56 results on '"Ramón Díaz de León"'
Search Results
2. Author response for 'Modelling and parameter estimation of trans ‐ β ‐farnesene coordination polymerization'
- Author
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null Marília Caroline C. de Sá, null Teresa Córdova, null Príamo A. Melo, null Ramón Díaz de León, and null José Carlos Pinto
- Published
- 2023
3. Easy Synthesis of Doped Graphitic Carbon Nitride Nanosheets as New Material for Enhanced DNA Extraction from Vegetal Tissues Using a Simple and Fast Protocol
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Manuel Eduardo Martínez-Cartagena, Juan Bernal-Martínez, Arnulfo Banda-Villanueva, Víctor D. Lechuga-Islas, Teresa Córdova, Ilse Magaña, José Román Torres-Lubián, Salvador Fernández-Tavizón, Jorge Romero-García, Ana Margarita Rodríguez-Hernández, and Ramón Díaz-de-León
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General Medicine ,DNA extraction ,graphitic carbon nitride ,DNA purification ,PCR ,solvothermal synthesis - Abstract
Conventional and commercially available DNA extraction methods have several limitations regarding, for instance, contamination, and complex and slow precipitation and recovery processes. Herein, we report the synthesis of oxygen and phosphorus-doped Graphitic carbon nitride structures (g-POCN), via a novel Zinc-catalyzed one-pot solvothermal approach, and its application in the extraction of genomic DNA (gDNA) from a vegetal matrix (P. argentatum). Experimental and molecular modeling analyses demonstrate the high affinity of gDNA with g-POCN, which provided highly efficient gDNA extraction processes, with extraction yield, as well as integrity and quality of the extracted gDNA, comparable or superior to a commercial extraction kit and isopropanol extraction. Moreover, under suitable elution conditions, this method allows the easy removal of high concentrations of gDNA from g-POCN, rendering this method as a low-cost, simple, and fast approach for the extraction of even small amounts of gDNA. Remarkably, the extracted gDNA shows no degradation, and no inhibition of the polymerase chain reaction. Therefore, g-POCN represents a promising material for the highly efficient, cost-effective, and biocompatible extraction of DNA, which could stimulate research focused on broad DNA sources, e.g., RNA extraction, plasmids, ssDNA, etc.
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- 2022
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4. Development of Biodegradable Polyesters: Study of Variations in Their Morphological and Thermal Properties through Changes in Composition of Alkyl-Substituted (ε-DL) and Non-Substituted (ε-CL, EB, L-LA) Monomers
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Felipe Robles-González, Teresa Rodríguez-Hernández, Antonio S. Ledezma-Pérez, Ramón Díaz de León, Marco A. De Jesús-Téllez, and Héctor Ricardo López-González
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Polymers and Plastics ,ROP ,biodegradable polyesters ,TBD ,organic catalyst ,General Chemistry - Abstract
Three series of polyesters based on monomer combinations of ε-caprolactone (ε-CL), ethylene brassylate (EB), and l-Lactide (LLA) with the alkyl substituted lactone ε-decalactone (ε-DL) were synthesized at different molar ratios. Copolymers were obtained via ring opening polymerization (ROP) employing TBD (1,5,7-triazabicyclo-[4.4.0]-dec-5-ene), an organic catalyst which can be handled under normal conditions, avoiding the use of glove box equipment. The molar monomer composition of resulting copolymers differed from theoretical values due to lower ε-DL reactivity; their Mn and Mw values were up to 14 kDa and 22.8 kDa, respectively, and distributions were (Ɖ) ≤ 2.57. The thermal stability of these materials suffered due to variations in their ε-DL molar content. Thermal transitions such as melting (Tm) and crystallization (Tc) showed a decreasing tendency as ε-DL molar content increased, while glass transition (Tg) exhibited minor changes. It is worth mentioning that changes in monomer composition in these polyesters have a strong impact on their thermal performance, as well as in their crystallization degree. Consequently, variations in their chemical structure may have an effect on hydrolyic degradation rates. It should be noted that, in future research, some of these copolymers will be exposed to hydrolytic degradation experiments, including characterizations of their mechanical properties, to determine their adequacy in potential use in the development of soft medical devices.
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- 2022
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5. A Comparative Study of Biomimetic Synthesis of EDOT-Pyrrole and EDOT-Aniline Copolymers by Peroxidase-like Catalysts: Towards Tunable Semiconductive Organic Materials
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Manuel Eduardo Martínez-Cartagena, Juan Bernal-Martínez, Arnulfo Banda-Villanueva, Ilse Magaña, Teresa Córdova, Antonio Ledezma-Pérez, Salvador Fernández-Tavizón, and Ramón Díaz de León
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General Chemistry - Abstract
It has been two decades since biomimetic synthesis of conducting polymers were first reported, however, the systematic investigation of how catalysts influence the properties of the conducting polymers has not been reported yet. In this paper, we report a comparative study between peroxidase-like catalyst, dopants, and their effect on the properties of poly (3,4-ethylenedioxythiophene) (PEDOT), polypyrrole (PPY), and polyaniline (PANI). We also investigate the EDOT-Pyrrole and EDOT-Aniline copolymerization by enzymomimetic synthesis using two catalysts (Ferrocene and Hematin). It was found that, chemically, there are no detectable effects, only having small contributions in molar ratios greater than 0.7–0.3. Spectroscopic data provide solid evidence concerning the effect in the variation of the molar fractions, finding that, as the molar fraction of EDOT decreases, changes associated with loss of the conjugation of the structure and the oxidation state of the chains were observed. The electrical conductivity was considerably modified depending on the type of catalyst. Hematin produces conductive homopolymers and copolymers when doped with p-toluene sulfonic acid (TSA), while ferrocene produces low conductive copolymers under the same conditions. The mole fraction affects conductivity significantly, showing that as the EDOT fraction decreases, the conductivity drops drastically for both EDOT-PY and EDOT-ANI copolymers. The type of dopant also notably affects conductivity; the best values were obtained by doping with TSA, while the lowest were obtained when doping with polystyrene sulfonate (PSS). We also draw a biomimetic route to tailor the fundamental properties of conducting homopolymers and copolymers for their design and scaled-up production, as they have recently been found to have use in a broad range of applications.
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- 2022
6. Coordinative Chain Transfer Polymerization of Sustainable Terpene Monomers Using a Neodymium-Based Catalyst System
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Teresa Córdova, Francisco Javier Enríquez-Medrano, Eduardo Martínez Cartagena, Arnulfo Banda Villanueva, Luis Valencia, Edgar Nazareo Cabrera Álvarez, Ricardo López González, and Ramón Díaz-de-León
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myrcene ,farnesene ,biobased monomer ,coordinative chain transfer polymerization ,Polymers and Plastics ,General Chemistry - Abstract
The present investigation involves the coordinative chain transfer polymerization (CCTP) of biobased terpenes in order to obtain sustainable polymers from myrcene (My) and farnesene (Fa), using the ternary Ziegler–Natta catalyst system comprising [NdV3]/[Al(i-Bu)2H]/[Me2SiCl2] and Al(i-Bu)2H, which acts as cocatalyst and chain transfer agent (CTA). The polymers were produced with a yield above 85% according to the monomeric consumption at the end of the reaction, and the kinetic examination revealed that the catalyst system proceeded with a reversible chain transfer mechanism in the presence of 15–30 equiv. of CTA. The resulting polyterpenes showed narrow molecular weight distributions (Mw/Mn = 1.4–2.5) and a high percent of 1,4-cis microstructure in the presence of 1 equiv. of Me2SiCl2, having control of the molecular weight distribution in Ziegler–Natta catalytic systems that maintain a high generation of 1,4-cis microstructure.
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- 2022
7. Tuning Bolometric Parameters of Sierpinski Fractal Antenna-Coupled Uncracked/Cracked SWCNT Films by Thermoelectric Characterization at UHF Frequencies
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Gustavo Vera-Reveles, José Vulfrano González-Fernández, Juan Francisco Castillo-León, Francisco Javier González, Ramón Díaz de León-Zapata, Ariel Benjamín de la Rosa-Zapata, Norma Orocio-Castro, and Jorge Simón
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Computer Networks and Communications ,Hardware and Architecture ,Control and Systems Engineering ,Signal Processing ,Electrical and Electronic Engineering ,bolometric parameters ,thermoelectric characterization ,uncracked and cracked SWCNT ,Sierpinski fractal antenna ,UHF frequencies - Abstract
In this work, the bolometric parameters of Sierpinski fractal antenna-coupled SWCNT semi-metallic films are obtained by thermoelectric characterization, this in order to find out the performance as bolometer. The method was based on an experimental setup considering a line-of-sight wireless link between two identical planar fractal antennas, infrared thermography, and electrical resistance measurements. The experimental setup considered the antennas resonant frequencies. Both the transmitting and receiving antenna were third-iteration Sierpinski fractal dipoles designed to work at UHF frequencies. Films made either of cracked or uncracked SWCNT films were each separately coupled to the receiving fractal antenna. Measurements showed that the receiving antenna that was impinged with radiation at UHF frequencies coming from the transmitting antenna, experienced as it was expected an induction of electric current, the induced current flowed through the film producing a temperature change, which in turn caused changes in the radiated heat of the film, as well as changes in the electrical resistance known as Temperature Coefficient of Resistance TCR. The maximum value of TCR for uncracked SWCNT films was −3.6%K−1, higher than the one observed for cracked SWCNT films which exhibited a maximum value of −1.46%K−1. Measurements for conversion of incident radiation to electrical signals known as the Voltage Responsivity ℜv, exhibited values of 9.4 mV/W and 1.4 mV/W for uncracked SWCNT films and cracked SWCNT films, respectively.
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- 2022
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8. Synthesis and Vulcanization of Polymyrcene and Polyfarnesene Bio-Based Rubbers: Influence of the Chemical Structure over the Vulcanization Process and Mechanical Properties
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Arnulfo Banda-Villanueva, José Luis González-Zapata, Manuel Eduardo Martínez-Cartagena, Ilse Magaña, Teresa Córdova, Ricardo López, Luis Valencia, Sergio García Medina, Alejandro Medina Rodríguez, Florentino Soriano, and Ramón Díaz de León
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Polymers and Plastics ,General Chemistry ,bioelastomers ,crosslinking ,vulcanization ,bio-based rubbers ,bio-based monomers - Abstract
The overuse of fossil-based resources to produce thermoplastic materials and rubbers is dramatically affecting the environment, reflected in its clearest way as global warming. As a way of reducing this, multiple efforts are being undertaken including the use of more sustainable alternatives, for instance, those of natural origin as the main feedstock alternative, therefore having a lower carbon footprint. Contributing to this goal, the synthesis of bio-based rubbers based on β-myrcene and trans-β-farnesene was addressed in this work. Polymyrcene (PM) and polyfarnesene (PF) were synthesized via coordination polymerization using a neodymium-based catalytic system, and their properties were compared to the conventional polybutadiene (PB) and polyisoprene (PI) also obtained via coordination polymerization. Moreover, different average molecular weights were also tested to elucidate the influence over the materials’ properties. The crosslinking of the rubbers was carried out via conventional and efficient vulcanization routes, comparing the final properties of the crosslinking network of bio-based PM and PF with the conventional fossil-based PB and PI. Though the mechanical properties of the crosslinked rubbers improved as a function of molecular weight, the chemical structure of PM and PF (with 2 and 3 unsaturated double bonds, respectively) produced a crosslinking network with lower mechanical properties than those obtained by PB and PI (with 1 unsaturated double bond). The current work contributes to the understanding of improvements (in terms of crosslinking parameters) that are required to produce competitive rubber with good sustainability/performance balance.
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- 2022
9. Bioelastomers: Current state of development
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Ilse Magaña, Ricardo López, Francisco Javier Enríquez-Medrano, Sugam Kumar, Andrea Aguilar-Sanchez, Rishab Handa, Ramón Díaz de León, and Luis Valencia
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Renewable Energy, Sustainability and the Environment ,General Materials Science ,General Chemistry - Abstract
Considering the current trend of finding sustainable alternatives to the existing fossil-based plastics, in this review we describe what makes a bioelastomer “bio” and what this implies in terms of materials design. We analyze the current state of development of bioelastomers, including the most important types, their current and upcoming use, and their synthetic pathways. Moreover, we provide a general landscape of the hybridization or composite preparation of elastomers to acquire specific functionalities and their implementation in advanced applications, focusing mainly on electronics and biomedicine. Furthermore, we show how through the use of bioelastomers, one can, besides helping the environment, achieve materials with exceptional performances (e.g., very high mechanical properties and/or self-healing properties), which can be processed via novel techniques such as 3/4D-(bio)printing.
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- 2022
10. Applications of the Fundamentals of Bézier Curves
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Mayra Angélica Bárcenas-Castro, Ramón Díaz de León-Zapata, Saúl Almazán-Cuéllar, Efrén Flores-García, Gustavo Vera-Reveles, and José Vulfrano González-Fernández
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- 2022
11. Automatización de obturadores de sistema de crecimiento por haces moleculares usando arduino mega en una interfaz de Labview
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Ismael Lara-Velázquez, Ramón Díaz de León-Zapata, Efrén Flores-García, Victor Hugo Méndez García, Leticia Ithsmel Espinosa Vega, and Felipe Eduardo Perea Parrales
- Abstract
En este trabajo reportamos el desarrollo de un control de obturadores para un sistema de crecimiento por Haces Moleculares (EHM) o del Ingles Molecular Beam Expitaxy (MBE) utilizando una interfaz gráfica de LabView y la plataforma de Arduino Mega para la adquisición de datos. La técnica de epitaxia por haces moleculares permite controlar espesores a escala nanométrica de muy alta calidad cristalina, para la fabricación de dispositivos electrónicos y optoelectrónicos.
- Published
- 2019
12. Conectando lo discreto con lo continuo; propuesta metodológica para el cálculo de ancho de bin gráfico en el análisis estadístico de datos
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Mayra Angélica Bárcenas Castro, Lorenzo Borselli, Ramón Díaz de León-Zapata, Efrén Flores-García, and Ariel Benjamín De la Rosa-Zapata
- Abstract
Se presenta una propuesta metodológica para el análisis de resultados de gráficos estadísticos, en donde el ancho de bin es el principal factor de cambio para su representación. Se implementa un pseudocódigo que permite visualizar los pasos a seguir para obtenerlo. Se realizó un ejercicio para mostrar la pérdida o ganancia de información al implementar la Densidad de Kernel y también la ausencia de esta. La propuesta se hizo directamente con la metodología de Bowman y Azzalini (1997) en Matlab y el generado en este trabajo. Se utilizó el test de Kolmogorov-Smirnov para validar las ventajas del método propuesto. Se encontró que el método propuesto permite una mejor tendencia de los datos ya sea positiva, negativa o simétrica y poca o escasa pérdida de información con respecto evaluación estadística aplicando densidad de kernel; de este modo es una opción para obtener un mejor análisis estadístico cuantitativa y cualitativamente y además puede ser reproducido en temas similares.
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- 2019
13. β‐Myrcene Coordination Polymerization: Experimental and Kinetic Modeling Study
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Marília Caroline C. de Sá, Teresa Córdova, Príamo Albuquerque Melo, Ramón Díaz de León, and José Carlos Pinto
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Polymers and Plastics ,General Chemical Engineering ,General Chemistry - Published
- 2022
14. Surface Modification of Cellulose Nanocrystals with Lactone Monomers via Plasma-Induced Polymerization and Their Application in ABS Nanocomposites
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Ilse Magaña, Guadalupe Neira, Ediberto Guzmán, Ramón Díaz de León, Luis Valencia, Alejandro Díaz Elizondo, Adali Castañeda Facio, and Ricardo López González
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Nanocomposite ,Materials science ,Polymers and Plastics ,Organic chemistry ,Nanoparticle ,Context (language use) ,General Chemistry ,δ-decalactone ,Article ,chemistry.chemical_compound ,QD241-441 ,Monomer ,Polymerization ,chemistry ,Chemical engineering ,Nanocrystal ,Surface modification ,Fourier transform infrared spectroscopy ,plasma-induced polymerization ,surface modification ,ε-caprolactone ,cellulose nanocrystals - Abstract
The growing concern for environmental problems has motivated the use of materials obtained from bio-based resources such as cellulose nanocrystals which have a promising application acting as fillers or reinforcements of polymeric materials. In this context, in this article, plasma-induced polymerization is proposed as a strategy to modify nanocrystals at different plasma power intensities using ε-caprolactone and δ-decalactone to improve their compatibility with polymeric matrices. The characterization was carried out using techniques such as FTIR, TGA, XRD, XPS, and AFM, with which a successful functionalization was demonstrated without altering the inherent properties of the nanocrystals. The preparation of ABS nanocomposites was carried out with the modified nanoparticles and the evaluation of the mechanical properties indicates an increase in Young’s modulus and yield stress under certain concentrations of modified cellulose nanocrystals.
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- 2021
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15. Biomimetic Synthesis of PANI/Graphitic Oxidized Carbon Nitride for Supercapacitor Applications
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Manuel Eduardo Martínez-Cartagena, Juan Bernal-Martínez, Arnulfo Banda-Villanueva, Javier Enríquez-Medrano, Víctor D. Lechuga-Islas, Ilse Magaña, Teresa Córdova, Diana Morales-Acosta, José Luis Olivares-Romero, and Ramón Díaz-de-León
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polyaniline ,graphitic carbon nitride ,supercapacitor ,conductive polymer ,biomimetic synthesis ,Polymers and Plastics ,General Chemistry - Abstract
Polyaniline (PANI) composites have gained momentum as supercapacitive materials due to their high energy density and power density. However, some drawbacks in their performance remain, such as the low stability after hundreds of charge-discharge cycles and limitations in the synthesis scalability. Herein, we report for the first time PANI-Graphitic oxidized carbon nitride composites as potential supercapacitor material. The biomimetic polymerization of aniline assisted by hematin, supported by phosphorous and oxygen-modified carbon nitrides (g-POCN and g-OCN, respectively), achieved up to 89% yield. The obtained PAI/g-POCN and PANI/g-OCN show enhanced electrochemical properties, such as conductivity of up to 0.0375 S/cm, specific capacitances (Cs) of up to 294 F/g (at high current densities, 5 A/g) and a stable operation after 500 charge-discharge cycles (at 3 A/g). In contrast, the biomimetic synthesis of Free PANI, assisted by stabilized hematin in cosolvents, exhibited lower performance properties (65%). Due to their structural differences, the electrochemical properties of Free PANI (conductivity of 0.0045 S/cm and Cs of up to 82 F/g at 5 A/g) were lower than those of nanostructured PANI/g-POCN and g-OCN supports, which provide stability and improve the properties of biomimetically synthesized PANI. This work reveals the biomimetic synthesis of PANI, assisted by hematin supported by modified carbon nitrides, as a promising strategy to produce nanostructured supercapacitors with high performance.
- Published
- 2022
16. Synthesis and Insecticidal Evaluation of Chiral Neonicotinoids Analogs: The Laurel Wilt Case
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Alfredo Rodríguez-Hernández, Saúl A. Luna-Hernández, Felipe Barrera-Méndez, Irving David Pérez-Landa, Gabriel Suarez-Mendez, Israel Bonilla-Landa, Ramón Díaz de León-Gómez, Alfonso Reyes-Luna, Ulises Cuapio-Muñoz, José Luis Olivares-Romero, Luis Arturo Ibarra-Juárez, and Francisco Javier Enríquez-Medrano
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0106 biological sciences ,Insecticides ,enantiopure compound ,Stereochemistry ,Pharmaceutical Science ,Fungus ,010402 general chemistry ,01 natural sciences ,Laurel wilt ,Article ,Analytical Chemistry ,insecticidal activity ,Trees ,Xyleborus ,Neonicotinoids ,QD241-441 ,Drug Discovery ,Animals ,Physical and Theoretical Chemistry ,Plant Diseases ,biology ,Host (biology) ,Chemistry ,Organic Chemistry ,Fungi ,Hydrogen Bonding ,biology.organism_classification ,0104 chemical sciences ,chiral ,Coleoptera ,010602 entomology ,nitroguanidines ,Chemistry (miscellaneous) ,Docking (molecular) ,Molecular Medicine ,Weevils ,Ericaceae ,Ambrosia ,Tree species - Abstract
Xyleborus sp beetles are types of ambrosia beetles invasive to the United States and recently also to Mexico. The beetle can carry a fungus responsible for the Laurel Wilt, a vascular lethal disease that can host over 300 tree species, including redbay and avocado. This problem has a great economic and environmental impact. Indeed, synthetic chemists have recently attempted to develop new neonicotinoids. This is also due to severe drug resistance to “classic” insecticides. In this research, a series of neonicotinoids analogs were synthesized, characterized, and evaluated against Xyleborus sp. Most of the target compounds showed good to excellent insecticidal activity. Generally, the cyclic compounds also showed better activity in comparison with open-chain compounds. Compounds R-13, 23, S-29, and 43 showed a mortality percent of up to 73% after 12 h of exposure. These results highlight the enantioenriched compounds with absolute R configuration. The docking results correlated with experimental data which showed both cation-π interactions in relation to the aromatic ring and hydrogen bonds between the search cavity 3C79 and the novel molecules. The results suggest that these sorts of interactions are responsible for high insecticidal activity.
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- 2021
17. Pozos Cuánticos de AlGaAs/GaAs/AlGaAs Crecidos por MBE: Análisis Estructural y de Composición
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José Vulfrano González Fernández, Ramón Díaz de León-Zapata, Efrén Flores-García, and Jorge Ortega-Gallegos
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En este trabajo se presentan estudios de composición química y de control de crecimiento de pozos cuánticos semiconductores basados en semiconductores III-V (AlGaAs/GaAs/AlGaAs, utilizando una composición del Al de 33 %) y fabricados en un sistema de epitaxia por haces moleculares. Se utilizó la técnica de difracción de electrones reflejados de alta energía (in-situ) para la caracterización por composición química, así como la técnica de espectroscopía por fotoluminiscencia (ex-situ) a baja temperatura para el análisis de los niveles de energía de tres diferentes pozos cuánticos no-acoplados. Se obtuvo una buena correlación entre el monitoreo superficial y la caracterización espectroscópica de la muestra estudiada.
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- 2019
18. Plasma surface-modification of cellulose nanocrystals: a green alternative towards mechanical reinforcement of ABS
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Aji P. Mathew, Josué Hernández Valdés, Luis Valencia, Ramón Díaz de León, Ricardo Lopez, Ricardo Mendoza, Andrés Alanis, and Neira-Velázquez María Guadalupe
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chemistry.chemical_classification ,Thermoplastic ,Materials science ,General Chemical Engineering ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Styrene ,chemistry.chemical_compound ,Monomer ,chemistry ,X-ray photoelectron spectroscopy ,Nanocrystal ,Chemical engineering ,Surface modification ,Fourier transform infrared spectroscopy ,0210 nano-technology ,Caprolactone - Abstract
This article proposes a strategy to functionalize cellulose nanocrystals by means of plasma-surface modification utilizing monomers of different nature: caprolactone, styrene and farnesene. The surface characteristics of the nanocrystals were studied by different techniques including XPS, FTIR and STEM, demonstrating that this technique allows a successful functionalization, yielding homogenous functionalization which does not alter the rod-like shape of the nanocrystals, and therefore their anisotropic behavior. We have furthermore studied the employment of the modified nanocrystals as reinforcement additive of ABS, which significantly enhanced the impact resistance of the thermoplastic, which could have great implications for industrial applications.
- Published
- 2019
19. Evaluation of the Antimicrobial, Thermal, Mechanical, and Barrier Properties of Corn Starch–Chitosan Biodegradable Films Reinforced with Cellulose Nanocrystals
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Claudio Alonso Díaz-Cruz, Carolina Caicedo, Enrique Javier Jiménez-Regalado, Ramón Díaz de León, Ricardo López-González, and Rocio Yaneli Aguirre-Loredo
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Polymers and Plastics ,food and beverages ,General Chemistry ,biodegradable film ,corn starch ,chitosan ,cellulose nanocrystals ,antimicrobial film ,nanocomposite - Abstract
Packaging materials play an essential role in the preservation and marketing of food and other products. To improve their conservation capacity, antimicrobial agents that inhibit bacterial growth are used. Biopolymers such as starch and chitosan are a sustainable alternative for the generation of films for packaging that can also serve as a support for preservatives and antimicrobial agents. These substances can replace packaging of synthetic origin and maintain good functional properties to ensure the quality of food products. Films based on a mixture of corn starch and chitosan were developed by the casting method and the effect of incorporating cellulose nanocrystals (CNC) at different concentrations (0 to 10% w/w) was studied. The effect of the incorporation of CNC on the rheological, mechanical, thermal and barrier properties, as well as the antimicrobial activity of nanocomposite films, was evaluated. A significant modification of the functional and antimicrobial properties of the starch–chitosan films was observed with an increase in the concentration of nanomaterials. The films with CNC in a range of 0.5 to 5% presented the best performance. In line with the physicochemical characteristics which are desired in antimicrobial materials, this study can serve as a guide for the development this type of packaging for food use.
- Published
- 2022
20. Dispositivo láser semiconductor con puntos cuánticos para emisión en el cercano infrarrojo
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J.V. González-Fernández, Ramón Díaz de León-Zapata, Jorge Ortega-Gallegos, and Ismael Lara-Velázquez
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General Physics and Astronomy ,Education - Abstract
espanolEn este trabajo se reporta la fabricacion de un dispositivo laser de semiconductores III-V de confinamiento separado. La heteroestructura se crecio usando la tecnica de epitaxia por haces moleculares y se caracterizo optica, topografica y electricamente por medio de fotoluminiscencia, microscopia de tunelamiento, electroluminiscencia, relaciones de corriente-voltaje y corriente-potencia, respectivamente. El confinamiento electronico es llevado a cabo por un emparedamiento del area activa con pozos cuanticos de InGaAs con una composicion que permite un acople estructural entre el pozo cuantico y los puntos cuanticos autoensamblados de InAs disminuyendo las dislocaciones que darian lugar a una mala calidad del dispositivo. El objetivo es obtener una emision laser en las ventanas de menor absorcion de las fibras opticas situadas en el cercano infrarrojo en las que se basan los sistemas de telecomunicacion. EnglishIn this work the fabrication of III-V semiconductor laser device with separate confinement is reported. The heterostructure was grown by molecular beam epitaxy technique and it was characterized by optical, morphological and electrical techniques such as photoluminescence, scanning tunneling effect, electroluminescence, current-voltage and current-power relations, respectively. The electronic confinement was carried out by sandwiching the active area with InGaAs quantum well with an appropriated Indium composition that allows a structural coupling between quantum wells and self-assembled InAs quantum dots decreasing dislocations that could commit the device quality. Our aim is to obtain the laser emission in the lower absorption windows for optical fiber telecommunications systems located in the near-infrared.
- Published
- 2018
21. Campo electromagnético amplificado con nanoestructuras de geometría estelar
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Iván Alberto Cruz García, Ramón Díaz de León-Zapata, Ariel Benjamín De la Rosa Zapata, Efrén Flores-García, José Vulfrano González Fernández, and Francisco Javier González
- Abstract
Se presenta el estudio de nanoantenas de geometría estelar como elementos plasmónicos amplificadores y direccionales del campo electromagnético. El estudio se llevó a cabo con análisis numérico basado en la técnica del elemento finito. Fueron analizados varios materiales, dimensiones arreglos geométricos y frecuencias para la simulación y el análisis de datos. La geometría estelar fue elegida con base en la propiedad de autoensamblado de los materiales de plata-óxido de zinc (Ag-ZnO). La direccionalidad y la amplificación del campo eléctrico fueron simulados tanto en campo cercano como en campo lejano. Adicionalmente se discuten algunas aplicaciones de estas nanoestructuras.
- Published
- 2018
22. Ethylene Polymerization via Zirconocene Catalysts and Organoboron Activators: An Experimental and Kinetic Modeling Study
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Enrique Saldívar-Guerra, Ramón Díaz de León, José Díaz-Elizondo, Francisco Javier Enríquez-Medrano, Priscila Quiñonez-Angulo, Luis Valencia, Iván Zapata-González, and Ricardo López-González
- Subjects
Bioengineering ,02 engineering and technology ,lcsh:Chemical technology ,010402 general chemistry ,Kinetic energy ,01 natural sciences ,Catalysis ,lcsh:Chemistry ,symbols.namesake ,chemistry.chemical_compound ,Cyclopentadienyl complex ,Computational chemistry ,Polymer chemistry ,Chemical Engineering (miscellaneous) ,lcsh:TP1-1185 ,automotive_engineering ,Alkyl ,chemistry.chemical_classification ,Arrhenius equation ,metallocene ,Process Chemistry and Technology ,Polyethylene ,021001 nanoscience & nanotechnology ,kinetic modeling ,Toluene ,ethylene polymerization ,organoboron compounds ,zirconium-based catalyst ,0104 chemical sciences ,Organoboron compounds ,lcsh:QD1-999 ,Polymerization ,chemistry ,Ethylene polymerization ,symbols ,Coordination polymerization ,0210 nano-technology ,Metallocene - Abstract
Forty years after the discovery of metallocene catalysts, there are still several aspects that remain unresolved, especially when the &ldquo, conventional&rdquo, alkylaluminum activators are not used. Herein, we systematically investigated the synthesis of polyethylene (PE) via three different zirconocene catalysts, with different alkyl substituents, activated via different organoboron compounds. The polymerization behavior, as well as the properties of the materials, were evaluated. The results demonstrate that the highest catalytic activity is shown by bis(cyclopentadienyl)dimethylzirconium activated by trityl tetra(pentafluorophenyl)borate. Additionally, it was found that toluene is the optimum solvent for these systems and at these reaction conditions. Moreover, to validate our experimental results, a comprehensive mathematical model was developed on the basis of thermodynamic and kinetic principles. The concentration of ethylene transferred to the solvent phase (toluene) in a liquid&ndash, vapor equilibrium (LVE) system was estimated based on Duhem&rsquo, s theorem. Arrhenius expressions for the kinetic rate constants of a proposed kinetic mechanism were estimated by a kinetic model, in which the rate of polymerization was fitted by a least-square optimization procedure and the molecular weight averages by the method of moments. The simulations of the coordination polymerization suggest the presence of two types of active sites, principally at low temperatures, and the reactivation of the deactivated sites via a boron-based activator. However, the effect of the temperature on the reactivation step was not clear, a deeper understanding via designed experiments is required.
- Published
- 2021
- Full Text
- View/download PDF
23. Contributors
- Author
-
Vera Alejandra Alvarez, Mariana Altenhofen da Silva, Ioannis Anastopoulos, Rogério Aparecido Bataglioli, Marisa Masumi Beppu, Andrea Cristiane Krause Bierhalz, Fernanda Carla Bombaldi de Souza, Renata Francielle Bombaldi de Souza, Adrián Bonilla-Petriciolet, Josiane Gonçalves Borges, Tito Roberto Sant’Anna Cadaval, Bruna Gregatti de Carvalho, Rosemary Aparecida de Carvalho, Tecia Vieira Carvalho, Pascale Chevallier, Viktor Oswaldo Cárdenas Concha, Luana Roland Ferreira Contini, Rodrigo Cué-Sampedro, João Dias-Ferreira, Guilherme Luiz Dotto, Meryem Sedef Erdal, Júlia Vaz Ernesto, Ana R. Fernandes, Emanuel M. Fernandes, Eduardo de Paulo Ferreira, Classius Ferreira da Silva, Ronaldo Ferreira do Nascimento, Leonardo Fernandes Fraceto, Vitor Augusto dos Santos Garcia, Lucimara Gaziola de la Torre, Sandy Danielle Lucindo Gomes, Sevgi Güngör, Saartje Hernalsteens, Carmen Guadalupe Hernández-Valencia, Ahmad Hosseini-Bandegharaei, Mohd Ikmar Nizam Mohamad Isa, Emine Kahraman, Theo Guenter Kieckbusch, Henryk Koroniak, Ramón Díaz de León, Éder Cláudio Lima, Patricia Santos Lopes, Vinícius Borges Vieira Maciel, Diego Mantovani, Gustavo Martínez-Castellanos, Agnes Batista Meireles, Enayde de Almeida Melo, Ângela Maria Moraes, Mariana Agostini de Moraes, Anaftália Felismino Morais, Nur Hafiza Mr Muhamaruesa, Roberto Nasser, Beatriz C. Naveros, Deise Ochi, Romina Paola Ollier, Yıldız Özsoy, Neith Pacheco, Anderson Espirito Santo Pereira, Laura Oliveira Péres, Ana Luiza Resende Pires, Rui L. Reis, Ansorena María Roberta, João Batista Maia Rocha Neto, Luísa C. Rodrigues, Laura Mabel Sanchez, J.A. Sánchez-Fernández, Andrelina Maria Pinheiro Santos, Gilberto Dantas Saraiva, Patricia Severino, Keiko Shirai, Simone S. Silva, Mariangela de Fátima Silva, Jackson Wesley Silva dos Santos, Vicente de Oliveira Sousa Neto, João Vinícios Wirbitzki da Silveira, José L. Soriano, Eliana B. Souto, Clayton Campelo de Souza, Thiago Bezerra Taketa, Bruno Thorihara Tomoda, Fernanda Maria Vanin, Anna Cecilia Venturini, Rodrigo Silveira Vieira, Justyna Walkowiak-Kulikowska, Joanna Wolska, Patrícia Hissae Yassue-Cordeiro, and Cristiana Maria Pedroso Yoshida
- Published
- 2020
24. Pharmaceutical and synthetic hormone removal using biopolymer membranes
- Author
-
Rodrigo Cué-Sampedro, Ramón Díaz de León, and J.A. Sánchez-Fernández
- Subjects
Chemistry ,medicine.medical_treatment ,engineering.material ,Aquatic organisms ,Steroid ,Membrane technology ,Membrane ,Steroidal hormones ,Synthetic Hormone ,medicine ,engineering ,Organic chemistry ,Biopolymer ,Hormone - Abstract
Synthetic steroid hormones are widely used in our daily lives for contraception, in the treatment of diseases, and in the livestock industry. However, steroidal hormones are considered emerging contaminants in wastewater worldwide, due to their widespread presence and adverse effects on both aquatic organisms and humans. There are also existing compounds that alter the endocrine system, such as steroidal hormones, degradation products of nonionic surfactants such as alkylphenols, plasticizers, inorganic compounds, and pharmaceutical products. The present review opens with a general introduction of membrane separation, followed by a review on the fabrication of membranes. Continuing with these general fabrication aspects, a brief theoretical section of the basic principles of mass transport through a membrane is presented. Furthermore, some generalities about the removal of pharmaceuticals and hormones are provided, finalizing with a look toward the future of membrane separation processes.
- Published
- 2020
25. Towards Bioelastomers via Coordination Polymerization of Renewable Terpenes Using Neodymium-Based Catalyst Systems
- Author
-
Judith Cabello, Ricardo Mendoza, Ramón Díaz de León, Javier Enríquez, Ricardo Lopez, and Luis Valencia
- Subjects
Thesaurus (information retrieval) ,Materials science ,business.industry ,Mechanical Engineering ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Neodymium ,0104 chemical sciences ,Catalysis ,Renewable energy ,Terpene ,chemistry ,Mechanics of Materials ,Coordination polymerization ,General Materials Science ,0210 nano-technology ,business ,Process engineering - Abstract
Syntheses of biolestomers through the coordination polymerization of terpenes, such as ocimene (Oc), β-myrcene (My) andtrans-β-farnesene (Fa), using catalyst systems based on neodymium versatate (NdV3) are reported in this work. All polymerization products were characterized by size exclusion chromatography, differential scanning calorimetry and nuclear magnetic resonance in order to determine their macromolecular, thermal and structural characteristics. The NdV3in combination with diisobutylaluminum hydride as cocatalyst and diethylaluminum chloride (DEAC) as halogen source was found effective for Oc polymerizations providing polyocimenes with molecular weights (Mn) in the order of 20 to 57 Kg/mol, broad molecular weight distributions (Mw/Mn) since 3.8 until 8.2, preferablycis-1,4 content (61-69 %) and glass transition temperatures (Tg) in the range of-30 to-26 °C. On the other hand, the same NdV3but now activated by modified methylaluminoxane and DEAC was found considerably active in My and Fa polymerizations, affording polymyrcenes and polyfarnesenes withMnbetween 155 and 243 Kg/mol, as well asMw/Mnranging between 3.1-3.9 and 1,4 content values were found higher than 94 % for this subfamily of polyterpenes, being the 3,4 content the complement for completing 100 %. Moreover, it was demonstrated thatTgof polyterpenes studied depends on the size of pendant group, shifting it towards lower temperatures as increasing the size of the pendant group.
- Published
- 2018
26. Curvas Bézier controladas por algoritmo genético como método para la obtención de geometrías continuas optimizadas
- Author
-
Mayra Angélica Bárcenas Castro and Ramón Díaz de León-Zapata
- Abstract
Se presenta un método para modelado geométrico aplicando un algoritmo genético en el que la población (individuos) son los puntos de control de curvas Bézier de primer, segundo o tercer grado. Con la aplicación de este método se obtienen figuras sólidas, continuas y suavizadas y se discuten algunas aplicaciones que van desde la ingeniería de nanomateriales, pasando por el modelado de prótesis hasta macro estructuras mecánicas complejas y ciencias sociales.
- Published
- 2018
27. Fully Bio-Based Elastomer Nanocomposites Comprising Polyfarnesene Reinforced with Plasma-Modified Cellulose Nanocrystals
- Author
-
Francisco Javier Enriquez Medrano, Dimitrios Georgouvelas, Hector Ricardo Lopez Gonzalez, Luis Valencia, Ramón Díaz de León, Ilse Magaña, Rishab Handa, and Maria Guadalupe Neira Velazquez
- Subjects
Materials science ,Polymers and Plastics ,Organic chemistry ,Elastomer ,Article ,trans-β-farnesene ,chemistry.chemical_compound ,QD241-441 ,elastomer nanocomposites ,plasmainduced polymerization ,Cellulose ,cellulose nanocrystals ,Nanocomposite ,General Chemistry ,Dynamic mechanical analysis ,Monomer ,chemistry ,Chemical engineering ,Polymerization ,bio-based ,Coordination polymerization ,Surface modification ,plasma-induced polymerization ,surface modification - Abstract
This article proposes a process to prepare fully bio-based elastomer nanocomposites based on polyfarnesene and cellulose nanocrystals (CNC). To improve the compatibility of cellulose with the hydrophobic matrix of polyfarnesene, the surface of CNC was modified via plasma-induced polymerization, at different powers of the plasma generator, using a trans-β-farnesene monomer in the plasma reactor. The characteristic features of plasma surface-modified CNC have been corroborated by spectroscopic (XPS) and microscopic (AFM) analyses. Moreover, the cellulose nanocrystals modified at 150 W have been selected to reinforce polyfarnesene-based nanocomposites, synthesized via an in-situ coordination polymerization using a neodymium-based catalytic system. The effect of the different loading content of nanocrystals on the polymerization behavior, as well as on the rheological aspects, was evaluated. The increase in the storage modulus with the incorporation of superficially modified nanocrystals was demonstrated by rheological measurements and these materials exhibited better properties than those containing pristine cellulose nanocrystals. Moreover, we elucidate that the viscoelastic moduli of the elastomer nanocomposites are aligned with power–law model systems with characteristic relaxation time scales similar to commercial nanocomposites, also implying tunable mechanical properties. In this foreground, our findings have important implications in the development of fully bio-based nanocomposites in close competition with the commercial stock, thereby producing alternatives in favor of sustainable materials.
- Published
- 2021
28. Controlled (Co)Polymerization of Methacrylates Using a Novel Symmetrical Trithiocarbonate RAFT Agent Bearing Diphenylmethyl Groups
- Author
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Claude St Thomas, Francisco Javier Enríquez-Medrano, José Román Torres-Lubián, Alvaro Leonel Robles Grana, Ramón Díaz de León, José Luis Olivares-Romero, Luis Valencia, and Hortensia Maldonado-Textle
- Subjects
Butyl acrylate ,Dispersity ,Pharmaceutical Science ,02 engineering and technology ,010402 general chemistry ,Methacrylate ,01 natural sciences ,Article ,Analytical Chemistry ,chemistry.chemical_compound ,QD241-441 ,Drug Discovery ,Polymer chemistry ,Copolymer ,Reversible addition−fragmentation chain-transfer polymerization ,Physical and Theoretical Chemistry ,RAFT polymerization ,Organic Chemistry ,Chain transfer ,Raft ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,block copolymers ,chemistry ,Polymerization ,Chemistry (miscellaneous) ,methacrylates ,Molecular Medicine ,0210 nano-technology - Abstract
Herein, we report a novel type of symmetrical trithiocarbonate chain transfer agent (CTA) based diphenylmethyl as R groups. The utilization of this CTA in the Reversible Addition-Fragmentation chain Transfer (RAFT) process reveals an efficient control in the polymerization of methacrylic monomers and the preparation of block copolymers. The latter are obtained by the (co)polymerization of styrene or butyl acrylate using a functionalized macro-CTA polymethyl methacrylate (PMMA) previously synthesized. Data show low molecular weight dispersity values (Đ <, 1.5) particularly in the polymerization of methacrylic monomers. Considering a typical RAFT mechanism, the leaving groups (R) from the fragmentation of CTA should be able to re-initiate the polymerization (formation of growth chains) allowing an efficient control of the process. Nevertheless, in the case of the polymerization of MMA in the presence of this symmetrical CTA, the polymerization process displays an atypical behavior that requires high [initiator]/[CTA] molar ratios for accessing predictable molecular weights without affecting the Đ. Some evidence suggests that this does not completely behave as a common RAFT agent as it is not completely consumed during the polymerization reaction, and it needs atypical high molar ratios [initiator]/[CTA] to be closer to the predicted molecular weight without affecting the Đ. This work demonstrates that MMA and other methacrylic monomers can be polymerized in a controlled way, and with “living” characteristics, using certain symmetrical trithiocarbonates.
- Published
- 2021
29. Preparation of ultrafine poly(methyl methacrylate-co-methacrylic acid) biodegradable nanoparticles loaded with ibuprofen
- Author
-
Hened Saade, Francisco Javier Enríquez-Medrano, Ramón Díaz de León-Gómez, and Raúl G. López
- Subjects
Materials science ,Surface Properties ,Biomedical Engineering ,Biophysics ,Nanoparticle ,Ibuprofen ,Bioengineering ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,Polymerization ,Biomaterials ,chemistry.chemical_compound ,Polymethacrylic Acids ,Polymer chemistry ,Copolymer ,Particle Size ,Drug Carriers ,Anti-Inflammatory Agents, Non-Steroidal ,Hydrogen-Ion Concentration ,021001 nanoscience & nanotechnology ,Biodegradable polymer ,Poly(methyl methacrylate) ,0104 chemical sciences ,Drug Liberation ,Methacrylic acid ,chemistry ,visual_art ,visual_art.visual_art_medium ,Nanoparticles ,Particle size ,0210 nano-technology ,Drug carrier ,Nuclear chemistry - Abstract
Ibuprofen-loaded polymeric particles with around 9.2 nm in mean diameter, as determined by electron microscopy, dispersed in an aqueous media containing up to 12.8% solids were prepared by semicontinuous heterophase polymerization. The polymeric material is a (2/1 mol/mol) methyl methacrylate-co-methacrylic acid copolymer similar to Eudragit S100, deemed safe for human consumption and used in the manufacturing of drug-loaded pills as well as micro- and nanoparticles. The loading efficiency was 100%, attaining around 10-12% in drug content. Release studies showed that the drug is released from the nanoparticles at a slower rate than that in the case of free IB. Given their size as well as the pH values required for their dissolution, it is believed that this type of particles could be used as a basis for preparing nanosystems loaded with a variety of drugs.
- Published
- 2016
30. Mechanical reinforcement of thermoplastic vulcanizates using ground tyre rubber modified with sulfuric acid
- Author
-
Ramón Díaz de León, Maria Guadalupe Neira Velazquez, José Francisco Hernández Gámez, Lorena Farías Cepeda, Ernesto Hernández Hernández, Salvador Fernandez Tavizon, Silvia Guadalupe Solis Rosales, Florentino Soriano Corral, Pablo González Morones, and Rosa Idalia Narro Céspedes
- Subjects
Materials science ,Thermoplastic ,Polymers and Plastics ,02 engineering and technology ,law.invention ,chemistry.chemical_compound ,Differential scanning calorimetry ,020401 chemical engineering ,Natural rubber ,law ,Materials Chemistry ,Copolymer ,0204 chemical engineering ,Composite material ,chemistry.chemical_classification ,Vulcanization ,Sulfuric acid ,General Chemistry ,Ethylene propylene rubber ,021001 nanoscience & nanotechnology ,chemistry ,visual_art ,Ceramics and Composites ,visual_art.visual_art_medium ,High-density polyethylene ,0210 nano-technology - Abstract
Thermoplastic vulcanizates (TPVs) based on high density polyethylene (HDPE), ethylene propylene diene terpolymer (EPDM) were reinforced with ground tyre rubber (GTR) modified with sulfuric acid and dynamically vulcanized with dicumyl peroxide (DCP). TPVs were composed by 40% of HDPE, 30% of EPDM and 30% of GTR at 50 and 100 mesh and the concentration of DCP was varied from 0.3 to 3.6 parts per hundred rubber (phr). The properties of the TPVs containing GTR were determined by infrared spectroscopy, gel content and differential scanning calorimetry (DSC) analyses. The mechanical properties of the composites were also obtained. An increase of about 207% in the Young's modulus was obtained in blends containing GTR modified with sulfuric acid (GTR-SA) in relation with blends containing pristine GRT. Good compatibility of compounds containing GTR-SA was observed, GTR-SA presented high specific area as a consequence of the modification with sulfuric acid. POLYM. COMPOS., 2016. © 2016 Society of Plastics Engineers
- Published
- 2016
31. Synthesis of High cis-Polybutadiene in Styrene Solution with Neodymium-Based Catalysts: Towards the Preparation of HIPS and ABS via In Situ Bulk Polymerization
- Author
-
Luis Francisco Ramos de Valle, Gabriela Bosques Ibarra, Francisco Hernández Gámez, Héctor Ricardo López-González, Patricia de León Martínez, Florentino Soriano Corral, Francisco Javier Enríquez-Medrano, and Ramón Díaz de León
- Subjects
Materials science ,Article Subject ,Polymers and Plastics ,Bulk polymerization ,lcsh:Chemical technology ,Catalysis ,Styrene ,chemistry.chemical_compound ,Polybutadiene ,chemistry ,Polymerization ,Polymer chemistry ,lcsh:TP1-1185 ,Polystyrene ,Acrylonitrile ,Glass transition - Abstract
In a first step, 1,3-butadiene was selectively polymerized at 60°C in styrene as solvent using NdV3/DIBAH/EASC as the catalyst system. The catalyst system activation process, the addition order of monomers and catalyst components, and the molar ratios [Al]/[Nd] and [Cl]/[Nd] were studied. The catalyst system allowed the selective 1,3-butadiene polymerization, reaching conversions between 57.5 and 88.1% with low polystyrene contents in the order of 6.3 to 15.4%. Molecular weights ranging from 39,000 to 150,000 g/mol were obtained, while cis-1,4 content was found in the interval of 94.4 to 96.4%. On the other hand, the glass transition temperatures of synthesized materials were established in the range of −101.9 to −107.4°C, explained by the presence of polystyrene segments in the polybutadiene chains; in the same sense, the polybutadienes did not show the typical melting endotherm of high cis-polybutadienes. In a second step, the resulting styrene/high cis-1,4 polybutadiene solutions were used to synthesize ABS (adding a fraction of acrylonitrile monomer) and HIPS via in situ bulk polymerizations and the results were discussed in terms of morphological development, molecular parameters, dynamical mechanical behavior, and mechanical properties.
- Published
- 2016
32. Polymerization Reactor Monitoring by In-line Raman Spectrometry
- Author
-
Beatriz Reyes Vielma, Ramiro Infante Martínez, Ricardo López González, Esther Treviño Martínez, Ramón Díaz de León, Alejandro Díaz Elizondo, André Olivos Ramírez, and Luis A. Villarreal Cárdenas
- Subjects
Materials science ,Analytical chemistry ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Mass spectrometry ,01 natural sciences ,0104 chemical sciences ,symbols.namesake ,Polymerization reactor ,symbols ,Line (text file) ,0210 nano-technology ,Raman spectroscopy - Published
- 2017
33. Synthesis and Characterization of NBR´s by RAFT Technique and their use as Rubber Precursor in ABS Type Resins
- Author
-
Francisco Javier Enríquez-Medrano, Hened Saade-Caballero, Luis Alexandro Valencia López, E.N. Cabrera-Álvarez, Adali O. Castañeda-Facio, Florentino Soriano-Corral, Ramón Díaz de León-Gómez, and Pablo Acuna-Vazquez
- Subjects
Materials science ,02 engineering and technology ,General Chemistry ,Raft ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,chemistry.chemical_compound ,Polybutadiene ,Polymerization ,chemistry ,Natural rubber ,visual_art ,Polymer chemistry ,visual_art.visual_art_medium ,Copolymer ,Acrylonitrile ,0210 nano-technology ,Nitrile rubber ,Cis–trans isomerism - Abstract
Different rubbers based on polybutadiene were synthesized in solution by the reversible addition-fragmentation chain-transfer polymerization (RAFT) technique using 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl] entanoic acid as RAFT agent and 1,1’-azobiscyclohexanecarbonitrile (Vazo-88) as initiator. The results obtained in the polymerization of polybutadiene and poly(butadiene-co-acrylonitrile) (NBR) are discussed in terms of molecular weight distribution, composition and microstructure. Composition of polybutadiene in NBR´s was kept constant along the copolymerization, and the vinyl, cis and trans isomers are shown in values of around 12, 26 and 62% in all cases. Resulting rubbers were used to synthesize acrylonitrilebutadiene-styrene (ABS) type resins through an in situ bulk polymerization. Dynamic-mechanical properties and the morphology were analyzed in all the different ABS resins. In DMA analyses, the rubber component presented two transitions as well as an increase in the magnitude of the transition located around -75 °C, which is explained by the significant amount of SAN occlusions in the morphology, analyzed by TEM.
- Published
- 2017
34. Polyethylene-Waste Tire Dust Composites Via In Situ Polymerization
- Author
-
Maria Guadalupe Neira Velazquez, Rosa Idalia Narro Céspedes, Luis Alexandro Valencia López, Hened Saade Caballero, Yadira Karina Reyes Acosta, María Elena Ramos Aguiñaga, Ramón Díaz de León, Francisco Javier Enríquez-Medrano, and José Díaz Elizondo
- Subjects
Thermogravimetric analysis ,Materials science ,Size-exclusion chromatography ,02 engineering and technology ,General Chemistry ,Polyethylene ,Post-metallocene catalyst ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,chemistry.chemical_compound ,chemistry ,Cyclopentadienyl complex ,Polymerization ,Composite material ,In situ polymerization ,0210 nano-technology ,Aluminoxane - Abstract
Polyethylene/waste tire dust (WTD) composites were obtained by an in situ polymerization technique. The surface of the WTD was modified with deposition of polyethylene by using plasma polymerization. Ethylene polymerization was carried out using bis(cyclopentadienyl) titanium dichloride (Cp2TiCl2) as homogeneous metallocene catalyst, while diethylaluminum chloride (DEAC), ethylaluminum sesquichloride (EASC) and methyl aluminoxane (MAO) were used as co-catalysts at two different [Al]/[Ti] molar ratio. The main characteristics of the obtained polyethylenes were determined by size exclusion chromatography, thermogravimetric analysis, differential scanning calorimetry and wide-angle X-ray diffraction. The results showed that by using EASC and MAO the highest catalytic activities were presented at a [Al]/[Ti] molar ratio of 9.17 and 18.33 respectively. Even though it was possible to obtain polyethylene using WTD (modified or unmodified) the catalytic activity was lower than in the case in which no WTD was added in ethylene polymerization. Scanning transmission electronic microscopy images evidenced that the original morphology of the polyethylenes was not modified by the presence of WTD.
- Published
- 2017
35. Geometry of nanostructures analyzed for terahertz applications
- Author
-
Ramón Díaz de León-Zapata, Ismael Lara-Velázquez, Efrén Flores-García, and Francisco Javier González
- Subjects
Nanostructure ,Terahertz radiation ,Computer science ,Evolutionary algorithm ,020206 networking & telecommunications ,Geometry ,02 engineering and technology ,01 natural sciences ,Range (mathematics) ,0103 physical sciences ,0202 electrical engineering, electronic engineering, information engineering ,Radio frequency ,010306 general physics ,Plasmon - Abstract
A study on the geometry of antennas is proposed in order to find those that provide the optimal conditions of operation for applications in the terahertz range. We used an analysis based on evolutionary algorithms for that purpose, showing that the optimal geometries are not similar to those used in radio frequency applications.
- Published
- 2017
36. Polymerization of 1,3-butadiene with neodymium chloride tripentanolate/triisobutylaluminum binary catalyst system: effect of aging time and reaction temperature
- Author
-
Luis Alexandro Valencia López, Florentino Soriano Corral, Yair Agustín de Santiago-Rodríguez, Francisco Javier Enríquez-Medrano, María L. López Quintanilla, Hened Saade Caballero, and Ramón Díaz de León-Gómez
- Subjects
chemistry.chemical_classification ,Neodymium chloride ,Materials science ,Polymers and Plastics ,General Chemical Engineering ,Inorganic chemistry ,Industrial chemistry ,1,3-Butadiene ,Polymer ,Catalysis ,chemistry.chemical_compound ,Reaction temperature ,chemistry ,Polymerization ,Materials Chemistry - Abstract
1,3-Butadiene monomer was polymerized at 40°C and 60°C by means of a catalyst comprising neodymium (Nd) chloride/1-pentanolate/triisobutylaluminum (TIBA) in cyclohexane as solvent; the catalyst system was aged at 5 and 30 min. The effects on conversion, catalytic activity and polymer final properties were evaluated. The obtained polybutadienes (PBs) were characterized by size exclusion chromatography (SEC), nuclear magnetic resonance (NMR) and differential scanning calorimetry (DSC) techniques and the results were discussed in terms of the effect of aging time and reaction temperature.
- Published
- 2014
37. Thermoelectric efficiency optimization of nanoantennas for solar energy harvesting
- Author
-
Ramón Díaz de León-Zapata, Javier Méndez-Lozoya, Gabriel González, Edgar Guevara, and Francisco Javier González
- Subjects
Materials science ,business.industry ,Terahertz radiation ,Photodetector ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Solar energy ,Thermoelectric materials ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,010309 optics ,Dipole ,0103 physical sciences ,Thermoelectric effect ,Optoelectronics ,Solar simulator ,0210 nano-technology ,business ,Energy harvesting - Abstract
We compared 9 × 9 arrays of bimetallic Ni(Nickel)-Pt(Platinum) nanoantennas for a classic and evolutive dipole configuration. We fabricated the nanoantennas by e-beam lithography and characterized them with a solar simulator to analyze the I − V curves. From these curves, a thermoelectric voltage dependence associated by classic and evolutive dipole configuration was observed. We show that the evolutive dipole nanoantennas (EDN) generate up to three times more voltage in contrast with the classic dipole nanoantenna (CDN). Indeed, the evolutive configuration is 1.3 times more efficient than its classical counterpart. The results are corroborated by absorbance of these nanoantennas in the 20 to 36 THz range, where EDN is 40% more efficient than CDN and 30% in the range of 36.1 to 90 THz. Moreover, the experimental results match the thermoelectric behavior obtained using numerical simulations. The EDN can be used in applications ranging from aerospace technology to energy harvesting, photodetector, and sensors, where high thermoelectric efficiency is needed.
- Published
- 2019
38. Chitosan-Coated Magnetic Nanoparticles Prepared in One Step by Reverse Microemulsion Precipitation
- Author
-
Salvador Fernández, Hened Saade, María G. Pineda, Ramón Díaz de León, Raúl G. López, Darío Bueno, and Gilberto Hurtado
- Subjects
Materials science ,Maghemite ,Nanoparticle ,engineering.material ,Article ,Catalysis ,chitosan magnetic nanoparticles ,Inorganic Chemistry ,lcsh:Chemistry ,Magnetics ,one-step microemulsion precipitation ,chitosan low content ,chemistry.chemical_compound ,Chemical Precipitation ,Microemulsion ,Particle Size ,Physical and Theoretical Chemistry ,Molecular Biology ,lcsh:QH301-705.5 ,Spectroscopy ,Magnetite ,Chitosan ,Chromatography ,Aqueous solution ,Precipitation (chemistry) ,Organic Chemistry ,Temperature ,General Medicine ,Ferrosoferric Oxide ,Computer Science Applications ,chemistry ,lcsh:Biology (General) ,lcsh:QD1-999 ,engineering ,Nanoparticles ,Magnetic nanoparticles ,Emulsions ,Superparamagnetism ,Nuclear chemistry - Abstract
Chitosan-coated magnetic nanoparticles (CMNP) were obtained at 70 °C and 80 °C in a one-step method, which comprises precipitation in reverse microemulsion in the presence of low chitosan concentration in the aqueous phase. X-ray diffractometry showed that CMNP obtained at both temperatures contain a mixture of magnetite and maghemite nanoparticles with ≈4.5 nm in average diameter, determined by electron microscopy, which suggests that precipitation temperature does not affect the particle size. The chitosan coating on nanoparticles was inferred from Fourier transform infrared spectrometry measurements; furthermore, the carbon concentration in the nanoparticles allowed an estimation of chitosan content in CMNP of 6%-7%. CMNP exhibit a superparamagnetic behavior with relatively high final magnetization values (≈49-53 emu/g) at 20 kOe and room temperature, probably due to a higher magnetite content in the mixture of magnetic nanoparticles. In addition, a slight direct effect of precipitation temperature on magnetization was identified, which was ascribed to a possible higher degree of nanoparticles crystallinity as temperature at which they are obtained increases. Tested for Pb2+ removal from a Pb(NO3)2 aqueous solution, CMNP showed a recovery efficacy of 100%, which makes them attractive for using in heavy metals ion removal from waste water.
- Published
- 2013
39. Polymerization of 1,3-Butadiene with Several Catalytic Systems Based on Neodymium or Lithium in Presence of Ionic Liquids
- Author
-
Adali Castañeda Facio, Aldo Romo Quiroz, José Díaz Elizondo, Rosa Idalia Narro Céspedes, Ramón Díaz de León, María Teresa Alonso Córdova, Francisco Javier Enriquez Medrano, and Odilia Pérez Camacho
- Subjects
Materials science ,Polymers and Plastics ,Cyclohexane ,Organic Chemistry ,Inorganic chemistry ,1,3-Butadiene ,chemistry.chemical_element ,Condensed Matter Physics ,Catalysis ,Solvent ,chemistry.chemical_compound ,Polymerization ,chemistry ,Ionic liquid ,Polymer chemistry ,Materials Chemistry ,Molar mass distribution ,Lithium - Abstract
Summary: The anionic and Ziegler-Natta polymerizations of 1,3-butadiene initiated with n-BuLi and NdV/TIBA/DEAC respectively were carried out in presence of ionic liquids and cyclohexane as solvent in both cases. Polybutadienes obtained were characterized by SEC, NMR and DSC techniques and results were compared with polybutadienes synthesized under similar conditions but in absence of ionic liquids. In all cases, the presence of ionic liquids caused a decrease in the reaction exothermal and also a diminution in the molecular weight distribution. The ionic liquids increased the microstructure cis-1,4 in both kind of polymerizations, and promotes a shift towards lower temperatures in the glass-transition temperature.
- Published
- 2013
40. Kinetic Modeling of 1,3-Diene Polymerization Using a Neodymium-Based Catalytic System: A New Approach for Calculating the Molecular Weight Distribution
- Author
-
Jorge Herrera-Ordonez, Ramón Díaz de León, and Yair A. de Santiago‐Rodriguez
- Subjects
Polymers and Plastics ,Diene ,Organic Chemistry ,Dispersity ,Kinetics ,Binary number ,chemistry.chemical_element ,Thermodynamics ,Condensed Matter Physics ,Kinetic energy ,Neodymium ,chemistry.chemical_compound ,chemistry ,Polymerization ,Materials Chemistry ,Organic chemistry ,Molar mass distribution - Abstract
Summary: A new lumping-based approach for calculating the molecular weight distribution (MWD) in polymerization systems is proposed. In order to illustrate its applicability the proposed methodology is used for modelling the kinetics of a 1,3-diene polymerization using a binary neodymium-based catalytic system. The model is capable of reproducing experimental data after fitting for the evolution of molecular weight and polydispersity. The results of this preliminary simulation are used as a guide to design kinetics experiments that may lead to improve the kinetic model and to deepen the knowledge of the system under study.
- Published
- 2013
41. Evolutionary Algorithm Geometry Optimization of Optical Antennas
- Author
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Gabriel González, Efrén Flores-García, Ramón Díaz de León-Zapata, Francisco Javier González, and Ángel Rodríguez
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Physics ,Directional antenna ,Article Subject ,business.industry ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Energy minimization ,lcsh:HE9713-9715 ,01 natural sciences ,Electromagnetic radiation ,Finite element method ,010309 optics ,Printed circuit board ,Dipole ,Optics ,0103 physical sciences ,Dispersion (optics) ,lcsh:Cellular telephone services industry. Wireless telephone industry ,Radio frequency ,lcsh:Electrical engineering. Electronics. Nuclear engineering ,Electrical and Electronic Engineering ,0210 nano-technology ,business ,lcsh:TK1-9971 - Abstract
Printed circuit antennas have been used for the detection of electromagnetic radiation at a wide range of frequencies that go from radio frequencies (RF) up to optical frequencies. The design of printed antennas at optical frequencies has been done by using design rules derived from the radio frequency domain which do not take into account the dispersion of material parameters at optical frequencies. This can make traditional RF antenna design not suitable for optical antenna design. This work presents the results of using a genetic algorithm (GA) for obtaining an optimized geometry (unconventional geometries) that may be used as optical regime antennas to capture electromagnetic waves. The radiation patterns and optical properties of the GA generated geometries were compared with the conventional dipole geometry. The characterizations were conducted via finite element method (FEM) computational simulations.
- Published
- 2016
42. Responsivity and resonant properties of dipole, bowtie, and spiral Seebeck nanoantennas
- Author
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Francisco Javier González, Jorge L. Flores, Guillermo Garcia-Torales, Javier Alda, Brhayllan Mora-Ventura, and Ramón Díaz de León
- Subjects
Materials science ,Infrared ,Physics::Optics ,Optoelectrónica ,02 engineering and technology ,01 natural sciences ,010309 optics ,Responsivity ,Condensed Matter::Materials Science ,Optics ,Condensed Matter::Superconductivity ,0103 physical sciences ,Thermoelectric effect ,Electromagnetismo ,Optica ,Óptica ,Spiral antenna ,Renewable Energy, Sustainability and the Environment ,business.industry ,021001 nanoscience & nanotechnology ,Polarization (waves) ,Thermoelectric materials ,Atomic and Molecular Physics, and Optics ,Computer Science::Other ,Wavelength ,Dipole ,Optoelectronics ,0210 nano-technology ,business - Abstract
Seebeck nanoantennas, which are based on the thermoelectric effect, have been proposed for electromagnetic energy harvesting and infrared detection. The responsivity and frequency dependence of three types of Seebeck nanoantennas is obtained by electromagnetic simulation for different materials. Results show that the square spiral antenna has the widest bandwidth and the highest induced current of the three analyzed geometries. However, the geometry that presented the highest temperature gradient was the bowtie antenna, which favors the thermoelectric effect in a Seebeck nanoantenna. The results also show that these types of devices can present a voltage responsivity as high as 36 μV/W36 μV/W for titanium–nickel dipoles resonant at far-infrared wavelengths.
- Published
- 2016
43. Multi-objective evolutionary algorithm as a method to obtain optimized nanostructures
- Author
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Ariel B. de la Rosa Zapata, J.V. González-Fernández, Ramón Díaz de León-Zapata, Ismael Lara-Velázquez, and Efrén Flores-García
- Subjects
Computer simulation ,Field (physics) ,Computer science ,Evolutionary algorithm ,Physics::Optics ,020206 networking & telecommunications ,02 engineering and technology ,Function (mathematics) ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Electromagnetic radiation ,Finite element method ,Electronic, Optical and Magnetic Materials ,Genetic algorithm ,0202 electrical engineering, electronic engineering, information engineering ,Point (geometry) ,0210 nano-technology ,Instrumentation ,Algorithm - Abstract
The field of plasmonics, an optics discipline that studies the interaction of light with matter for structures with dimensions similar to the wavelength of the electromagnetic radiation affecting them, has been further developed with the support of computational technologies that are capable of performing calculations with large volumes of data to solve the complex problems of this discipline. Some of the problems in plasmonics require the use of algorithmic techniques that can simultaneously handle more than one function that tend not to present their maximum or minimum at the same point, i.e., their optimal performances conflict with each other. In this paper, we present the results of the use of a multi-objective genetic algorithm to obtain the maximum plasmonic resonance in nanoparticles assuming three relevant factors: geometry, current density, and electric field, which are, in turn, the three objective functions for the proposed algorithm. The method used for the characterization of the nanoparticles was a numerical simulation using the finite element method. To verify the results, the electromagnetic radiation patterns and other optical properties of the obtained nanoparticles were compared with those of nanoparticles reported in the literature. Possible applications and work in progress are also discussed.
- Published
- 2018
44. Morphologic Modification in ABS by the Incorporation 'in Situ' of Nano-ZnO: Study of the Effect on Characteristics and Final Properties
- Author
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Bertha A. Puente Urbina, Rebeca Betancourt-Galindo, Ramón Díaz de León, Pablo Acuña, and Luís Falcón
- Subjects
Materials science ,Morphology (linguistics) ,Mechanical Engineering ,technology, industry, and agriculture ,Nanoparticle ,chemistry.chemical_element ,Zinc ,Benzoyl peroxide ,Condensed Matter Physics ,Polybutadiene ,chemistry ,Chemical engineering ,Mechanics of Materials ,Polymer chemistry ,Nano ,medicine ,General Materials Science ,Fourier transform infrared spectroscopy ,Phase inversion ,medicine.drug - Abstract
The synthesis of poly(acrylonitrile-butadiene-styrene) (ABS) was carried out using the mass-suspension process, high cis polybutadiene (PB), benzoyl peroxide (BPO) as the initiator and modified and unmodified nanoparticles of zinc oxide (nano-ZnO). X-ray diffraction (XRD) and Fourier transform infrared (FTIR) were used to characterize the ZnO nanoparticles. A Universal tensiometer, Brokfield viscosimeter and transmission electronic microscopy (TEM) were used to characterize ABS. The employment of nano-ZnO induced an impressive morphologic modification and transformed the highly occluded salame morphology of poly(styrene-acrylonitrile) (SAN) to a highly dispersed one in its matrix. During the reaction, a decrease in the total production of SAN was observed due to the interaction between radicals produced by the initiator and nano-ZnO, causing a molecular weight increase of SAN. The nano-ZnO also induced a decline in the phase inversion and extended the period of occurrence. ABS without nano-ZnO yielded higher mechanical properties than one without any nanoparticles.
- Published
- 2010
45. Phenomenon of phase inversion in high impact polystyrene: Physico-chemical, rheological and morphological study in the presence of chain transfer agent and using different tapered block copolymers as the precursor rubber
- Author
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Graciela Morales, Ramón Díaz de León, Florentino Soriano, and Pablo Acuña
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Materials science ,Polymers and Plastics ,Radical polymerization ,Chain transfer ,General Chemistry ,Styrene ,chemistry.chemical_compound ,Polymerization ,Chemical engineering ,chemistry ,Natural rubber ,visual_art ,Polymer chemistry ,Materials Chemistry ,visual_art.visual_art_medium ,Copolymer ,Polymer blend ,Phase inversion - Abstract
Different high impact polystyrenes were synthesized using styrene/butadiene copolymers (SB) with PS/PB composition: 30/70 and 20/80 as the precursor rubber, benzoyl peroxide (BPO) as the initiator, and ter-dodecyl mercaptane (TDM) as the chain transfer agent. During the polymerization, several samples were taken and analyzed under different techniques to evaluate the phase inversion (PI) phenomenon. The PI was determined through transmission electron microscopy (TEM) and through dynamic oscillatory behavior, where the PI takes places when the relaxation process presents the lower value of activation energy. Finally, the Choi and Schowalter emulsion model was employed to elucidate the PI, and relevant information was revealed about the interfacial tension in the PI. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers
- Published
- 2009
46. A Mathematical Model of the Bulk Copolymerization of Styrene and Acrylonitrile in the Presence of Polystyrene‐block‐Polybutadiene
- Author
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Daniel Elizarrarás, Ramón Díaz de León, Diana Alejandra Estenoz, Graciela Morales, and Carla Vanesa Luciani
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Molar mass ,Polymers and Plastics ,Organic Chemistry ,Condensed Matter Physics ,Grafting ,Block (periodic table) ,Styrene ,Inorganic Chemistry ,chemistry.chemical_compound ,Polybutadiene ,chemistry ,Chemical engineering ,Polymer chemistry ,Materials Chemistry ,Copolymer ,Polystyrene ,Acrylonitrile - Abstract
The bulk copolymerization of styrene and acrylonitrile in the presence of SB using BPO as initiator was investigated. Reactions were carried out at 80°C with different initial SB concentrations. Global variables, such as conversion and cumulative grafting efficiency of SAN, were determined during the prepolymerization. The isolated non-grafted SAN was also analyzed to determine its average molar masses and composition. A mathematical model was developed, and theoretical predictions were compared with experimental data. A good agreement between measurements and simulations was obtained from a heterogeneous model when BPO was evenly distributed between phases.
- Published
- 2008
47. Seebeck nanoantennas for the detection and characterization of infrared radiation
- Author
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Stefan McMurtry, Joel Briones, Alexander Cuadrado, Michel Hehn, J. C. Martinez-Anton, Ramón Díaz de León, Francisco Javier González, Edgar Briones, Javier Alda, François Montaigne, Universidad Autonoma de San Luis Potosi [México] (UASLP), Universidad Complutense de Madrid = Complutense University of Madrid [Madrid] (UCM), Universidad de Santiago de Chile [Santiago] (USACH), Institut Jean Lamour (IJL), and Institut de Chimie du CNRS (INC)-Université de Lorraine (UL)-Centre National de la Recherche Scientifique (CNRS)
- Subjects
Conductometry ,Light ,Infrared ,Infrared Rays ,Transducers ,Metal Nanoparticles ,Radiation Dosage ,7. Clean energy ,Sensitivity and Specificity ,Photometry ,Responsivity ,Optics ,Thermocouple ,Thermoelectric effect ,Nanotechnology ,Scattering, Radiation ,Computer Simulation ,Radiometry ,Image resolution ,Circular polarization ,Physics ,business.industry ,Reproducibility of Results ,Equipment Design ,Models, Theoretical ,Polarization (waves) ,Atomic and Molecular Physics, and Optics ,Equipment Failure Analysis ,Wavelength ,Thermography ,[PHYS.COND.CM-MS]Physics [physics]/Condensed Matter [cond-mat]/Materials Science [cond-mat.mtrl-sci] ,Optoelectronics ,business - Abstract
Équipe 101 : Nanomagnétisme et électronique de spin; International audience; Arrays of metallic thermocouples in the shape of spiral nanoantennas are proposed as infrared detectors, which use the thermoelectric properties of the metallic interfaces to generate electrical DC signals. The responsivity of these types of antennas is evaluated from both theoretical and numerical perspectives pointing out its potential as infrared sensors. Moreover, the same structures can be used to characterize the state of polarization of the optical near fields with a spatial resolution comparable to the wavelength.
- Published
- 2015
48. Thermal Degradation of Synthetic Rubber Nanocomposites
- Author
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Aidé Sáenz Galindo, Ramón Díaz de León-Gómez, Lluvia López López, Lorena Farias Cepeda, and Adalí Castañeda Facio
- Subjects
chemistry.chemical_classification ,Materials science ,Nanocomposite ,Carbon nanotube ,Polymer ,Elastomer ,Synthetic rubber ,Silsesquioxane ,law.invention ,chemistry.chemical_compound ,chemistry ,Natural rubber ,law ,visual_art ,visual_art.visual_art_medium ,Thermal stability ,Composite material - Abstract
In recent years, synthetic rubbers nanocomposites have captured and held the attention of scientists because are the materials for the future, which have improved resistance to thermal degradation and stability of the nanocomposite. Commonly fillers like layered silicates, carbonaceous nanofillers (carbon nanotubes, carbon naanofibers and exfoliated nanographite), spherical particles (Silica, TiO2, ZnO, CaSO4, CaCO3, ZnFe2O4) and polyhedral oligomeric silsesquioxane (POSS) are used for reinforcing elastomers. This new materials exhibit enhanced properties at very low filler level, usually ≤5 wt%. The properties of rubber nanocomposites strongly depend on the dispersion state of fillers and method of preparation. The effect to different nanoparticles on rubber properties is studied with thermal stability. This is mainly studied using TGA, TGA-MS, TGA-FTIR and other techniques. The thermal degradation mechanism of the rubber synthetic nanocomposites is generally considered to be related to the kind of used nanoparticles and its amount, the interactions between inorganic nanoparticles and polymer reactive group. Rubber synthetic nanocomposites play an important role in engineering, automotive, aerospace, construction, packaging and medical devices applications due to is possible to design new materials with unprecedented and improvements in their physical properties, particularly from the perspective of applications.
- Published
- 2015
49. Recycling of high impact polystyrene in coextruded sheet: Influence of the number of processing cycles on the microstructure and macroscopic properties
- Author
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Graciela Morales, Ramón Díaz de León, and Florentino Soriano
- Subjects
Materials science ,Polymers and Plastics ,Izod impact strength test ,General Chemistry ,Microstructure ,Stress (mechanics) ,chemistry.chemical_compound ,Natural rubber ,Rheology ,chemistry ,Phase (matter) ,visual_art ,Materials Chemistry ,visual_art.visual_art_medium ,Polystyrene ,Composite material ,Melt flow index - Abstract
High impact polystyrene(HIPS) was repeatedly coextruded at 220°C, maintaining a constant composition of 70 wt% of virgin HIPS and 30 wt% of recycled HIPS. The gel content (GC), grafting degree (GD), swell index (SI), morphology of the rubber phase, and average molecular weight of the polystyrene (PS) matrix (w) were characterized after each processing cycle. The effect of these parameters on the melt flow index (MFI), the shear viscosity (η), the power law index (n), the Izod impact, and the stress at break were evaluated. The results demonstrated that the rheological properties changed with the number of processing cycles, e.g. the MFI decreased in the first cycle from 2.8 to 1.7 g/10 min, while from the second to the sixth cycle increased to 3.4 ± 0.2 g/10 min. The power law index increased from n = 0.29, after the first processing cycle, to n = 0.34 in the sixth cycle. The changes in MFI and n were attributed to changes in the physical structure of the rubber phase and to chain scissions in the PS matrix, caused by the recycling. Finally, the impact strength decreased with the increasing number of processing cycles, while the tensile stress at break remained constant. POLYM. ENG. SCI., 46:1698–1705, 2006. © 2006 Society of Plastics Engineers
- Published
- 2006
50. Thermoformability study of virgin and regrind high impact polystyrene coextruded sheets: Influence of the number of processing cycles on the processing parameters
- Author
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Florentino Soriano, Graciela Morales, Ramón Díaz de León, and Felipe Avalos Belmontes
- Subjects
Materials science ,Polymers and Plastics ,Mold ,Materials Chemistry ,medicine ,General Chemistry ,Composite material ,medicine.disease_cause ,Wall thickness ,Thermoforming ,High impact polystyrene - Abstract
High impact polystyrene was extruded repeatedly at 220°C and thermoformed under different heat time (Ht), plug assist time (PAt), mold time (Mt), and mold temperature (MT). The optimum thermoforming process conditions were determined for a material processed in one cycle, using an experimental design of the four variables mentioned before at two levels. Mt has no influence on the coefficient of wall thickness variation (CV), while the rest of the variables present a noticeable influence on CV, and they can be modified to obtain lower values of CV (i.e. CV = 1.3, using Ht = 46 s, PAt = 2.5 s, and MT = 80°C). These conditions were then employed for a material processed under six cycles, resulting in an increase in the CV value to 3.5. The normalized thickness (NT) of HIPS with one and six processing cycles was also evaluated. It depends on Ht, Mt, and PAt. With the values of the calculated parameters for CV, it was possible to obtain NT values close to 1, using a material processed one cycle. The NT value obtained for six cycles processed HIPS was far from unity. The changes on thermoforming variables' responses are a consequence of the changes occurred in HIPS inner structure. POLYM. ENG. SCI. 46:503–509, 2006. © 2006 Society of Plastics Engineers.
- Published
- 2006
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