Dispositivo portamuestras para medidas simultáneas utilizando radiación de sincrotrón

Referencia OEPM: P200001388.-- Fecha de solicitud: 31/05/2000.-- Titular: Consejo Superior de Investigaciones Científicas (CSIC).Dispositivo portamuestras para medidas simultáneas utilizando radiación de sincrotrón (ver figura en archivo de texto adjunto). La presente invención describe el desarrollo de un nuevo prototipo de portamuestras para utilización simultánea en una línea de difracción de rayos-X utilizando la para detección simultánea de dispersión en ángulos altos y bajos y espectroscopia dieléctrica. El prototipo consiste en: (i) dos bloques metálicos con cuatro resistencias calefactoras empotradas que permiten calentar los bloques metálicos y la muestra hasta 350ºC. Uno de los bloques esta atravesado por un tubo en forma de U por el cual circula aire de refrigeración y que al mismo tiempo conecta el bloque principal del portamuestras con la tapa; (ii) dos discos metálicos con orificios efectuados en el centro (electrodos); (iii) dos discos finos de aluminio; (iv) una placa superior (tapa), para cerrar el horno donde se introduce el portamuestras, con las correspondientes conexiones para el cableado.Peer reviewe

Evidence of early stage precursors of polymer crystals by dielectric spectroscopy

Dielectric spectra of the polyester poly(propylene succinate) were measured upon crystallization. For this model aliphatic polyester the α and β relaxations appear simultaneously and are well resolved in the experimental frequency window. During isothermal crystallization, this fact allows one to use the β relaxation to characterize the crystalline structural development while the α relaxation provides information about the evolution of the amorphous phase dynamics. In this way structure development and dynamics evolution can be characterized by a single experiment during the crystallization process. The unambiguous analysis of the dielectric loss clearly supports the existence of precursors of crystallization in the induction period. © 2007 The American Physical Society.Finnancial support from the MCYT (Grant No. MAT2005-01768), Spain.Peer Reviewe

Broadband ac conductivity of conductor-polymer composites

The electrical conductivity of a composite model system formed by highly structured carbon black (CB) filled, within an amorphous polymer, poly(ethylene terephtalate) composite is studied. The dc conductivity as a function of CB content follows a scaling law of the type σ∝(p−pc)t yielding for the percolation concentration, pc=0.011 and for the exponent, t=2.17. The analysis of the temperature dependence of the conductivity suggests that for temperatures larger than 45 K, conduction can be ascribed to thermal fluctuation induced tunneling of the charge carriers through the insulating layer of polymer separating two CB aggregates. At lower temperatures, conductivity becomes temperature independent, which is typical of conventional tunneling. The frequency dependence of the conductivity is also studied between dc and 109 Hz. By the introduction of a shift factor ap, a procedure for the construction of a master curve based on a “time-length equivalence principle” is proposed. Finally, a model is introduced to describe the frequency dependence of the conductivity of CB-filled composites based on the behavior of charge carriers placed in a fractal object

Simultaneous crystalline-amorphous phase evolution during crystallization of polymer systems

Despite the fact that polymer crystallization has been the object of intense research, this process is far from being fully understood. Traditional polymer crystallization studies using X-ray scattering techniques mainly provide information about the ordered regions. To obtain a more complete information about the time evolution of both the crystalline and the amorphous phase during polymer crystallization, we have developed a technique which allows one to obtain information about both the crystalline and the amorphous phase simultaneously. We report here simultaneous information about three key aspects of the isothermal polymer crystallization process: i) polymer chain ordering, through Wide-Angle X-ray Scattering; ii) lamellar crystals arrangement, through Small-Angle X-ray Scattering; iii) amorphous phase evolution through dielectric spectroscopy. Our results probe that during primary crystallization the average mobility of the amorphous phase is not notably affected. Upon passing through the crossover time, marking the transition from primary to secondary crystallization, the restriction to the mobility of the amorphous phase mainly occurs in the regions between the lamellar stacks regions and not in the amorphous regions within the lamellar stacks. We hypothesize that molecular mobility in the amorphous regions located between consecutive crystals become strongly arrested as soon as the lamellar stack is formed. © EDP SciencesMCYT (grants FPA2001-2139, BMF2000-1474), Spain. MEC “Científicos y Tecnólogos Extranjeros” program. IHP-Contract HPRI-CT-1999-00040 of the European Commission (EC(ERBFMGEDT 950059) and II-00-015 EC).Peer Reviewe

Laser nanostructuring of polymers: Ripples and applications

Polymer nanostructures and nanopatterns are being profusely used for developing next-generation organic devices with analytical and biological functions and photonic applications. Laser based strategies constitute an advantageous approach for the assembly and control of this type of soft matter nanostructures as they afford the sought versatility and reliability. Recent and on-going research on laser nanostructuring of thin films of synthetic polymers and natural biopolymers will be exemplified by studies on the generation of laser induced periodic surface structures (LIPSS) and their use for surface enhanced Raman spectroscopy (SERS) based sensors. © 2012 American Institute of PhysicsFunded by MICINN, Spain, Projects CTQ2010-15680 and MAT2009-07789. MICINN, Spain, Juan de la Cierva contract and an FPI fellowshipPeer Reviewe

Tunable electromagnetic interference shielding properties of binary thermoplastic composites prepared by reactive microencapsulation

The Supporting Information is available free of charge at: https://pubs.acs.org/doi/10.1021/acsapm.2c00084Thermoplastic composites integrating carbon nanotubes (CNT) and micron-sized metal particles dispersed in polymer matrices can address emerging multifunctional needs, e.g., good electrical conductivity and electromagnetic interference (EMI) shielding combined with easy processing and affordable costs. Herein, an approach based on reactive microencapsulation is reported to prepare polyamide 6 (PA6)-based composites comprising binary loads of CNT and Al, Cu, or Fe particles. The microencapsulation is performed by activated anionic polymerization of ε-caprolactam in solution, in the presence of the metal/CNT loads. The resulting hybrid microparticles are compression-molded into plates containing effective metal/CNT loads in the range of 12–17 wt %. Among the materials synthesized, the one containing Al/CNT binary load (3:7 wt %) displays the highest EMI shielding effectiveness (SE) of 43.5 dB at 12 GHz, with a 2 mm thickness and an electrical conductivity σdc of 6.61 × 10–3 S/cm. A synergetic effect is observed in all of the metal/CNT PA6 samples in terms of both σdc and SE increase. Evidently, the presence of metal particles well dispersed in the conductive CNT network contributes to the mobility of the carriers and thus to the effective attenuation of the electromagnetic waves. Therefore, the binary composites of this study can be efficient thermoplastic EMI shielding materials.The authors gratefully acknowledge the technical support of Hugo Mostardinha from the Instituto de Telecomunicações Aveiro during the EMI shielding measurements and the financial support of Fundação para a Ciência e Tecnologia (FCT), Project UID/CTM/50025/2019. F.M.O. thanks FCT for the Ph.D. grant PD/BD/114372/2016 (AdvaMTech Ph.D. Program in Advanced Materials and Processing). The assistance of Prof. Nuno Carvalho from the University of Aveiro, Portugal, in the EMI shielding experiments is also gratefully acknowledged

Breve Introducción a la Física de los Materiales Poliméricos

Se presenta una introducción general a la física de los materiales poliméricos y a sus aplicaciones en el siglo XX

Molecular dynamics of ferroelectric polymeric systems as studied by incoherent quasielastic neutron scattering

11 págs.; 15 figs.We have studied by incoherent quasielastic neutron scattering the molecular dynamics of the ferroelectric copolymers of vinylidene fluoride and trifluoroethylene with two different molar ratios. Thermal hysteresis effects accompanying the structural changes observed in these materials are found. In the temperature range investigated three motions were identified: (i) a vibrational motion of Debye-Waller type which shows increasing amplitude until the vicinity of the Curie temperature and then it follows a Q4 law, (ii) a slow jump diffusive motion of each chain in the restricted volume defined by other chains, thermally activated with an activation barrier of 8 kcal/mol, and (iii) a fast local diffusive motion with only some fraction of the chains concerned. © 1994 The American Physical Society.Grateful acknowledgments is due to DGICYT (Grant No. PB91-0355), to CICYT (Grant No. MAT92-148), to CICYT (Grant No. MAT94-0740E), to the Consejeria de Educacion de la Comunidad de Madrid (Grant No. 284/92) and to Fundacion Domingo Martinez (Grant No. 1992/93) for the generous support of this investigation.Peer Reviewe

Electrically conductive PTT-block-PTMO/SWCNTs+Graphene Nanoplatelets hybrid nanocomposites prepared by in situ polymerization

Hybrid Materials 2015; Sitges, Barcelona, Spain, 9 - 13 March 2015The studies were financed by the National Science Centre within project PRELUDE no 2013/11/N/ST8/00404.Peer Reviewe

Molecular dynamics of the α relaxation during crystallization of a glassy polymer: A real-time dielectric spectroscopy study

9 págs.; 12 figs.; 1 tab.The change of the α relaxation process occurring during isothermal crystallization of a glassy polymer, poly(aryl ether ketone ketone), has been followed in real time through measurement of the dielectric complex permittivity. The dielectric strength has been correlated with the degree of crystallinity derived from real time wide angle x-ray patterns using synchrotron radiation. The phenomenological Havriliak-Negami description has been used to analyze the changes of the dielectric strength, central relaxation time and shape parameters describing the relaxation, as crystallization proceeds. The evolution of the dielectric magnitudes with crystallization time has been interpreted in the light of the Schönhals-Schlosser model. According to this model, a restriction of the long scale motions of the polymeric chains as the material is filled in with crystals is observed. The derived dipole moment time correlation functions have been calculated for different crystallization times and fitted by the Kohlrausch-Williams-Watts function. The variation of the stretching parameters with crystallization time can be interpreted in terms of the coupling model assuming an increase of the intermolecular cooperativity of the α relaxation as the polymeric chains are constrained to move between crystalline regions. These results offer a contribution to the understanding of molecular dynamics of a glassy polymers during crystallization. © 1994 The American Physical Society.The authors are indebted to the CICYT (Grant No. MAT 94-0740E), Spain, for generous support of this investigation. J.M. thanks the Tempus Program (JEP 0644) for the support of his investigations.Peer Reviewe