INQUIMAE 12526

INSTITUTO DE QUIMICA, FISICA DE LOS MATERIALES, MEDIOAMBIENTE Y ENERGIA

Unidad Ejecutora - UE

congresos y reuniones científicas

Título:

Sol-gel process: effect of precursors on the microstructure and optical quality of silica hydrogels

Autor/es:

M. PERULLINI; M. JOBBÁGY; S. A. BILMES; I. L. TORRIANI; R. CANDAL

Lugar:

Buenos Aires, Argentina

Reunión:

Congreso; VI Reunión Anual de la Asociación Argentina de Cristalografía; 2010

Institución organizadora:

Asociacion Argentina de Cristalografia

Resumen:

Sol-gel process is an attractive route for the synthesis of new inorganic and hybrid materials ranging from ceramics to biocompatible soft inorganic gels. The properties of the final product can be tuned by controlling the solution parameters from which a sol and a particulate or polymeric network is formed. However, the close relationship between synthesis and ageing parameters, microstructure and macroscopic properties is still a challenge for the design of hybrid materials.
Silica based hydrogels are recognized as suitable matrices for building materials with biological activity, as well as precursors of optical materials such as lenses, waveguides and optical fibres. In all these cases, the optimization of optical quality must fulfil other needs, such as porosity, density, hardness and elasticity that require a fine control of the synthesis parameters and a detailed characterization of their structure in the 0.1 nm to 1 ìm range.
In this work we explore the microstructure-optical quality relationship of silica hydrogels prepared by hydrolysis of tetraethoxysilane (TEOS) in acid media, following the alcohol free procedure1. The analysis was focused on the role of several synthesis parameters: pH in the 2.5-7.1 range, total silica concentration (3.6 to 10.7%) and the effect of additives derived from silanes, such as glycidoxypropyltrimethoxysilane (GPTMS).
In all cases, the obtained hydrogel has an amorphous nanoporous monolithic structure. The optical properties of samples aged 24 h in phosphate buffer (pH 6.5, 0.1 M) were evaluated by measuring the attenuance at 400 and 500 nm. The microstructure characterization was performed at the LNLS SAXS2 beamline in Campinas, Brazil, working at ë=0.1488 nm, wave vector range: 0.09 nm-1 < q < 2.2 nm-1 and a sample stage in vacuum with mica windows (standard for liquids)2. Data analysis was performed with SASfit program from which we obtained the correlation distance of the aggregates, the fractal dimension and the typical size of the basic unit of formation of the structures as a function of synthesis parameters.
The log-log SAXS intensity plots are indicative of scattering from a mass fractal system, as is frequently observed for wet gels. The fractal dimension (D) is estimated from the power-law decrease of the SAXS intensity in a q-range between the characteristic lengths of the fractal structure (R) and the characteristic length of the primary particles composing the structure (a).
The values of the parameter a strongly depend on the pH of synthesis but are independent of the silica concentration whereas the values of D and R change significantly with silica concentration for a fixed pH. On the other hand, the difference observed in optical properties can be explained in terms of the fractal dimension and structure as both R and D decrease with increasing silica concentration indicating that smaller and less branched fractal structures produce lower light scattering in the visible range.
The values of the parameter a strongly depend on the pH of synthesis but are independent of the silica concentration whereas the values of D and R change significantly with silica concentration for a fixed pH. On the other hand, the difference observed in optical properties can be explained in terms of the fractal dimension and structure as both R and D decrease with increasing silica concentration indicating that smaller and less branched fractal structures produce lower light scattering in the visible range.
The log-log SAXS intensity plots are indicative of scattering from a mass fractal system, as is frequently observed for wet gels. The fractal dimension (D) is estimated from the power-law decrease of the SAXS intensity in a q-range between the characteristic lengths of the fractal structure (R) and the characteristic length of the primary particles composing the structure (a).
The values of the parameter a strongly depend on the pH of synthesis but are independent of the silica concentration whereas the values of D and R change significantly with silica concentration for a fixed pH. On the other hand, the difference observed in optical properties can be explained in terms of the fractal dimension and structure as both R and D decrease with increasing silica concentration indicating that smaller and less branched fractal structures produce lower light scattering in the visible range.
The values of the parameter a strongly depend on the pH of synthesis but are independent of the silica concentration whereas the values of D and R change significantly with silica concentration for a fixed pH. On the other hand, the difference observed in optical properties can be explained in terms of the fractal dimension and structure as both R and D decrease with increasing silica concentration indicating that smaller and less branched fractal structures produce lower light scattering in the visible range.
In all cases, the obtained hydrogel has an amorphous nanoporous monolithic structure. The optical properties of samples aged 24 h in phosphate buffer (pH 6.5, 0.1 M) were evaluated by measuring the attenuance at 400 and 500 nm. The microstructure characterization was performed at the LNLS SAXS2 beamline in Campinas, Brazil, working at ë=0.1488 nm, wave vector range: 0.09 nm-1 < q < 2.2 nm-1 and a sample stage in vacuum with mica windows (standard for liquids)2. Data analysis was performed with SASfit program from which we obtained the correlation distance of the aggregates, the fractal dimension and the typical size of the basic unit of formation of the structures as a function of synthesis parameters.
The log-log SAXS intensity plots are indicative of scattering from a mass fractal system, as is frequently observed for wet gels. The fractal dimension (D) is estimated from the power-law decrease of the SAXS intensity in a q-range between the characteristic lengths of the fractal structure (R) and the characteristic length of the primary particles composing the structure (a).
The values of the parameter a strongly depend on the pH of synthesis but are independent of the silica concentration whereas the values of D and R change significantly with silica concentration for a fixed pH. On the other hand, the difference observed in optical properties can be explained in terms of the fractal dimension and structure as both R and D decrease with increasing silica concentration indicating that smaller and less branched fractal structures produce lower light scattering in the visible range.
The values of the parameter a strongly depend on the pH of synthesis but are independent of the silica concentration whereas the values of D and R change significantly with silica concentration for a fixed pH. On the other hand, the difference observed in optical properties can be explained in terms of the fractal dimension and structure as both R and D decrease with increasing silica concentration indicating that smaller and less branched fractal structures produce lower light scattering in the visible range.
The log-log SAXS intensity plots are indicative of scattering from a mass fractal system, as is frequently observed for wet gels. The fractal dimension (D) is estimated from the power-law decrease of the SAXS intensity in a q-range between the characteristic lengths of the fractal structure (R) and the characteristic length of the primary particles composing the structure (a).
The values of the parameter a strongly depend on the pH of synthesis but are independent of the silica concentration whereas the values of D and R change significantly with silica concentration for a fixed pH. On the other hand, the difference observed in optical properties can be explained in terms of the fractal dimension and structure as both R and D decrease with increasing silica concentration indicating that smaller and less branched fractal structures produce lower light scattering in the visible range.
The values of the parameter a strongly depend on the pH of synthesis but are independent of the silica concentration whereas the values of D and R change significantly with silica concentration for a fixed pH. On the other hand, the difference observed in optical properties can be explained in terms of the fractal dimension and structure as both R and D decrease with increasing silica concentration indicating that smaller and less branched fractal structures produce lower light scattering in the visible range.
1. The analysis was focused on the role of several synthesis parameters: pH in the 2.5-7.1 range, total silica concentration (3.6 to 10.7%) and the effect of additives derived from silanes, such as glycidoxypropyltrimethoxysilane (GPTMS).
In all cases, the obtained hydrogel has an amorphous nanoporous monolithic structure. The optical properties of samples aged 24 h in phosphate buffer (pH 6.5, 0.1 M) were evaluated by measuring the attenuance at 400 and 500 nm. The microstructure characterization was performed at the LNLS SAXS2 beamline in Campinas, Brazil, working at ë=0.1488 nm, wave vector range: 0.09 nm-1 < q < 2.2 nm-1 and a sample stage in vacuum with mica windows (standard for liquids)2. Data analysis was performed with SASfit program from which we obtained the correlation distance of the aggregates, the fractal dimension and the typical size of the basic unit of formation of the structures as a function of synthesis parameters.
The log-log SAXS intensity plots are indicative of scattering from a mass fractal system, as is frequently observed for wet gels. The fractal dimension (D) is estimated from the power-law decrease of the SAXS intensity in a q-range between the characteristic lengths of the fractal structure (R) and the characteristic length of the primary particles composing the structure (a).
The values of the parameter a strongly depend on the pH of synthesis but are independent of the silica concentration whereas the values of D and R change significantly with silica concentration for a fixed pH. On the other hand, the difference observed in optical properties can be explained in terms of the fractal dimension and structure as both R and D decrease with increasing silica concentration indicating that smaller and less branched fractal structures produce lower light scattering in the visible range.
The values of the parameter a strongly depend on the pH of synthesis but are independent of the silica concentration whereas the values of D and R change significantly with silica concentration for a fixed pH. On the other hand, the difference observed in optical properties can be explained in terms of the fractal dimension and structure as both R and D decrease with increasing silica concentration indicating that smaller and less branched fractal structures produce lower light scattering in the visible range.
The log-log SAXS intensity plots are indicative of scattering from a mass fractal system, as is frequently observed for wet gels. The fractal dimension (D) is estimated from the power-law decrease of the SAXS intensity in a q-range between the characteristic lengths of the fractal structure (R) and the characteristic length of the primary particles composing the structure (a).
The values of the parameter a strongly depend on the pH of synthesis but are independent of the silica concentration whereas the values of D and R change significantly with silica concentration for a fixed pH. On the other hand, the difference observed in optical properties can be explained in terms of the fractal dimension and structure as both R and D decrease with increasing silica concentration indicating that smaller and less branched fractal structures produce lower light scattering in the visible range.
The values of the parameter a strongly depend on the pH of synthesis but are independent of the silica concentration whereas the values of D and R change significantly with silica concentration for a fixed pH. On the other hand, the difference observed in optical properties can be explained in terms of the fractal dimension and structure as both R and D decrease with increasing silica concentration indicating that smaller and less branched fractal structures produce lower light scattering in the visible range.
ë=0.1488 nm, wave vector range: 0.09 nm-1 < q < 2.2 nm-1 and a sample stage in vacuum with mica windows (standard for liquids)2. Data analysis was performed with SASfit program from which we obtained the correlation distance of the aggregates, the fractal dimension and the typical size of the basic unit of formation of the structures as a function of synthesis parameters.
The log-log SAXS intensity plots are indicative of scattering from a mass fractal system, as is frequently observed for wet gels. The fractal dimension (D) is estimated from the power-law decrease of the SAXS intensity in a q-range between the characteristic lengths of the fractal structure (R) and the characteristic length of the primary particles composing the structure (a).
The values of the parameter a strongly depend on the pH of synthesis but are independent of the silica concentration whereas the values of D and R change significantly with silica concentration for a fixed pH. On the other hand, the difference observed in optical properties can be explained in terms of the fractal dimension and structure as both R and D decrease with increasing silica concentration indicating that smaller and less branched fractal structures produce lower light scattering in the visible range.
The values of the parameter a strongly depend on the pH of synthesis but are independent of the silica concentration whereas the values of D and R change significantly with silica concentration for a fixed pH. On the other hand, the difference observed in optical properties can be explained in terms of the fractal dimension and structure as both R and D decrease with increasing silica concentration indicating that smaller and less branched fractal structures produce lower light scattering in the visible range.
D) is estimated from the power-law decrease of the SAXS intensity in a q-range between the characteristic lengths of the fractal structure (R) and the characteristic length of the primary particles composing the structure (a).
The values of the parameter a strongly depend on the pH of synthesis but are independent of the silica concentration whereas the values of D and R change significantly with silica concentration for a fixed pH. On the other hand, the difference observed in optical properties can be explained in terms of the fractal dimension and structure as both R and D decrease with increasing silica concentration indicating that smaller and less branched fractal structures produce lower light scattering in the visible range.a strongly depend on the pH of synthesis but are independent of the silica concentration whereas the values of D and R change significantly with silica concentration for a fixed pH. On the other hand, the difference observed in optical properties can be explained in terms of the fractal dimension and structure as both R and D decrease with increasing silica concentration indicating that smaller and less branched fractal structures produce lower light scattering in the visible range.