The control of porosity at nano scale in resorcinol formaldehyde carbon aerogels

Organic aerogels were synthesized by sol-gel polymerization of resorcinol (R) with formaldehyde (F) catalyzed by sodium carbonate (C) followed by vacuum drying. The influence of the resorcinol/sodium carbonate ratio (R/C) on the porous structure of the resultant aerogels was investigated. The nitrogen adsorption-desorption measurements show that the aerogels possess a well developed porous structure and mesoporosity was found to increase with increasing the R/C ratio. Carbon aerogels were obtained by carbonization of RF aerogels. The carbonization temperature impacts the microstructure of the aerogels by pore transformations during carbonization probably due to the formation of micropores and shrinkage of the gel structure. The results showed that a temperature of 1073 K is more effective in the development of the pore structure of the gel. Activated carbon aerogels were obtained from the CO2 activation of carbon aerogels. Activation results in an increase in the number of both micropores and mesopores, indicative of pore creation in the structure of the carbon. Activation at higher temperatures results in a higher degree of burn off and increases the pore volume and the surface area remarkably without change of the basic porous structure, pore size, and pore size distribution. separation [1, 2], electrode materials for energy storage [3-5], catalyst supports [6], packing materials for chromatography [7], host materials for gas storage[8], thermal and/or phonic insulators [9, 10], etc. For many advanced applications such as double layer supercapacitors the control of porosity at nano-level is very essential. Resorcinol formaldehyde (RF) aerogels are special type of highly cross-linked aromatic polymers with a high pore volume (0.25-1.25 cm3/g) [11], low density (0.06-0.103 g/cm3) [12], large specific surface area (400-1000 m2/g) [13], and mostly amorphous structure [14]. The morphology of RF aerogels can be modified as a function of different synthesis parameters. This characteristic allows the tailoring of the internal structure of these porous materials on a nanometer scale and makes them particularly well suited for a variety of applications. RF aerogels can be used as precursors for the preparation of porous carbons with similar appearance and macrostructure, but having slight differences in microstructure

Hydrophobic silica aerogel production at KEK

We present herein a characterization of a standard method used at the High Energy Accelerator Research Organization (KEK) to produce hydrophobic silica aerogels and expand this method to obtain a wide range of refractive index (n = 1.006-1.14). We describe in detail the entire production process and explain the methods used to measure the characteristic parameters of aerogels, namely the refractive index, transmittance, and density. We use a small-angle X-ray scattering (SAXS) technique to relate the transparency to the fine structure of aerogels.Comment: To be published in Nucl. Instr. and Meth. A, 9 pages, 10 figures, 1 tabl

Recent progress in silica aerogel Cherenkov radiator

In this paper, we present recent progress in the development of hydrophobic silica aerogel as a Cherenkov radiator. In addition to the conventional method, the recently developed pin-drying method for producing high-refractive-index aerogels with high transparency was studied in detail. Optical qualities and large tile handling for crack-free aerogels were investigated. Sufficient photons were detected from high-performance aerogels in a beam test.Comment: Proceedings of 2nd International Conference on Technology and Instrumentation in Particle Physics (TIPP 2011), to be published in Physics Procedia, 8 pages, 7 figure

Optimization of 4-Mercaptobenzoic Acid in SiO2-Ag Colloid Aerogel Using Surface-Enhanced Raman Spectroscopy

Aerogels have been studied as potential insulating and conducting materials, but little research has been conducted characterizing organic molecules in aerogel matrices using surface-enhanced Raman spectroscopy (SERS). In this study, SiO2-Ag colloid aerogels were used as enhanced surfaces for SERS. SERS spectra of 4-mercaptobenzoic acid (4-MCBA) adsorbed to acid- and base-catalyzed SiO2-Ag colloid aerogels were obtained. It was observed that acid-catalyzed silver sol gels with 4-MCBA mixed within the matrix provided SERS spectra with sharper and more enhanced peaks than the base-catalyzed silver sol gels

Ultra-Sensitive Piezo-Resistive Sensors Constructed with Reduced Graphene Oxide/Polyolefin Elastomer (RGO/POE) Nanofiber Aerogels.

Flexible wearable pressure sensors have received extensive attention in recent years because of the promising application potentials in health management, humanoid robots, and human machine interfaces. Among the many sensory performances, the high sensitivity is an essential requirement for the practical use of flexible sensors. Therefore, numerous research studies are devoted to improving the sensitivity of the flexible pressure sensors. The fiber assemblies are recognized as an ideal substrate for a highly sensitive piezoresistive sensor because its three-dimensional porous structure can be easily compressed and can provide high interconnection possibilities of the conductive component. Moreover, it is expected to achieve high sensitivity by raising the porosity of the fiber assemblies. In this paper, the three-dimensional reduced graphene oxide/polyolefin elastomer (RGO/POE) nanofiber composite aerogels were prepared by chemical reducing the graphene oxide (GO)/POE nanofiber composite aerogels, which were obtained by freeze drying the mixture of the GO aqueous solution and the POE nanofiber suspension. It was found that the volumetric shrinkage of thermoplastic POE nanofibers during the reduction process enhanced the compression mechanical strength of the composite aerogel, while decreasing its sensitivity. Therefore, the composite aerogels with varying POE nanofiber usage were prepared to balance the sensitivity and working pressure range. The results indicated that the composite aerogel with POE nanofiber/RGO proportion of 3:3 was the optimal sample, which exhibits high sensitivity (ca. 223 kPa-1) and working pressure ranging from 0 to 17.7 kPa. In addition, the composite aerogel showed strong stability when it is either compressed with different frequencies or reversibly compressed and released 5000 times

Reinforced silica-carbon nanotube monolithic aerogels synthesised by rapid controlled gelation

This work introduces a new synthesis procedure for obtaining homogeneous silica hybrid aerogels with carbon nanotube contents up to 2.50 wt.%. The inclusion of nanotubes in the highly porous silica matrix was performed by a two-step sol–gel process, resulting in samples with densities below 80 mg/cm3. The structural analyses (N2 physisorption and SEM) revealed the hierarchical structure of the porous matrix formed by nanoparticles arranged in clusters of 100 and 300 nm in size, specific surface areas around 600 m2/g and porous volumes above 4.0 cm3/g. In addition, a relevant increase on the mechanical performance was found, and an increment of 50% for the compressive strength and 90% for the maximum deformation were measured by uniaxial compression. This reinforcement was possible thanks to the outstanding dispersion of the CNT within the silica matrix and the formation of Si–O–C bridges between nanotubes and silica matrix, as suggested by FTIR. Therefore, the original synthesis procedure introduced in this work allows the fabrication of highly porous hybrid materials loaded with carbon nanotubes homogeneously distributed in the space, which remain available for a variety of technological applications

The cluster model: A simulation of the aerogel structure as a hierarchically-ordered arrangement of randomly packed spheres

A new structural model based on the premises widely used for describing the structure of aerogels has been introduced. These structures have been described as an assemblage of randomly-packed spheres in several hierarchically-ordered levels. A new algorithm has been developed for constructing our models from these premises using computer simulation. Subsequently, several applications have been simulated to characterize real systems, obtaining textural parameters such as the specific surface area, specific porous volume or the apparent density of the systems, based on the Monte Carlo technique and on geometrical considerations. The object of these is to test the ability of the models to explain the structure of some real aerogels. This Cluster Model has also been applied as an initial approach to the study of the mechanical properties of aerogels. Results support the general conclusion that these models are useful for explaining the structure of aerogels.Ministerio de Ciencia y Tecnología MAT2002-00859Junta de Andalucía TEP 011