The effect of humidity on the electrical susceptibility of mesoporous silicates formed from organosilane substitution on octylamine micelles
| Autor: | W.M. Sears, S.M. Hartzke, K.L. Hardy, J. T. Banks |
|---|---|
| Rok vydání: | 2004 |
| Předmět: |
Aqueous solution
Materials science Silicon Inorganic chemistry Metals and Alloys chemistry.chemical_element Humidity Conductivity Condensed Matter Physics Micelle Surfaces Coatings and Films Electronic Optical and Magnetic Materials chemistry.chemical_compound chemistry Chemical engineering Siloxane Materials Chemistry Electrical and Electronic Engineering Mesoporous material Instrumentation Water vapor |
| Zdroj: | Sensors and Actuators B: Chemical. 102:86-96 |
| ISSN: | 0925-4005 |
| DOI: | 10.1016/j.snb.2003.11.020 |
| Popis: | Mesoporous silicates are formed when organosilanes aggregate around octylamine micelles in aqueous solution, with the silicon part on the outside forming siloxane linkages that form the backbone of the structure. The octylamine is removed with an ethanol wash to produce a network of pores. By using different organosilanes the degree of hydrophilic interaction of the silicate, with humid air, can be varied. The silicates are then ground to a fine powder and placed between a co-axial tube capacitor arrangement connected to a standard impedance bridge. From this the frequency variation of the complex susceptibility is measured from 20 Hz to 1 MHz at three fixed humidity values of 11, 43, and 75%, using standard salt solutions. The best performing sample was (3-mercaptopropyl) trimethoxysilane (MPTMS) mixed with tetraethylorthosilicate (TEOS), where at 5 kHz the conductance was enhanced by a factor of 12 for the medium over the low humidity, and a factor of 4.5 for the high over the medium humidity conditions. The capacitance value is enhanced by factors of 4.4 and 1.6 respectively. This may mean that there is an optimal balance of hydrophobic versus hydrophilic interaction, as MPTMS is intermediate in these properties for the compounds tested. The absolute value of the conductivity is also important as higher levels are easier to measure. MPTMS performs best by this criteria as well, at about 4×10 −6 S/m for high humidity. The susceptibility of a mesoporous powder containing absorbed water vapor follows Jonscher’s universal dielectric response more closely then the standard Debye model. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|
Full Text from ScienceDirect