What Factors Control the Structure of Silica Aerogels
نویسنده
چکیده
By manipulating polymerization conditions in solution precursors, it is possible to control the structure of silica aerogels. Porosity varies from grain-like to polymer-like. When produced from alkoxides, pH is the dominant factor that determines structure. Under strongly basic conditions (pH > 12) compact colloidal particles are observed. In the range pH = 8-12, particles of varying surface roughness result. In the neutral range, polymerization is self-limiting, producing polymers with the geometry of percolation clusters at threshold. Under acidic conditions, highly ramified branched polymers are realized. Using the concept of fractal geometry, different growth processes are identified that account for the observed structure. These processes include Eden growth (reaction-limited monomer-cluster aggregation) under basic conditions and the cluster-cluster analogue under acidic conditions. Kinetic percolation is postulated for the neutral regime.
منابع مشابه
Adsorption of Fluconazole Drug on Silica Aerogel by Immersion Method and Investigation of the Rate and Mechanism of Drug Release
In this study, adsorption of fluconazole on silica aerogel was performed successfully by the immersion method in the 1% solution of fluconazole-ethanol at the ambient condition and without using the supercritical method. The hydrophobic and hydrophilic silica aerogels were synthesized by the two-stage sol-gel method and dried at the ambient temperature. This method had most of drug loading at 2...
متن کاملIn-vitro study of Ketoprofen release from synthesized silica aerogels (as drug carriers) and evaluation of mathematical kinetic release models
Silica aerogels are porous and extremely lightweight nano-materials shows interesting properties. These materials, because of biocompatibility, non-harmful to the body and special physical characteristics such as large surface area and low density have great potential for use in a drug delivery system (DDS). The focus of this study is the evaluation of the effects of silica aerogels on improvin...
متن کاملPreparation of Silica Aerogels with Improved Mechanical Properties and Extremely Low Thermal Conductivities through Modified Sol-Gel Process
Reported silica aerogels have a thermal conductivity as low as 15 mW/mK. The fragility of silica aerogels, however, makes them impractical for structural applications. The purpose of the study is to improve the ductility of aerogels while retain the low thermal conductivity of silica aerogels. We have established a new synthesis route, a 3-step sol-gel processing method. The method provides bet...
متن کاملIn-vitro study of Ketoprofen release from synthesized silica aerogels (as drug carriers) and evaluation of mathematical kinetic release models
Silica aerogels are porous and extremely lightweight nano-materials shows interesting properties. These materials, because of biocompatibility, non-harmful to the body and special physical characteristics such as large surface area and low density have great potential for use in a drug delivery system (DDS). The focus of this study is the evaluation of the effects of silica aerogels on improvin...
متن کاملAdsorption and Desorption Isotherms Of Desiccants for Dehumidification Applications: Silica Aerogels and Silica Aerogel Coatings on Metal Foams
Silica aerogels are frequently employed as solid desiccants in enthalpy wheels for dehumidifying the supply stream in air-conditioning systems. These desiccant materials possess good moisture adsorption and desorption characteristics due to their porous structure. Analysis of adsorption and desorption isotherms is critical for performance characterization and is often performed to evaluate the ...
متن کامل