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Search Results: 1 - 10 of 462250 matches for " Katime Issa A "
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Swelling Properties of New Hydrogels Based on the Dimethyl Amino Ethyl Acrylate Methyl Chloride Quaternary Salt with Acrylic Acid and 2-Methylene Butane-1,4-Dioic Acid Monomers in Aqueous Solutions  [PDF]
Issa Katime, Eduardo Mendizábal
Materials Sciences and Applications (MSA) , 2010, DOI: 10.4236/msa.2010.13026
Abstract: Hydrogels of dimethylaminoethyl acrylate methyl chloride quaternary salt (Q9) have been synthesized with different monomer ratio by copolymerization of this poorly studied monomer either with acrylic acid or with 2-methylene bu-tane-1,4-dioic acid. Hydrogel swelling was measured as a function of the composition of the hydrogel and of the crosslinking agent ratio. High values of swelling have been obtained at very high crosslinking values (< 14 wt %) and the equilibrium swelling was reached at very low time (less than 15 minutes). The swelling isotherms consisted of a steep initial portion and then levelled off as asymptotically to the equilibrium swelling limit. The experimental data suggest clearly that the swelling process obeys second-order kinetics. According to this, the kinetics rate constant and the equilibrium water content were determined at different comonomer composition and crosslinker concentration. The calculated kinetic constants ranged from 0.48 to 3.76 × 10-2 min-1 for poly (acrylic acid-co-Q9) hydrogels and from 0.68 to 4.0 × 10-2 min-1 for poly (2-methylene butane-1,4-dioic acid-co-Q9) hydrogels depending on the hydrogels composition. The diffusion process was evaluated for each hydrogel showing a non-Fickian type diffusion. In all cases was observed a considerable increase in diffusion coefficient as Q9 content increases.
Empleo de una sonda infrarroja in situ para monitorear reacciones de esterificación
Sánchez C.,Francisco J.; Cesteros,Carlos; Katime,Issa A.;
Ingeniería e Investigación , 2006,
Abstract: a batch reactor was employed having ph meter, ir probe and continuous operation detectors so that it could work as a cstr reactor. as esterification advanced, then ir bands corresponding to the carboxyl acid cooh group and the alcohol c-oh group decreased whilst a parallel increase was presented in the ester -coor group band which was forming. reaction progress could be observed by continuous ir spectrum registration. the ir band for hoh (water) could not be studied because it needed a completely anhydrous medium for doing so. standard solutions could be prepared for quantifying ir band peak intensity, according to a component?s composition in the mixture. however, when phase changes occurred in the reaction mixture, this method could not be employed for following the course of a particular reaction because random variation was detected in band intensity.
Empleo de una sonda infrarroja in situ para monitorear reacciones de esterificación Using an infrared probe for in situ monitoring of esterifying reactions
Sánchez Castellanos Francisco José,Cesteros Carlos,Katime Issa A
Ingeniería e Investigación , 2006,
Abstract: Se empleó un reactor batch (por lotes), dotado de tres detectores: pH, Sonda IR y operación en continuo, de tal forma que puede operarse como un reactor CSTR. En la medida en que la esterificación procede, decrecen las bandas correspondientes al grupo -COOH del ácido carboxIlico y la del grupo C-OH del alcohol, presentándose al mismo tiempo incremento en la banda del grupo -COOR del ester que se está formando. El progreso de la reacción se puede seguir por el registro continuo de los espectro IR. La banda correspondiente a H-O-H del agua no se puede seguir ya que se requiere de un ambiente absolutamente anhidro para hacerlo. De otro lado, por aparte pueden prepararse soluciones patrones para poder cuantificar la intensidad de los picos en el espectro IR, segün la composición del componente en la mezcla. Sin embargo, cuando se presentan cambios de fase en la mezcla reactiva, este metodo no puede emplearse para seguir el curso de una reacción, ya que se presenta una variación muy aleatoria en la senal de intensidad de los picos. A batch reactor was employed having pH meter, IR probe and continuous operation detectors so that it could work as a CSTR reactor. As esterification advanced, then IR bands corresponding to the carboxyl acid COOH group and the alcohol C-OH group decreased whilst a parallel increase was presented in the ester -COOR group band which was forming. Reaction progress could be observed by continuous IR spectrum registration. The IR band for HOH (water) could not be studied because it needed a completely anhydrous medium for doing so. Standard solutions could be prepared for quantifying IR band peak intensity, according to a component’s composition in the mixture. However, when phase changes occurred in the reaction mixture, this method could not be employed for following the course of a particular reaction because random variation was detected in band intensity.
Síntesis de mono y diitaconatos de alquilo y arilo
Sánchez Francisco J.,Katime Issa A.,Meaurio Emilio
Ingeniería e Investigación , 1997,
Abstract: Se presenta una técnica para la síntesis en laboratorio de mono y diitaconatos y la separación de los mismos por extracción selectiva con solventes orgánicos. La pureza de los productos se determina por cromatografía en capa fina y por espectroscopia infrarroja.
Influência do comon?mero e do método de polimeriza??o na cinética de libera??o de fenobarbitona a partir de hidrogéis
Barcellos, Ivonete O.;Katime, Issa A.;Soldi, Valdir;Pires, Alfredo T. Nunes;
Polímeros , 2000, DOI: 10.1590/S0104-14282000000200013
Abstract: the release of water-soluble drugs from initially hydrated hydrogels matrices generally involves the simultaneous water absorption and drug desorption through a swelling-controlled diffusion mechanism. the diffusional behaviour of phenobarbitone from a hydrogel formed by a 2-hydroxyethylmethacrylate (hema) and methyl monoitaconate (mmi) copolymer was reported. the drug release into water was performed by high pressure liquid cromatography and the results showed that the phenobarbitone release from the hydrogels studies, considering the diffusion coefficient values did not change with the temperature and the polymerization method. the activation energy values suggested a more favorable phenobarbitone release from the hydrogels p(hema-co-mmi) polymerized in mass and bulk solution.
Influência do comon mero e do método de polimeriza o na cinética de libera o de fenobarbitona a partir de hidrogéis
Barcellos Ivonete O.,Katime Issa A.,Soldi Valdir,Pires Alfredo T. Nunes
Polímeros , 2000,
Abstract: A libera o de drogas solúveis em água a partir de matrizes de hidrogéis hidratados, geralmente envolve simultaneamente a absor o de água e a libera o da droga via mecanismo de difus o controlada. Foi analisado o comportamento difusional da fenobarbitona no hidrogel do copolímero 2-hidroxietil metacrilato (HEMA) e monoitaconato de metila (MMI). A libera o da droga no meio aquoso foi acompanhada por cromatografia líquida de alta press o e os resultados mostraram que a libera o da fenobarbitona a partir dos hidrogéis estudados, considerando-se os valores dos coeficientes de difus o, n o variou com a temperatura e com o método de polimeriza o. Os valores de energia de ativa o sugerem um favorecimento na libera o da fenobarbitona a partir dos hidrogéis de p(HEMA-co-MMI) polimerizados em massa e em solu o.
Obtención de hidrogeles derivados del ácido itacónico
Sánchez Francisco J.,Novoa Rosa M.,Díaz de Apodaca Helena,Katime Issa A.
Ingeniería e Investigación , 1996,
Abstract: Se presenta una técnica para la obtención de hidrogeles de acrilamida, empleando comonámeros monoésteres del ácido itacántco. A estos hidrogeles se les determina su cinética de hinchamiento a pH neutro y 20°C.
Cationic Microemulsion Polymerization of Alkyl Acrylates  [PDF]
Issa Katime, Jesús Arellano, Eduardo Mendizábal, Jorge Flores
Materials Sciences and Applications (MSA) , 2010, DOI: 10.4236/msa.2010.15043
Abstract: Here we present the polymerization of n-butyl acrylate (BA), ethyl acrylate (EA) and methyl acrylate (MA) in tri-component microemulsions, using a cationic surfactant such as dodecyl trimetyl ammonium bromide in water, as a function of temperature, initiator type and, monomer and initiator concentration. The final latexes are transparent and blue color, with particle size ranging between 20 and 60 nm determined by quasielastic light scattering (QLD) and SEC molar masses of the order of 106 g/mol. Reaction times are short and reaction rates are high with final conversions between 70 and 98% depending on the monomer and the reaction conditions.
Temperature- and pH-Sensitive Nanohydrogels of Poly(N-Isopropylacrylamide) for Food Packaging Applications: Modelling the Swelling-Collapse Behaviour
Clara Fuci?os, Pablo Fuci?os, Martín Míguez, Issa Katime, Lorenzo M. Pastrana, María L. Rúa
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0087190
Abstract: Temperature-sensitive poly(N-isopropylacrylamide) (PNIPA) nanohydrogels were synthesized by nanoemulsion polymerization in water-in-oil systems. Several cross-linking degrees and the incorporation of acrylic acid as comonomer at different concentrations were tested to produce nanohydrogels with a wide range of properties. The physicochemical properties of PNIPA nanohydrogels, and their relationship with the swelling-collapse behaviour, were studied to evaluate the suitability of PNIPA nanoparticles as smart delivery systems (for active packaging). The swelling-collapse transition was analyzed by the change in the optical properties of PNIPA nanohydrogels using ultraviolet-visible spectroscopy. The thermodynamic parameters associated with the nanohydrogels collapse were calculated using a mathematical approach based on the van't Hoff analysis, assuming a two-state equilibrium (swollen to collapsed). A mathematical model is proposed to predict both the thermally induced collapse, and the collapse induced by the simultaneous action of two factors (temperature and pH, or temperature and organic solvent concentration). Finally, van't Hoff analysis was compared with differential scanning calorimetry. The results obtained allow us to solve the problem of determining the molecular weight of the structural repeating unit in cross-linked NIPA polymers, which, as we show, can be estimated from the ratio of the molar heat capacity (obtained from the van't Hoff analysis) to the specific heat capacity (obtained from calorimetric measurements).
La densidad de carga de polielectrolitos y su capacidad de neutralización en sistemas coloidales
Lárez Velásquez,Cristóbal; Lozada Cabezas,Lorena; Millán Barrios,Enrique; Katime2,Issa; Sasía,Pedro;
Revista Latinoamericana de Metalurgia y Materiales , 2003,
Abstract: abstracts chitosan, n,n,n - trimethylchitosan (tmc) and poly (acryloxy - ethyl - trimetheylammoniun chloride) (q9) have been evaluated as flocculant agents in aqueous caolin suspensions. a comparative study of these flocculant aggents in un-stabilized kaolin susspension is reported. a strong disturbance of the system was observed when chitosan was employed due to the excess of acid normally employed to solubilize it. the tmc showed an excellent flocculation capacity comparable to commercial polymer q9, even though tmc charge density is smaller. on the other hand, agood correlation between charge density and the ammount required to induce in the systema zero charge was obtained.
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