It appears very challenging to construct ultrathin films with a supramolecular architecture in which the individual organic molecules are macroscopically oriented and where the molecules with different functionalities can be incorporated into individual layers [1]. Layer-by-layer (LBL) assembly processes based on electrostatic or other molecular forces are an unique technique that presents a new approach to the formation of supramolecular architectures by adsorption of consecutively alternating polyelectrolytes [2]. The most substantial advantage of the LBL self-assembly is the quite accurately controlled average thickness of the polyelectrolytes layers, where the macroscopic properties of the molecular film can be controlled by the microscopic structure. Besides the technological interest for the use of LBL bilayers in biosensors and microelectronics (i.e. LED and displays), a number of issues for fundamental science are more exciting, namely the investigation of surface morphology, the kinetics of deposition and the ionic strength effects on the deposition of polyelectrolytes LBL layers. The stability of the film, the stoichiometry of multilayers and the better understanding of the film formation are under investigation [1-3].
A potential application of LBL technique could be the fabrication of homogenous ultrathin film of conjugated polymers. Molecular-level processing of conjugated polymers (i.e. polypyrrole, polyaniline, poly(phenylene vinylene), poly(o-anisidine)) by LBL technique was shown in literature [4]. Among conducting polymers, the polypyrrole and polyaniline class has received greater attention due to its environmental stability, ease in preparation, exciting electrochemical, optical and electrical properties and possible applications in rechargeable batteries, microelectronics devices, biosensors, and protective coating against corrosion and chemical sensors [5]. Recently, it was shown that polyaniline as well as polypyrrole with poly(styrene sulfonate) bilayers can be formed [4, 6]. The polyelectrolytes films are fabricated by alternate dipping in polyanion and polycation solutions and drying by the blowing of nitrogen gas after each successive deposition. The fabricated films, however, contains water and oxygen molecules. The water and gas molecules removal from conducting films causes a change in electrical and optical properties [7]. It could be interesting to see also if this phenomenon, in some way, affects the surface morphology by using an insitu scanning probe microscope, from atmospheric pressure down to 10-6 Torr.
Keeping this in mind, the aim of this manuscript is the fabrication of polystyrene sulphonate (PSS)/PANI and PSS/PPY and their characterization in terms of electrochemical and electrical conductivity. The building up of such multilayers films was characterized by the increment of adsorbed amount through UV-visible spectroscopy. The insitu surface investigation as a function of vacuum level of layer by layer films were performed in a high vacuum chamber, equipped with an atomic force microscopy and suitable for electrical characterizations. The chamber allowed establishing a relationship between the electrical behaviour and the morphological conditions of well characterized polyelectrolytes films.
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