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Características estructurales en mezclas de etanol y agua reveladas por la anisotropía de fluorescencia en

G S Beddard, T Doust, J Hudales

|February 17, 2018

Resumen

La difusión rotacional molecular se desvía de la ecuación de Debye-Stokes-Einstein en las mezclas de etanol y agua. Este estudio revela que la composición del disolvente, no sólo la viscosidad, impacta los tiempos de relajación de rotación molecular.

Área de la Ciencia:

La fotofísica
Física y Química
Dinámica molecular

Sus antecedentes:

La excitación con luz polarizada crea una anisotropía de orientación molecular.
El movimiento de rotación molecular causa desintegración de anisotropía y despolarización de fluorescencia.
La teoría hidrodinámica típicamente predice las tasas de movimiento de rotación.

Objetivo del estudio:

Investigar las desviaciones de la ecuación de Debye-Stokes-Einstein (DSE) en la difusión rotacional molecular.
Determinar la influencia de la composición del disolvente en los tiempos de relajación rotacional.
Analizar el comportamiento de rotación en mezclas de etanol y agua.

Principales métodos:

Espectroscopia de picosegundos.
Utilizando el tinte violeta cresyl como una sonda.
Utilizando mediciones de despolarización por fluorescencia.

Principales resultados:

Se observaron desviaciones significativas del comportamiento DSE para el violeta de cresilo en mezclas de etanol y agua.
Se identificaron diferentes tiempos de relajación rotacional en soluciones con idéntica viscosidad pero diferentes composiciones.
Se demostró que las interacciones solvente-solute juegan un papel crucial.

Conclusiones:

La ecuación de Debye-Stokes-Einstein es insuficiente para explicar la difusión rotacional en todos los sistemas de disolventes.
La composición del disolvente tiene un impacto significativo en la dinámica de rotación molecular.
Los modelos propuestos anteriormente para mezclas de agua y etanol pueden racionalizar el comportamiento observado.

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