Corral-Flores V.,Research Center for Applied Chemistry |
Perez-Herrera J.J.,Mexican Center for Research and Advanced Studies |
Torres-Moye E.,International Advanced Research Center for Powder Metallurgy And New Materials |
Romero-Garcia J.,Research Center for Applied Chemistry |
And 2 more authors.
Materials Science Forum | Year: 2010
Piezoelectric fibrous membranes of barium titanate (BTO) - polyvinylidene fluoride (PVDF) nanocomposites were studied. BTO nanoparticles of about 40 nm were synthesized by the sol-gel method and mixed in PVDF-dimethyl formamide solutions at 0, 0.1, 1 and 3 wt.% relative to the polymer weight. The suspensions were electrospun using a horizontal set-up with an applied voltage of 15 kV. The samples were heat treated for 24 hours at 100°C in air to increase the crystallinity of the polymer. The heat treatment induced a phase transformation from α to β phase in the pure polymer sample, while the nanocomposite membranes did not undergo such phase transformation. It was found that the addition of nanoparticles affected not only the morphology and diameter of the fibers, but also the content of beta phase of the polymer. In order to pursue the crystallization of β phase, additional samples were prepared by surface modification of the BTO nanoparticles and the addition of tetraisopentyl ammonium chloride. The best results were obtained with the last additive, which lead to the crystallization of only β phase and a homogeneous fibrous morphology. All these aspects were strongly correlated and consequently, governed the ferroelectric behavior of the samples. © (2010) Trans Tech Publications.
Munguia-Lopez J.,Research Center for Applied Chemistry |
Quezada-Martin R.,Research Center for Applied Chemistry |
Arellano-Garcia M.A.,Research Center for Applied Chemistry |
Ibarra-Jimenez L.,Research Center for Applied Chemistry |
And 2 more authors.
Acta Horticulturae | Year: 2014
Previous studies have been conducted to evaluate the effect of plastic mulch on the temperature of the upper soil profile and its relations to the growth and yield of crops. However, the presence of plastic mulch on the soil surface also affects all components of the energy balance (net radiation, Rn; sensible heat flux, H; latent heat flux, LE and soil heat flux, G). In this study, the energy balance components through the different growth stages of the chili crop were measured and the daily and seasonal partitioning of the surface energy balance was evaluated. The results showed that net radiation was the major term of the energy balance. At the early stage of the crop growth most of the net radiation was dissipated in sensible heat flux (H), because the crop only covered a small part of the bed. Once the crop reached full foliage growth, Rn was dissipated mainly in LE. During crop senescence, most of the Rn was dissipated in H in a lower rate in G, and small proportion on LE.
Valenzuela-Soto J.H.,Research Center for Applied Chemistry |
Alvarez-Mejia C.,Technologic Institute Superior of Abasolo |
Rodriguez-Rios D.,CINVESTAV |
Hernandez-Guzman G.,University of Guanajuato |
And 2 more authors.
Journal of Pure and Applied Microbiology | Year: 2016
Pseudomonas syringae pv. maculicola M2 (Psm) is a phytopathogenic bacteria and one of about 50 pathovars reported in the Pseudomonas syringae group. The host range of Psm included collard, cauliflower, broccoli and others cruciferae plants, producing blight, and among other cruciferae host plants, Arabidopsis thaliana as model study in plant-pathogen i nteractions. To understand the traits that could regulate the pathogenicity of Psm, the physical map was constructed employing transposable elements as pTn5cat1 and pTn5Spcat (endowed with restriction sites for the rare cutting restriction endonucleases PacI, PmeI and SwaI) derived from transposon Tn5 to obtain insertional mutants. The chromosome from the wild type Psm was digested with the rare-cutting endonucleases PacI, PmeI and SwaI, producing 14, 15 and 16 fragments, respectively. All fragments were separated using pulsed field gel electrophoresis (PFGE) and the size of the chromosome was determinate to be around 6.53 Mb. To assemble all fragments caused by single restriction, random insertional mutants of Psm carrying an extra site for PacI, PmeI and SwaI were evaluated. Around 11 different insertional mutants were selected after screening using PFGE analysis and confirmed by Southern-blot hybridization, partial digestions were done in DNA of wild type Psm to complete the physical map.
Quintanilla F.,University of the Valley of Mexico |
Rodriguez J.R.,National Autonomous University of Mexico |
Vargas S.,National Autonomous University of Mexico |
Solis S.G.,Research Center for Applied Chemistry |
And 5 more authors.
Materials Research Innovations | Year: 2016
Chitosan was grafted onto poly(3-hydroxybutyrate) (P(3HB)) as in our earlier work by using gamma radiation-induced polymerization reaction. We now provide structural and surface characteristics of the graft copolymer in view of potential applications. The modified P(3HB) was characterized by 1H/solid-state 13C CP-MAS nuclear magnetic resonance, Fourier transform infrared spectroscopy, thermogravimetric analysis, atomic force microscopy, contact angles and scratch resistance determination. Copolymer surfaces resemble those of neat P(3HB) and are unsuitable for membranes. However, a novel composite based on grafting copolymer and polyurethane was developed. It displays good properties for the preparation of 3D-scaffolds with potential uses in tissue engineering. © 2016 Taylor &Francis.
Espinoza-Gonzalez C.,Research Center for Applied Chemistry |
Avila-Orta C.,Research Center for Applied Chemistry |
Martinez-Colunga G.,Research Center for Applied Chemistry |
Lionetto F.,University of Salento |
Maffezzoli A.,University of Salento
IEEE Transactions on Nanotechnology | Year: 2016
The need for new measurement techniques able to assess the nanofiller dispersion is still receiving great consideration when nanocomposites are developed. This occurs since different routes to disperse nanostructures generate molecular changes in polymer matrices that promote complex polymer-polymer and polymer-nanofiller interactions, which make difficult a suitable estimation of the dispersion. In this paper, ultrasonic waves at different frequencies and power were used for preparing nanocomposite samples and for evaluating the nanofiller dispersion. First, a patented method was used to disperse multiwall carbon nanotubes (MWCNTs) in polyamide 12 through extrusion assisted by low-frequency and high power ultrasound (with frequency ranging between 20 and 50 kHz). This 'green' processing method was able to induce different states of dispersion of the nanofillers, as well as chemical modifications to polymer chains promoting branching reactions. Then, ultrasonic dynamic mechanical analysis (UDMA with ultrasound frequency in the megahertz range) was used to estimate the dispersion of the different nanocomposite samples. Compared to rheological measurement methods, UDMA provided a better estimation of the quality of dispersion, being sensitive both to the complex molecular architectures in polymer matrices and to the scattering due to MWCNT agglomerates. © 2002-2012 IEEE.
Gonzalez-Blanco R.,Research Center for Applied Chemistry |
Gonzalez-Blanco R.,Queen's University |
Cunningham M.F.,Queen's University |
Saldivar-Guerra E.,Research Center for Applied Chemistry
Journal of Polymer Science, Part A: Polymer Chemistry | Year: 2016
A bicomponent initiation system consisting of 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) and the water soluble initiator potassium persulfate (KPS) was used to develop a robust and versatile semibatch emulsion polymerization process to obtain polystyrene (PS) latexes with solids contents of 5-40 wt %. A window of operating conditions was found that yielded high conversion (>95%) stable latexes and well controlled polymers, overcoming limitations found in previous attempts at developing similar processes using TEMPO. The critical parameters studied were surfactant concentration, monomer concentration in the nucleation step and the monomer feed rate in the semibatch step. Methyl acrylate (MA) was used in the nucleation step to improve the nitroxide efficiency (NEff). Latexes having molecular weight distribution (MWD) with dispersity (D strok sign) lower than 1.5, average particle size (Dp) from ≈32 to ≈500 nm, nitroxide efficiencies NEff up to ≈1.0 and monomer conversions >90% were obtained in less than 12 h with solids contents up to 40 wt %. These results constitute a significant advance over prior efforts in TEMPO-mediated polymerization in aqueous dispersions. © 2015 Wiley Periodicals.
Application of the low vacuum scanning electron microscope to the study of glass-ceramic spherical materials [Aplicación del modo de bajo vacío en microscopia electronica de barrido para el estudio de materiales esféricos vitro-ceramicos]
Ceniceros-Reyes M.,Research Center for Applied Chemistry |
Rodriguez F.,Research Center for Applied Chemistry |
Perera-Mercado Y.,Research Center for Applied Chemistry |
Saucedo-Salazar E.,Research Center for Applied Chemistry |
Barriga-Castro E.D.,Research Center for Applied Chemistry
Acta Microscopica | Year: 2014
The use of a scanning electron microscope in low vacuum mode (or reduced pressure) permits to obtain secondary electron images of specimens that are non-conductive or specimens which have not been coated with a conductive material such as gold or carbon. This technique is advantageous for the observation of specimens like biological samples, moist samples, liquids, polymers and ceramics among others . Unlike high vacuum mode (HighVac), the regime pressure of the low vacuum mode (LowVac) stands in the range of 10 to 130 Pa which assist to eliminate the effects of charge accumulation onto the surface and preserve fragile structures (biological samples) as well. The use of this mode of observation to the study of glass-ceramic spherical materials has been evaluated. Also this material was observed applying the HighVac mode in order to compare viewing conditions between both observation modes. The spherical material is obtained from crystalline blast furnace slags (BFS) generated by steelmaking industry . The process involves a natural gas/oxygen thermal projection process and conversion of the BFS precursors into glass-ceramic spheres. The study and characterization of the new glass-ceramic spherical particles is required because their chemical properties depend on the morphology, finally these materials can be incorporated into specific cementing slurries formulation as lightweight aggregates and is expected that they will improve the thermal and acoustic isolation properties of the final concrete and/or cement systems. This study has demonstrated that the use of the LowVac mode is adequate to study the morphology of these structures over the HighVac mode, besides allowed to set operating parameters in order to obtain images with free-charge accumulation.