M. Grimau

Ibero American University

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E. Laredo

Simón Bolívar University

Alfredo Bello

Azienda Sanitaria Locale Alessandria

A. Bello

Kaduna Polytechnic

A. Bello

University of Padua

Alejandro J. Müller

University of the Basque Country

María Hernández

Pontificia Universidad Católica del Ecuador

Defeng Wu

Yangzhou University

N. Suárez

Simón Bolívar University

Vittoria Balsamo

Ecolab (United Kingdom)

Francisco López‐Carrasquero

University of the Andes

Cooperative Institutions

Simón Bolívar University

Centre National de la Recherche Scientifique

Consejo Superior de Investigaciones Científicas

Universidad Simón Bolívar

University of Minnesota

Instituto de Ciencia y Tecnología de Polímeros

Yangzhou University

Université Toulouse III - Paul Sabatier

Université de Toulouse

Université de Caen Normandie

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Analysis of Thermally Stimulated Depolarization Currents (TSDC) Spectra Using the KWW Streched Exponential Function.

APS March Meeting Abstracts (1996)

A. Bello E. Laredo M. Grimau N. Suárez

Stretched exponential function

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Comparative Analysis of Dielectric Spectra by Using a Distribution of Relaxation Times or a KWW Decay Function

APS March Meeting Abstracts (1998)

A. Bello E. Laredo M. Grimau

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Conductividad eléctrica de nanocompuestos polímero/nanotubos de carbono en PCL y en la mezcla PCL/PLA

Revista de la Facultad de Ingeniería Universidad Central de Venezuela (2014)

Alfredo Bello M. Grimau E. Laredo

DC and AC conductivities of bionanocomposites based on a polymer matrix such as Poly(e-caprolactone), PCL, or on the polymer blend PCL/PLA (Polylactide) with multi-walled carbon nanotubes, CNT, as a nanofiller, have been studied in wide frequency ( 10 -3 Hz to 1 MHz) and temperature (133 to 323 K) ranges. These matrices were loaded with multi-walled carbon nanotubes, CNT, up to a concentration of 4 % in weight. X-Ray diffractograms showed that PCL was always semicrystalline with an orthorhombic structure, spatial group P2 1 2 1 2 1 . The crystallinity degrees were estimated to 46 % for neat PCL and 55 % for PCL in the blend. The minority phase, PLA, due to its higher viscosity, excluded the CNT which were selectively located in the PCL phase and decorating the interphases. The adhesion among the two blend components was drastically improved in the CNT presence. Molecular dynamics at different scales, local or segmental, were studied through the dielectric spectrum obtained for low concentrations, below the percolation threshold. No differences were observed among neat PCL and the blend, thus confirming the blend immiscibility. The Universal Dynamic Response proposed by Jonscher, which explains conductivity behavior, either ionic or electronic, was applied to describe the results in the whole frequency range. The parameters characteristic of the percolation process were determined for both nanocomposites and the threshold values were found to be 1 wt% for the blend and 0.3 % for neat PCL. In both cases an important contribution to the conductivity through carrier tunneling among CNT not yet in physical contact was evidenced. Also, differences in the validity of the universal curves were observed: only in neat PCL time-temperature-concentration superposition existed.

Orthorhombic crystal system

Percolation (cognitive psychology)

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Lamellar thickness distribution in copolymer crystals computed with the Gibbs-Thomson relationship and the Sadler-Gilmer model for copolymer crystallization.

APS March Meeting Abstracts (1998)

M. Grimau A. Bello E. Laredo

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Electrical conductivity in polymer/carbon nanotube nanocomposites in PCL and PCL/PLA blends

Revista de la Facultad de Ingeniería Universidad Central de Venezuela (2014)

Alfredo Bello M. Grimau E. Laredo

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Miscibility in Bisphenol-A Polycarbonate/ Poly(∊ -caprolactone)

APS March Meeting Abstracts (2004)

M. Grimau Alfredo Bello E. Laredo Dinorah Herrera Alejandro J. Müller

Miscibility

Polycarbonate

Caprolactone

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Coherent vibrations in percolative oil-resin systems: A Böse condensation effect observed by the technique of thermostimulated currents

Journal of materials research/Pratt's guide to venture capital sources (1999)

O. Pagès M. Grimau A. Lamure A. Zaoui B. Légendre

Coalescence (physics)

10.1557/jmr.1999.0086

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Local and segmental dynamics in homopolymer and triblock copolymers with one semicrystalline block

Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics (2002)

E. Laredo María Hernández A. Bello M. Grimau Alejandro J. Müller

Thermally stimulated depolarization currents, TSDC, experiments have been performed on a series of poly(styrene)-$b$-poly(butadiene)-$b$-poly$(\ensuremath{\epsilon}$-caprolactone) triblock copolymers SBC with different proportions of the poly$(\ensuremath{\epsilon}$-caprolactone) crystallizable block, PCL. The morphology of the segregated microphases varies with the PCL content and has been observed by transmission electron microscopy. The crystallinity of the PCL block is estimated by wide angle x-ray scattering, WAXS. The relaxation times distribution is extracted by a numerical decomposition of the TSDC spectra and it is shown that this distribution is not significantly changed on going from the homopolymer to the triblock copolymer with 16 wt % to 77 wt % of PCL in the original samples. Better segregation of the mesophase structure is reached when the samples are annealed at 413 K and important variations in the TSDC and WAXS spectra are observed as a result of the thermal treatment. For the ${\mathrm{S}}_{09}{\mathrm{B}}_{14}{\mathrm{C}}_{77}$ triblock copolymer the results obtained can be explained by postulating the existence of a rigid amorphous phase in the PCL block. Such rigid amorphous phase is located between the core-shell cylinders formed by the other blocks [with poly(styrene)(PS) as core and poly(butadiene)(PB) as shell] and is constrained by undulated lamellae of crystalline PCL material. In the case of ${\mathrm{S}}_{35}{\mathrm{B}}_{15}{\mathrm{C}}_{50}$ triblock copolymer, an important amount of diffuse PS-PCL interphase where the homopolymers are mixed must be present before annealing. The results for the material with the less abundant PCL block are explained as a result of the confinement in nanotubes of PCL surrounded by PB embedded in a vitreous PS matrix. Broadband dielectric experiments on these same materials confirm the results obtained by TSDC spectroscopy.

Interphase

Small-angle X-ray scattering

10.1103/physreve.65.021807

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Effect of cold‐crystallization on the AC and DC conductive properties of polylactide biocomposites with carboxylic or neat large aspect ratio MWCNT

Polymer Composites (2012)

E. Laredo Alfredo Bello Jonas Diaz M. Grimau Daniel E. Martínez‐Tong

Abstract After DC and AC conductivity measurements, percolation parameters, universality, and time‐temperature‐concentration superposition are evaluated in biocomposites based on poly(lactide) loaded with multiwalled carbon nanotubes either carboxylic, PLA/c‐CNT, or pure but with a larger aspect ratio, PLA/LAR‐CNT, in weight concentrations up to 7%. The polymer matrix is either 100% amorphous or cold‐crystallized. Wide angle X‐ray scattering is used to extract the crystallinity at each temperature. The nucleating effect for the cold crystallization of the PLA is greater for the LAR‐CNT than for the carboxylic ones. DC and AC conductivities are measured in broad frequency and temperature ranges, from 1 mHz to 1 MHz and from 133 to 378 K, respectively. The critical percolation value increases for c‐CNTs (from 1.8 to 2.4 vol%) upon cold crystallization of the PLA matrix as the formation of a conductive path is hindered by the existence of a crystalline phase, which is dominant over the reduction of the amorphous regions. No significant changes upon crystallization were found in the critical concentration value (0.6 vol%) for the LAR composites, where the conductive path is 2D. The universal scaling found here for different concentrations is lost when temperature varies. However, time‐temperature superposition is present for each concentration of LAR or carboxylic CNTs. POLYM. COMPOS., 2013. © 2012 Society of Plastics Engineers

10.1002/pc.22378

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Miscibility in poly(L-lactide)- b -poly( $ \upvarepsilon$ -caprolactone) double crystalline diblock copolymers

The European Physical Journal E (2007)

E. Laredo N. Prutsky A. Bello M. Grimau Reina Verónica Castillo

Miscibility

Caprolactone

10.1140/epje/i2007-10191-6

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Citations (42)