Mixed Langmuir and Langmuir-Blodgett Films of a Proton Sponge and a Fatty Acid: Influence of the Subphase Nature on the Interactions between the Two Components
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- 作者：Marta Haro ; Pilar Cea ; Ignacio Gascó ; n ; Fé ; lix M. Royo ; M. Carmen Ló ; pez
- 刊名：Journal of Physical Chemistry B
- 出版年：2007
- 出版时间：March 22, 2007
- 年：2007
- 卷：111
- 期：11
- 页码：2845 - 2855
- 全文大小：1548K
- 年卷期：v.111,no.11(March 22, 2007)
- ISSN：1520-5207
文摘
The H+ acceptor activity of a proton sponge, namely, diphenyl bis(octadecylamino)phosphonium bromide,has been studied at the air-liquid interface using several subphases. Mixed Langmuir and Langmuir-Blodgett(LB) films containing the proton sponge and a fatty acid (behenic acid) in the whole composition range havebeen prepared. Surface pressure versus area per molecule isotherms were recorded and excess Gibbs energiesof mixing calculated. The existence of strong interactions between the proton sponge and the fatty acid isobserved when the subphase is either pure water or a NaOH aqueous solution. A stoichiometric 1:1 reactionbetween both molecules takes place at the air-water interface. This reaction has an efficiency close to 100%at high surface pressures, provided the majority anion present in the subphase is OH-. However, when themajority anion is another one, this complex is hardly formed. From the experimental results, we concludethat the acid-base reaction is highly dependent on the protonation state of the proton sponge at the air-liquid interface that is a function of the present counterion in the subphase. The floating films were alsotransferred onto solid substrates and characterized by means of IR spectroscopy, atomic force microscopy(AFM), and X-ray diffraction to investigate in more detail the complex formation. The interactions betweenthe complex (when formed) and the excess component have been studied in terms of the subphase nature. Itwas found that the complex is immiscible with the proton sponge, yielding films made of different domains.Nevertheless, the complex is miscible with the fatty acid when the subphase used is an alkaline solution,presumably due to electrostatic interactions between the carboxylate group of the acid and the complex.