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Los efectos de iones no aditivos impulsan el colapso y la hinchazón de los polímeros termorresponsivos en el agua

Ellen E Bruce¹, Pho T Bui², Bradley A Rogers²

¹Eduard-Zintl-Institut für Anorganische und Physikalische Chemie , Technische Universität Darmstadt , Alarich-Weiss-Straße 10 , D-64287 Darmstadt , Germany.

Journal of the American Chemical Society

|March 29, 2019

Resumen

Las mezclas de aniones fuertemente y débilmente hidratados afectan a las soluciones poliméricas de manera no aditiva. La competencia iónica influye en la temperatura crítica inferior de la solución (LCST) del poli (N-isopropilacrilamida) al alterar la hidratación y las interacciones de la interfaz.

Área de la Ciencia:

Química Física
Ciencia de los Polímeros
Química de la solución

Sus antecedentes:

El comportamiento de las soluciones poliméricas es sensible a la presencia de iones.
La serie Hofmeister describe los efectos específicos de iones en la solubilidad de proteínas y polímeros.
Comprender los efectos de la mezcla iónica es crucial para controlar las propiedades de la solución de polímero.

Objetivo del estudio:

Investigar los efectos no aditivos de los aniones mixtos (sulfato y yoduro) en la temperatura crítica inferior de la solución (LCST) del poli (N-isopropilacrilamida) (PNiPAM).
Para aclarar los mecanismos moleculares detrás de estos efectos no aditivos utilizando métodos computacionales y experimentales.

Principales métodos:

Se emplearon simulaciones de dinámica molecular (DM) para modelar las interacciones de iones y polímeros.
Se utilizó la espectroscopia de frecuencia de suma vibratoria (VSFS) para sondear la interfaz polímero/agua.
Se realizaron experimentos con concentraciones fijas de sulfato de sodio (Na2SO4) y variables de yoduro de sodio (NaI).

Principales resultados:

A bajas concentraciones de NaI, los cationes Na+ se asocian preferentemente con los aniones SO42- fuertemente hidratados, dejando a los aniones I- más hidratados.
En concentraciones más altas de NaI, los aniones SO4 ((2-) compiten efectivamente, forzando a los aniones I hacia la interfaz PNiPAM/agua.
Estas interacciones entre la hidratación y la interfaz conducen a efectos no aditivos en el PNiPAM LCST.

Conclusiones:

El LCST de PNiPAM en soluciones de sales mixtas está regulado por la interacción entre la hidratación iónica y las interacciones iónico-polímero.
Los hallazgos ponen de relieve la importancia de considerar los efectos de iones competidores en sistemas de soluciones complejas.
Este concepto es aplicable a diversas mezclas que involucran aniones fuertemente y débilmente hidratados de la serie Hofmeister.

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