Fenómenos de transporte

 

Langmuir adsorption isotherms for different organic solutions of cholesterol

 

Isotermas de adsorción de Langmuir para diferentes soluciones orgánicas de colesterol

 

C. Barnaba^1,2*, M.A. García-Alvarado¹, I.G. Medina-Meza³ and J.M. Tejero-Andrade¹

 

¹ UNIDA, Instituto Tecnológico de Veracruz, Miguel Ángel de Quevedo 2779, Veracruz, Ver., 91897, México. *Corresponding author. E-mail: carlo.barnaba2@gmail.com

² Departamento de Procesos Tecnológicos e Industriales, Instituto Tecnológico y de Estudios Superiores de Occidente (ITESO), Periférico Sur Manuel Gómez Morín 8585, 45604 Tlaquepaque, Jal., México.

³ Center for Nonthermal Processing of Food, Washington State University, Pullman, WA 99164-6120, USA.

 

Recibido 7 de Noviembre de 2012
Aceptado 22 de Marzo de 2013

 

Abstract

In this work, the surfactant properties of cholesterol in organic solvents are studied. Hexane, iso-octane, iso-dodecane and toluene were used as the hydrophobic phase, and bidistilled water was used as the water phase. The captive bubbles were supported on a quartz surface and the axisymmetric drop shape analysis (ADSA) routine was performed to obtain contact angles (θ) and surface tension values (γ). Cholesterol was effective in reducing the interfacial tension of the oil/water system in all organic solvents. The appearance of turbidity associated with cholesterol crystallization is observed to be below concentration limits in all samples, because the liquid-liquid interface reduces the energy barrier required for nucleation. Experimental values of γ were adjusted with theoretical values obtained by applying Szyszkowski-Langmuir isotherm, showing good correlation between data. Finally, Szyszkowski-Langmuir constant (K_L) and Gibbs energy of absorption were calculated for the binary systems.

Keywords: cholesterol, ADSA, surface tension, captive bubble, Szyszkowski-Langmuir equation.

 

Resumen

En este trabajo se estudian las propiedades del colesterol como surfactante en soluciones orgánicas. Se utilizaron hexano, iso-octano, iso-dodecano y tolueno como fase hidrofóbica y agua bi-destilada como fase acuosa. Las burbujas cautivas se apoyan sobre una superficie de cuarzo y la rutina ADSA (Axisymmetric Drop Shape Analysis) se realizó para obtenea los angulos de contacto (θ) y los valores de tensión superficial (γ). El colesterol fue eficaz en la reducción de la tensión interfacial del sistema de aceite/agua en todos los disolventes orgánicos. En todas las muestras se observó una turbidez asociada a la cristalización del colesterol, por abajo de los límites de concentración, debido a la interfaz líquido-líquido que reduce la barrera de energía necesaria para la nucleación. Los valores experimentales de γ se ajustaron con los teóricos obtenidos aplicando la isoterma de Szyszkowski-Langmuir, mostrando una buena correlación. Por último, para los diferentes sistemas binarios se calcularon la constante de Szyszkowski-Langmuir (K_L) y la energía de adsorción de Gibbs.

Palabras clave: colesterol, ADSA, tensión superficial, burbujas cautivas, ecuación de Szyszkowski-Langmuir.

 

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