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La carga electrostática de las partículas hidrófilas debido a la adsorción de agua
Rubia F Gouveia1, Fernando Galembeck
1Institute of Chemistry, University of Campinas-UNICAMP, P.O. Box 6154, 13083-970 Campinas, SP, Brazil.
Journal of the American Chemical Society
|July 30, 2009
Resumen
La adsorción de agua atmosférica altera la carga superficial de las películas de sílice y fosfato de aluminio. Este proceso implica la partición de los iones hidroxilo e hidrógeno, cambiando el potencial electrostático sin inyección de carga externa.
Área de la Ciencia:
- Ciencia de los materiales Ciencia de los materiales.
- Química de las superficies.
- La electrostática es la electrostática.
Sus antecedentes:
- Las películas de sílice no cristalina y fosfato de aluminio exhiben propiedades superficiales complejas.
- La comprensión de la dinámica de carga en los materiales dieléctricos es crucial para diversas aplicaciones.
- El papel de los factores atmosféricos en la modificación de la carga superficial no está completamente aclarado.
Objetivo del estudio:
- Investigar la influencia de la humedad relativa en el potencial electrostático de las películas de sílice no cristalina y fosfato de aluminio.
- Determinar los mecanismos responsables de los cambios en la carga superficial.
- Para verificar la hipótesis de que la adsorción de agua atmosférica impulsa el particionamiento de la carga.
Principales métodos:
- Se empleó la microscopía de fuerza de Kelvin para medir patrones de potencial electrostático.
- Las mediciones se llevaron a cabo en películas delgadas de sílice no cristalina y partículas de fosfato de aluminio.
- Los experimentos se llevaron a cabo en un entorno electricamente blindado y conectado a tierra bajo humedad relativa controlada.
Principales resultados:
- Se observaron patrones complejos e irreversibles de potenciales electrostáticos.
- El potencial adyacente a las superficies de partículas fue consistentemente negativo.
- Se detectaron gradientes potenciales significativos superiores a +/- 10 MV/m en paralelo a la superficie de la película.
- La evidencia sugiere que la adsorción de agua conduce a la partición de iones OH ((-) y H ((+)).
Conclusiones:
- La atmósfera actúa como fuente y sumidero de cargas electrostáticas en estos materiales dieléctricos.
- La adsorción de agua y la posterior partición de iones son los principales impulsores de la modificación de la carga superficial.
- Los mecanismos de inyección de carga externa (contacto, triboquímica, electroquímica) no son necesarios para los cambios de estado de carga en estos sólidos hidrófilos.
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