کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
612172 880692 2007 9 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Influence of the Hofmeister series of anions on the molecular organization of positively ionized monolayers of a viologen derivative
موضوعات مرتبط
مهندسی و علوم پایه مهندسی شیمی شیمی کلوئیدی و سطحی
پیش نمایش صفحه اول مقاله
Influence of the Hofmeister series of anions on the molecular organization of positively ionized monolayers of a viologen derivative
چکیده انگلیسی

The effects of the Hofmeister series of ions are ubiquitous in chemistry and biology. In this paper specific ion effects on the surface behavior of a viologen dication, namely 1,1′1,1′-dioctadecyl-4,4′4,4′-bipyridilium, are shown. Surface pressure and surface potential vs area isotherms were obtained on aqueous subphases containing potassium salts with several representative counterions in the Hofmeister series (C6H5O3−7, SO2 −4, HPO2−4, Cl−, Br−, NO−3, I−, and ClO−4). The parameters obtained from the compression isotherms (area per molecule, phase transitions, Young modulus, initial surface potential, and variation of the surface potential upon compression) are dependent on the nature of the counterion, indicating ion specificity. Aqueous subphases containing C6H5O3−7, SO2−4, and HPO2−4 anions yield more expanded viologen monolayers and these anions do not effectively penetrate into the monolayer. Brewster angle microscopy was used to map the different phases of the viologen monolayers at the air–water interface. The Langmuir films were also characterized by UV–vis spectroscopy, with quantitative analysis of the reflection spectra supporting an organizational model in which the viologen chromophore undergoes a gradual transition to a more vertical position with respect to the water surface upon compression. A comparison of the tilt angles of the viologen on the different subphases indicates that anions that can more easily penetrate in the monolayer permit the viologen moieties to adopt a slightly more vertical position with respect to the water surface.

The influence of the Hofmeister series of anions on the surface behavior of a viologen derivative is analyzed. A different penetration ability of the anions into the positively charged viologen monolayer has been observed, together with a different orientation of the viologen chromophore upon the compression process depending on the subphase nature, revealing the existence of specific ion effects.Figure optionsDownload as PowerPoint slide

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Journal of Colloid and Interface Science - Volume 315, Issue 2, 15 November 2007, Pages 588–596
نویسندگان
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