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Capas bidimensionales de agua y hielo: estudios de difracción de neutrones a 278, 263 y 20 k
Christoph Janiak1, Tobias G Scharmann, Sax A Mason
1Institut für Anorganische und Analytische Chemie, Universität Freiburg, Albertstrasse 21, D-79104 Freiburg, Germany. janiak@uni-freiburg.de
Journal of the American Chemical Society
|November 21, 2002
Resumen
La difracción de neutrones revela estructuras de hielo 2D únicas en los nanospacios, que difieren del hielo a granel. Estas capas de hielo confinadas exhiben nuevas estructuras de anillos y transiciones de fase a temperaturas específicas.
Área de la Ciencia:
- Ciencia de los materiales Ciencia de los materiales.
- Física de la materia condensada Física de la materia condensada
- Química Física es la química física.
Sus antecedentes:
- Comprender el comportamiento del agua bajo confinamiento es crucial para varios campos científicos.
- El agua a granel y el hielo exhiben estructuras cristalinas bien definidas, pero el agua confinada puede formar nuevas fases.
- El nanoconfinamiento altera significativamente las redes de enlace de hidrógeno y el comportamiento de fase del agua.
Objetivo del estudio:
- Para aclarar las características estructurales de dos dimensiones (2D) de agua y hielo confinado dentro de un nanospacio orgánico.
- Para investigar las transiciones de fase de capas 2D de agua/hielo a diferentes temperaturas.
- Para comparar las estructuras de hielo 2D observadas con las de hielo a granel y otras polimorfas de hielo 2D.
Principales métodos:
- La difracción de neutrones se empleó para determinar las estructuras a nivel atómico de agua y hielo confinados.
- Se realizaron estudios termoquímicos para identificar los puntos de transición de fase.
- Los experimentos utilizaron óxido de deuterio (D2O) confinado dentro de un nanospacio orgánico en forma de hendidura.
Principales resultados:
- Se identificaron dos fases de hielo 2D distintas: una con anillos de ocho miembros o segmentos de cadena plegada (a 263 K) y otra con anillos irregulares de doce miembros (a 20 K).
- Estas estructuras difieren significativamente de las redes de panal hexagonal típicas de otras formas de hielo 2D.
- Se observó una transición de fase líquido-sólido para las capas 2D D2O alrededor de 277 K, seguida de una transición sólido-sólido entre 263 K y 20 K.
- Las moléculas de agua en las estructuras de baja temperatura están coordinadas por dos o tres moléculas de agua vecinas.
Conclusiones:
- El agua y el hielo 2D confinados exhiben motivos estructurales únicos y comportamientos de fase distintos del agua/hielo a granel.
- Las transiciones de fase observadas resaltan la sensibilidad de la estructura del agua al nanoconfinamiento y la temperatura.
- La difracción de neutrones es una herramienta poderosa para caracterizar las estructuras de los sistemas confinados de agua y hielo.
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