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Made available in DSpace on 2020-12-12T02:43:22Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-09-01 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) In this work, we employed impedance spectroscopy measurements to investigate the electrical properties of hybrid films obtained with the sol-gel process using 3-glycidoxypropyltrimethoxysilane (GPTMS) and tetraethylorthosilicate (TEOS) at different GPTMS/TEOS molar ratios and temperatures of thermal treatment. For the GPTMS/TEOS-derived samples with 1:1 composition, the DC conductivity (σdc) and charge carrier mobility (μdc) increased linearly with heat treatment temperature from 25 to 80 °C, while σdc increased from 3.2 to 22.4 nS/cm with a 7-fold increase in the GPTMS concentration. These results could be rationalized with the Miller-Abraham model using a charge carrier activation energy of 0.54 ± 0.03 eV. Using FTIR spectroscopy we demonstrated that the structural arrangement of the hybrid matrix involves epoxy ring opening, thus favoring proton conduction, which occurs as in the Grotthuss mechanism via hopping between nearest oxygen atoms of polymerized glycidoxypropyl groups. It is significant that electrical properties of organic/silica matrices can be predicted and tuned for tailored applications using the modeling presented here. Department of Physics Sao Paulo State University (UNESP) Institute of Geosciences and Exact Sciences Sao Carlos Institute of Physics University of Sao Paulo (USP), CP 369 Department of Physics Sao Paulo State University (UNESP) Institute of Geosciences and Exact Sciences FAPESP: 2011/18149-5 FAPESP: 2013/14262-7 CNPq: 427220/2018-1 CNPq: 444810/2014-5

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.

The self-doping mechanism for charge transport is investigated in layer-by-layer (LBL) films from two conducting polymers, namely poly( o -methoxyaniline) (POMA) and poly(3-thiophene acetic acid) (PTAA). The efficiency of charge intercalation, defined as the ratio between the charge and the mass change, is twice for the POMA/PTAA LBL film in comparison with a cast POMA film. This is attributed to differences in the diffusion-controlled charge and mass transport, where distinct ionic species participate in the LBL films, as demonstrated with experiments using a quartz crystal microbalance. The doping efficiency for LBL film is the same, i.e., 3.93 × 10 −4 and 3.56 × 10 −4 g/C for the Li + and (C 2 H 5 ) 4 N + doped films, and is different for the cast POMA film, i.e., 11.3 × 10 −4 for Li + and 6.45 × 10 −4 g/C for (C 2 H 5 ) 4 N + . Therefore, once no significant differences in the intercalation mechanism are observed when different cations, Li + or (C 2 H 5 ) 4 N + , are used with the LBL films, this indicates that the self-doping mechanism is controlled by the exchange of anions.

The temperature dependence has been investigated for the photoinduced birefringence in Langmuir–Blodgett (LB) films from the azocopolymer 4-[ N -ethyl- N -(2-hydroxyethyl)]amino-2′-chloro-4′-nitroazobenzene (MMA-DR13) mixed with cadmium stearate. The build-up and relaxation of the birefringence in the range from 20 to 296 K were fitted with a Kohlrausch–Williams–Watts (KWW) function, with a β -value of 0.78–0.98 for the build-up and 0.18–0.27 for the decay. This is consistent with a distribution of time constants for the kinetics of the birefringence processes. The maximum birefringence increased with increasing temperature up to 120 K because the free volume fluctuation also increased with temperature. Above 120 K, the birefringence decreased with temperature as thermal diffusion dominates. In the latter range of temperature, an Arrhenius behavior is inferred for both build-up and decay of birefringence. In each case two activation energies were obtained: 0.8 and 5 kJ/mol for the build-up and 10 and 30 kJ/mol for the decay. The energies for the build-up are much lower than those associated with motion of the polymer chain, which means that the dynamics is governed by the orientation of the chromophores. For the decay, local motion of lateral groups of the polymer chains becomes important as the activation energies are within the range of γ -relaxation energies.

Langmuir–Blodgett (LB) films from pure ytterbium bisphthalocyanine (YbPc 2 ) and mixtures of YbPc 2 and stearic acid have been produced, whose cyclic voltammetric response displays a redox activity strongly dependent on the scan rate and film thickness. Successive redox reactions are accompanied by color variations upon small changes in the electrode potential range which make these films promising for multi-color devices.

LB films have been fabricated by transferring poly(o-anisidine) (POA) monolayers from a pure water surface onto glass substrates using the conventional dipping method. The chemically synthesized poly(o-anisidine) consists of two fractions, one containing mainly octamers and another of high molecular weight (around 28000 g/mol). The low weight fraction forms condensed Langmuir monolayers which are anchored to the water surface through one single group, probably the metoxy-aniline, yielding an area per molecule of ca. 20 A2. The molecular configuration in the high-weight fraction monolayers appears to be such that one in each four or five segments of the polymer chain makes contact with the water. UV-visible spectra were obtained for the HW fraction LB films which were identical to those of POA in solution, changing from dark blue to green when the film is exposed to HCl vapour. Preliminary conductivity measurements were carried out on these LB films showing that the conductivity increases by three orders of magnitude upon exposure to HCl vapour.

The interactions between polyaniline (PANI) and mer-[RuCl 3 (PP)(py)] (PP= biphosphine, py= pyridine), Rupy, in cast films have been analyzed using cyclic voltammetry and the results are compared with those from Langmuir-Blodgett (LB) films. The mixed films were prepared from solutions containing 10 %, 30 %, 50 % in mol of Rupy. All cast films showed electroactivity, while for LB films an activity was observed only for the mixtures containing 10 % and 30 % of Rupy. The differences between cast and LB films are attributed to strong interactions in the LB films, which are absent in the cast films, probably owing to phase separation between Rupy and PANI aggregates. The order-induced color changes in the LB films are also absent in the cast films.

The adsorption process in layer-by-layer (LBL) films of poly(o-methoxyaniline) alternated with poly(vinyl sulfonic acid) is explained using the Avrami equation. This equation was used due to its mathematical simplicity and adequate description of experimental data in real polymer systems. The Avrami parameters are a convenient means to represent empirical data of crystallization, and if microscopic knowledge is available these parameters can also be associated with adsorption mechanisms. The growth of spherulites in the LBL films was studied as a function of time using atomic force microscopy and the data were used to estimate the number and radii of aggregates, from which the Avrami parameters were determined. We find that the adsorption mechanism may correspond to a tri dimensional, diffusion-controlled growth, with increasing nucleation rate, consistent with results from kinetics of adsorption.

We report an innovative experimental procedure to electrochemically synthesize modified polypyrrole (PPY) films, which consists in polymerizing pyrrole and an azo dye, viz. Brilliant Yellow (BY). The electrochemical polymerization of the composite PPY-BY films was carried out in an aqueous medium containing low concentrations of PY (7 mmol L -1 ) and the same molar ratio of BY. The resulting films were much thicker than those obtained by conventional electrochemical polymerization of unmodified PPY films on ITO substrates under the same experimental conditions. The thickness of the composite films was estimated to be ca 100 nm per each voltammetric cycle as compared to 5 nm from the unmodified PPY films. Furthermore, the voltammetric response of the PPY-BY films shows a stable and electroactive behavior.

Surface morphology changes induced by argon laser irradiation (514 nm) on disperse red 13 (DR13) films prepared by physical vapor deposition (PVD) were investigated. Atomic force microscopy was used to characterize the irradiated sample for different periods of irradiation. Needle-shape structures are observed which are attributed to the symmetry of DR13 molecules. The film becomes increasingly closely packed with the irradiation, with lower root mean square roughness for long exposure times. This is due to photoisomerization of DR13 molecules and probably heating of the sample, which can provide the required mobility for the molecular rearrangement. The rearrangement is such that voids in the film are filled in upon irradiating the sample, thus decreasing the film roughness and increasing the packing.

Electroactive films of iron tetrasulfonated phthalocyanine (FeTsPc) were assembled via the electrostatic layer-by-layer technique (LBL), in which FeTsPc layers were alternated with the polycationic poly(allylamine hydrochloride) (PAH). The multilayer formation was monitored via UV-Vis spectroscopy by measuring the increase in the Q Band of FeTsPc at 676 nm. Film thickness was estimated by profilometry as ca. 10 A per bilayer. Fourier transform infrared and UV-Vis absorption spectroscopy suggested specific interactions between FeTsPc and PAH. Cyclic voltammograms showed reproducible pairs of oxidation-reduction peaks at 0.92 mV and 0.70 mV, respectively, for a 50-bilayer PAH/FeTsPc film at 50 mV/s (vs Ag/AgNO 3 ).

Supramolecular structures of polyaniline (PANI) and vanadium oxide (V 2 O 5 ) have been assembled via the electrostatic layer-by-layer (LBL) technique. The films were characterized by vibrational analyses which indicated that the interactions between the two components lead to different properties in the films when compared to sol-gel films of the neat compounds. In particular, using surface enhanced Raman scattering we were able to probe LBL film properties that depend on which material comprises the topmost layer.

The complexes [RuCl 3 (dppb)(4-Mepy)](dppb=Ph 2 P(CH 2 ) 4 PPh 2 ) (PP) and [RuCl (etp)(2,2'-bipy)]Cl (etp=PhP(PPhCH 2 ) 2 (PPP) are chloroform soluble and amenable to form Langmuir-Blodgett (LB) films. The morphology of pure and mixed films of these complexes with stearic acid was analyzed using atomic force microscopy (AFM) in air. While complexation with stearic acid led to reasonably uniform LB films of (PP), films from PPP were extremely rough since stearic acid did not help in the transfer process owing to the lack of complexation of stearic acid and PPP molecules.

Langmuir-Blodgett (LB), Self-assembly (SA) and spin-coating films of a poly(p-phenylenevinylene) (PPV) precursor were prepared using the poly(xylylidenetetrahydrothiophenium chloride) (PTHT) precursor, where the counterion chloride was replaced by a long chain dodecylbenzenesulfonate (DBS) ion. The advantage of introducing DBS lies in the possibility of converting PPV films with a high conjugation length at 115 °C within only 3 min with enhanced optical properties. It is shown that LB and SA films with high thermal stability can be converted at even lower temperature (80 °C) than that for spin-coated films under atmospheric pressure conditions. In addition, the photoluminescence properties show the high quality and a well-resolved vibronic structure of the films.

Layer-by-layer thin films of sulfoniun poly(p-phenylene vinylene) (PPV) precursor have been processed using the long chain dodecylbenzenesulfonate (DBS) anion. Here we adopted the alternative approach consisting of the controlled substitution of the chloride counterion of a water-soluble PPV precursor by DBS. The internal layer structure of these films is therefore likely to be different from conventional layer-by-layer films, since DBS ions are expected to be incorporated into the PPV precursor chain. The main advantage of this novel procedure is that thermal conversion through the elimination of DBS may be realized at considerably lower temperatures (80-100 °C) in a few minutes, with enhanced optical properties. Using this new conversion procedure, the conjugation length can also be varied along the deposition direction by controlling the immersion time or DBS concentration in the film. This opens up a number of new possibilities to realize molecularly band-gap engineered structures such as asymmetric ladder type or V-type structures along the film.

We report on the optical storage characteristics of mixed Langmuir-Blodgett (LB) films from an azobenzene polymer (disperse red 19 1,4 diphenylmethane polyurethane, DR19-MDI) and cadmium stearate. This mixed LB film showed a great remaining birefringence (80%) due to its high rigidity.

Langmuir-Blodgett films of a poly(p-phenylene vinylene) (PPV) precursor were prepared using an amphiphilic precursor, where the counter-ion chloride was partially exchanged by a long chain dodecylbenzenesulfonate (DBS) ion. These LB-PPV films are strongly ordered along the dipping direction as demonstrated by linear dichroism experiments using linearly polarized optical absorption and emission. The consequence of this anisotropy is a strong circular dichroism (100 mdeg) in the π-π band and a circular polarization emission with an asymmetry factor g e =0.84.

We describe the optical properties of ytterbium bis-phthalocyanine (YbPc 2 ) dissolved in chloroform. A six-energy-level diagram is proposed to establish the population dynamics when laser pulses at 532nm are employed.

We report on the dynamic optical nonlinearities of a DR13-chloroform solution obtained with the Z-scan technique with pulse trains. Our results show that, upon resonant illumination, the DR13 solution presents a large accumulative nonlinear process, arising from thermal lensing effect.

Langmuir films of parent polypyrrole were investigated using surface pressure and surface potential isotherms, which showed that the films are not true monomolecular layers but multilayer stacks instead. The mean molecular area increased with decreasing subphase temperatures, but it did not change significantly when the compression speed was varied. These Langmuir films could be transferred onto solid substrates in the form of Langmuir-Blodgett (LB) films, with no need to mix the parent polypyrrole with builder materials such as cadmium stearate. Multilayer LB films were characterized by UV-vis, FTIR, surface potential and conductivity measurements.

The surface potential (VLB) of Langmuir-Blodgett (LB) films of pure emeraldine base polyaniline (PANi) and mixtures of PANi and cadmium stearate (CdSt) was investigated. Protonated PANi LB films produced from acidic subphases displayed higher VLB than the nonprotonated films transferred from moaolayers spread on pure water. For the mixed LB films, vlb increased with the amount of PANi, and it was always positive regardless of whether an odd or even number of layers were deposited, in contrast to the switch-over from positive to negative potential when going from an odd to an even number of layers for pure cadmium stearate LB films. The results have been analyzed by taking account of the negative contribution from the substrate/film interface.

X-ray irradiation is shown to affect electronic properties of polyaniline (PANi) in composite Langmuir-Blodgett (LB) films of PANi and cadmium stearate, in a similar way to acid doping. The time it takes for the shift in the UV-vis spectra, characteristic of PANi doping, increases linearly with the film thickness, thus indicating a surface-controlled process. The humidity of the environment under which the films are irradiated is also of extreme importance. No shift is observed under vacuum or under dry atmospheres of N 2 , O 2 and Ar. For humid environments the time for the shift decreases with increasing relative humidity.

Doping parent polyaniline (PANI) and its derivatives has been proven essential for obtaining stable Langmuir monolayers that are amenable to transfer onto solid substrates by the Langmuir-Blodgett (LB) technique. The doping process is generally carried out on the Langmuir trough, by spreading the polymer on an acidic subphase. The degree of doping affects the monolayer surface potential as the positive contribution from the double-layer increases with increasing protonation of the polymer molecules. One could then expect that the surface potential should increase with the acidic concentration in the subphase, but instead the potential diminishes for increasing concentration in the range 10−4 − 10.1 M. Interestingly, the results may be discussed in terms of the simple Gouy-Chapman theory, despite the complexity of the macromolecules involved.

The adsorption process of alternated, ultra-thin films of carboxymethylcellulose (CMC) and HCl-doped poly(o-ethoxyaniline) onto glass substrates via the self-assembly (SA) technique was studied using UV-vis spectroscopy. The kinetics of adsorption for the 1st, 2nd, 5th and 10th bilayers consists of a first order process for polymer concentrations from 10 −4 to 10 −2 M, with characteristic times of the order of 100 s, regardless of the solution pH in the range from 1 to 5. It was also observed that adsorption is faster and more effective for pH=1. This probably occurs because at lower pHs the polymer is more strongly doped which promotes an increase in the electrostatic attraction of the polymeric molecules to the substrate.

Monolayer characteristics of ytterbium and samarium phthalocyanines (YbPc 2 and SmPc 2 ) have been investigated by surface pressure and surface potential isotherms. It has been shown that the metal ion in the phthalocyanines can cause marked differences in the monolayer properties. The different monolayer characteristics of YbPc 2 and SmPc 2 may possibly be ascribed to either the extent of aggregation or the symmetry of the metallophthalocyanines.

Langmuir monolayers produced from a ferroelectric material, poly(vinylidenefluoride-trifluoroethylene (P(VDF-TrFE) copolymer (70:30) have been investigated through surface pressure and surface potential isotherms. The influence of spreading solvents, concentration of spreading solution and compression speed has been examined. In contrast to monolayers of traditional amphiphilic materials, the surface potential decreased upon film compression.

Thin films of parent polyaniline (PANi) were produced using the self-assembly (SA) technique, by immersing substrates into solutions of PANi in dimethylformamide and acetonitrile. The adsorbed polymer is undoped which means that the driving force for adsorption was probably H-bonding. Polymer adsorption depends on the polymer solution concentration, immersion time and washing procedures.

A systematic study on monolayer characteristics of parent polyaniline has shown that these characteristics are strongly affected by the processing methods. This has been done by investigating the influence of subphase temperature, pH, the addition of salt into the subphase, and of the volume spread on the monolayer characteristics.