Search results for "Langmuir"
showing 10 items of 205 documents
CEMS/XPS study of iron stearate Langmuir-Blodgett layers
1991
Langmuir-Blodgett mono- and multilayers of ferric stearate have been formed on oxidized silicon wafers. Thermodesorption of these layers was investigated by conversion electron Mossbauer and photoelectron spectroscopy and some complementary methods. Heating of samples in air up to 523 K leads to a desorption of the fatty acid chains, while the ferric ions are left on the substrate surface. These ions do not cluster laterally like it was found for Cd ions. They form a rather homogeneous, closed oxidic layer. This well defined layer may be used afterwards for further studies of surface reactions as well as interface and intra-layer interactions. The surface iron ions were found to exhibit a r…
Dual-emitting Langmuir-Blodgett film-based organic light-emitting diodes.
2010
Langmuir-Blodgett (LB) films containing alternating layers of the metallosurfactants bis(4,4'-tridecyl-2,2'-bipyridine)-(4,4'-dicarboxy-2,2'-bipyridine) ruthenium(II)-bis(chloride) (1) and bis[2-(2,4-difluorophenyl)pyridine](4,4'-dinonadecyl-2,2'-bipyridine)iridium(III) chloride (2) have been prepared. Langmuir monolayers at the air-water interface of 1 and 2 with different anions in the subphase have been characterized by pi-A compression isotherms and Brewster angle microscopy (BAM). The transferred LB films have been characterized by IR, UV-vis and emission spectroscopy, and atomic force microscopy (AFM). Electroluminescent devices formed by LB films containing alternating layers of thes…
Resin adsorption as a means to enrich rare stilbenes and coumarin from pigeon pea leaves extracts
2011
Abstract In this study, resin adsorption as a means to enrich rare stilbenes cajaninstilbene acid (CSA) and longistyline C (LLC), and coumarin cajanuslactone (CL) from pigeon pea leaves was investigated. Among widely used twenty macroporous adsorption resins, NKA-9 resin presented higher adsorption capacity and desorption ratio in static tests. The adsorption kinetic model fitted better depended on types of compounds and pH values. The experimental adsorption data were better fitted to Langmuir isotherm (R2 0.921–0.991) than Freundlich isotherm (R2 0.753–0.988). In order to optimize the operating parameters for separating CSA, LLC and CL, dynamic adsorption and desorption tests were carried…
Supercritical Fluid Adsorption of Domperidone on Silica Aerogel
2013
Silica aerogel (SA) was loaded with domperidone to demonstrate the potentiality of adsorption processes based on the usage of supercritical carbon dioxide to treat poorly water-soluble drugs, forming new kinds of drug delivery systems. The effects of pressure, temperature and solution concentration on loaded SA were studied. Adsorption isotherms were measured at 35℃ and 45℃ and fitted with Langmuir model. Release kinetics of the adsorbed drug were also evaluated by in vitro dissolution tests. Results showed that domperidone can be uniformly dispersed into the aerogel and that the release rate of domperidone from the composite, constituted by drug and silica aerogel, is much faster than that…
Pb(II) adsorption by a novel activated carbon - alginate composite material. A kinetic and equilibrium study.
2016
The adsorption capacity of an activated carbon – calcium alginate composite material (ACAA-Ca) has been tested with the aim of developing a new and more efficient adsorbent material to remove Pb(II) ion from aqueous solution. The study was carried out at pH = 5, in NaCl medium and in the ionic strength range 0.1–0.75 mol L−1. Differential Pulse Anodic Stripping Voltammetry (DP-ASV) technique was used to check the amount of Pb(II) ion removed during kinetic and equilibrium experiments. Different kinetic (pseudo first order, pseudo second order and Vermuelen) and equilibrium (Langmuir and Freundlich) models were used to fit experimental data, and were statistically compared. Calcium alginate …
Theoretical modeling of Langmuir monolayers
1999
Abstract We study coarse-grained continuum models for Langmuir monolayers by self-consistent field theory and by Monte Carlo simulations. Amphiphilic molecules are represented by stiff chains of monomers with one end grafted to a planar surface. In particular, we discuss the origin of successive fluid–fluid transitions, the possible origin of tilt order and the factors which determine the direction of tilt.
Monte Carlo Simulation of Langmuir Monolayer Models
1998
We study a coarse grained, continuum model for Langmuir monolayers, i.e., monolayers of amphiphilic molecules on a polar substrate. The amphiphiles are represented by stiff chains of beads with one end grafted to a planar surface. Monte Carlo Simulations at constant pressure have been performed, using simulation boxes of variable size and variable shape. A number of techniques have been explored in order to obtain an efficient simulation algorithm. We discuss the resulting phase diagram, characterize the different phases, and analyze the conditions, under which they can be found.
Orientational order of Langmuir–Blodgett films as determined by fluorescence anisotropy
1989
The orientational order parameters 〈P2〉 and 〈P4〉, of cadmium stearate Langmuir–Blodgett multilayers have been calculated from steady state fluorescence anisotropy experiments. It has been shown that it is valid to model the polarization components using the assumptions that the fluorescent probes are axially symmetric, the film is azimuthally symmetric within the plane, and that the rotational motion is slow enough to be neglected. Although the data do not preclude a dependence of anisotropy on thickness, within the sample‐to‐sample variations, there is no significant effect of thickness on orientational order. The order parameters for newly deposited films are 〈P2〉=0.33 and 〈P4〉=0.02. The …
Tailored conjugated polymer Langmuir-Schafer thin films in sensing transistors
2004
Organic Thin Film Transistors (OTFTs) have been fabricated, in a standard bottom gate configuration, with Langmuir-Schäfer (LS) or cast thin films of regioregular poly[1,4-(2,5-dioctyloxyphenylene)-2,5-thiophene], synthesized via an organometallic protocol, as active layers. The transistors electrical characterization has evidenced that LS based devices exhibit better performance level than cast film ones. Appealing perspectives for newly substituted conjugated polymers in OTFT sensing devices are discussed.
Quadratic Nonlinear Behaviour of Various Langmuir-Blodgett Molecules
1989
The Langmuir-Blodgett (L-B) technique is well known as a method of building-up ordered arrays of organic molecules, and especially as a means of imposing a noncentrosymmetric structure from molecules that crystallize in a centrosymmetric space group(1–3). L-B films for use in quadratic nonlinear optics can be ordered in a statistically noncentrosymmetric lattice. The method involves the compression of a mono-layer of the organic molecule, spread on top of a water surface, into a two-dimensional solid, followed by the repeated dipping of the substrate to be coated into and out of the subphase. Monolayers may be deposited onto the substrate both on immersion and withdrawal, resulting in a cen…