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The interaction between poly( o -ethoxyaniline) (POEA) adsorbed onto solid substrates and humic substances (HS) and Cu 2+ ions has been investigated using UV–vis spectroscopy and atomic force microscopy (AFM). Both HS and Cu 2+ are able to dope POEA and change film morphology. This interaction was exploited in a sensor array made with nanostructured films of POEA, sulfonated lignin and HS, which could detect small concentrations of HS and Cu 2+ in water.

Atomic force spectroscopy (AFS) was used to measure interaction forces between the tip and nanostructured layers of poly(o-ethoxyaniline) (POEA) in pure water and CuSO4solutions. When the tip approach and retraction were carried out at low speeds, POEA chains could be physisorbed onto the Si3N4tip via nonspecific interactions. We conjecture that while detaching, POEA chains were stretched and the estimated chain lengths were consistent with the expected values from the measured POEA molecular weight. The effects from POEA doping could be investigated directly by performing AFS measurements in a liquid cell, with the POEA film exposed to liquids of distinct pH values. For pH ≥ 6.0, the force curves normally displayed an attractive region for POEA, but at lower pH values—where POEA is protonated—the repulsive double-layer forces dominated. Measurements in the liquid cell could be further exploited to investigate how the film morphology and the force curve are affected when impurities are deliberately introduced in the liquid. The shape of the force curves and the film morphology depended on the concentration of heavy metal in the liquid cell. AFS may therefore be used to study the interaction between film and analyte, with important implications for the understanding of mechanisms governing the sensing ability of taste sensors.

Layer-by-layer (LbL) films have been produced with poly(o-ethoxyaniline) (POEA), chitosan and chitosan-poly(methacrylic acid) (CS-PMAA) nanoparticles. Because the adsorption of LbL films depends on ionic interactions and H-bonding, optimized conditions had to be established for the growth of multilayer films. Unusually thick films were obtained for POEA and CS-PMAA, thus demonstrating the importance of using chitosan in the form of nanoparticles. These nanostructured films were deposited on chromium electrodes to form a sensor array (electronic tongue) based on impedance spectroscopy. This system was used to detect copper ions in aqueous solutions

Nanostructured films of poly( o -ethoxyaniline) (POEA) were studied by atomic force microscopy (AFM), which indicated a globular morphology for films containing one or more layers of POEA. Consistent with the nucleation and growth model for the adsorption process, the mean roughness and fractal dimension were found to increase with the time of adsorption and with the number of POEA layers in the initial stages of adsorption, reached maximum values and then decreased after 10 min of adsorption or after deposition of five POEA layers. Such behavior has been explained in terms of the decrease in the film irregularities, with voids being filled with polymeric material leading to smoother surfaces.

Ultra-thin films of poly(o-ethoxyaniline)-POEA were deposited onto quartz slides by the self-assembly 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.

Adsorbed layers of poly(o-ethoxyaniline) (POEA) produced with the layer-by-layer technique have been studied with atomic force spectroscopy (AFS). The films were prepared under different conditions (pH and solution concentration), and measurements were carried out in air and in a liquid cell. Both the doping level and fabrication conditions affect the POEA film morphology and the interactions of the atomic force microscopy (AFM) tip with the polymer molecules. For example, a mapping of the forces indicates the presence of conducting islands surrounded by a less conductive matrix in POEA and PANI films, with the conducting islands being characterized by the presence of double-layer forces. The conducting islands are further visualized via transmission electron microscopy (TEM) pictures. At pH 5, POEA appears completely dedoped where PANI can preserve some of its conducting character, and this is confirmed in electron paramagnetic resonance (EPR) measurements.

The self-assembly technique is employed for producing alternating ultra-thin films of lysozyme and poly(styrene sulfonate) (PSS). The influence of important parameters in the self-assembly process, namely immersion time, drying method, solution pH and ionic strength, on adsorption kinetics is investigated by ultraviolet (UV) spectroscopy. The absorbance increases rapidly in the initial stages of adsorption for all pHs studied, before reaching a plateau indicative of complete adsorption. Adsorption is considerably more effective when the proton concentration in the solution increases, which is attributed to the increase in the positive charge density within the protein molecules. Furthermore, UV absorbance increases linearly with the number of bilayers (lysozyme/PSS), indicating that a constant amount of material is being adsorbed at each deposition process. These results are highly promising as the self-assembled films are of great interest for biotechnology and molecular electronic applications