Estudo de filmes de Langmuir e Langmuir-Blodgett de aminas anfifílicas utilizando a espectroscopia SFG

Abstract

AgradecimentosPrimeiramente a Deus, por apresentar os melhores caminhos em minha vida, de tal forma que é possível descobrir o fascinante mundo que vivemos, mesmo com um mundo com tantas adversidades.Aos meus familiares, avós, tios e primos, incentivando nos meus estudos, desde o tempo que eu me dedicava a graduação. The study of the interaction of organic molecules with water is of great importance for many areas of science, such as the understanding of biological systems. A large diversity of studies in this area have been performed, however some aspects of the study of thin films of amphiphilic amines have not been satisfactorily clarified. This dissertation focuses on Langmuir films of Octadecylamine as a function of pH and ionic strength of the aqueous subphase, investigating the structure of the organic monolayer and its interaction with water at various degrees of ionization. Sum-Frequency Vibrational Spectroscopy (SFG spectroscopy), a nonlinear optical technique to study surfaces and interfaces, was used in order to investigate the molecular conformation of the Langmuir films, its degree of ionization and the structure of water interacting with the organic monolayer. The monolayer ionization could be monitored by the intensity of the NH 3 + group stretch mode, and it was found that it depends on the local pH at the interface, which in turn is changed by the monolayer ionization and is sensitive to the subphase ionic strength. Water interacts with the monolayer by H bonds with NH 2 /NH 3 + groups, forming a layer with a high degree of orientational order along the surface normal, but relatively disordered regarding the H-bonding network (like in the bulk liquid). The conformation of the alkyl chains depends on the monolayer ionization, being compact and all-trans at high pHs, but more expanded and disordered at low pHs. In addition, Langmuir-Blodgett (LB) films of Octadecylamine were fabricated to compare their structure on the solid substrate to those on the water surface.

Caracterização De Óleo Em Folha-De-Flandres Por Elipsometria

“…Monocamadas de Langmuir [10,11] consistem de filmes com espessura monomolecular que se formam na interface líquido-gás (usualmente água-ar). De forma resumida, um filme de Langmuir consiste de uma monocamada de um material anfifílico (molécula com uma parte polar, hidrofílica e uma parte apolar, hidrofóbica).…”

“…A explicação detalhada pode ser encontrada em [10,11]. A balança hidrofil utiliza o mesmo princípio, mas o esquema é o inverso.…”