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Applied Surface Science (v.246, #4)
Langmuir–Blodgett and Langmuir–Schaefer films of homoleptic and heteroleptic phthalocyanine complexes as voltammetric sensors: by Serena Casilli; Mariangela De Luca; Constantin Apetrei; Vicente Parra; Álvaro A. Arrieta; Ludovico Valli; Jianzhuang Jiang; María L. Rodríguez-Méndez; José A. De Saja (pp. 304-312).
Double- and triple-decker phthalocyanine derivatives have been successfully used as the sensitive materials for liquid electrochemical sensors. The materials include homoleptic and heteroleptic phthalocyanine complexes formed by phthalocyanine, porphyrin and naphthalocyanine rings. A high degree of cross-selectiviy towards antioxidant compounds (including vannilic acid, pyrogallol, ascorbic acid and catechin) has been attained by using different phthalocyanine complexes. The features observed in the cyclic voltammograms reflect the rich electrochemistry of either the phthalocyanine molecules or the studied solutions. In consequence, each sensor shows a selective response to the antioxidant analysed.The obtained voltammograms from by using highly ordered electrodes prepared using the Langmuir–Blodgett (LB) or the Langmuir–Schaefer (LS) techniques show better resolution and stability than those of disordered electrodes prepared by casting. For this reason, ordered films have been chosen to construct an array of liquid sensors. The principal component analysis (PCA) of the obtained signals has allowed that a clear discrimination of the antioxidant solutions be achieved.The rich and varied responses produced by antioxidant molecules evidences that voltammetric electrodes based on phthalocyanines, are especially suitable for the analysis of compounds with electrochemical activity.
Keywords: Phthalocyanine; Bisphthalocyanine; Naphthalocyanine; Double-decker phthalocyanine; Triple-decker phthalocyanine; Voltammetric sensor; Electronic tongue
Use of cholesteryl polysulfides in self-assembly and soft lithography on Au(111) and ITO by Giuseppe Ciccarella; Annamaria Maffei; Giuseppe Vasapollo; Laura Blasi; Dario Pisignano; Ross Rinaldi (pp. 313-322).
Cholesteryl polysulfides derivatives, containing a number of sulfur atoms comprised from 2 to 6 and suitable for the formation of self-assembled monolayer have been prepared utilizing a known procedure modified by us. The compounds were isolated and characterized by HPLC–MS,1H NMR, FT-IR techniques. Self-assembly methodology was adopted in order to obtain uniform layers and the patterning suitability was tested with microcontact printing technique. Contact angle measurements and atomic force microscopy revealed interesting surface modifications.
Keywords: Cholesteryl polysulfides derivatives; Self-assembly methodology; Microcontact printing technique
Langmuir films of an amide extracted from Piperaceae and its interaction with phospholipids by P.A. Antunes; O.N. Oliveira Jr.; R.F. Aroca; G.O. Chierice; C.J.L. Constantino (pp. 323-326).
In this work, we investigate Langmuir monolayers from an amide extracted from dried roots of Ottonia propinqua, a native Brazilian plant believed to exhibit anesthetic and hallucinogen activities. In addition to producing monolayers from the amide itself, we probe the molecular-level action of the amide on phospholipids employed as simple membrane models. The surface pressure–molecular area ( π– A) isotherms for the amide were little affected by a number of subphase conditions. Almost no changes were observed upon varying the compression speed, spreading volume onto the surface, ions in the subphase, ionic strength and the solution solvent. However, stronger effects occurred when the subphase temperature and pH were altered, as the isotherms were shifted to larger areas with increasing temperatures and decreasing pHs. These results are discussed in terms of the molecular packing adopted by the amide at the air–water interface. In the mixed films with arachidic acid, the area per molecule varied linearly with the concentration of amide, probably due to phase separation. On the other hand, in the mixed films with dipalmitoyl phosphatidyl choline (DPPC), small amounts of the amide were sufficient to change the π– A isotherms significantly. This points to a strong molecular-level interaction, probably between the phosphate group in the zwitterion of DPPC and the nitrogen from the amidic group.
Keywords: Isotherms; Anesthetic; Membrane
Characterization of evaporated trivalent and tetravalent phthalocyanines thin films: different degree of organization by T. Del Caño; V. Parra; M.L. Rodríguez-Méndez; R.F. Aroca; J.A. De Saja (pp. 327-333).
Evaporated thin films of trivalent – chloroindiumphthalocyanine (ClInPc) and chlorogalliumphthalocyanine (ClGaPc) – and tetravalent phthalocyanines – vanadyl-phthalocyanine (VOPc) and titanylphthalocyanine (TiOPc) – have been characterized by means of electronic absorption and infrared spectroscopy (both in transmission and reflection–absorption modes). It was found that the ability of self-organization clearly differs between trivalent and tetravalent phthalocyanine derivatives. The results revealed that ClGaPc and ClInPc thin films result to be highly organized. On the other hand, the evaporation of tetravalent phthalocyanines powders forms amorphous thin films. However, further film treatments (thermal annealing and solvent exposure) lead to the phase transition from amorphous to α-form, and as a result, a high degree of molecular organization is induced.
Keywords: Phthalocyanines; Thin film; Molecular organization; RAIRS
BAM studies on the penetration of amphotericin B into lipid mixed monolayers of cellular membranes by P. Dynarowicz-Å?Ä…tka; J. Miñones Jr.; O. Conde; M. Casas; E. Iribarnegaray (pp. 334-341).
The penetration of the antifungal antibiotic – amphotericin B (AmB) – into Langmuir monolayers formed by cholesterol and ergosterol has been investigated by measuring the overpressure (Δ π) in the film after the injection of AmB into water subphase. In addition, the penetration of AmB into sterol monolayers was studied at the microscopic level with Brewster angle microscopy (BAM) by recording BAM images simultaneously with the surface pressure increase. The obtained results show that monolayers formed by cholesterol are more penetrable for AmB molecules while rigid and closely packed films of ergosterol are less accessible for the antibiotic. This does not imply that the interactions between AmB and ergosterol are weaker than those between AmB and cholesterol, but indicates that the extent of AmB penetration is related to a different space accessibility. To get insight into the role of phospholipids in the interactions between AmB and sterols, the penetration of the antibiotic into mixed ergosterol–dipalmitoyl phosphatidylcholine (DPPC) and cholesterol–DPPC monolayers have also been investigated. The extent of AmB penetration into mixed monolayers was found to be dependent both on AmB bulk concentration and DPPC–sterol proportion in the mixed film.
Keywords: Amphotericin B; Langmuir monolayers; Penetration; Air/water interface; Brewster angle microscopy
Properties of Langmuir monolayers from semifluorinated alkanes by M. Broniatowski; I. Sandez Macho; J. Miñones Jr.; P. Dynarowicz-Å?Ä…tka (pp. 342-347).
The aim of this study was to characterize several semifluorinated alkanes (SFA), of the general formula F(CF2) m(CH2) nH (in short F mH n), containing 25 carbon atoms in total (pentacosanes) differing in the m/ n ratio, as Langmuir monolayers at the free water surface. The following compounds have been studied: F6H19, F8H17, F10H15 and F12H13. Surface pressure ( π) and electric surface potential (Δ V) isotherms were recorded in addition to quantitative Brewster angle microscopy results. The negative sign of Δ V evidenced for the orientation of all the investigated semifluorinated pentacosanes, regardless the length of the hydrogenated segment, with their perfluorinated parts directed towards the air. As inferred from apparent dipole moment values and relative reflectivity results, the fluorinated pentacosanes with shorter perfluorinated fragment (F6H19 and F8H17) were found to be vertically oriented at the air/water interface, while those with longer perfluorinated moiety (F10H15 and F12H13) remain titled even in the vicinity of the film collapse.
Keywords: Langmuir monolayers; Semifluorinated alkanes; Air/water interface; Electric surface potential; Brewster angle microscopy
Influence of the deposition technique on the structural and optical properties of amorphous AsS films by J.M. González-Leal; M. Stuchlik; M. Vlcek; R. Jiménez-Garay; E. Márquez (pp. 348-355).
Amorphous chalcogenide films of stoichiometric composition As40S60 have been prepared by three different deposition techniques, namely, vacuum thermal evaporation, plasma-enhanced chemical vapour deposition (PECVD) and spin coating. Indications of film-thickness inhomogeneities were found in all samples. Thermally evaporated and chemically deposited samples showed wedge-shaped surface profiles, while significant surface roughness was evidenced in the spin-coated ones. Refractive-index values of the film samples were obtained, with accuracy better than 1%, by using the envelope method most suitable for each particular film surface profile. Structural information of the samples has been gained from X-ray diffraction experiments, and also inferred from the analysis of the dispersion of the refractive index, on the basis of a single-oscillator model. Analysis of the optical absorption spectra allowed both calculating the optical band gaps and estimating the localised-state tail width of these semiconducting films. In addition, information about the degree of structural randomness of these thin-film amorphous alloys was also obtained from this analysis, which is in good agreement with the conclusions derived from the X-ray diffraction results.
Keywords: As; S films; Thermal evaporation; Spin coating; PECVD
Mixed monolayers of dipalmitoyl phosphatidylcholine and ethyl palmitate at the air/water interface by Barbara Gzyl; Maria Paluch (pp. 356-361).
The behaviour of monolayers containing dipalmitoyl phosphatidylcholine and ethyl palmitate and their mixtures at different molar fraction, using surface pressure–molecular area results, was investigated. The negative deviation from additivity of the mean molecular areas as a function of the mixture composition indicates the miscibility. The miscibility was confirmed by applying the two-dimensional phase rule, since the collapse pressure values vary with the composition of the mixtures. Also the free energy of mixing Δ Gmix and the excess free energy of mixingΔGmixE were determined. The negative values of Δ Gmix andΔGmixE indicate that the mixed monolayers are thermodynamically more stable compared to the pure ones and that the compounds in the two dimensional state experience mainly attractive interactions.
Keywords: PACS; 68.10.CrLangmuir monolayers; Dipalmitoyl phosphatidylcholine; Ethyl palmitate; Lipid mixtures
Influence of active sites organisation on calcium carbonate formation at model biomolecular interfaces by S. Hacke; D. Möbius; V.-T. Lieu (pp. 362-366).
In an approach to understand the influence of structural parameters of interfaces on calcification in biomineralisation, the distribution and conformation of head groups as active sites in an inert matrix were varied using two-component phospholipid model monolayers. Dimyristoylphosphatidic acid (DMPA) and dipalmitoylphosphatidylcholin (DPPC), respectively, were the active components, and methyl octadecanoate (MOD) was used as inactive matrix. Surface pressure–area isotherms provide evidence for a different distribution of the active components in the matrix. Formation of solid calcium carbonate with two-component monolayers on subphases containing aqueous CaCO3 was observed in situ by Brewster angle microscopy, where CaCO3 domains appear bright. Striking differences in kinetics and extent of CaCO3 formation are observed between monolayers containing dimyristoylphosphatidic acid and those containing dipalmitoylphosphatidylcholin. The presence of κ-carrageenan in the subphase as a further active component resulted in partial inhibition of CaCO3 formation.
Keywords: Mixed model monolayers; Calcium carbonate formation; Phospholipids; Kinetics; Critical cluster
Photoelectrochemical properties of Zn(II) phthalocyanine/ZnO nanocrystals heterojunctions: nanocrystal surface chemistry effect by C. Ingrosso; A. Petrella; M.L. Curri; M. Striccoli; P. Cosma; P.D. Cozzoli; A. Agostiano (pp. 367-371).
Hetero-junctions prepared by deposition of unsubstituted Zn(II) phthalocyanines (Zn(II)Pc) onto a film of colloidal ZnO nanocrystals, were studied. Photoelectrochemical measurements were performed on the sensitized nanocrystalline ZnO films deposited onto optically transparent electrodes, to characterize the photoactivity of the heterojunction. A comparison between ZnO nanocrystals prepared by using a hydrolytic and non-hydrolytic route was performed in order to investigate the effect of nanocrystal surface chemistry on the photoelectrical response. The photoactivity was found to be significantly enhanced when non-hydrolytically prepared nanocrystals were used to form the heterojunction.
Keywords: PACS; 73.40.-c; 73.50.-h; 73.61.Tm; 82.45.+zDye-sensitized film; Colloidal nanocrystals; ZnO; Zn(II) phthalocyanine; Photoactivity
First-principles modeling of oligo(ethylene glycol)-terminated and amide group containing alkanethiolates by L. Malysheva; A. Onipko; R. Valiokas; B. Liedberg (pp. 372-376).
Recently, self-assemblies of HS(CH2)15CONH(CH2CH2O)6H were found to undergo a reversible temperature-driven conformational transition from the helical to all- trans state [R. Valiokas, M. Östblom, S. Svedhem, S.C.T. Svensson, B. Liedberg 104 (2000) 7565]. The transition reveals distinctive signatures in the reflection–absorption (RA) spectrum associated with different conformations of the OEG portion of the SAM [R. Valiokas, M. Östblom, S. Svedhem, S.C.T. Svensson, B. Liedberg 104 (2000) 7565]. Here we report an extensive ab initio modeling of infrared RA spectra of molecular constituents of OEG-terminated amide-containing SAMs. The model spectra for this type of molecules (with large OEG and alkyl portions) are obtained, for the first time, by using DFT methods with gradient corrections. The position and relative intensities of all characteristic bands, observed in the fingerprint region of the SAM RA spectrum, are shown to be well reproduced by the single-molecule model spectrum calculated for a certain relative orientation of the alkyl- and OEG portions and the amide bridge. This provides us additional information about actual structure, particularly, molecular orientation within the OEG-containing SAMs in focus.
Keywords: PACS; 31.15.A; 33.20.EInfrared spectra; Self-assembled monolayers
Mixed Langmuir monolayers of an amphiphilic chromo-ionophore and the phospholipid DMPC by T.I. Sergeeva; S.P. Gromov; A.I. Vedernikov; M.S. Kapichnikova; M.V. Alfimov; D. Möbius; S.Yu. Zaitsev (pp. 377-380).
The amphiphilic chromo-ionophore 2-[(1E,3E)-4-(2,3,5,6,8,9,11,12,14,15-decahydro-1,7,10,16,4,13-benzotetraoxadithiacyclooctadecin-18-yl)-1,3-butadienyl]-3-octadecyl-1,3-benzothiazol-3-ium perchlorate (AB211) forms mixed monolayers at the air–water interface with the phospholipidl-α-dimyristoylphosphatidylcholine (DMPC) as deduced from surface pressure–area and surface potential–area isotherms. In contrast to the behaviour of pure monolayers of AB211 on water, no association of the chromophores is observed by reflection spectroscopy. Upon compression of the mixed monolayer AB211:DMPC=1:5, a re-orientation of the chromophores from flat to tilted is observed, presumably assisted by the stretching of the choline group of the phospholipid molecules acting a matrix.
Keywords: Abbreviations; AB211; 2-[(1E,3E)-4-(2,3,5,6,8,9,11,12,14,15-decahydro-1,7,10,16,4,13-benzotetraoxadithiacyclooctadecin-18-yl)-1,3-butadienyl]-3-octadecyl-1,3-benzothiazol-3-ium perchlorate; DMPC; l; -α-dimyristoylphosphatidylcholineLangmuir monolayer; Chromo-ionophore; Amphiphilic
Total internal reflection ellipsometry and SPR detection of low molecular weight environmental toxins by A.V. Nabok; A. Tsargorodskaya; A.K. Hassan; N.F. Starodub (pp. 381-386).
The environmental toxins, such as herbicides simazine and atrazine, and T2 mycotoxin were registered with the optical methods of surface plasmon resonance (SPR) and recently developed total internal reflection ellipsometry (TIRE). The immune assay approach was exploited for in situ registration of the above low molecular weight toxins with specific antibodies immobilised onto the gold surface via (poly)allylamine hydrochloride layer using electrostatic self-assembly (ESA) technique. The comparison of two methods of SPR and TIRE shows a higher sensitivity of the latter.
Keywords: Total internal reflection ellipsometry; SPR; Atrazine; Simazine; Mycotoxin; Immune assay
Influence of different factors on the phase transitions of non-ionic Langmuir monolayers by Marina Nieto-Suárez; Nuria Vila-Romeu; Inmaculada Prieto (pp. 387-391).
The design and use of Langmuir–Blodgett (LB) films involve a thorough knowledge of the behavior of molecules at the interface. Among many factors that affect the properties of films, i.e. the transformation from 2D into 3D phase, the presence of ions in the subphase has to be taken into account. Thus, this paper describes the characteristics of Langmuir monolayers composed by ethyl and methyl ester molecules, spread on water and aqueous solutions containing Na+ and Ca2+. Under different experimental conditions, Brewster angle microscopy (BAM), surface pressure ( Π) and stability measurements are applied to investigate the behavior and morphology of systems.
Keywords: Langmuir monolayers; Phase transition; Brewster angle microscopy; Esters
Deposition of TTF derivative on carboxyl terminated self-assembled monolayers by Hitoshi Ohnuki; Mitsuru Izumi; Stéphane Lenfant; David Guerin; Tatsuro Imakubo; Dominique Vuillaume (pp. 392-396).
Oxygen-substituted tetrathiafulvalene (TTF) derivatives of bis(ethlenedioxy)tetrathiafulvalene (BEDO-TTF) were deposited onCOOH-terminated alkylsilane self-assembled monolayers (SAMs). The BEDO-TTF molecules were effectively attached on theCOOH-terminated SAMs. A formation of mixed valence state (MVS), which is a characteristic conducting phase of TTF, was observed by Fourier transform infrared spectroscopy. Such MVS formation is estimated to be brought about by an appearance of charge–transfer complex of (BEDO-TTF)2(COO⋯H⋯OOC) through a chemical reaction withCOOH group of the surface. Atomic force microscopy images revealed the existence of many small islands on the surface. It is expected that the first layer of BEDO-TTF molecules are absorbed ontoCOOH group of the surface through the reaction, then the first layer stimulates a crystallization of BEDO-TTF above it, giving rise to the islands formation.
Keywords: PACS; 81.16.Dn; 81.07.Pr; 73.61.PhSelf-assembled monolayers; Tetrathiafulvalene; Organic–inorganic hybrid nanostructures
Nanoscale manipulation of CdSe quantum dots in layer-by-layer films: influence of the host polyelectrolyte on the luminescent properties by V. Zucolotto; K.M. Gattás-Asfura; T. Tumolo; A.C. Perinotto; P.A. Antunes; C.J.L. Constantino; M.S. Baptista; R.M. Leblanc; O.N. Oliveira Jr. (pp. 397-402).
Thioglycolic acid-capped CdSe quantum dots (QDs) were assembled on glass substrates with two distinct polyelectrolytes, viz poly(allylamine hydrochloride) (PAH) and poly(amidoamine) (PAMAM), generation 4 dendrimer, via the layer-by-layer (LbL) technique. Films containing up to 30polyelectrolyte/QD bilayers were prepared. The growth of the multilayers was monitored with UV–vis spectroscopy, which showed an almost linear increase in the absorbance of the 2.8nm QDs at 535nm with the number of deposited bilayers. AFM measurements estimated a film thickness of 3nm per bilayer for the PAH/CdSe films. The adsorption process and the optical properties of the PAMAM/CdSe LbL films were further analyzed layer-by-layer using surface plasmon resonance (SPR), from which a thickness of 3.2nm was found for a PAMAM/CdSe bilayer. Photoluminescence measurements revealed higher photooxidation of the quantum dots in PAH/CdSe than in PAMAM/CdSe films.
Keywords: Quantum dots; Poly(allylamine hydrochloride); Poly(amidoamine); Layer-by-layer
Self-assembled monolayers of a novel diacetylene on gold by O. Cavalleri; M. Prato; A. Chincarini; R. Rolandi; M. Canepa; A. Gliozzi; M. Alloisio; L. Lavagnino; C. Cuniberti; C. Dell’Erba; G. Dellepiane (pp. 403-408).
We report on the preparation and characterization of self-assembled monolayers (SAMs) of a novel diacetylene monomer, the 14- N-carbazolyltetradeca-10,12-diyndisulfide. The SAM/gold interface was investigated by means of spectroscopic ellipsometry (SE), X-ray photoelectron spectroscopy (XPS) and scanning tunnelling microscopy (STM). SE data indicate a layer thickness compatible with the formation of a monomolecular layer. The occurrence of molecular chemisorption is confirmed by XPS measurements which indicate the formation of a thiolate species. This result is confirmed by STM imaging which shows the formation of small pits, one gold layer deep, a typical feature of self-assembled organosulfur monolayers on gold.
Keywords: PACS; 81.16.Dn; 33.60.Fy; 68.37.Ef; 78.6.QnSelf-assembled monolayers (SAMs); Diacetylene; Gold; Spectroscopic ellipsometry (SE); X-ray photoelectron spectroscopy (XPS); Scanning tunnelling microscopy (STM)
Colloidal photonic crystals obtained by the Langmuir–Blodgett technique by Stéphane Reculusa; Serge Ravaine (pp. 409-414).
Monodispersed silica spheres with diameters of 220–1100nm were prepared by hydrolysis of tetraethyl orthosilicate (TEOS) in an alcoholic medium in the presence of water and ammonia. By grafting vinyl or amine groups on silica surfaces using the coupling agents allyltrimethoxysilane and aminopropyltriethoxysilane, respectively, amphiphilic silica spheres were obtained and could be organized to form a stable Langmuir film at the air–water interface. The control led transfer of this monolayer of particles onto a solid substrate gave us the ability to build three-dimensional regular crystals with well-defined thickness and organization. These colloidal crystals diffract light in the UV, visible and the near-infrared (NIR) spectral regions, depending on the size of the silica spheres and according to the Bragg's law.
Keywords: Colloidal crystals; Silica; Langmuir–Blodgett technique; Controlled architecture
Layer-by-layer deposition of TiO2 nanoparticles by Kerstin Schulze; Stefan Kirstein (pp. 415-419).
In this paper we report on the fabrication of nanoporous films using layer-by-layer deposition of TiO2 nanoparticles utilizing the sol–gel process. TiO2 nanoparticles with a mean diameter of 40nm are dispersed in aqueous solutions either in the acidic or alkaline pH range. It is shown that the adsorption of the TiO2 particles is not governed by electrostatic forces as it was suspected from previous experiments of alternate adsorption with polyelectrolytes. This is concluded from the fact that no polyelectrolytes can be found in films prepared by the electrostatic layer-by-layer (ELBL) deposition method. This is proven by the use of dye-labeled polyelectrolytes for the ELBL procedure in combination with absorption spectroscopy. It is suggested that the films are formed by a sol–gel process of each layer of TiO2 nanoparticles. This is demonstrated further by the preparation of TiO2 films by alternate dipping into solutions of TiO2 nanoparticles and a buffer solution. The films obtained by this technique are characterised by AFM imaging for determination of roughness and thickness.
Keywords: Solar cell; Mesoporous films; Layer-by-layer deposition; TiO; 2; nanoparticles; Sol–gel
The ESR study of chemical interactions in triple solid silver–carbon tetrachloride–mesogenic cyanobiphenyl co-condensate system by V.A. Timoshenko; T.I. Shabatina; A.A. Belyaev; Yu N. Morosov; G.B. Sergeev (pp. 420-424).
The possibilities of new metal–mesogenic complexes formation and their solid phase chemical reactions have been demonstrated using low temperature co-condensation technique and ESR-spectroscopy for solid triple system, containing silver, mesogenic ligand 4-pentyl-4-cyanobiphenyl (5CB) and alternative electron-acceptor ligand or the third reactive component carbon tetrachloride (CCl4). It was shown by ESR-spectroscopy that the existence of four paramagnetic products are stabilized in the system at low temperatures: silver atom π-complex with two cyanobiphenyl molecules, silver atom σ-complex with cyanobiphenyl molecule stabilized by CCl4 co-ligand, complex of AgCl molecule with trichloromethyl radical – AgCl·CCl3 and silver nanoclusters – Ag x, formed by silver atoms aggregation in mesogenic matrix. The relative thermal stability of these silver species and mechanism of their thermal behavior are discussed.
Keywords: Metal–mesogenic complexes; Electron-acceptor ligand; Mesogenic matrix
Brewster angle microscopy and surface potential measurements of Langmuir–Blodgett films of zinc tri( tert-butyl)-4-sulphophthalocyanine by Florencio Peñacorada; Jorge Souto; José A. de Saja; Ludwig Brehmer (pp. 425-429).
The formation of a Langmuir monolayer of an amphiphilic derivative of zinc phthalocyanine (Na[ZnPctSO3]) has been studied by means of surface potential technique and Brewster angle microscopy. The experiments were undertaken in order to understand the behaviour of this monolayer with a well-defined surface pressure isotherm. The floating film is described as a truly monomolecular layer formed by very rigid islands in which the phthalocyanine units tend to take on a preferential orientation with their planes perpendicular to the air–water interface, for high values of the surface pressure.
Keywords: PACS; 68.18.+p; 68.55.−a; 81.70.FyLangmuir films; Zn(II) phthalocyanine; Brewster angle microscopy
Multilayer membranes of p-sulfonato-calix[8]arene and polyvinylamine and their use for selective enrichment of rare earth metal ions by Ali Toutianoush; Ashraf El-Hashani; Judit Schnepf; Bernd Tieke (pp. 430-436).
Using alternating electrostatic layer-by-layer assembly of p-octasulfonato-calix[8]arene and polyvinylamine, multilayer assemblies were built up on porous polymer supports. The resulting composite membranes with ultrathin separation layer were studied on their permeability for various metal chloride salts in aqueous solution. The membranes were permeable for sodium chloride, but much less permeable for divalent metal chlorides such as magnesium and zinc chloride, the theoretical separation factors α (NaCl/MgCl2) and α (NaCl/ZnCl2) being 43 and 20. Rare earth metal chlorides LnCl3 with Ln being La, Ce, Pr and Sm and the related YCl3 were strongly rejected from the membrane, the theoretical separation factors α (NaCl/LaCl3) and α (NaCl/YCl3) being 138 and 160, for example. Possible origins for the selective ion transport are discussed in terms of Donnan rejection of the highly charged ions and complex formation of the rare earth metal ions with the p-sulfonato-calixarene units in the membrane.
Keywords: Multilayer; Membrane; Layer-by-layer; Water-soluble calixarene; Polyelectrolyte; Polyvinylamine; Rare earth metal; Ion separation
Polyelectrolyte multilayer membranes for desalination of aqueous salt solutions and seawater under reverse osmosis conditions by Ali Toutianoush; Wanqin Jin; Hüseyin Deligöz; Bernd Tieke (pp. 437-443).
Ultrathin, multilayered membranes of polyvinylamine (PVA) and polyvinylsulfate (PVS) were electrostatically adsorbed on a porous polymer (polyacrylonitrile/polyethylene terephthalate) support. Their use for desalination of aqueous salt solutions, diluted and non-diluted artificial seawater was investigated under reverse osmosis conditions. Using 60 layer pairs of PVA/PVS as separating membrane, it was possible to completely reject MgCl2 and MgSO4 from feed solutions of 1 and 10mM concentration independently from the operative pressure applied. The rejection of NaCl and Na2SO4 increased from 84 and 96% at 5bar to 93.5 and 98.5% at 40bar, respectively. From diluted seawater (1:10; 1:100; 1:1000), 99±1% of Mg2+, 97.0±1% of Ca2+, and 92.5±1% of Na+ were rejected at 40bar, and from non-diluted seawater, 98±1% of Mg2+, 96.4±1% of Ca2+, and 74.5±0.8% of Na+ were rejected at 40bar. The permeation flux J increased linearly with the pressure applied. For a membrane of 60 PVA/PVS layer pairs, a flux value of 4±0.2Lm−2h−1 was found at 40bar. The influence of the number of deposited layer pairs on R and J was also investigated.
Keywords: Multilayer; Membrane; Layer-by-layer; Seawater desalination; Reverse osmosis; Polyelectrolyte; Ion separation
Size- and charge-selective transport of aromatic compounds across polyelectrolyte multilayer membranes by Wanqin Jin; Ali Toutianoush; Bernd Tieke (pp. 444-450).
The transport of various neutral and charged aromatic compounds across poly(diallyl dimethylammonium chloride)/poly(sodium styrenesulfonate) (PDADMA/PSS) and poly(allylamine hydrochloride)/poly(sodium styrenesulfonate) (PAH/PSS) multilayer membranes was investigated. The solutes were phenol (Ph), hydroquinone (1,4-BD), naphthalene (Np), pyrene (Py), triphenylene (Tp), alkali metal salts of benzene sulfonate (Bs), naphthalene 2-sulfonate (Ns), methyl orange (MO), and isomeric benzene disulfonates (1,2-, 1,3-BDS). For the neutral compounds, a size-selective transport was found, the transport being controlled by the pore size of the membrane and the size of the aromatic solute. The sieving effect from the membranes was so pronounced that mean pore sizes of 0.82±0.09 and 0.67±0.04nm could be determined for PDADMA/PSS and PAH/PSS, respectively. Size exclusion leads to separation factors α(Ph/Py)≈13 and α(Ph/Np)≈28 using PDADMA/PSS and PAH/PSS membranes, respectively. For charged aromatic compounds, the transport is both size- and charge-selective. The charge-selectivity is based on Donnan rejection of permeating ions from the equally charged parts of the membrane, the rejection for dianions being much stronger than for monoanions comparable with the rejection of mono- and divalent inorganic ions. While size-based separation across PAH/PSS is only moderate (α(Bs/Ns)≈4), the charge-based separation is high (α(Bs/1,3-BDS)≈65).
Keywords: Layer-by-layer; Polyelectrolyte; Multilayer; Membrane; Molecular sieving; Ion separation
Optical and structural studies of Langmuir–Blodgett films of polyalkoxystilbazole complexes of iridium(I) by J.E. Wong; B. Donnio; D.W. Bruce; T.H. Richardson (pp. 451-457).
Studies have been focused on Langmuir films of a family of iridium polyalkoxystilbazole metallo-organic complexes. We report that these polyalkoxystilbazole complexes form stable Langmuir monolayers on water as subphase, and are successfully transferred onto glass substrates for structural and optical characterisations using UV–vis spectroscopy. The area per molecule obtained for the polyalkoxystilbazole films is larger than that for the corresponding monoalkoxystilbazole films, and cannot simply be explained by the cross-sectional area of the Ir(CO2)Cl headgroup, which is common to all of them. The length of the alkoxy chains as well as their position of substitution have an influence on the orientation of the molecules.
Keywords: Langmuir; Langmuir–Blodgett; Organo-metallic; Stilbazole; Thin film
Green light-emitting devices based on soluble oligo(phenylenevinylenes) by J.E. Wong; H. Detert; L. Brehmer; S. Schrader (pp. 458-463).
In this work, we report our investigations on the film-forming properties as well as the optical and electroluminescent characterisations of a series of lateral-substituted soluble oligo(phenylenevinylenes) of various conjugation length. Preliminary investigations show that these materials are potential candidates for use in organic light-emitting devices (OLEDs). Two types of OLEDs were fabricated: single layer (SL) and single heterostructure (SHS), with poly( p-phenylenevinylene) (PPV) as hole transporting layer. Our best results were obtained with single layer device emitting green light with a luminance of 0.18cdm−2 and 0.24cdm−2 at a driving voltage of 10V.
Keywords: Oligo(phenylenevinylenes); Photoluminescence; Electroluminescence