Structure Of Langmuir-Blodgett Films Research Articles

Langmuir-Blodgett film structure

Langmuir-Blodgett (LB) films occupy a unique niche at the crossroads of materials science, complex fluids, and biophysics. They have many similarities to inorganic epitaxial films due to the layer by layer deposition process; however, the amphiphilic nature of the constituent molecules provides the connection to lyotropic liquid crystals and membranes. A great deal is known about LB film structure and thermodynamic behavior; both from classical studies as well as from recent experiments using sophisticated characterization techniques such as synchrotron X-ray scattering and scanning probe microscopy. This article summarizes the current understanding of these systems from a physical/structural point of view. Included are discussions of the deposition process, the layered nature of LB films, intralayer molecular packing, defects, stability, and phase transitions.

Bioactive nanostructure with glutamate dehydrogenase associated with LB films: protecting role of the enzyme molecules on the structural lipidic organization

The enzyme glutamate dehydrogenase (GIDH) was adsorbed onto hydrophilic or hydrophobic surfaces of behenic acid Langmuir-Blodgett (LB) films. FTIR spectroscopy shows that the GIDH molecules can be retained onto both types of surfaces without modifying the LB film structure; the enzyme adsorption is only responsible for a superficial hydration of the multilayers. Epi-fluorescence microscopy shows that the enzyme remains active. The enzyme retention was investigated in the conditions of enzyme activity detection by immersion of the protein-lipid LB films in the suitable alkaline buffer. This study showed that the interactions between the enzyme and either the head or the tail groups of behenic acid were strong enough to avoid enzyme desorption during overnight immersion in the buffer. Furthermore, the retained enzyme preserves the structure of the behenic acid multilayers during their immersion in the alkaline buffer; transformation into behenate multilayers which normally occurs if the enzyme is not present. This protecting role of the GIDH molecules against the modification of the behenic acid multilayer structure, probably contributes to a slowing down of the hydration of the underlaying layers by the buffer.

Structural study of Langmuir-Blodgett films built from Langmuir mono- and bilayers of a copper phthalocyanine derivative

The compression isotherms of copper tetrakis (n-alkyloxycarbonyl) phthalocyanines present a well-defined monolayer to bilayer transition. The structure of Langmuir-Blodgett films built from both types of Langmuir film is investigated by X-ray diffraction using one representative compound of the series. A similar square columnar organization of the molecules is found in both cases. Conclusions concerning the structure of the bilayer at the air-water interface are drawn.

X ray diffraction study of Langmuir-Blodgett mono- and multi-layers

Langmuir-Blodgett (LB) films are often proposed as candidates for molecular electronics. In fact, the deposition technique allows an easy and good control of the structure along the normal to the surface (B. Belbeoch, M. Roulliay, M. Tournarie, 82 (1985) 701–706). However, only few information has been obtained about in plane structure of LB films. Mono- and multi-layers of docosanoic acid have been studied by X-ray transmission diffraction and infrared spectroscopy. For that purpose, LB layers have been deposited onto collodion membranes which present good mechanical properties and give rise to low background signal for the two characterisation techniques. Deposition of the layers occurred at room temperature and a surface pressure π = 36 mN/m. No salt was added to the underlying water. Different samples were prepared, either with a single monolayer deposited on the upstroke, with a double layer (with first layer deposited on the down stroke) or with multilayers. X-ray diffraction has been performed on beam line D24 at LURE by using a Weissenberg chamber equipped with image plates and infrared absorption was used to control the quality and the number of deposited layers. X-ray diffraction is known to work well with multilayers. In the present work, good signal has been obtained from only 2 layers (one on each side of the collodion membrane). Several diffraction rings have been obtained in these conditions. The structure of the monolayer is compared to that of the multilayers.

Highly ordered structure in polymerizable N-alkylacrylamide LB films

The molecular orientations in N-octadecylacrylamide, nonadecylacrylamide and icosylacrylamide Langmuir-Blodgett (LB) films, which show high capability of the polymerization, are investigated by Fourier transform infrared (FTIR) measurements. A drastic IR dichroism caused by the considerable anisotropic arrangement of these N-alkylacrylamide molecules along the dipping direction was observed. It is found from the comparison with the FTIR spectra of some amphiphile derivatives that the in-plane orientation in these alkylacrylamide LB films is characteristic of the acrylamide chemical structure.

Electrical properties of conductive Langmuir-Blodgett films comprised of head-to-tail poly (3-hexylthiophene)

Conductive Langmuir-Blodgett (LB) films were fabricated from mixed monolayers containing structurally homogeneous poly (3-hexylthiophene) and stearic acid in different molar ratios. The structure of these mixed LB films was probed by visible absorption and X-ray diffraction measurements. These regioregular polymers containing almost 100% head-to-tail couplings showed the self-organized properties and affected the molecular structure in the LB films. Conductivities of the LB films doped with strong oxidizing agents were dramatically improved due to their well-defined polymer structure and were in the range of 10 2-10 1 S cm −1.

Correlations in the interface structure of Langmuir-Blodgett films observed by x-ray scattering.

Correlations in the interface structure of Langmuir-Blodgett films observed by x-ray scattering.

Z-type Langmuir–Blodgett film structures: surface plasmon resonance, second harmonic generation and fibre optic devices

Second harmonic generation (SHG) from Langmuir–Blodgett (LB) films of the iodide (I) and octadecylsulfate (II) salts of E-N-octadecyl-4-[2-(4-dibutylaminophenyl)ethenyl]quinolinium and from films of a related pyridinium dye (III) increases with the number of layers. The LB film structures are non-centrosymmetric (Z-type) and have high second-order susceptibilities, χ(2)zzz, of 120 pm V–1 for dye I (20 layers), 80 pm V–1 for dye II (100 layers) and 30 pm V–1 for dye III (160 layers) at λω= 1.064 µm. The values are resonantly enhanced but for dye III the absorbance is very weak at the harmonic wavelength. The real and imaginary parts of the dielectric permittivity of dye I, derived from the surface plasmon resonance (SPR), are 3.14 ± 0.06 and 0.66 ± 0.03, respectively, at 532 nm and, with the exception of the monolayer, the thickness is 3.0 ± 0.3 nm layer–1. Waveguiding overlays of dye I, evanescently coupled to side-polished optical fibres, have resulted in useful in-line wavelength-selective elements. The LB technique allows the necessary control of film thickness for such devices.

Photophysical investigation of Langmuir-Blodgett films of amphiphilic discotic penta-alkynes

Amphiphilic discotic pentakis (arylethynyl) benzene compounds 1 and 2 containing an enlarged aromatic core functioning as a chromophoric π-electron system were studied with regard to their photophysical properties within Langmuir-Blodgett (LB) films. The results obtained from steady-state absorption as well as fluorescence excitation and emission measurements will be discussed with regard to interchromophoric interactions in the LB films. Time-resolved fluorescence investigations revealed the formation of a ground-state complex as well as excimer formation. Thermal treatment causes irreversible destruction of the LB film structure of the discotic amphiphiles. Within droplets the reorganization of the original nematic-discotic (N D) mesophase of the bulk materials was found for the alcohol 2 as indicated by a Maltese Cross texture, whereas the acid 1 remained isotropic.

Enzymatic activities and infrared studies of glutamate dehydrogenase immobilized on Langmuir-Blodgett films

A technique is described for the immobilization of active glutamate dehydrogenase (GDH) on behenic acid Langmuir-Blodgett (LB) films. The optimization of the immobilization conditions shows that the activities of GDH bound on hydrophobic and hydrophilic LB films were similar and decreased dramatically when the immobilized enzyme was dried. The GDH binding was followed by Fourier transform infrared (FTIR) spectroscopy. Modifications of GDH conformation and LB film structure were observed during the enzyme binding. After GDH activity test, a partial dissociation of behenic acid occurred and the β-sheet band of the enzyme increased by comparison with the α-helix band.

Counterion Effects on the Structure of Langmuir-Blodgett Films of a Benzothiazolium Dye

Langmuir-Blodgett films of salts of the two-legged cationic dye, E-N-hexadecyl-2-[2-(4-docosylaminophenyl)ethenyi]benzothiazolium, are Z-type. The molecular configuration within the Langmuir—Blodgett film is either U-shaped or stretched depending upon the nature of the anion, the thickness per layer being 35.1 Α for the octadecylsulphate and 54.1 Α for the iodide. For the Langmuir—Blodgett monolayers the principal components of the second order susceptibility (0 1) are 70 pm V -1 and 34 pm V -1 respectively at 532 nm. In the case of the octadecylsulphate salt it was possible to fabricate thick multilayer Langmuir-Blodgett films; the second harmonic intensity increased with the number of Z-type layers, albeit subquadratically, and this may be ascribed to a progressive variatioii in the chromophore tilt angle. PACS numbers: 73.20.Μf, 81.15.Lm

Molecular-Scale Structures of Langmuir-Blodgett Films of Fatty Acids Observed by Atomic Force Microscopy

Langmuir-Blodgett films of arachidic acid, barium arachidate, and a mixture of arachidic and behenic acids on a chemically flattened silicon substrate were observed by atomic force microscopy. The films were found to contact tightly with the substrate with a molecular slip at its steps. Lattice expansion due to barium ions was found on the barium arachidate film but not on the pure acid film. In addition, the 2×2 superlattice was found on the barium arachidate film. The superlattice structure may be caused by the formation of a hydrogen salt. Although no phase separation was found on the film made of a 9:1 mixture of the acids, the image of the expected molecular mixture has not been obtained so far.

Molecular Aggregation, Orientation, and Structure in Langmuir-Blodgett Films of 2,4-Bis[(3,3-dimethyl-1-octadecyl-2,3-dihydro-2-indolylidene)methyl]-1,3-cyclobutadienediylium-1,3-diolate Studied by Visible Absorption and Infrared Spectroscopies

Molecular aggregation, orientaiton, and structure in Langmuir-Blodgett (LB) films of a squarylium dye,2,4-bis[(3,3-dimethyl-1-octadecyl-2,3-dihydro-2-indolylidene)methyl]- 1,3-cyclobutadienediylium- 1,3-diolate (SQ-VI), have been investigated by using visible absorption and infrared (IR) spectroscopies. The visible absorption spectra show that SQ-VI forms H-aggregates as well as monomer in the LB films and that the proportion of the H-aggregates increases significantly with surface pressure. IR spectra of the LB films of SQ-VI are largely different from those of SQ-VI in solid and cast film. The former show bands at 1718 and 1660 cm -1 assignable to C=O and C=N + stretching modes, respectively, while the latter do not give such bands, indicating that SQ-VI takes the structure shown in Figure 1, parts b and a, respectively, in the LB films and the solid and cast film. Vibrational frequencies of CH 2 stretching bands are also different between the former and the latter ; it is suggested from the frequencies that the hydrocarbon chains of SQ-VI take a nearly trans-zigzag conformation in the solid and cast film, but a few parts of the chains assume a gauche conformation in the LB films. Comparison of the IR transmission and reflection-absorption (RA) spectra of the LB films of SQ-VI suggests that the chromophoric part is fairly perpendicular to the substrate surface and that both the hydrocarbon chains and the molecular axis of the chromophore are tilted considerably with respect to the substrate normal. The molecular orientation and structure of the LB films of SQ-VI are also discussed in comparison with those of the LB films of another type of squarylium dye, 2,4-bis[4-(methyloctadecylamino)-2-methylphenyl]cyclobutadienediylium-1,3-diolate (SQ-II), which we previously investigated.

Structure of Langmuir-Blodgett Films of Star-Shaped Oligomeric Discogens

We have used atomic force microscopy (AFM) and X-ray diffraction (XRD) to study ultrathin films of star-shaped oligomeric molecules with mesogenic triphenylene subunits. At the air-water interface, the molecules undergo a conformational change such that the peripheral triphenylene substituents sit perpendicular to, and the central core sits parallel to, the interface. AFM measurements indicate that the conformation of the molecules is preserved upon transfer to a solid substrate and that the triphenylene subunits are organized in columns with average alignment along the direction of deposition. XRD shows that there is a 40 o distribution of column orientations, centered on the direction of deposition

Optical methods of investigation of the protein Langmuir—Blodgett films

The structure of multilayer Langmuir-Blodgett (LB) films made of a protein (bovine serum albumine)-coproporphyrin(III) conjugate was investigated by means of a fluorescence microscope coupled with the time-correlated single-photon counting registration system. The map of coproporphyrin fluorescence from the surface of protein LB films was measured with picosecond time resolution and spatial resolution of 15 μm. The sample area of 225 × 225 μm was irradiated step-by-step by a focused beam of a Nd:YAG laser with the accumulation time of 3 s per point. Two different kinds of samples with a regular and irregular distribution of fluorescent labels over the sample were observed. It is worthwhile to note that the fluorescence level of the studied samples is close to the limit of sensitivity of the fluorescence microscope. Another method to optically investigate the structure of the protein LB films is laser interferometry with consequent computer processing of images.

Monolayer Properties and Structure of Langmuir-Blodgett (LB) Films in Mixtares of Arachidic Acid and Cellulose Derivatives

The surface properties and structures of mixed monolayers were studied to establish an assembled model for a detergent system. Surface pressure-area curves of the mixed monolayers of arachidic acid and cellulose derivatives showed a sinuous aspect with apparent inflection points. The curves of the mixed monolayers were consistent with the isotherms calculated on the assumption of the fractional summation in isotherms of pure monolayers, thus demonstrating the separation of molecules in a mixed monolayer, LB films with a single layer were prepared as a mixed monolayer of arachidic acid and cellulose derivative at a mixing ratio of 1/1. The monolayer was transferred onto a specimen grid covered with carbon supporting film at different surface pressures by the horizontal attachment method. LB film structures were then observed by dark-field electron microscopy. Micrographs of the films indicated inhomogeneous structures, thus showing phase separation in the mixed monolayer. The microscopically phase-separated monolayer would thus appear usable as a model detergent system in which arachidic acid is incorporated into the cellulose derivative.

Structure of Langmuir-Blodgett Films of Copper Phthalocyanine Derivatives

Structure of Langmuir-Blodgett Films of Copper Phthalocyanine Derivatives

Structural investigations of polyion complex Langmuir-Blodgett films containing fluorocarbon chains

The structures of the polyion complex Langmuir-Blodgett (LB) film, in particular the effects of the side-chain of the polymer cation on the structure, were investigated by using X-ray diffraction, ellipsometry, Fourier-transform infrared reflection-absorption spectroscopy and contact angle measurement. It was found that the side-chain of polymer cations affects the layered struture and surface structure of polyion complex LB films, and that the LB film of perfluoroundecanoic acid (PFUA)-poly(vinylbenzyltrimetylammonium chloride) containing a longer side-chain has a more disordered structure than those of PFUA-poly(vinylamine) and PFUA-poly(allylamine), which have a well-ordered layered structure.

Structural study of Langmuir–Blodgett films by scanning surface potential microscopy

In this paper we describe the structural study of Langmuir–Blodgett (LB) films with a scanning surface potential microscope (SSPM) together with an ordinary atomic force microscope (AFM). The SSPM is a new type of high-resolution potentiometry due to electrostatic force microscopy and is a member of the AFM family. Our SSPM is a modified Kelvin probe force microscope, and is based upon the design of a recently developed scanning Maxwell stress microscope (SMM). This microscope can be used to study distribution of the surface potential or the contact potential difference (CPD) with submicrometer spatial resolution. We have applied this microscope to the study of molecular orientation of amphiphilic molecules in LB films. The surface dipole moments due to the terminal CH3 group of the long alkyl chain and the hydrophilic head group are used to study the orientation in the multilayered structures of LB films. In the present work, we focused on reorientation of the amphiphilic molecules in LB films during monolayer transfer and by oxidation of the substrate surface.

The electromotive force generation in metal-insulator-metal structures of Langmuir-Blodgett films

It was found that several hundred millivolts of d.c. voltage is generated in a metal-insulator-metal structured device of Langmuir-Blodgett (LB) films. The voltage generation is caused by LB films only or by a chemical reaction between LB films and the electrode. In the work reported in this paper, the experiments are processed for a sample which has been left under atmospheric conditions since its fabrication in 1986. We measured the same voltage as at the time of fabricating the LB films. The thickness of the LB films and the evaporated electrode used for the experiment is about 20∼30 Å and 2000 Å respectively. Therefore, we cannot think that a chemical reaction which is generating several hundred millivolts takes place continuously for 6∼7 years. It is proper that the chemical reaction has terminate. In our experimental results, the cause is some kind of e.m.f. which has occured at elements of the film.