oalib

Publish in OALib Journal

ISSN: 2333-9721

APC: Only $99

Submit

Any time

2019 ( 2 )

2018 ( 17 )

2017 ( 19 )

2016 ( 23 )

Custom range...

Search Results: 1 - 10 of 8631 matches for " Carmina Menchaca-Campos "
All listed articles are free for downloading (OA Articles)
Page 1 /8631
Display every page Item
Natural, Synthetic, and Recycled Polymers in Composite Materials
Gonzalo Martínez-Barrera,Osman Gencel,Carmina Menchaca-Campos,Enrique Vigueras-Santiago
International Journal of Polymer Science , 2013, DOI: 10.1155/2013/389162
Abstract:
Nylon/Porphyrin/Graphene Oxide Fiber Ternary Composite, Synthesis and Characterization  [PDF]
César García-Pérez, Carmina Menchaca-Campos, Miguel A. García-Sánchez, Elsa Pereyra-Laguna, Ociel Rodríguez-Pérez, Jorge Uruchurtu-Chavarín
Open Journal of Composite Materials (OJCM) , 2017, DOI: 10.4236/ojcm.2017.73009
Abstract: This research was based on the manufacture of new composite materials that offer technological possibilities in the development of new devices with greater efficiency. Electrospinning was used to form nylon 66/-tetra-(para-aminophenyl) porphyrin (H2T(p-NH2)PP)/graphene oxide (GO) composite film. Graphene oxide coatings were obtained from graphite, through mechanical exfoliation followed by calcination and ultrasonic agitation in an oxidant solution. These samples were characterized under SEM, FTIR, Raman spectroscopy, UV-vis and R-X techniques. On the other hand, H2T(p-NH2)PP was synthesized in two steps?process by the Rothemun reaction and the Adler Method and it was integrated within nylon polyamide fibers by direct addition of a hexamethylenediamine/adipoyl chloride reactant mixture. The polymerization of the nylon/H2T(p-NH2)PP species occurs in such a way that it starts or ends on the four peripherals-NH2 groups, connected and located in the same molecular plane of H2T(p-NH2)PP, forming nylon chains at the periphery of the macrocycle. The association of GO with nylon/H2T(p-NH2)PP fibers is performed
Nylon/Graphene Oxide Electrospun Composite Coating
Carmina Menchaca-Campos,César García-Pérez,Iván Casta?eda,Miguel A. García-Sánchez,René Guardián,Jorge Uruchurtu
International Journal of Polymer Science , 2013, DOI: 10.1155/2013/621618
Abstract: Graphite oxide is obtained by treating graphite with strong oxidizers. The bulk material disperses in basic solutions yielding graphene oxide. Starting from exfoliated graphite, different treatments were tested to obtain the best graphite oxide conditions, including calcination for two hours at 700°C and ultrasonic agitation in acidic, basic, or peroxide solutions. Bulk particles floating in the solution were filtered, rinsed, and dried. The graphene oxide obtained was characterized under SEM and FTIR techniques. On the other hand, nylon 6-6 has excellent mechanical resistance due to the mutual attraction of its long chains. To take advantage of the properties of both materials, they were combined as a hybrid material. Electrochemical cells were prepared using porous silica as supporting electrode of the electrospun nylon/graphene oxide films for electrochemical testing. Polarization curves were performed to determine the oxidation/reduction potentials under different acidic, alkaline, and peroxide solutions. The oxidation condition was obtained in KOH and the reduction in H2SO4 solutions. Potentiostatic oxidation and reduction curves were applied to further oxidize carbon species and then reduced them, forming the nylon 6-6/functionalized graphene oxide composite coating. Electrochemical impedance measurements were performed to evaluate the coating electrochemical resistance and compared to the silica or nylon samples. 1. Introduction Graphite oxide is a compound of carbon, oxygen, and hydrogen in variable ratios, commonly obtained by treating graphite with strong oxidizers. Strictly speaking “oxide” is an incorrect but historically established name, since graphite is not a metal. The bulk material disperses in basic solutions yielding monomolecular sheets, known as graphene oxide by analogy to graphene, the single-layer form of graphite [1]. Graphene oxide (GO) sheets have recently attracted substantial interest as a possible intermediate for the manufacture of graphene. It typically preserves the layer structure of the parent graphite, but the layers are buckled and the interlayer spacing is about two times larger (~0.7?nm) than that of graphite. Graphene oxide layers are about ?nm thick [2–6]. The edges of each layer are terminated with carboxyl and carbonyl groups. The detailed structure is still not understood due to the strong disorder and irregular packing of the layers [1]. One of the methods used to separate the layers of graphite consists in an aggressive oxidative processes which functionalize the periphery and some places of the graphene
Effects of the Addition of Ortho- and Para-NH2 Substituted Tetraphenylporphyrins on the Structure of Nylon 66
Luis A. Díaz-Alejo,E. Carmina Menchaca-Campos,J. Uruchurtu Chavarín,R. Sosa-Fonseca,Miguel A. García-Sánchez
International Journal of Polymer Science , 2013, DOI: 10.1155/2013/323854
Abstract: The synthetic tetrapyrrole macrocycles, such as porphyrins (H2P) and phthalocyanines (H2Pc), exhibit interesting physicochemical properties suitable to be used in modern technology. For many applications, those species should be trapped or fixed inside graphite, hydrotalcites, silica, TiO2, or polymers. Methodologies for the optimization of the properties of porphyrins, trapped or fixed inside polymers, have been barely developed. Our research works in the development of methodologies for the optimization of incorporation and display of properties of tetrapyrrole macrocycles inside inorganic, polymeric, or hybrid networks. This paper shows some results about the effect of the spatial disposition of the amine (–NH2) groups attached on the periphery of substituted tetraphenylporphyrins, on the Nylon 66 structure and on the display of the physicochemical properties of the trapped macrocycles. Nylon 66 was synthesized from adipoyl chloride and hexamethylenediamine in presence of tetraphenylporphyrins substituted with –NH2 groups localized at the ortho- or para-positions of the phenyls. Cobalt complexes formation was used to quantify the amount of porphyrins in the polymer fibers. Characterization results show that the spatial position of amine groups of the porphyrins has important structural and textural effect on the Nylon 66 fibers and on the fluorescence of the porphyrins integrated into the fibers. 1. Introduction Porphyrins are tetrapyrrole macrocyclic compounds playing a transcendental role in nature as one of the principal components of molecules such as (i) chlorophyll, (ii) the heme group in blood and cytochromes and (iii) cyanocobalamin (Vitamin B12) [1–3]. Formally, porphyrins are modified or substituted aromatic tetrapyrrole macrocyclic compounds derived from porphin (Figure 1), which consists of four pyrrole rings bonded through methine (=CH) bridges in order to form a planar and highly conjugated macrocycle. In the free bases of porphyrins, the two pyrrolic hydrogens can be substituted by a cation, and the remaining two nitrogens tend to easily coordinate with a metal nucleus as to form a stable metalloporphyrin. Synthetic porphyrinic complexes, involving practically all metallic elements of the periodic table, have been synthesized already [2–4]. The central space of porphyrins can only accommodate ions having an atomic radius smaller than 0.201?nm [2–4]; thus, causing that in the porphyrinic complexes containing the larger ions, the metallic element must be located outside of the molecular plane. Similar to the size of the cation, the
Electrochemical Evaluation of a Recycled Copolymer Coating for Cultural Heritage Conservation Purposes
Marco Hernández-Escampa,Fausto Rodríguez-Acu?a,Franco Millán-Cruz,Pilar Rodríguez-Rojas,Miguel Hernández-Gallegos,Alba Covelo,Carmina Menchaca-Campos,Jorge Uruchurtu
International Journal of Polymer Science , 2013, DOI: 10.1155/2013/751056
Abstract: Acrylonitrile-butadiene-styrene (ABS) is a well-known discard product from the industry. This copolymer can be dissolved in organic solvents, and thin films can be created by immersion. Two requirements for coatings used for cultural heritage conservation purposes are transparency and reversibility, both fulfilled by ABS films. The aim of this work was to characterize the copolymer and to evaluate the electrochemical properties of ABS coatings applied to copper. Such performance was compared to that of a commercial varnish commonly used in conservation. The results indicate high protection values of the ABS film, generating a potential application for this waste material. The electrochemical techniques included electrochemical noise, impedance spectroscopy, and potentiodynamic polarization. 1. Introduction Cultural heritage conservation constitutes a relevant field of research which frequently relies on material science to solve the challenges posed by the degradation of artifacts, architectural structures, and ornaments [1–5]. Historic, artistic, and archaeological items are frequently built of metals. Through the ages, copper and its alloys constitute a particular set of metals widely used in such manufactures [6]. Even when these materials tend to form protective patinas due to their interactions with the environment, such natural protective layers may fail, especially in highly polluted atmospheres [7]. Therefore, the application of coatings to both clean and patina covered metallic surfaces has proved to be useful to preserve cultural heritage [8]. Two highly desirable conditions of conservation-oriented coatings are transparency in order not to affect the aesthetical traits of the artifacts and reversibility, which refers to an easy removal process [9]. On the other hand, acrylonitrile-butadiene-styrene (ABS) waste and residues represent a well-known discard product from the automotive industry. Since law usually forbids the recycling of this material because all pieces must be brand new, considerable amounts of ABS become unused waste and a nuisance to dispose due to environmental restrictions. Therefore, research has been done trying to find usable recycling applications with added value to this and other polymer discards. Due to the finite reserve of hydrocarbon in the world, a proposal has been obtaining degradation oils from plastics, potentially useful as fuel [10]. However, such processes cannot avoid the presence of heteroatoms such as chlorine from poly(vinyl chloride) (PVC) or nitrogen from ABS. These heteroatoms relate to corrosion of
Crossed and Linked Histories of Tetrapyrrolic Macrocycles and Their Use for Engineering Pores within Sol-Gel Matrices
Miguel A. García-Sánchez,Fernando Rojas-González,E. Carmina Menchaca-Campos,Salvador R. Tello-Solís,R. Iris Y. Quiroz-Segoviano,Luis A. Diaz-Alejo,Eduardo Salas-Ba?ales,Antonio Campero
Molecules , 2013, DOI: 10.3390/molecules18010588
Abstract: The crossed and linked histories of tetrapyrrolic macrocycles, interwoven with new research discoveries, suggest that Nature has found in these structures a way to ensure the continuity of life. For diverse applications porphyrins or phthalocyanines must be trapped inside solid networks, but due to their nature, these compounds cannot be introduced by thermal diffusion; the sol-gel method makes possible this insertion through a soft chemical process. The methodologies for trapping or bonding macrocycles inside pristine or organo-modified silica or inside ZrO 2 xerogels were developed by using phthalocyanines and porphyrins as molecular probes. The sizes of the pores formed depend on the structure, the cation nature, and the identities and positions of peripheral substituents of the macrocycle. The interactions of the macrocyclic molecule and surface Si-OH groups inhibit the efficient displaying of the macrocycle properties and to avoid this undesirable event, strategies such as situating the macrocycle far from the pore walls or to exchange the Si-OH species by alkyl or aryl groups have been proposed. Spectroscopic properties are better preserved when long unions are established between the macrocycle and the pore walls, or when oligomeric macrocyclic species are trapped inside each pore. When macrocycles are trapped inside organo-modified silica, their properties result similar to those displayed in solution and their intensities depend on the length of the alkyl chain attached to the matrix. These results support the prospect of tuning up the pore size, surface area, and polarity inside the pore cavities in order to prepare efficient catalytic, optical, sensoring, and medical systems. The most important feature is that research would confirm again that tetrapyrrolic macrocycles can help in the development of the authentic pore engineering in materials science.
Anemia Hemolítica aguda adquirida
DANIEL CAMPOS MENCHACA
Revista chilena de pediatría , 1948,
Abstract:
Use of Silica Tubes as Nanocontainers for Corrosion Inhibitor Storage
Cesia ávila-Gonzalez,Rodolfo Cruz-Silva,Carmina Menchaca,Selene Sepulveda-Guzman,Jorge Uruchurtu
Journal of Nanotechnology , 2011, DOI: 10.1155/2011/461313
Abstract: A new alkyd paint anticorrosion smart coating was developed by using silica nanoparticles as corrosion inhibitor nanocontainers. Silica particles were mixed with the paint at different concentrations to study their performance and ensure their free transportation to the damaged metal. The filling up of silica particles was done preparing three solutions: distilled water, acetone, and a mixture of both, with Fe(NO3)3 and silica particles immersed in each of the solutions to adsorb the inhibitor. Acetone solution was the best alternative determined by weight gain analysis made with the inhibitor adsorbed in silica nanocontainers. Steel samples were painted with inhibitor silica nanocontainer coatings and immersed in an aqueous solution of 3% sodium chloride. Polarization curves and electrochemical noise techniques were used to evaluate the corrosion inhibitor system behavior. Good performance was obtained in comparison with samples without inhibitor nanocontainer coating. 1. Introduction Every corrosive protection action effort may be lost or become more costly if the mechanisms are effective but not efficient and/or applied in an area ill prepared or under nonideal conditions. So it is necessary to develop new avant garde design schemes to achieve effective protection. Currently, smart coating applied in nanotechnology promise solutions to this problem and benefits everything from new applications, existing structures under more efficient solution. Storage of the inhibitor is based on the use of particles, which can play the role of nanocontainers for corrosion inhibitors adsorbed inside [1–3]. A new generation of anticorrosion coatings that respond to changes in the environment has sparked great interest because corrosion is one of the most important causes of destruction of structures that involve the loss of material, and prevention is paramount. This type of protection is intended to retard corrosion of the metal substrate and/or control it. In this paper, a smart system for corrosion protection was developed based on the synthesis of silica (SiO2) nanotubes and the storage and containment of ferric nitrate (Fe(NO3)3) as an oxidant corrosion inhibitor, mixed in a polymer coating to achieve a “smart inhibitor coating” performance. The coating releases the active ions, which act as a local trigger mechanism inhibiting or passivating the active metal surface, when it is required. The direct introduction of components of the protective coating inhibitor often leads to the deactivation of the corrosion inhibitor and polymer matrix degradation. To overcome
OPTICAL ABSORPTION ANISOTROPY OF SOME AZODYES, DETECTED BY UV-VIS SPECTROSCOPY IN POLARIZED LIGHT
Carmina Plosceanu
Analele Universitatii Bucuresti : Chimie , 2008,
Abstract: The work presents a study on the optical absorption anisotropy (linear dichroism) of the p-p* absorption band of a series of azodyes. The azodyes have been oriented in the nematic liquid crystal 4-cyanophenyl-4’-pentyl benzoate. The linear dichroism of the dye molecules in the nematic matrix is also evaluated as function of the temperature.
ELECTRIC FIELD EFFECT ON OPTICAL DICHROISM OF SOME AZODYES DISSOLVED IN COMPENSATED CHOLESTERIC LIQUID CRYSTAL
Carmina Plosceanu
Analele Universitatii Bucuresti : Chimie , 2009,
Abstract: In the paper are presented the results obtained in the study of the optical dichroism of some azodyes dissolved in a compensated mixture of cholesteryl chloride and cholesteryl-nonanoate under the electric field action. The electric field dependence of the order parameter S of the dyes is presented and discussed.
Page 1 /8631
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.