

Polymer blends based on poly(vinylidene fluoride) (PVDF) and poly(ethylene oxide) (PEO) have been prepared to analyze the crystallization kinetics of poly(ethylene oxide) confined in semicrystalline PVDF with different ratios of both polymers. Both blend components were dissolved in a common solvent, dimethyl formamide. Blend films were obtained by casting from the solution at 70 degrees C. Thus, PVDF crystals are formed by crystallization from the solution while PEO (which is in the liquid state during the whole process) is confined between PVDF crystallites. The kinetics of crystallization of the confined PEO phase was studied by isothermal and nonisothermal experiments. Fitting of Avrami model to the experimental DSC traces allows a quantitative comparison of the influence of the PVDF/PEO ratio in the blend on the crystallization behavior. The effect of melting and further recrystallization of the PVDF matrix on PEO confinement is also studied.The authors thank the assistance and advice of Electron Microscopy Service of the UPV. This work was supported by the Spanish Ministry of Economy and Competitiveness (MINECO) through the project MAT2016-76039-C4-1 and 3-R (including the FEDER financial support); CIBER-BBN is an initiative funded by the VI National R&D&i Plan 2008-2011, Iniciativa Ingenio 2010, Consolider Program, CIBER Actions, and by the Instituto de Salud Carlos III with assistance from the European Regional Development Fund; 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; the FCT grant SFRH/BPD/112547/2015 (to C.M.C.); support from the Basque Government Industry Department under the ELKARTEK Program; the doctoral grant from the Programa de Ayudade Investigacion y Desarrollo (PAID) of the Universitat Politecnicade Valencia (to M.N.T.-M.).info:eu-repo/semantics/publishedVersio

Influence of cation and anion type on the formation of the electroactive β-phase and thermal and dynamic mechanical properties of poly(vinylidene fluoride)/ionic liquids bends

Films based on poly(vinylidene fluoride) (PVDF) blended with ionic liquids (ILs) comprising different cations and anions were developed to investigate the IL influence on the resulting PVDF crystalline phase. Blends with 25 wt % IL content were produced by solvent casting followed by solvent evaporation at 210 °C in an air oven. Five different ILs containing the same cation 1-ethyl-3-methylimidazolium [Emim] and five ILs containing the same anion bis(trifluoromethylsulfonyl)imide [TFSI] were selected. The formation of the different phases and the resulting thermal and dynamic mechanical properties were studied by Fourier transform infrared spectroscopy, differential scanning calorimetry, and dynamic mechanical analysis. The incorporation of [Emim]-based ILs successfully directs the PVDF crystallization from the nonpolar α-phase toward the electroactive and highly polar β-phase. On the contrary, blends containing [TFSI] as a common anion yield a mixture of α and β phases. Overall, the induced β-phase ranges between 14 and 95% depending on the incorporated IL type. Interestingly, 1-ethyl-3-methylimidazolium chloride [Emim][Cl] is the most effective IL among the studied ones to significantly enhance the β-phase content, showing also a marked nucleating effect. The results suggest that ions favorably interact with PVDF chains and are located occupying the amorphous interlamellar PVDF regions. Furthermore, the studied ILs act as plasticizers, yielding lower glass-transition temperatures of the amorphous phase and decreasing mechanical storage modulus at room temperature.This work was supported by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UID/FIS/04650/2019. The authors thank FEDER funds through the COMPETE 2020 Programme and National Funds through FCT under the projects PTDC/BTM-MAT/28237/2017, PTDC/EEI-SII/5582/2014, and PTDC/FIS-MAC/28157/2017. D.M.C. and C.M.C. also acknowledge the FCT for grants SFRH/BPD/121526/2016 and SFRH/BPD/112547/2015, respectively. The financial supports from the Spanish Ministry of Economy and Competitiveness (MINECO) through the project MAT2016-76039-C4-(1 and 3)-R (AEI/FEDER, UE) (including the FEDER financial support) and from the Basque Government Industry and Education Departments under the ELKARTEK, HAZITEK, and PIBA (PIBA-2018-06) programs, respectively, are acknowledged. CIBER-BBN is an initiative funded by the VI National R&D&I Plan 2008–2011, Iniciativa Ingenio 2010, Consolider Program. CIBER Actions are financed by the Instituto de Salud Carlos III with assistance from the European Regional Development Fund