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Doctoral Thesis
DOI
Document
Author
Full name
Maria de Fátima Guerreiro da Silva Campos Raposo
Institute/School/College
Knowledge Area
Date of Defense
Published
São Carlos, 1999
Supervisor
Committee
Oliveira Junior, Osvaldo Novais de (President)
Figueiredo Neto, Antonio Martins
Lobo, Rui Filipe dos Reis Marmont
Tabak, Marcel
Ticianelli, Edson Antonio
Title in Portuguese
Processos de adsorção em filmes automontados de poli(o-metoxianilina): evidência de pontes de hidrogênio além da interação iônica
Keywords in Portuguese
Adsorção
Automontagem
Poli(o-metoxianilina)
Abstract in Portuguese
Neste trabalho foram estudados filmes automontados de poli(ometoxianilina) (POMA) e de poli(ácido vinilsulfônico) (PVS). Os filmes automontados de POMA/PVS podem crescer linearmente com o número de bicamadas sem que cada camada fique completamente adsorvida desde que o tempo de adsorção seja mantido constante. A cinética de adsorção de uma camada de POMA sobre diferentes substratos sólidos e sobre bicamadas de POMA/PVS já depositadas foi associada a dois processos: um muito rápido, de primeira ordem, e um mais lento controlado por difusão de Johnson-Mehl-Avrami, correspondendo, respectivamente, a nuc1eação e a um processo de crescimento, que foram confirmados por AFM. O processo de adsorção de POMA é favorecido quando já se encontram depositadas bicamadas de POMA/PVS. Os mecanismos de adsorção foram sugeridos a partir de isotermas de adsorção a diferentes temperaturas e da aplicação de modelos analíticos. A partir de medidas de dessorção termoestimulada foram identificados nos filmes de / POMA/PVS3 tipos de interação: forças de Van der Waals, uma interação com uma energia de ativação de 75 kJImoI que foi associada a pontes de hidrogênio e interações iônicas. As pontes de hidrogênio foram confirmadas por FTIR e adsorção a diferentes pHs. Finalmente, foi verificado que a condutividade destes filmes é fortemente dependente da atmosfera que os rodeia, característica que os toma muito interessantes para sensores de gases
Title in English
Adsorption processes for poly(o-methoxyaniline) in layer-by-layer films: evidence for H-bonding in addition to ionic interactions
Keywords in English
Adsorption
Layer-by-layer
Poly(o-methoxyaniline)
Abstract in English
Poly(o-methoxyaniline) (POMA) and poly(ethenesulfonic acid) (PVS)layer-by-Iayer f1lmswere studied. It has been demonstrated that POMA/PVS layer-by-Iayer films can grow linearly with the number of bilayers without complete layer formation as long as the adsorption interval time is maintained constant. The adsorption kinetics of the POMA layer onto solid substrates and onto already deposited POMA/PVS bilayers was found to take place in two steps: an initial, fast adsorption characteristic of a first -order kinetics, followed by a much slower process that is described by a Johnson-Mehl-Avrami function, respectively corresponding to nucleation and growth mechanisms, as demonstrated in AFM studies. The POMA adsorption process is favored when several alternated layers of POMA and PVS have already been deposited, because the surface area and the number of sites for adsorption increase. Adsorption mechanisms were proposed from adsorption isotherms fitted by analytical models, and from thermally stimulated desorption experiments in aqueous solutions 3 types of interaction were identified in POMA/PVS f1lms: van der Waals forces, an interaction with an activation energy for desorption of ca. +75 kJ/mole which was associated to H-bonding and an ionic interaction. Hydrogen bonding was confirmed by FTIR and adsorption at different pHs. Finally, it was demonstrated that the conductivity of POMA/PVS f1lms is strongly dependent of the surrounding atmosphere which makes these f1lms interesting for gas sensors
 
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Publishing Date
2014-11-20
 
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