Abstract This work presents the results obtained in the production of poly (vinyl alcohol) (PVA) nanofibers with different concentrations of polypyrrole (PPy) doped with dodecylbenzene sulfonic acid (DBSA) - PPy.DBSA. The morphology of the nanofibers was studied by scanning electron microscopy (SEM) technique. The nanofibers were deposited on interdigitated electrodes (IDEs) for direct current electrical characterization (DC) and tested as ammonia gas sensors. The results showed a rapid detection of ammonia gas for higher concentrations of PPy.DBSA and for several alternating cycles in atmospheric N2.

Abstract Carbon Nanotubes (CNTs) are materials of wide applicability, either due to their physical stability, rigidity of the structure and/or high electrical conductivity. These nanotubes can be manipulated using different techniques, as long as their idiosyncrasy and possible advantages of proper processing are known. One way to organize and manipulate this material is in the form of thin films, which despite the low solubility in organic solvents, when functionalized, the CNTs allow for satisfactory handling. In this work, we aimed to analyze the behavior of CNTs in an aqueous subphase, controlling the quality of the produced films. For that, it was observed the level of aggregation and rigidity of Langmuir films and carried out analyses of the monolayer reorganization and interaction of the mixture between CNTs and Stearic Acid. Quantitative estimations of the aforementioned features were done through an in-situ study that was performed using the Langmuir technique including analysis of isotherms, compressibility module, Gibbs interaction, and Brewster Angle Microscopy. In order to compare the monolayer after its removal from the Langmuir trough, UV-vis spectroscopy was carried out. The results showed that they form non-ideal mixtures, but they favor a better organized and less agglomerated film comparing to the pure CNT.

Fullerene is considered to be the third carbon allotrope after diamond and graphite. The study of fullerene derivatives has been growing due to their exceptional electron affinity. This work proposes th study of three different fullerene derivatives, being phenyl-C61-butyric acid methyl ester (PCBM), oligo {(phenyl-C61-butyric acid methyl ester)-alt-[1,4-bis(bromomethyl)-2,5-bis(octyloxy)benzene]} (OPCBMMB) and poly {[bispyrrolidino(phenyl-C61-butyric acid methyl ester)]-alt-[2,5-bis(octyloxy)benzene]} (PPCBMB), and their application as NH3 sensors. Experimental results showed that these materials have a reproducible response to NH3, with PCBM resulting in the highest observed current peak, followed by OPCBMMB and PPCBMB. These results imply that PCBM, OPCBMMB and PPCBMB can be used to produce NH3 sensors.

The supramolecular structure of organic thin films is a key factor in their optical and electrical properties and, consequently, in the technological applications involving organic electronic. Here, thin films of a perylene derivative, the bis butylimido perylene (BuPTCD), were produced by vacuum thermal evaporation (PVD, physical vapor deposition). The main objective is to investigate the supramolecular structure of the BuPTCD in these PVD films, which implies to control their thickness at nanometer scale and to determine their molecular organization, morphology at micro and nanometer scales and crystallinity. The ultraviolet-visible absorption reveals a uniform growth of the PVD films. The optical and atomic force microscopy images show a homogeneous surface of the film at micro and nanometer scales, respectively. The X-ray diffraction indicates that both powder and PVD film are in the crystalline form. Complementary, a preferential head-on orientation of the molecules in the PVD films is determined via infrared absorption spectroscopy. Besides, the annealing process (200oC) did not affect the molecular organization of the PVD films, revealing a thermal stability of the BuPTCD molecules within the PVD films. Through DC electrical measurements, an electrical conductivity of 7.45x10-10 S/m was determined for BuPTCD PVD films onto Au interdigitated electrodes (IDE-structured devices), which can be enhanced, under illumination, by two orders of magnitude (photoconductivity effect). As proof-of-concept, the IDE-structured devices are tested as gas sensor for trifluoroacetic acid.

A study is reported on Langmuir and Langmuir-Blodgett (LB) films obtained by adding different percentages of stearic acid (SA) to poly(3-octylhiophene) (P3OT). Surface pressure - mean molecular area (π - A) isotherms, ultraviolet-visible (UV-Vis) absorption spectrum, atomic force microscope (AFM) and dc electrical measurements have been used for characterization. From π - A isotherms, the area per monomer for condensed films (of SA) increased according to P3OT amount. Good transfer ratios were obtained for LB deposition from P3OT/SA films with higher percentage of SA. LB films revealed linear growth as monitored by UV-Vis absorption spectra. Electrical characterization showed higher conductivity for LB film with 54 wt.% of SA. AFM images of the same film revealed high roughness and presence of large size agglomerates. Finally, interdigitated electrodes (IDE) coated with P3OT/SA LB films showed to be sensitive to the presence of volatile organic compounds.