Horizontal Lifting Research Articles

Langmuir-Blodgett films of polyheterocyclic compounds with long alkyl chains

By introducing long alkyl chains into polyheterocyclic compounds, such as quinacridone, triphenodithiazine and carbazoledioxadine, monolayers of functional pigments were obtained. These monolayers could be deposited on solid supports by a horizontal lifting method with well-defined orientation and packing of the chromophores.

Flow Orientation in Langmuir-Blodgett Films of a Charge-Transfer Complex (TMTTF)3(C14TCNQ)2

The occurrence of flow orientation during the deposition of Langmuir-Blodgett films of (TMTTF)3(C14TCNQ)2 is shown through studies of in-plane molecular orientation in films deposited by two types of the vertical dipping method, with the substrates parallel and perpendicular to the barrier, using ESR and polarized UV-visible spectroscopies. Larger in-plane anisotropy is observed toward the edge of the substrates, which is consistent with the prediction of the recent theory of flow orientation during the deposition process. Furthermore, in-plane anisotropy in the films deposited by the horizontal lifting method is detected, suggesting the existence of a compression orientation at the air-water interface.

Orientation control of liquid crystals by Langmuir-Blodgett films

Abstract Orientations of liquid crystals on modified surfaces with different chemical groups were investigated using Langmuir-Blodgett (LB) films, in order to clarify the alignment mechanism in liquid crystal cells. The surfaces, covered with carboxyl, hydroxyl, amine, cyano and alkyl groups, were prepared by combination of a conventional LB method and a horizontal lifting method. It has been found that the molecular alignment in liquid crystal cells depend on the dipole interaction term in the surface energy of the substrate film. LB films with polar groups, such as carboxyl and hydroxyl, at the outermost surface, used for the substrate, produced good liquid crystal cell properties, involving small pre-tilt angles, clear in-plane anisotropy of transmittance and sharp voltage response, as compared with polyimide films.

Characterization of Langmuir-Blodgett films of 3,4-didecyloxy-2,5-di(4-nitrophenylazomethine) thiophene in a stearic acid matrix

The surface pressure π of two component monolayers of stearic acid (SA) and 3,4-didecyloxy-2,5-di(4-nitrophenylazomethine) thiophene (DNAT) has been measured at the air-water interface by the Wilhelmy method as a function of mean molecular area at various compositions. The surface properties of these mixed films were interpreted in terms of both the additivity rule of molecular areas and the two-dimensional phase rule applied to collapse pressures. Results indicate that SA is miscible with DNAT to up to χSA = 0.5. At χSA > 0.5 phase separation occurs and at π > 14 mN m-1 DNAT is ejected from the highly ordered SA film matrix. The index of refraction and thickness of these films dielectrics were determined through surface plasmon (SP) measurements on approximately 500 Å thick silver substrates. Horizontal lifting was used to transfer the Langmuir-Blodgett monolayers to glass slides coated with silver. Mixed solid films of DNAT up to 10% (by weight) in polystyrene matrices with thicknesses ranging from 4 to 12 μm were also prepared, indices and thicknesses being measured using the m-line technique. This allowed us to estimate the index of pure DNAT as a cross-check on the SP results. Since index determinations from these techniques are in essential agreement in terms of linear refractivity, we are able to discuss the structural implications of the SP-measured monolayer film thicknesses.

Langmuir‐Blodgett films of rigid rod oligoimides on gold: An x‐ray photoelectron spectroscopy study

AbstractAngular‐resolved x‐ray photoelectron spectroscopy (ARXPS) was used to study mono‐ and multilayer films of rigid oligoimides prepared on gold‐coated glass slides by the Langmuir‐Blodgett (LB) horizontal lifting technique. The experimentally obtained total atomic ratios were in a good agreement with molecular formulae. The attenuation of the substrate Au 4f photoemissio intensities was recorded as a function of both the number of LB dips and the take‐off angles. The ratio of the thickness to the attenuation length was determined for three different oligoimides from the slopes of the linear attenuation regions. Interpretation of the thickness/attenuation length ratio was based on the models for the oligoimide LB films of oriented structures. The average tilt angle and the area/molecule used in modeling the oligoimide film structures were determined in independent experiments involving grazing angle infrared (GIR) spectroscopy, electrochemistry and LB pressure‐area isotherms. The thicknesses of the oligoimide films were calculated from the models and used to derive the value of the attenuation length from the ARXPS slopes. The attenuation length value for Au 4f core‐level photoelectrons (Ek = 1169.6 eV) was estimated to be 66–70 Å in the LB films of all three different oligoimides.

Polar Glass Structure for Second-Order Nonlinear Optics Prepared by the Langmuir-Blodgett Method Using Amorphous Polymers with an Azo-Dye

In order to obtain Langmuir-Blodgett (LB) films for second-order nonlinear optics, LB films of the amorphous copolymers synthesized from methyl methacrylate and 2-(N-ethyl-N-(4-(4-nitrophenyl)azo)phenyl)aminoethyl acrylate were investigated. From the measurement of F-A isotherms and UV and visible spectra of the Langmuir (L) film, it was estimated that the azo-dye moiety was squeezed out from the air-water interface into the subphase, and the dipoles of azo-dye align uniaxially in the direction perpendicular to the interface. The L film could be deposited into X-type multilayers by the horizontal lifting method, resulting in the formation of “polar glass.”

Frictional electrification of fatty acid LB films of which the uppermost layer was deposited on Y-type films by the horizontal lifting method

Frictional electrification was studied for LB films of stearic acid of which the uppermost layer was deposited on Y-type films by the horizontal lifting method. In these films, the carboxyl groups were expected to exist at the film/air interface. Though experimentally obtained films were not always ideal, it was clarified that the state of molecular aggregation, the species of atomic groups and the ratio of existence of atomic groups in the surface have an effect on the frictional electrification.

Ultra-thin films of conjugated polymers for opto-electronic applications

Ultra-thin films of precursor polymers for poly(benzimidazole) (PBI), poly(benzoxazole) (PBO), or poly(benzthiazole) (PBT) were formed at air/water interface by spreading monomers and then polymerizing on the water surface. These thin films could be deposited onto appropriate substrates such as quartz by using the Langmuir-Blodgett (LB) method of horizontal lifting. Moreover, the heat treatment of the built-up films of the precursor polymers transformed the films into corresponding PBI, PBO, or PBT, which were high-temperature polymers. The resulting films had uniform and controllable thickness. Electronic and opto-electronic properties of these thin films were evaluated in terms of electric conductivities and nonlinear optical properties.

Molecular orientation in thin Langmuir–Blodgett films of dipalmitoylphosphatidylcholine as studied by FTIR transmission and reflection–absorption spectroscopy

Langmuir–Blodgett (LB) films of DPPC were prepared by the horizontal lifting technique at various surface pressures encompassing the plateau region of its surface pressure (π) – area (A) isotherm. Molecular orientation in the LB films was quantitatively evaluated by a method recently proposed by Umemura et al. (J. Phys. Chem. 94, 62 (1990)) using Fourier transform infrared (FTIR) transmission and reflection–absorption (RA) spectra. From the results obtained, it is apparent that (i) in the LB films deposited at higher surface pressures above the plateau, the hydrocarbon chains are of all-trans conformation and well oriented at the tilting angle of ca. 20° from the surface normal; (ii) at lower surface pressures below the plateau, the chain segments are almost randomly oriented (like in a liquid-crystalline state) with an increased amount of the gauche conformers; and (iii) in the films deposited within the plateau, the hydrocarbon chains are in an intermediate state between the above two states. It is therefore concluded that the plateau corresponds to a process of the reorientation of the hydrocarbon chains from an almost randomly-oriented state to a highly-oriented one with the increase in the number of the all-trans conformers. Key words: dipalmitoylphosphatidylcholine, Langmuir–Blodgett film, molecular orientation, infrared reflection–absorption spectra, surface pressure–area isotherm.

Proton-Pumping by Purple Membrane in Combined Multilayers with a Phthalocyanine Derivative

Abstract Combined multilayers of purple membrane and octa-n-butoxyphthalocyanine as a pH sensitive dye were prepared by horizontal lifting method. The photo-induced proton-pumping activity of bacteriorhodopsin was observed by change of absorption spectra of the multilayers in water, and the one-way transport of proton was confirmed.

Synthesis of ultra‐thin films of aromatic polymers at air/water interface

AbstractUltra‐thin films of and precursor polymers for polybenzimidazole (PBI), polybenzoxazole (PBO), or polybenzothiazole (PBT) were formed at air/water interface by spreading monomers and then polymerizing on the water surface. These thin films could be deposited onto appropriate substrates by using the LB method of horizontal lifting. Moreover, the heat‐treatment of the built‐up films of the precursor polymers of PBI, PBO, and PBT formed the ultra‐thin films of high temperature polymers. The resulting ultra‐thin films had uniform and controllable thickness, but remained fairly stable when subjected to temperature up to 300°C. They also had good solvent resistance.

Accumulation of monomolecular polystyrene particles from a water surface onto a substrate

AbstractMonomolecular particles of polystyrene (Mw/Mn = 1.04, Mw = 3.84 ? 106) formed by spreading of a dilute solution in benzene over a water surface were successfully accumulated onto a hydrophobic substrate by the horizontal lifting method. The accumulation was quantitative (up to 66 layers) to give a multilayer film. The substrates used were silicon single crystals, quartz coated with an iron(III) stearate monolayer, and poly(methylmethacrylate) plates. The film contained voids amounting to 20‐30 vol%. The surface structure observed by transmission electron microscopy clearly showed a multilayer, particle structure. These facts indicate that the molecules exist as monomolecular particles in the film. The film should be a suitable material to study properties of polymeric monomolecules in a very unusual state as compared with the ordinary solid.

Rigid rod oligoimides form oriented Langmuir–Blodgett films

Organized monolayers of oligoimides were transferred from a water surface to solid substrates by horizontal lifting and studied by UV–VIS and polarized IR–ATR (ATR = attenuated total reflection) spectroscopy.

Characterization of Langmuir-Blodgett films of cadmium stearate by penning ionization electron spectroscopy

The characterization of cadmium stearate films prepared on silicon substrates by the conventional Langmuir-Blodgett method (for 1 layer) and those by the horizontal lifting (HL) method (for 2–4 layers) was carried out by means of Penning ionization electron spectroscopy and UV photoelectron spectroscopy. The analysis of the relative band intensities of the Penning spectrum indicates that the hydrocarbon end of the stearate ion is exposed outside the surface for all the films studied. The combination of this result and those of an X-ray diffraction study suggests that the films prepared by the HL method have a Y-type structure. The structural changes in the film due to increases in film thickness and to thermal annealing were also studied by Penning ionization and photoelectron spectroscopies.

Langmuir-Blodgett films of long-chain derivatives of amino acid containing aromatic rings

For long-chain derivatives of amino acid containing naphthalene, the arrangement of the chromophore in Langmuir-Blodgett (LB) films was examined by circular dichroism (CD) together with UV absorption and fluorescence spectroscopies. The monolayer of ϵ N-stearoyl- L-lysyl- L-1-naphthylalanine methylester exhibits a region of transition from expanded to condensed states. The absorption spectra of the LB films show a slight red shift of 1B b and 1L a bands for naphthalene in comparison with the solution spectrum. The CD spectra of the LB films vary significantly with surface pressure and type of deposition. In particular, the Y-type LB films prepared at high pressure beyond the transition region show a strong Cotton effect due to the interaction of the chromophore. The multilayers prepared using the horizontal lifting method show a weaker Cotton effect than conventional LB films. Therefore the Cotton effect is ascribed to the strong interlayer interaction of the chromophore together with intralayer interaction.

Vertical dipping method as a means of controlling the in-plane molecular orientation in Langmuir-Blodgett films

The flow orientation model has been extended to cases with arrays of substrates, asymmetric deposition, discontinuity in the monolayer and stretching of the monolayer. Predictions are derived as the guidelines for controlling the in-plane molecular orientation in Langmuir-Blodgett (LB) films prepared using the vertical dipping method. The conventionally prepared LB films are found to be inevitably associated with degradation in the edge region. The remedies for reducing the edge effect are shown on the basis of the present model. They are the use of cylindrical substrates within the framework of the conventional vertical dipping method, and the introduction of the horizontal lifting method and of the Kumehara-Miyata version of the vertical dipping method with moving walls.

Langmuir-Blodgett films of octa-alkyl phthalocyanines

Phthalocyanine (Pc) derivatives attached directly to eight alkyl chains were synthesized. The Pc monolayers were spread on water from toluene solution and were transferred onto solid plates using the horizontal lifting method. The polarized visible and IR spectra of the multilayers, the film thickness and the molecular areas of the monolayers showed that Pc macrocycles were oriented nearly parallel to the surface. Reversible electrochromism was observed for the Pc multilayers on indium-tin oxide (ITO) electrodes in an aqueous solution of KCl.

On the Minimum Principle for Controlled Diffusions on Manifolds

This paper concerns optimal control of a family of nondegenerate diffusions evolving on a compact manifold. Feedback controls based on complete observations are used. The controlled process is constructed by the horizontal lifting technique of Eells and Elworthy, and a minimum principle is derived from a dynamic programming argument. It is shown that the adjoint variable appearing in the minimum principle, which here is a one-form valued stochastic process, can be evaluated by solving a “heat equation” on the manifold.

Conductive and optically non-linear polymeric langmuir-blodgett films of poly(3-dodecylthiophene)

Monolayer film formation at the air/water interface was investigated for both electrochemically and chemically prepared poly(3-dodecylthiophene) using surface pressure-molecular area isotherms. Only the electrochemically prepared polymer formed a stable monolayer, which was successfully transferred using the horizontal lifting method. The transferred Langmuir-Blodgett films were characterized by u.v.-visible spectroscopy, quartz crystal microbalance measurements, electrical conductivity measurements and femtosecond degenerate four-wave mixing studies of the third-order optical non-linearity. The third-order optical susceptibility of undoped poly(3-dodecylthiophene) was found to be χ (3) ∼ 10 −9, esu, large enough to allow the first reported observation of a degenerate four-wave mixing signal from ultrathin Langmuir-Blodgett films. In situ iodine-doping studies of u.v.-visible absorption, electrical conductivity and third-order non-linear optical susceptibility were carried out. Upon doping, the conductivity increased by more than eight orders of magnitude and the χ (3) value decreased to within ten percent of the original value.

Structure Study of Langmuir–Blodgett Films of Stearic Acid and Cadmium Stearate Deposited by Different Techniques

Abstract Structure of LB films of stearic acid and cadmium stearate was studied by X-ray diffraction and infrared ATR methods. Stearic acid LB films prepared by the horizontal lifting method were mixtures of the A- and C-crystal forms, but those prepared by the vertical dipping method mainly consisted of the C-form. Cadmium stearate LB films gave X-ray diffraction peaks indicating the long spacing of 5.03 nm, irrespective of the deposition method.