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Master's Dissertation
DOI
10.11606/D.88.2010.tde-24032010-103946
Document
Author
Full name
Thiers Massami Uehara
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Carlos, 2010
Supervisor
Committee
Miranda, Paulo Barbeitas (President)
Borissevitch, Iouri
Misoguti, Lino
Title in Portuguese
Estudo de filmes de Langmuir e Langmuir-Blodgett de aminas anfifílicas utilizando a espectroscopia SFG
Keywords in Portuguese
Aminas de cadeias longas
Espectroscopia SFG
Espectroscopia vibracional
Estrutura da agua
Filmes de Langmuir
Filmes de Langmuir-Blodgett
Abstract in Portuguese
O estudo da interação de moléculas orgânicas com a água é de grande importância para diversas áreas das ciências, como por exemplo, na compreensão de sistemas biológicos. Uma elevada diversidade de estudos nesta área já foram realizados, no entanto, alguns aspectos do estudo de filmes finos de aminas anfifílicas não foram satisfatoriamente esclarecidos. Este trabalho aborda filmes de Langmuir de octadecilamina em função do pH e da força iônica de subfases aquosas, investigando a estrutura da monocamada orgânica e sua interação com a água, em diversos graus de ionização. Foi utilizada a Espectroscopia Vibracional por Geração de Soma de Frequências (Sum Frequency Generation - SFG), uma técnica que utiliza o princípio da óptica não-linear para estudar superfícies e interfaces, com o objetivo de investigar a conformação molecular dos filmes de Langmuir de aminas anfifílicas de cadeias longas, seu grau de ionização e a estrutura da água interagindo com a monocamada orgânica. Pôde-se acompanhar a ionização da monocamada em função do pH da subfase pela intensidade do modo de estiramento do grupo NH3+, e verificou-se que ela depende do pH local da interface, que por sua vez é alterado pela ionização da monocamada e é sensível à força iônica da subfase. A água interage com a monocamada via ligações de H com os grupos NH2/NH3+ e forma uma camada com alto grau de orientação perpendicular à superfície, mas relativamente desordenada do ponto de vista da rede de ligações de H (como na água líquida). A conformação das cadeias alquila depende da ionização do filme de Langmuir, sendo bastante compacta e ordenada a altos pHs (filme neutro) e mais expandida e desordenada a baixos pHs. Além disso, foram fabricados filmes de Langmuir-Blodgett (LB) de octadecilamina para comparar a estrutura dos filmes na superfície da água e em substratos sólidos.
Title in English
The interaction of water with Langmuir films of amphiphilic amines as a function of pH probed by Pi-A isotherms and SFG spectroscopy
Keywords in English
Langmuir films
Langmuir-Blodgett Monolayers
Long chain amines
SFG spectroscopy
Vibrational spectroscopy
Water structure
Abstract in English
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 non-linear 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 NH3+ 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 NH2/NH3+ 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
 
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Publishing Date
2010-03-26
 
WARNING: The material described below relates to works resulting from this thesis or dissertation. The contents of these works are the author's responsibility.
  • Silva, Heurison S., et al. Molecular Ordering in Layer-by-Layer Polyelectrolyte Films Studied by Sum-Frequency Vibrational Spectroscopy: The Effects of Drying Procedures [doi:10.1166/jnn.2008.125]. Journal of Nanoscience and Nanotechnology [online], 2008, vol. 8, p. 3399-3405.
  • BERGAMASKI, Kleber, et al. Characterization of alkanethiol self-assembled monolayer by SFG vibrational spectroscopy. In 2nd International symposium on advanced materials and nanostructures, São Carlos, SP, 2007. Book of Abstracts, 2nd International symposium on advanced materials and nanostructures., 2007. Resumo.
  • BERGAMASKI, Kleber, et al. Characterization of an alkanethiol self-assembled monolayer via sum-frequency vibrational spectroscopy. In V Encontro da SBPMat, Florianópolis, SC, 2006. Livro de resumos doV Encontro da SBPMat. : SBPMat, 2006. Resumo.
  • SILVA, Heurison da Sousa e, et al. Sum-frequency vibrational spectroscopy of self-assembled ultrathin organic layers. In The 7th Pacific Rim Conference on Lasers and Electro-optics, Seoul, 2007. Final program of the 7th Pacific Rim Conference on Lasers and Electro-optics.Seoul, Coréia do Sul, 2007. Resumo.
  • UEHARA, Thiers Massami, et al. Characterization of an alkanethiol self-assembled monolayervia sum-frequency vibrational spectroscopy. In VII Encontro da SBPMat, Guarujá, 2008. CD de resumos do VII Encontro da SBPMat., 2008. Resumo.
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