El Laboratorio de Ingeniería para el Tratamiento de Aguas de la Universidad Carlos III de Madrid,... more El Laboratorio de Ingeniería para el Tratamiento de Aguas de la Universidad Carlos III de Madrid, de investigación y servicios en el tratamiento de aguas residuales, optimiza el diseño y puesta a punto de reactores biológicos de membranas (MBR), indicados para obtener agua depurada de alta calidad y/o aumentar la capacidad de tratamiento.
The fluorescence response of the dansyl chromophore has been used to study the kinetic of epoxy c... more The fluorescence response of the dansyl chromophore has been used to study the kinetic of epoxy curing processes. With this new method, comparison between the curing at the interface of a glass fiber/epoxy and in the epoxy bulk of a composite material was studied. The effect of two glass fiber surface treatments was investigated. Commercial E-glass fibers were surface coated with 3-aminopropyltriethoxysilane (APTES) and 3-aminopropylmethyldiethoxysilane (APDES). Fluorimetry (using fluorescent labels) and FT-NIR (Fourier transformed infrared spectroscopy in the near range) techniques were used to monitor the curing process in these composite materials. From the analysis of the data obtained, different simple kinetic models were discussed and apparent activation energies were obtained. Furthermore, from those techniques the respective results were compared to obtain complementary information. Independently of the sample and the technique used for the kinetic analysis, no variation of the activation energy of the epoxy curing reaction was found, which suggests that there are no changes in the mechanism of the reaction along the process. Fluorescence from dansyl located at the glass fiber/epoxy interface reflected that the kind of reinforcement treatment clearly affects the epoxy curing process exactly in that region. However, when analytical response comes from the whole system the mechanism of the reaction does not seem to change with the silane coating used although is quite different in comparison with the process at the interface.
The fluorescence response of the dansyl chromophore has been used to study the kinetic of epoxy c... more The fluorescence response of the dansyl chromophore has been used to study the kinetic of epoxy curing processes. With this new method, comparison between the curing at the interface of a glass fiber/epoxy and in the epoxy bulk of a composite material was studied. The effect of two glass fiber surface treatments was investigated. Commercial E-glass fibers were surface coated with 3-aminopropyltriethoxysilane (APTES) and 3-aminopropylmethyldiethoxysilane (APDES). Fluorimetry (using fluorescent labels) and FT-NIR (Fourier transformed infrared spectroscopy in the near range) techniques were used to monitor the curing process in these composite materials. From the analysis of the data obtained, different simple kinetic models were discussed and apparent activation energies were obtained. Furthermore, from those techniques the respective results were compared to obtain complementary information. Independently of the sample and the technique used for the kinetic analysis, no variation of the activation energy of the epoxy curing reaction was found, which suggests that there are no changes in the mechanism of the reaction along the process. Fluorescence from dansyl located at the glass fiber/epoxy interface reflected that the kind of reinforcement treatment clearly affects the epoxy curing process exactly in that region. However, when analytical response comes from the whole system the mechanism of the reaction does not seem to change with the silane coating used although is quite different in comparison with the process at the interface.
Commercial glass fibers have been subjected to different activation treatments under neutral and ... more Commercial glass fibers have been subjected to different activation treatments under neutral and acidic conditions to achieve different coating degrees when silanized with y-aminopropyltriethoxisilane (APES). A fluorescent sulfonamide (PSA) was formed between the amine residue and a fluorescent probe, pyrenesulfonyl chloride (PSC). Reflectance UV-Vis spectra of the pyrene-doped fibres show that pyrene is present in the form of preassociated dimers when the coating degree is low. Emission and excitation fluorescence spectra reveal the existence of a charge transfer groundstate complex with exciplex emission at 460-515 nm and absorption red-shifted with respect to the S 0 -> S 1 transition. Lifetime measurements yield three lifetimes, which are assigned to dimer, exciplex, and monomer emission. From the photophysical data it is concluded that the fibers with the highest silane content have an open structure with the highest fraction of isolated fluorescent moieties.
E-type glass fibers were coated with poly(␥-aminopropyltriethoxysilane), treating them with a 1% ... more E-type glass fibers were coated with poly(␥-aminopropyltriethoxysilane), treating them with a 1% (v/v) monomer aqueous solution. The fibers were labeled with a dansyl-sulfonamide conjugate by reaction of acetonitrile solutions of dansyl chloride with the amine groups immobilized on the glass fiber surface. Interactions of the labeled coating polymer with solvents of different polarities were estimated by measurements of the fluorescence band shifts of the label. It was found that for aprotic solvents, the solvent dipolar coupling relaxation mechanism is dominated by thermodynamic interactions of the solvent with the polymer matrix, while for protic solvents this mechanism is dominated by specific interactions between solvent molecules and the excited state of the chromophore. Different experimental excited-state dipole moments were obtained for nonpolar and polar solvents (* NP ϭ 7.2 Ϯ 1.6 D, * P ϭ 11.9 Ϯ 1.5 D). Using the AM1 method, excited-state dipole moments for the first and second singlets were calculated and it was concluded that * NP Ϸ ͗* 2 1 ͘ 1/2 and * P Ϸ ͗* 2 2 ͘ 1/2 . Accordingly, neither the glass support nor the coating polar influence the excited-state properties of dansyl. The temperature dependence of dansyl emission allows the determination of the relaxation temperature of the coating polymer, which was estimated as 175 K for the coating used.
E-glass fibers were silanized using a 1% (v/v) aqueous solution of ␥-aminopropyltriethoxysilane (... more E-glass fibers were silanized using a 1% (v/v) aqueous solution of ␥-aminopropyltriethoxysilane (APES). Pyrene-sulfonamide conjugates were formed by reaction of 1-pyrenesulfonyl chloride (PSC) in acetonitrile (AcN), with the amine groups immobilized on the glass fiber surface. These pyrene-sulfonamide conjugates were used as fluorescence probes, being a relatively simple analytical method to study the coating microstructure of polyorganosiloxane layer on glass fibers. The first aim of this work was to estimate possible interactions of the polyaminosiloxane coating with surrounding molecules of different solvents (solvent accessibility to the chromophore). For this study, the fluorescence response of pyrene-sulfonamide dye (PSA) was correlated with solvent polarity parameters. It was concluded that all the studied solvents were accessible to the chromophore, and they can gather in two groups, depending on their ability to swell the poliorganosiloxane layer. The second objective was to estimate the rigidity of the coating polymer from the temperature dependence of PSA emission. At about 180 K, a sudden change in the behavior of different photophysical parameters of PSA were observed. This phenomenon was interpreted as a density change in the polyaminosiloxane attached to the glass fibers.
Commercial glass ®bres were calcinated for the removal of organic matter, activated for surface s... more Commercial glass ®bres were calcinated for the removal of organic matter, activated for surface silanol regeneration and silanizated with -aminopropyltri-ethoxysilane. Two different activation methods were used: re¯ux with neutral water and re¯ux with 10% HCl aqueous solution. Acid treatments hydrolize Si±O bonds, greatly changing the composition of the glass and regenerating silanol groups, some of them being of intraglobular nature. Water treatment does not change appreciably the glass composition, but its surface free energy value is the lowest. The degree of silanization is the greatest for the acid activated samples and the lowest for the water activated one. The polar contribution to the total surface free energy, once the samples are silanizated, is the highest for the ®bres activated with boiling water whilst the dispersion component is about the same for all of them. SEM observations indicate that for the greatest degree of coating, debonding of the ®laments may induce a peeling-out fractural mechanism. # 1999 Elsevier Science S.A. All rights reserved. es (A.J. Aznar) 0924-0136/99/$ ± see front matter # 1999 Elsevier Science S.A. All rights reserved. PII: S 0 9 2 4 -0 1 3 6 ( 9 9 ) 0 0 2 1 2 -5
Aqueous solutions of three silanes to cover silica microfibres were used, being the 3-aminopropyl... more Aqueous solutions of three silanes to cover silica microfibres were used, being the 3-aminopropyltriethoxysilane (APTES) and the 3-aminopropylmethyldiethoxysilane (APDES) the reagents for preparing them at the proportion of (APTES/APDES): 1/0, 1/1 and 0/1. The 1-pyrene sulphonyl chloride (PSC) fluorescent moiety was chemically attached to the silanised substrate via the sulphonamide formation. The hydrolytic degradation phenomenon of the silane coupling layer was studied as a function of: (i) temperature, (ii) coating layer type and (iii) pH (4, 7 and 10). The hydrolytic damage in the coupling region of the silica microfibres composite materials occurs under an equilibrium process. It was obtained the activation energies (E a ) for the hydrolytic damage considering the rate to reach the equilibrium. The values of E a depended on the type of coating and on the pH. As a consequence, the rate of hydrolytic damage could be related to the proportion of Si silane -O-Si silane , while the OH − groups were thought to catalyse the reaction.
The fluorescence response of the dansyl chromophore has been used to study the kinetic of epoxy c... more The fluorescence response of the dansyl chromophore has been used to study the kinetic of epoxy curing processes. With this new method, comparison between the curing at the interface of a glass fiber/epoxy and in the epoxy bulk of a composite material was studied. The effect of two glass fiber surface treatments was investigated. Commercial E-glass fibers were surface coated with 3-aminopropyltriethoxysilane (APTES) and 3-aminopropylmethyldiethoxysilane (APDES). Fluorimetry (using fluorescent labels) and FT-NIR (Fourier transformed infrared spectroscopy in the near range) techniques were used to monitor the curing process in these composite materials. From the analysis of the data obtained, different simple kinetic models were discussed and apparent activation energies were obtained. Furthermore, from those techniques the respective results were compared to obtain complementary information. Independently of the sample and the technique used for the kinetic analysis, no variation of the activation energy of the epoxy curing reaction was found, which suggests that there are no changes in the mechanism of the reaction along the process. Fluorescence from dansyl located at the glass fiber/epoxy interface reflected that the kind of reinforcement treatment clearly affects the epoxy curing process exactly in that region. However, when analytical response comes from the whole system the mechanism of the reaction does not seem to change with the silane coating used although is quite different in comparison with the process at the interface.
Journal of Macromolecular Science, Part B- Physics, 2001
Modified glass fibers with three different amino silanes-(1) 3aminopropyltriethoxysilane (APTES),... more Modified glass fibers with three different amino silanes-(1) 3aminopropyltriethoxysilane (APTES), (2) 3-aminopropylmethyldiethoxysilane (APDES), and (3) 3-aminopropyldimethylethoxysilane (APMES)-were labeled with 5-dimethylaminonaphthalene-1-sulfonylchloride (DNS), and its fluorescence was followed as a function of curing time for two epoxide formulations (TRIEPOX-LM, Gairesa, Spain, and diglycidyl ester bisphenol Aethylenediamine), as well as a function of water uptake. It was demonstrated that the fluorescence response from fluorophores directly attached to the coupling region in glass fibers/epoxy composites is a very sensible method for nondestructive and "in situ" monitoring of any changes that appear at the interphase (rigidity and solvent accessibility). In addition, fluorescence from a dansyl label shows more rigidity when APMES is used as the coupling agent. This suggests that the greater the cross-linking degree at the coupling region, the smaller the epoxy chain interdiffusion. Finally, the water uptake process in glass fiber/epoxy composites can be divided into two steps; the first step corresponds to the diffusion of water to the coupling region, and the second step corresponds to the hydrolysis of siloxane bonds in the interphase. Both steps are dependent on the surface treatment of the glass fibers.
The cure process of an epoxy-amine system was studied in composite materials based on an epoxy po... more The cure process of an epoxy-amine system was studied in composite materials based on an epoxy polymer matrix filled with silica particles. FT-NIR and Fluorimetry (based on the use of fluorescent labels) were used as analytical techniques. In order to study the effect of the structure of the interphase, the silica particles were surface coated with two different silanes: 3-aminopropyltriethoxysilane and 3-aminopropylmethyldiethoxysilane. 1-pyrene-sulfonylchloride was chemically bonded to: (i) the coated silica particles and (ii) to the epoxy polymer matrix, using its fluorescence response to independently monitor the epoxy curing at the interface region and in the bulk respectively. The cure process was followed at different temperatures to subsequently study its kinetics either by fluorescence or by FT-NIR. An extent of reaction in terms of integrated fluorescence intensity was defined and the subsequent kinetic analysis allowed us to calculate apparent activation energies of the process. Comparing the curing reaction in the polymer bulk and at the interface it could be concluded that the epoxy curing at the interface proceeded faster but only during the first stages of the reaction. This result was attributed to a higher local concentration of amino groups at the interface. Finally, a comparison between FTIR and fluorescence results showed that both techniques provide complementary information about the curing reaction. q
The analysis of the fluorescent response from the dansyl moiety as a function of temperature has ... more The analysis of the fluorescent response from the dansyl moiety as a function of temperature has been used to estimate the thermal transitions in silica particle/epoxy-based composite materials. Silica particles were surface-coated with 3-aminopropyltriethoxysilane (APTES) and 3-aminopropylmethyldiethoxysilane (APDES). 5-Dimethylamino-1-naphtalenesulfonyl chloride (DNS) and 5-dimethylaminonaphthalene-1-(2-aminoehyl)) sulfonamide (DNS-EDA) were selectively attached to the silanized silica particles and to the epoxy matrix respectively. The fluorescence results, interpreted in terms of the model of interpenetrating polymer networks, suggest that (i) independent of the silane coating, the interfacial region is slightly more rigid and heterogeneous than the epoxy bulk and (ii) the interface generated with APTES seems to be more flexible than that obtained with APDES.
Glass fibers have been treated with y-aminopropyl-triethoxysilane (APES) through different silani... more Glass fibers have been treated with y-aminopropyl-triethoxysilane (APES) through different silanizating procedures, which include APES aqueous solutions and APES vapor adsorption.
... Posteriormente, el polímero obtenido se mantuvo a vacío a 60 ºC durante 24 h con objeto de se... more ... Posteriormente, el polímero obtenido se mantuvo a vacío a 60 ºC durante 24 h con objeto de secarlo y obtener un alto grado de polimerización. 2.3. Técnicas instrumentales ... 39 Núm. 3 Mayo-junio 2000 J. GONZáLEZ-BENITO, AJ AZNAR, A. MAÇANITA, J. BASELGA 3.1. PSA ...
The adsorption isotherm of methylene blue (MB) on sepiolite gels is of the Langmuir type, indicat... more The adsorption isotherm of methylene blue (MB) on sepiolite gels is of the Langmuir type, indicating a great affinity of the MB towards the sepiolite; the adsorption is quantitative up to adsorption of MB of 0.1 mmol/g sepiolite. The differences observed in the absorption spectrum in the region 500-650 nm for different MB Ioadings are interpreted in terms of aggregation of MB molecules on the sepiolite surface with the formation of MB dimers, trimers and higher aggregates. The progressive coverage of the sepiolite surface by MB produces a sharp decrease in the viscosity of the gels, and the suspension becomes peptized for an MB loading of 0.21 mmol/g which corresponds to the adsorption of MB dimers. These results indicate that MB avoids particle-to-particle interactions. The viscosity decrease is parallel to the perturbation of the Si-OH groups on the sepiolite surface as observed by IR spectroscopy, suggesting that these silanol groups can also play an important role in the theological behaviour of aqueous sepiolite dispersions.
We report in this paper the synthesis and characterization of a new class of biopolymer-clay nano... more We report in this paper the synthesis and characterization of a new class of biopolymer-clay nanocomposites based in the assembling of chitosan to sepiolite, which is a natural magnesium silicate showing a microfibrous texture. CHN and ICP/AES chemical analyses, XRD, FTIR spectroscopy, 13 C solid-state NMR, LT-SEM, and thermal analysis have been employed in the characterization of the resulting nanocomposites. The adsorption isotherm of chitosan on sepiolite in acidic medium reveals a significant coverage of the biopolymer at high equilibrium concentration values indicating a multilayer adsorption. The arrangement of chitosan chains on the surface of the silicate microfibers is discussed on the basis of physicochemical data obtained by application of the different techniques. The potentiometric response of this new type of bio-nanocomposites incorporated in carbon paste electrodes toward aqueous salt solutions was employed for the first time as a valuable technique for a rapid assessment of the ionexchange behaviors. Thermal behaviors and mechanical properties have been determined by DTA-TG and DMTA, respectively. As these materials are well-processed as self-supporting films, in view of their properties they show potential interest as membranes for different processes related to separation of ions and gases, as well as components in electrochemical devices (fuel-cell, potentiometric sensors).
El Laboratorio de Ingeniería para el Tratamiento de Aguas de la Universidad Carlos III de Madrid,... more El Laboratorio de Ingeniería para el Tratamiento de Aguas de la Universidad Carlos III de Madrid, de investigación y servicios en el tratamiento de aguas residuales, optimiza el diseño y puesta a punto de reactores biológicos de membranas (MBR), indicados para obtener agua depurada de alta calidad y/o aumentar la capacidad de tratamiento.
The fluorescence response of the dansyl chromophore has been used to study the kinetic of epoxy c... more The fluorescence response of the dansyl chromophore has been used to study the kinetic of epoxy curing processes. With this new method, comparison between the curing at the interface of a glass fiber/epoxy and in the epoxy bulk of a composite material was studied. The effect of two glass fiber surface treatments was investigated. Commercial E-glass fibers were surface coated with 3-aminopropyltriethoxysilane (APTES) and 3-aminopropylmethyldiethoxysilane (APDES). Fluorimetry (using fluorescent labels) and FT-NIR (Fourier transformed infrared spectroscopy in the near range) techniques were used to monitor the curing process in these composite materials. From the analysis of the data obtained, different simple kinetic models were discussed and apparent activation energies were obtained. Furthermore, from those techniques the respective results were compared to obtain complementary information. Independently of the sample and the technique used for the kinetic analysis, no variation of the activation energy of the epoxy curing reaction was found, which suggests that there are no changes in the mechanism of the reaction along the process. Fluorescence from dansyl located at the glass fiber/epoxy interface reflected that the kind of reinforcement treatment clearly affects the epoxy curing process exactly in that region. However, when analytical response comes from the whole system the mechanism of the reaction does not seem to change with the silane coating used although is quite different in comparison with the process at the interface.
The fluorescence response of the dansyl chromophore has been used to study the kinetic of epoxy c... more The fluorescence response of the dansyl chromophore has been used to study the kinetic of epoxy curing processes. With this new method, comparison between the curing at the interface of a glass fiber/epoxy and in the epoxy bulk of a composite material was studied. The effect of two glass fiber surface treatments was investigated. Commercial E-glass fibers were surface coated with 3-aminopropyltriethoxysilane (APTES) and 3-aminopropylmethyldiethoxysilane (APDES). Fluorimetry (using fluorescent labels) and FT-NIR (Fourier transformed infrared spectroscopy in the near range) techniques were used to monitor the curing process in these composite materials. From the analysis of the data obtained, different simple kinetic models were discussed and apparent activation energies were obtained. Furthermore, from those techniques the respective results were compared to obtain complementary information. Independently of the sample and the technique used for the kinetic analysis, no variation of the activation energy of the epoxy curing reaction was found, which suggests that there are no changes in the mechanism of the reaction along the process. Fluorescence from dansyl located at the glass fiber/epoxy interface reflected that the kind of reinforcement treatment clearly affects the epoxy curing process exactly in that region. However, when analytical response comes from the whole system the mechanism of the reaction does not seem to change with the silane coating used although is quite different in comparison with the process at the interface.
Commercial glass fibers have been subjected to different activation treatments under neutral and ... more Commercial glass fibers have been subjected to different activation treatments under neutral and acidic conditions to achieve different coating degrees when silanized with y-aminopropyltriethoxisilane (APES). A fluorescent sulfonamide (PSA) was formed between the amine residue and a fluorescent probe, pyrenesulfonyl chloride (PSC). Reflectance UV-Vis spectra of the pyrene-doped fibres show that pyrene is present in the form of preassociated dimers when the coating degree is low. Emission and excitation fluorescence spectra reveal the existence of a charge transfer groundstate complex with exciplex emission at 460-515 nm and absorption red-shifted with respect to the S 0 -> S 1 transition. Lifetime measurements yield three lifetimes, which are assigned to dimer, exciplex, and monomer emission. From the photophysical data it is concluded that the fibers with the highest silane content have an open structure with the highest fraction of isolated fluorescent moieties.
E-type glass fibers were coated with poly(␥-aminopropyltriethoxysilane), treating them with a 1% ... more E-type glass fibers were coated with poly(␥-aminopropyltriethoxysilane), treating them with a 1% (v/v) monomer aqueous solution. The fibers were labeled with a dansyl-sulfonamide conjugate by reaction of acetonitrile solutions of dansyl chloride with the amine groups immobilized on the glass fiber surface. Interactions of the labeled coating polymer with solvents of different polarities were estimated by measurements of the fluorescence band shifts of the label. It was found that for aprotic solvents, the solvent dipolar coupling relaxation mechanism is dominated by thermodynamic interactions of the solvent with the polymer matrix, while for protic solvents this mechanism is dominated by specific interactions between solvent molecules and the excited state of the chromophore. Different experimental excited-state dipole moments were obtained for nonpolar and polar solvents (* NP ϭ 7.2 Ϯ 1.6 D, * P ϭ 11.9 Ϯ 1.5 D). Using the AM1 method, excited-state dipole moments for the first and second singlets were calculated and it was concluded that * NP Ϸ ͗* 2 1 ͘ 1/2 and * P Ϸ ͗* 2 2 ͘ 1/2 . Accordingly, neither the glass support nor the coating polar influence the excited-state properties of dansyl. The temperature dependence of dansyl emission allows the determination of the relaxation temperature of the coating polymer, which was estimated as 175 K for the coating used.
E-glass fibers were silanized using a 1% (v/v) aqueous solution of ␥-aminopropyltriethoxysilane (... more E-glass fibers were silanized using a 1% (v/v) aqueous solution of ␥-aminopropyltriethoxysilane (APES). Pyrene-sulfonamide conjugates were formed by reaction of 1-pyrenesulfonyl chloride (PSC) in acetonitrile (AcN), with the amine groups immobilized on the glass fiber surface. These pyrene-sulfonamide conjugates were used as fluorescence probes, being a relatively simple analytical method to study the coating microstructure of polyorganosiloxane layer on glass fibers. The first aim of this work was to estimate possible interactions of the polyaminosiloxane coating with surrounding molecules of different solvents (solvent accessibility to the chromophore). For this study, the fluorescence response of pyrene-sulfonamide dye (PSA) was correlated with solvent polarity parameters. It was concluded that all the studied solvents were accessible to the chromophore, and they can gather in two groups, depending on their ability to swell the poliorganosiloxane layer. The second objective was to estimate the rigidity of the coating polymer from the temperature dependence of PSA emission. At about 180 K, a sudden change in the behavior of different photophysical parameters of PSA were observed. This phenomenon was interpreted as a density change in the polyaminosiloxane attached to the glass fibers.
Commercial glass ®bres were calcinated for the removal of organic matter, activated for surface s... more Commercial glass ®bres were calcinated for the removal of organic matter, activated for surface silanol regeneration and silanizated with -aminopropyltri-ethoxysilane. Two different activation methods were used: re¯ux with neutral water and re¯ux with 10% HCl aqueous solution. Acid treatments hydrolize Si±O bonds, greatly changing the composition of the glass and regenerating silanol groups, some of them being of intraglobular nature. Water treatment does not change appreciably the glass composition, but its surface free energy value is the lowest. The degree of silanization is the greatest for the acid activated samples and the lowest for the water activated one. The polar contribution to the total surface free energy, once the samples are silanizated, is the highest for the ®bres activated with boiling water whilst the dispersion component is about the same for all of them. SEM observations indicate that for the greatest degree of coating, debonding of the ®laments may induce a peeling-out fractural mechanism. # 1999 Elsevier Science S.A. All rights reserved. es (A.J. Aznar) 0924-0136/99/$ ± see front matter # 1999 Elsevier Science S.A. All rights reserved. PII: S 0 9 2 4 -0 1 3 6 ( 9 9 ) 0 0 2 1 2 -5
Aqueous solutions of three silanes to cover silica microfibres were used, being the 3-aminopropyl... more Aqueous solutions of three silanes to cover silica microfibres were used, being the 3-aminopropyltriethoxysilane (APTES) and the 3-aminopropylmethyldiethoxysilane (APDES) the reagents for preparing them at the proportion of (APTES/APDES): 1/0, 1/1 and 0/1. The 1-pyrene sulphonyl chloride (PSC) fluorescent moiety was chemically attached to the silanised substrate via the sulphonamide formation. The hydrolytic degradation phenomenon of the silane coupling layer was studied as a function of: (i) temperature, (ii) coating layer type and (iii) pH (4, 7 and 10). The hydrolytic damage in the coupling region of the silica microfibres composite materials occurs under an equilibrium process. It was obtained the activation energies (E a ) for the hydrolytic damage considering the rate to reach the equilibrium. The values of E a depended on the type of coating and on the pH. As a consequence, the rate of hydrolytic damage could be related to the proportion of Si silane -O-Si silane , while the OH − groups were thought to catalyse the reaction.
The fluorescence response of the dansyl chromophore has been used to study the kinetic of epoxy c... more The fluorescence response of the dansyl chromophore has been used to study the kinetic of epoxy curing processes. With this new method, comparison between the curing at the interface of a glass fiber/epoxy and in the epoxy bulk of a composite material was studied. The effect of two glass fiber surface treatments was investigated. Commercial E-glass fibers were surface coated with 3-aminopropyltriethoxysilane (APTES) and 3-aminopropylmethyldiethoxysilane (APDES). Fluorimetry (using fluorescent labels) and FT-NIR (Fourier transformed infrared spectroscopy in the near range) techniques were used to monitor the curing process in these composite materials. From the analysis of the data obtained, different simple kinetic models were discussed and apparent activation energies were obtained. Furthermore, from those techniques the respective results were compared to obtain complementary information. Independently of the sample and the technique used for the kinetic analysis, no variation of the activation energy of the epoxy curing reaction was found, which suggests that there are no changes in the mechanism of the reaction along the process. Fluorescence from dansyl located at the glass fiber/epoxy interface reflected that the kind of reinforcement treatment clearly affects the epoxy curing process exactly in that region. However, when analytical response comes from the whole system the mechanism of the reaction does not seem to change with the silane coating used although is quite different in comparison with the process at the interface.
Journal of Macromolecular Science, Part B- Physics, 2001
Modified glass fibers with three different amino silanes-(1) 3aminopropyltriethoxysilane (APTES),... more Modified glass fibers with three different amino silanes-(1) 3aminopropyltriethoxysilane (APTES), (2) 3-aminopropylmethyldiethoxysilane (APDES), and (3) 3-aminopropyldimethylethoxysilane (APMES)-were labeled with 5-dimethylaminonaphthalene-1-sulfonylchloride (DNS), and its fluorescence was followed as a function of curing time for two epoxide formulations (TRIEPOX-LM, Gairesa, Spain, and diglycidyl ester bisphenol Aethylenediamine), as well as a function of water uptake. It was demonstrated that the fluorescence response from fluorophores directly attached to the coupling region in glass fibers/epoxy composites is a very sensible method for nondestructive and "in situ" monitoring of any changes that appear at the interphase (rigidity and solvent accessibility). In addition, fluorescence from a dansyl label shows more rigidity when APMES is used as the coupling agent. This suggests that the greater the cross-linking degree at the coupling region, the smaller the epoxy chain interdiffusion. Finally, the water uptake process in glass fiber/epoxy composites can be divided into two steps; the first step corresponds to the diffusion of water to the coupling region, and the second step corresponds to the hydrolysis of siloxane bonds in the interphase. Both steps are dependent on the surface treatment of the glass fibers.
The cure process of an epoxy-amine system was studied in composite materials based on an epoxy po... more The cure process of an epoxy-amine system was studied in composite materials based on an epoxy polymer matrix filled with silica particles. FT-NIR and Fluorimetry (based on the use of fluorescent labels) were used as analytical techniques. In order to study the effect of the structure of the interphase, the silica particles were surface coated with two different silanes: 3-aminopropyltriethoxysilane and 3-aminopropylmethyldiethoxysilane. 1-pyrene-sulfonylchloride was chemically bonded to: (i) the coated silica particles and (ii) to the epoxy polymer matrix, using its fluorescence response to independently monitor the epoxy curing at the interface region and in the bulk respectively. The cure process was followed at different temperatures to subsequently study its kinetics either by fluorescence or by FT-NIR. An extent of reaction in terms of integrated fluorescence intensity was defined and the subsequent kinetic analysis allowed us to calculate apparent activation energies of the process. Comparing the curing reaction in the polymer bulk and at the interface it could be concluded that the epoxy curing at the interface proceeded faster but only during the first stages of the reaction. This result was attributed to a higher local concentration of amino groups at the interface. Finally, a comparison between FTIR and fluorescence results showed that both techniques provide complementary information about the curing reaction. q
The analysis of the fluorescent response from the dansyl moiety as a function of temperature has ... more The analysis of the fluorescent response from the dansyl moiety as a function of temperature has been used to estimate the thermal transitions in silica particle/epoxy-based composite materials. Silica particles were surface-coated with 3-aminopropyltriethoxysilane (APTES) and 3-aminopropylmethyldiethoxysilane (APDES). 5-Dimethylamino-1-naphtalenesulfonyl chloride (DNS) and 5-dimethylaminonaphthalene-1-(2-aminoehyl)) sulfonamide (DNS-EDA) were selectively attached to the silanized silica particles and to the epoxy matrix respectively. The fluorescence results, interpreted in terms of the model of interpenetrating polymer networks, suggest that (i) independent of the silane coating, the interfacial region is slightly more rigid and heterogeneous than the epoxy bulk and (ii) the interface generated with APTES seems to be more flexible than that obtained with APDES.
Glass fibers have been treated with y-aminopropyl-triethoxysilane (APES) through different silani... more Glass fibers have been treated with y-aminopropyl-triethoxysilane (APES) through different silanizating procedures, which include APES aqueous solutions and APES vapor adsorption.
... Posteriormente, el polímero obtenido se mantuvo a vacío a 60 ºC durante 24 h con objeto de se... more ... Posteriormente, el polímero obtenido se mantuvo a vacío a 60 ºC durante 24 h con objeto de secarlo y obtener un alto grado de polimerización. 2.3. Técnicas instrumentales ... 39 Núm. 3 Mayo-junio 2000 J. GONZáLEZ-BENITO, AJ AZNAR, A. MAÇANITA, J. BASELGA 3.1. PSA ...
The adsorption isotherm of methylene blue (MB) on sepiolite gels is of the Langmuir type, indicat... more The adsorption isotherm of methylene blue (MB) on sepiolite gels is of the Langmuir type, indicating a great affinity of the MB towards the sepiolite; the adsorption is quantitative up to adsorption of MB of 0.1 mmol/g sepiolite. The differences observed in the absorption spectrum in the region 500-650 nm for different MB Ioadings are interpreted in terms of aggregation of MB molecules on the sepiolite surface with the formation of MB dimers, trimers and higher aggregates. The progressive coverage of the sepiolite surface by MB produces a sharp decrease in the viscosity of the gels, and the suspension becomes peptized for an MB loading of 0.21 mmol/g which corresponds to the adsorption of MB dimers. These results indicate that MB avoids particle-to-particle interactions. The viscosity decrease is parallel to the perturbation of the Si-OH groups on the sepiolite surface as observed by IR spectroscopy, suggesting that these silanol groups can also play an important role in the theological behaviour of aqueous sepiolite dispersions.
We report in this paper the synthesis and characterization of a new class of biopolymer-clay nano... more We report in this paper the synthesis and characterization of a new class of biopolymer-clay nanocomposites based in the assembling of chitosan to sepiolite, which is a natural magnesium silicate showing a microfibrous texture. CHN and ICP/AES chemical analyses, XRD, FTIR spectroscopy, 13 C solid-state NMR, LT-SEM, and thermal analysis have been employed in the characterization of the resulting nanocomposites. The adsorption isotherm of chitosan on sepiolite in acidic medium reveals a significant coverage of the biopolymer at high equilibrium concentration values indicating a multilayer adsorption. The arrangement of chitosan chains on the surface of the silicate microfibers is discussed on the basis of physicochemical data obtained by application of the different techniques. The potentiometric response of this new type of bio-nanocomposites incorporated in carbon paste electrodes toward aqueous salt solutions was employed for the first time as a valuable technique for a rapid assessment of the ionexchange behaviors. Thermal behaviors and mechanical properties have been determined by DTA-TG and DMTA, respectively. As these materials are well-processed as self-supporting films, in view of their properties they show potential interest as membranes for different processes related to separation of ions and gases, as well as components in electrochemical devices (fuel-cell, potentiometric sensors).
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Papers by Antonio Aznar