Influence of the pH and substrate immersion time on the adsorption of poly(o-ethoxyaniline) in self-assembled films

Abstract

Filmes ultrafinos de poli(o-etoxianilina)-POEA foram depositados sobre lâminas de quartzo pela técnica de automontagem a partir de soluções aquosas desse polímero em pH 3 e 5. A influência das condições de preparação sobre a quantidade de POEA adsorvida foi avaliada por meio de espectroscopia UV-Vis, microscopia de força atômica e voltametria cíclica. Verificou-se que em pH 5 a quantidade de POEA adsorvida é sempre maior que em pH 3, independentemente do tempo de imersão do substrato na solução polimérica. Imersões sucessivas do substrato na solução de POEA contribuíram para um aumento significativo da quantidade de polímero adsorvido. Quando as imersões foram realizadas em tempos longos o processo de adsorção atingiu um equilíbrio em cerca de 3 min. Por outro lado, se imersões sucessivas são feitas em curtos períodos de tempo, a quantidade de POEA nos filmes pode ser aumentada indefinidamente o que indica a existência de um processo de não-equilíbrio.Ultra-thin films of poly(o-ethoxyaniline)-POEA were deposited onto quartz slides by the selfassembly technique from aqueous solutions of this polymer in pH 3 and 5. The influence of the experimental conditions on the amount of POEA adsorbed was evaluated by UV-Vis spectroscopy, atomic force microscopy and cyclic voltammetry. It was observed that in pH 5 the amount of POEA adsorbed is always greater than that in pH 3, regardless the time of substrate immersion into the polymeric solution. Repeatedly immersions of quartz substrate into the POEA solutions contributed to an increase on the amount of polymer adsorbed. When long time immersions were made the adsorption process reached a maximum around 3 minutes. However, if repeatedly short time immersions were adopted the amount of POEA adsorbed could be increased indefinitely indicating the existence of a non-equilibrium process.Keywords: conducting polymers, poly(o-ethoxyaniline), self-assembled films, thin films IntroductionThe fabrication of ultra-thin films of conducting polymers using the self-assembly technique (SA) has become very popular in the last years.1 This technique is based on the spontaneous adsorption of molecules from solutions onto a solid substrate and it has been used for the deposition of mono and multilayer films from different classes of materials, including polyelectrolytes, conducting polymers, proteins, fullerenes, etc.2,3 Among the advantages offered by using SA technique on the preparation of ultra-thin films we can include the low cost of experimental apparatus, short-time intervals for film fabrication and the control over the film properties by manipulating the experimental conditions. 2,3 The films obtained present very low thickness (around tens to hundreds of angstrons), smoothness and exhibit structural organization at the molecular level.2,3 Prototypes of molecular electronic devices such as light emitting diodes, 4 gas and taste sensors 5,6 and biosensors 7 have already been produced by using the SA technique.After the first work proposing the use of SA technique for the fabricatio...

Study on the adsorption of poly(o-ethoxyaniline) nanostructured films using atomic force microscopy

“…The LbL technique allows film production within short time intervals, and therefore it is important to evaluate the kinetics of polymer adsorption in order to optimize the time of film fabrication. A few minutes are usually sufficient to form a stable and continuous layer of different kinds of materials [8,14]. Here, we shall describe the evolution of POEA film morphology using AFM.…”

Nanoscale conformational ordering in polyanilines investigated by SAXS and AFM

“…Reproducibility in the experimental results for any given type of sample or measurement is relatively poor, especially if one compares with the inorganic semiconductors. In the specific case of nanostructured films from polyanilines, several studies have shown that the adsorption mechanisms and the film properties are entirely altered by a mere change in pH [14]. Parent polyaniline (PANI) and its derivatives have been widely used mainly due to their remarkable electrochemical, optical, electrical and mechanical properties, and good environmental stability in the emeraldine base (EB) and emeraldine salt (ES) states [15,16].…”

Atomic Force Microscopy Study of Conductive Polymers

“…Other studies exist involving conducting polymer films using the static (contact) and dynamic modes (noncontact and tapping) [8,50,[57][58][59][60][61][62][63][64][65][66][67][68].…”