Preparation, characterization and taste sensing properties of Langmuir-Blodgett Films from mixtures of polyaniline and a ruthenium complex

Langmuir-Blodgett (LB) films from a ruthenium complex, mer-[RuCl3(dppb)(py)] (dppb = PPh2(CH2)(4)PPh2; py = pyridine) (Rupy), and from mixtures with varied amounts of polyaniline (PANi) were fabricated. Molecular-level interactions between the two components are investigated by surface potential, dc conductivity and Raman spectroscopy measurements, particularly for the mixed film with 10% of Rupy. For the latter, the better miscibility led to an interaction with Rupy inducing a decrease in the conducting state of PANi, as observed in the Raman spectra and conductivity measurement. The interaction causes the final film properties to depend on the concentration of Rupy, and this was exploited to produce a sensor array made up of sensing units consisting of 11-layer LB films from pure PANi, pure Rupy and mixtures with 10 and 30% of Rupy. It is shown that the combination of only four non-specific sensing units allows one to distinguish the basic tastes detected by biological systems, viz. saltiness, sweetness, sourness and bitterness, at the muM level. (C) 2003 Elsevier B.V. Ltd. All rights reserved.

Soliton model for proton conductivity in Langmuir films

A soliton model for proton conductivity in Langmuir films is presented. The model contains three real scalar fields describing the hydrogen involved in the conduction, the hydrophilic head of the Langmuir film, and the water. Soliton solutions that describe proton motion along the hydrogen bonds are found. Under compression of the film, the distance between the minima of the proton potential and the strength of the hydrogen bonds between the film molecule and the water are changed. Such changes increase the probability of soliton creation. The model. presented allows proton conductivity data in Langmuir films to be explained. (C) 2001 Published by Elsevier B.V. B.V.

Morphological characterization of Langmuir-Blodgett films from polyaniline and a ruthenium complex (Rupy): influence of the relative concentration of Rupy

We report on the use of dynamic scale theory and fractal analyses in a study of the growth stages of Langmuir-Blodgett (LB) films of polyaniline and a neutral biphosphinic ruthenium complex, namely mer-[ RuCl3 (dppb)(py)] (dppb = 1,4-bis(diphenylphosphine) buthane, py = pyridine), Rupy. The LB films were deposited onto indium-tin-oxide substrates and characterized with atomic force microscopy. From the granular morphology exhibited by the films one could infer growth processes inside and outside the grains. Growth outside was found to follow the Kardar-Parisi-Zhang model, with fractal dimensions of about 2.7. As one would expect, inside the grains the morphology is close to a Euclidian surface with fractal dimension of about 2.

Surface morphology and molecular organization of lignins in Langmuir-Blodgett films

Atomic force microscopy (AFM) and Fourier transform infrared spectroscopy (FTIR) are used to investigate molecular organization in Langmuir-Blodgett (LB) films of two kinds of lignins. The lignins were extracted from sugar cane bagasse using distinct extraction processes and are referred to here as ethanol lignin (EL) and saccharification lignin (SAC). AFM images show that LB films from EL have a flat surface in comparison with those from SAC. For the latter, ellipsoidal aggregates are seen oriented perpendicularly to the substrate. This result is confirmed by a combination of transmission and reflection FTIR measurements, which also point to lignin aggregates preferentially oriented perpendicularly to the substrate. For LB films from EL, on the other hand, aggregates are preferentially oriented parallel to the substrate, again consistent with the flat surface observed in AFM data. The vibrational spectroscopy data for cast films from both lignins show random molecular organization, as one should expect.

Photoinduced birefringence at low temperatures in Langmuir-Blodgett films of azobenzene-functionalized copolymers

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 buildup and relaxation of the birefringence in the range from 20 to 296 K were fitted with a Kohlrausch-Williams-Watts (KWW) function, with a beta-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 gamma-relaxation energies. (C) 2003 Elsevier B.V. B.V. All rights reserved.

Langmuir-Blodgett films incorporating an ionic europium complex

Langmuir-Blodgett (LB) technique is a powerful tool to fabricate ultrathin films with highly ordered structures and controllable molecular array for efficient energy and electron transfer, allowing the construction of devices at molecular level. One method to obtain LB films consists in the mixture of classical film-forming molecules, for example Stearic Acid (SA) and functional metal complex. In this work NH(4)[Eu(bmdm)(4)], where the organic ligand bmdm is (butyl methoxy-dibenzoyl-methane) or (1-(4-methoxyphenyl)-3-(4-tert-butylphenyl)propane-1,3-dione) was used to build up Langmuir and LB films. Langmuir isotherms were obtained from (i) NH(4)[Eu(bmdm)(4)] complex and (ii) NH(4)[Eu(bmdm)(4)]/SA (1:1). Results indicated that (i) form multilayer structure; however the surface pressure was insufficient to obtain LB films, and (ii) can easily reproduce and build LB films. The dependence of number of layers in the UV absorption spectra suggest that the complex did not hydrolyze or show decomposition, UV spectral differences observed between the solution and the LB film indicate that the complex has a highly ordered arrangement in the film and the complex has an interaction with SA. Excitation spectra confirm a ligand-europium energy transfer mechanism. The transition lines of Eu(3+) ion were observed in emission spectra of all films, the photoluminescence spectra indicate a fluorescence enhanced effect with the number of LB layers. (C) 2009 Elsevier B.V. All rights reserved.

Optical, electrical, and thermochromic properties of polyazothiophene Langmuir-Blodgett films

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

A Dielectric Model of Self-Assembled Monolayer Interfaces by Capacitive Spectroscopy

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Optically anisotropic and photoconducting Langmuir-Blodgett films of neat poly(3-hexylthiophene)

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Capacitance Spectroscopy: A Versatile Approach To Resolving the Redox Density of States and Kinetics in Redox-Active Self-Assembled Monolayers

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Spectroscopy and electrochemical characterization of Langmuir-Blodgett and physical vapor thin films of 29-membered diazocrown ether 1 with two n-octyl substituents

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Detection of catechol using mixed Langmuir-Blodgett films of a phospholipid and phthalocyanines as voltammetric sensors

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Synthesis of a functionalized europium complex and deposition of luminescent Langmuir-Blodgett (LB) films

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Applicability of the equations of Freundlich and Langmuir to the adsorption of the azo dye procion scarlet on paramorphic colonies of Neurospora crassa.

Experiments on the adsorption of Procion Scarlet MX-G by normal hyphae and by paramorphic colonies of Neurospora crassa were performed at pH 2.5, 4.5 and 6.5 at 30 degrees C. The measured adsorption isotherms were evaluated by the Freundlich and Langmuir equations. The removal of dye was most effective at pH 2.5 and more dye was adsorbed per unit mass of cells in the paramorphic cultures than in the normal hyphae. The statistical tests showed Langmuir's equation to give a better fit to the adsorption data.