Preparation and characterization of poly(amide-imide) multilayer films

Multilayer films of poly(amide-imide)s were prepared as follows: (1) monolayers of long alkyl amine salts of poly(amide-amic acid) were prepared at the air- water interface; (2) these monolayers were deposited on an appropriate plate by the Langmuir-Blodgett method; (3) the multilayers of poly(amide-amic acid) salts on the solid support were treated with acetic anhydride to afford poly(amide-imide) multilayer films. The monolayer thickness of the poly(amide-imide) multilayer films were 0.43–0.55 nm.     

Surface properties of LB monolayers composed of aminimide derivatives having two alkyl chains

Langmuir-Blodgett monolayers were prepared using a series of aminimide derivatives having two alkyl chains. One of the alkyl chains had 19 carbons, while the number of the other alkyl chain was systematically changed from 8 to 20. Molecular organization of the aminimides on the water surface reflected the length of alkyl chains. Inter-chain packing and conformational order of the alkyl chains in the monolayer were affected by the length of the two alkyl chains. Steric and dynamic contact angles of a series of aprotic liquid having low surface tension were measured to investigate surface properties of the films with varying molecular organization of alkyl tail groups. Fluid-like monolayers having molecularly rough surface indicated high wettabilities for both of n-alkanes and naphthalene derivatives. However, contact angle hyteresis on the monolayer was sensitive to the sort of probe liquids owing to the interaction between the uppermost portion of the alkyl chains aligned homeotropically on the fluid-like monolayers. In contrast, the monolayer containing well-ordered, well-packed alkyl chains indicated low wettabilities, small hysteresis and random orientation of liquid crystals.     

Thermochromic Langmuir-Blodgett films of a novel amphiphilic azo dye with homogeneous chromophore orientation

Langmuir-Blodgett (LB) multilayers have been prepared from a novel amphiphilic azobenzene derivative. These films were transparent and showed homogeneous polarization of visible light over the whole film area. They exhibit reversible thermochromism with a red shift of 60 nm over a temperature range of less than 10°C. This thermochromism can be explained by a “J-like” aggregation of the azo chromophores that is slightly effected by temperature.     

Preparations of Langmuir-Blodgett films of enzyme-lipid complexes: A glucose sensor membrane

A stable monolayer of water-soluble enzyme (glucose oxidase (GOD)) could be prepared by spreading an organic solution of lipid-coated GOD on a water subphase. Langmuir-Blodgett (LB) films of the GOD-lipid monolayers could be deposited on a platinum electrode and these acted as a glucose-sensing ultrathin membrane with a high sensitivity and a short response time. The complexing of enzyme with lipid molecules in advance is a useful technique for producing a water- insoluble monolayer and LB films of water-soluble enzymes. This technique will become a new tool not only for preparing sensor membrane but also for assembling water-soluble proteins on biological electrical components, so-called “biochips”.     

Spectroscopic properties of mixed Langmuir-Blodgett films of rhodamine dyes and poly(N,N-diallyl-N-octadecylamine-alt-maleic acid)

Langmuir-Blodgett (LB) films of poly(N,N-diallyl-N-octadecylamine-alt-maleic acid) as well as mixed films consisting of polyampholyte and two amphiphilic fluorophores - alkyl substituted rhodamine dyes - were prepared and investigated. The π-A isotherm of the polyampholyte at air-water interface is typical for monolayer in the liquid state. Mixed monolayers of polyampholyte and rhodamine amphiphiles show improved packing of the hydrophobic chains. Absorption and fluorescence spectroscopic studies of the mixed LB films reveal the aggregation of dyes in the densely packed multilayer films.     

Linear and non-linear optical and spectroscopic properties of Langmuir-Blodgett films

Optical and spectroscopic properties of Langmuir-Blodgett (LB) monolayers and multilayers are being measured to characterize the films, to understand their two-dimensional behavior and to follow chemical and physical changes. Orientation of groups and molecular packing have been analyzed by Fourier transform IR spectroscopy at glancing angle, from waveguide Raman scattering and from near- edge X-ray fine structure. Use in electronic and optical devices has excited many, especially with non-linear phenomena needed to control or modify light optically for communication and storage. Recent optical results on thin monolayer and multilayer assemblies will be reviewed, including both the linear and non-linear aspects. Effects and phenomena will be illustrated with examples to give an appreciation for their use and to display some of our new knowledge about LB films.     

Surface modification using polymer Langmuir-Blodgett films

We describe a simple and effective approach to introduce a functional group into polymer film on a solid surface using reactive polymer LB films. N-dodecylacrylamide copolymers containing terminal amino groups in the side chains as the reactive moiety form a stable monolayer, and the monolayer was transferred onto a solid support to modify the solid surface using the Langmuir-Blodgett method. The transferred coatings were characterized with fluorescence, IR spectroscopies, and X-ray diffraction. The reactivity of the terminal amino group incorporated in the LB films was investigated in detail using fluorescein isothiocyanate (FITC) as a fluorescent probe. The chemical reaction between amino groups in the LB films and FITC in the bulk solution was completed within approximately 30 minutes and the chemical bond formation was confirmed by infrared spectroscopy. Furthermore, the fluorescent image of the multilayers reacted with FITC were observed with fluorescent microscopy. This method is effective for tailoring functional organic ultrathin films on solid substrates.     

Langmuir-Blodgett films of oligo- and polythiophenes with well-defined structure

Using terthiophene and its derivatives, quater-, quinque-, sexi-, and - or β-septithiophenes, Langmuir-Blodgett (LB) films including oligo- or polythiophenes with well-defined alignments have been obtained. Esters of terthiophene with a short alkyl chain form stable condensed monolayers on water and can be deposited by the LB method. -polythiophenes without any hydrophilic groups can be incorporated in LB films of mixed monolayers with arachidic acid. In these monolayer assemblies, the long axes of oligo- or polythiophenes stand nearly vertically. LB films of the terthiophene ester derivatives showed a large dielectric constant and a high conductivity which were enhanced by iodine doping.     

Structural and morphological changes of monolayers of a block copolymer with dendron and perfluoroalkyl side chains by mixing a perfluorooctadecanoic acid

Hybrid Langmuir and Langmuir-Blodgett monolayers of a perfluorooctadecanoic acid mixed with a rigid block copolymer, poly(3,5-bis(3,5-bis(benzyloxy)benzyloxy)benzyl methacrylate-randommethacrylic acid)-block-poly(2-perfluorooctylethyl acrylate), which is composed of benzyloxy dendron side chains and perfluorinated side chains, were prepared and characterized by surface pressure-surface area isotherms, atomic force microscopic images and neutron and X-ray reflectometries. The two-dimensionally phase-separated structures of monolayer films and their morphologies with plateau and terrace were confirmed. The monolayers were separated into a dendron layer, a perfluorinated layer, and a carboxyl layer. The layer formation is originated not only in the intermolecular interaction between a perfluorooctadecanoic acid and a block copolymer but also in the geometry of the molecules. Especially, the amphiphilicity of perfluorinated surfactant plays a role to the ordered array of the block copolymers.     

Electrical manifestation of dielectric non-centrosymmetry using Langmuir-Blodgett multilayers of ω-tricosenoic acid

Centrosymmetric (Y-type) and non-centrosymmetric (Z-type) Langmuir-Blodgett (LB) multilayers of ω-tricosenoic acid have been deposited as part of an M¦LB¦M structure and the electrical characteristics measured. The symmetry of the LB film was manifested in the electrical properties of the junction, with the behaviour of centrosymmetric LB films being independent of the applied bias sense and non-centrosymmetric LB films possessing a distinct bias sense dependence.     

Stability and characterization of phospholipid Langmuir-Blodgett films

The regularity of the bilayer structure was compared between dipalmitoylphosphatidic acid (DPPA) Langmuir-Blodgett (LB) films and “oriented multilayers” of DPPA, using X-ray diffraction and electron spectroscopy for chemical analysis (ESCA). The angular variation of the (001) Bragg spot due to the irregularity of the lamellar repeat was remarkable in the system of oriented multilayers. In contrast, the spot of DPPA LB films exhibited only a slight angular variation, suggesting a regular structure of this film. The take-off angle dependence of the phosphorus:carbon ratio obtained by ESCA indicates that the regular layered structure in DPPA LB film is maintained after 49 layers are deposited.     

Guides “bimorphes” d''ondes ultrasoniques “bimorph” ultrasonic wave guides”

An analysis of the dispersion of elastic waves is presented for two types of long ultrasonics wave-guides that we qualify of “bimorph”: (i) a “three-layer” guide made of two different materials and (ii) a “clad core” guide built up of a rectangular core surrounded by a cladding, the materials of the rod and cladding having different properties. An analytical model is proposed to describe the extensional, flexural and torsional motions in “bimorph” wave guides having two geometrical and material symmetry axes. The asymptotic behaviour of the model allows one to select the material properties which lead to modes guided essentially either in the central layer or in the core of the bimorph guide. Moreover, the dispersive properties of a “bimorph” can be controlled through the choice of geometrical and material parameters.     

Addition of “Living” Polymers onto C60.

Various “living” polymers were grafted onto C₆₀ The number of arms of the so obtained “star” molecules can be controlled by stoechiometry and/or by varying the reactivity of the carbanion on the “living” chain against a double bond on the C₆₀. Even the oxanion of “living” polyethylenoxide is able to add onto the reactive double bonds on C₆₀. In some conditions, the carbanions present on these alkaline salts of grafted fullerenes becomes able to initiate anionic polymerization of vinyl monomers. Using “living” poly(phenylvinylsulfoxide) as a precursor polymer for PA, polyacetylene chains could be attached to the fullerene.     

Second-harmonic generation in Langmuir-Blodgett films of hemicyanine-poly(octadecyl methacrylate) and hemicyanine-behenic acid

Second-harmonic generation (SHG) is used to probe the structure and order in monolayer and multilayer Langmuir-Blodgett (LB) films of highly polarizable dye molecules deposited on glass. Optical measurements on LB monolayers of hemicyanine-poly(octadecyl methacrylate) (PODMA) and hemicyanine-behenic acid mixtures in conjuction with data from compression isotherms show that the hemicyanine-PODMA system is immiscible and that the hemicyanine-behenic acid system is miscible. Incomplete Y-type LB multilayers of 54 mol.% hemicyanine in PODMA exhibited an erratic increase, which was less than linear, in the SHG with the number of layers deposited on the upstroke. Multilayer films of hemicyanine interleaved with behenic acid showed a slightly greater than quadratic increase in SHG with the number of hemocyanine layers deposited.     

Heat-stable aromatic polymer precursors as Langmuir-Blodgett film materials

New amphiphilic precursors of polyimide-isoindroquinazolinedione, polyamide-imide, polyimidazopyrrolone and polybenzoxadinone were synthesized. The monolayers of all the precursors on the water surface could be deposited onto various substrates by the Langmuir-Blodgett technique. Subsequent thermal treatment of the built-up films under a nitrogen stream successfully produced the corresponding polymer films, which show high heat stabilities over 300–500°C and good insulating properties.     

The deposition and characterization of multilayers of the ionophore valinomycin

The deposition and characterization of Langmuir-Blodgett films of the ionophore valinomycin on single-crystal silicon and quartz substrates are described. To enable good monolayer transfer the substrates first need to be coated with a few fatty acid layers. The valinomycin is found to deposit onto either the hydrophobic or the hydrophilic surfaces of the fatty acid film. The valinomycin multilayers have been investigated using IR and UV spectroscopy. These techniques show that up to 60 layers of the ionophore may be built up with good reproducibility. A detailed investigation by ellipsometry has revealed a thickness gradient in the multilayers in the direction of dipping; the average thickness per monolayer is between 0.40 and 0.66 nm.     

Effect of side chain position on solar cell performance in cyclopentadithiophene-based copolymers

The photovoltaic properties of a series of low band-gap conjugated copolymers, in which alkyl side chains were substituted at various positions, were investigated using donor-acceptor (D-A) conjugated copolymers consisting of a cyclopentadithiophene derivative and dithienyl-benzothiadiazole. The base polymer, which has no alkyl side chains, yielded promising power conversion efficiency of 3.8%. Polymers with alkyl side chains, however, exhibited significantly decreased performance. In addition, the effects of processing additive became negligible. The results indicate that substituted side chains, which were introduced to improve solubility, critically affected the optical and electronic properties of D-A conjugated copolymers. Furthermore, the position of the side chain was also very important for controlling the morphological properties of the D-A conjugated copolymers.     

On the nature of “dynamic” strength of brittle bodies

The enhanced strength observed for bodies under dynamic loading has been attributed to fracturing duration, i.e. the time interval between the commencement of fracture at the most heavily loaded point of the body and the instant of completion of fracture which is recorded by a sensor. The “dynamic” strength of brittle bodies is shown to be related to the crack formation process.     

A.C. and D.C. conduction in lightly substituted anthracene Langmuir films

The a.c. and d.c. properties of short-chain derivatives of anthracene prepared by using the Langmuir-Blodgett technique are reported; these thin films display interesting conduction effects on account of their unusual molecular structure. Emphasis is placed on the 9-alkyl-10-anthrylpropionic acid derivatives in which the alkyl chain is either C₄H₉ (C4 anthracene) or C₆H₁₃ (C6 anthracene). As expected, the dark conduction properties are markedly different from those of unsubstituted crystalline anthracene. For example, there is a marked anisotropy in the conductivity of C4 anthracene, the in-plane value exceeding that in a direction perpendicular to the layers by a factor of 10⁸. By use of appropriate electrodes double injection effects accompanied by blue light emission were found. The admittance data for these novel films differ slightly from those of films of conventional fatty acid salts.     

Spectroscopic and structural characteristics of Langmuir-Blodgett films of bis[2,3,9,10,16,17,24,25-octakis(octyloxy)phthalocyaninato] rare earth complexes

The monolayer behavior of bis[2,3,9,10,16,17,24,25-octakis(octyloxy)phthalocyaninato] rare earth complexes M[Pc(OC₈H₁₇)₈]₂ (M = Eu, Dy, Er) at the air-water interface and their ordered molecular assemblies fabricated by Langmuir-Blodgett technique have been investigated by a series of techniques including surface pressure-area isotherms, electronic absorption spectra, polarized absorption spectra, low-angle X-ray diffraction patterns, and transmission electron microscope (TEM). The results indicated that bis(phthalocyaninato) rare earth molecules form well-ordered stable monolayers with a face-to-face configuration and edge-on arrangement to the water surface at the air-water interface and lamellar multilayers on solid substrates. The orientation angle of phthalocyanine rings with respect to the quartz plate surface in the Langmuir-Blodgett films has been determined to be 64.6°, 63.5°, and 63.3° for the Eu, Dy, and Er double-decker complexes, respectively, by the polarized absorption spectroscopy. High-resolution TEM reveals that a series of well-ordered rodlike aggregates of bis(phthalocyaninato) rare earth complexes, which can be considered as molecular cable arrays, were formed by self-organization in the monolayers.