Magnetic properties of ferrocenylmethylacrylate-N-dodecylacryl-amide copolymer Langmuir–Blodgett films

Langmuir–Blodgett (LB) films of the copolymer with ferrocenyl-methyl-acrylate (FcMA) and N-dodecyl-acrylamide (DDA) were fabricated. The magnetic moment of these LB films became about twenty times larger than that of the powder. In addition, the LB films had a magnetic anisotropy depending on the dipping direction. The FTIR results suggested that the polymer chains in the LB films were preferably aligned with the perpendicular of the dipping direction. These results were discussed by the intermolecular electron transfer.     

Langmuir–Blodgett multilayers of imidazoles

Langmuir–Blodgett (LB) multilayers have been formed from a wide variety of compounds but the basic studies from which others have developed have involved a long hydrocarbon chain terminated at one end by a hydrophilic group. The quaternary ammonium ion has a greater attraction for water than do the other groups which have been used and is so hydrophilic as to preclude the formation of LB layers of straight chain molecules terminated by this group. Certainly all such molecules up to and including octadecyl trimethyl ammonium bromide form micelles in preference to monolayers at the air/water interface though metastable monolayers of this compound have been reported. Quaternized imidazoles have, like quaternary ammonium ions, a positive charge but seem more likely to form LB films. We have thus explored the properties of several of these compounds with a view to producing one which has the desired properties. In order to combat the highly hydrophilic nature of the imidazole group it is necessary to employ a highly hydrophobic ‘tail group’. Thus our most successful compound contains two octadecyl alkyl chains. We have studied the behaviour of this compound at the air/water interface and have found that the nature of the subphase has a very marked influence on the shape of the isotherms. With nitric acid added to the subphase to bring about a pH of 3.5 it is possible to obtain good Y deposition with deposition ratios equal to one in both the upward and downward directions. However we have not been able to achieve LB deposition using any other acid. On heating, the compound in question it changes from a crystalline structure to a smectic structure at 55°C.     

Langmuir–Blodgett membranes for separation and sensing

The current status of Langmuir–Blodgett (LB) films is described with regard to biomimetic applications as separating membranes and sensor layers. In the first part, recent research activities on the utility of LB membranes for gas separation, liquid permeation, hyper- and ultrafiltration are reviewed. The morphological aspects of materials separation in LB films are discussed. In the second part, recent progress in the rapidly growing field of LB-film-based chemical sensors and blosensors is reviewed. The structure and function of gas and ion sensors, and enzyme and immunosensors is briefly discussed. Perspectives for future activities in the fields of LB membranes and sensors are outlined.     

An air-stable biomimetic Langmuir–Blodgett bilayer

The long-chain amphiphiles in biomembranes have their hydrophilic headgroups oriented outwards towards the aqueous environment, and their long aliphatic chains innermost. In Langmuir–Blodgett (LB) films the hydrophobic chains are normally outermost. LB films of long-chain derivatives can be prepared under water with the headgroups outermost and are stable while kept there, but the act of removing them from the aqueous environment removes the top monolayer. We demonstrate an adaptation of the LB technique which is appropriate for the preparation of biocompatible surfaces. It produces essentially bilayer films of long-chain derivatives on standard substrates with a hydrophilic outer surface. The films are stable in air. The films show large contact angle hysteresis with water, but the receding angle is in most cases less than 10°. The films can be immersed and withdrawn from water many times before wettability or average thickness change significantly. Compared to previously reported air-stable surfaces with a structure mimicking biological membranes, the substrate for the present surface is experimentally more convenient.     

Photoelectric responses of Langmuir–Blodgett film containing bacteriorhodopsin on ITO modified with polypyrrole film

In this study, we prepared composite film by depositing Langmuir–Blodgett (LB) film containing Bacteriorhodopsin (bR) on ITO coated with polypyrrole (PPy). We studied its photoelectric properties and the influence of PPy film on the photoelectric properties of LB films containing bR at different pH. The results showed that PPy film with a certain thickness could increase the photocurrent of bR LB film 30–50% in comparison with that of bR LB film at pH 8.3.     

Near-field microscopy of collapsed Langmuir–Blodgett films

Fluorescence near-field scanning optical microscopy (FL-NSOM) is used to probe the nanoscale structure in stained phospholipid monolayers deposited on glass substrates at moderate surface pressures. The FL-NSOM images reveal new liquid-expanded (LE) and liquid-condensed (LC) domains, including one-to-one correlation between fluorescence contrast and film topography. In particular, films of the phospholipid DPPC stained with DiIC₁₂ exhibit multilayer structures that are observed within the solid phase domains and have LE-like fluorescence signals. These features are attributed to clusters of dye molecules resulting from the localized collapse of the film upon compression. Such collapsed features are also observed in supported films of 100% DiIC₁₂ deposited at high surface pressure. In these films, spatially-resolved spectroscopy shows that the collapsed structures are amorphous based on the fluorescence spectrum while the molecules within the solid phase of the film have a fluorescence spectrum indicative of molecular aggregates.     

Studies on the formation of Langmuir monolayer and Langmuir–Blodgett films of octadecyl amine-bromocresol purple dye complex

Properties of the monolayer of octadecyl amine (ODA) molecules on aqueous solution of bromocresol purple (Bcp) dye have been studied over a wide range of pH by measuring the surface pressure-area isotherms. A strong interaction of ODA molecule was observed with the dye molecule in the pH range of 4–9. Under the present study, the dye molecules were adsorbed on the ODA monolayer at the water surface and subsequently a Langmuir–Blodgett (LB) film of ODA–dye complex was transferred from the air–water interface onto a solid substrate. Alternatively, dye molecules were incorporated into LB film by immersing the predeposited LB film of pure ODA into the dye solution, i.e. by adsorption of dye molecule at the solid–liquid interface. The adsorption behavior of ODA–Bcp dye complexes obtained through these two different routes was characterised with the help of UV–Visible spectroscopy. The nature of the ODA–dye complex deposited from air–water interface using the LB technique was found to be quite different from that of the complex formed by the adsorption of the dye into the pure ODA LB film. The adsorption spectra of the ODA–dye complex obtained from the air–water interface did not change with pH, while those of the ODA–dye complex formed from the solid–liquid interface showed pH dependence.     

Amperometric cholesterol biosensors based on hybrid organic–inorganic Langmuir–Blodgett films

Preparation and characterization of a thin-film cholesterol biosensor employing an organic–inorganic hybrid system of cholesterol oxidase (ChOx) and Prussian blue (PB) is described. ChOx was immobilized in Langmuir–Blodgett (LB) films consisting of positively charged octadecyltrimethylammonium (ODTA) and nano-sized PB clusters. Immobilization was performed by simple immersion of ODTA/PB LB films into an aqueous solution of ChOx. Subsequent ChOx absorption into LB films was confirmed by infrared reflection–absorption spectroscopy. Obtained ODTA/PB/ChOx LB films clearly exhibited a response current to cholesterol under an applied potential of 0.0 V (vs. Ag/AgCl). The linearity of current density versus cholesterol concentration was confirmed for the range 0.2–1.2 mmol/L. The present study indicates that simple immersion of ODTA/PB LB films into an enzyme solution is a promising method to produce many types of thin-film biosensors comprising a hybrid system of an oxidative enzyme and PB nano-clusters that work at a very low potential range.     

Investigation of dioctadecyl bilirubinamide in monolayers and Langmuir–Blodgett films

A new amphiphilic ligand, dioctadecyl bilirubinamide [B(CONHR)₂, R=C₁₈H₃₇] form stable monolayers at the air–water interface on neutral, acidic and basic subphases as well as on subphases containing metal ions. Changes in the pH of the subphase do not produce remarkable effects on monomolecular films. The interactions between metal ions and B(CONHR)₂ molecules were investigated by means of various techniques in monolayers and Langmuir–Blodgett (LB) films. B(CONHR)₂ with its complexing head group in contact with the aqueous phase can form metal complexes with many metal ions present in the aqueous phase. The formation of B(CONHR)₂–metal complexes leads to large changes in the area per B(CONHR)₂ molecule. LB films transferred from pure water and metal ions containing subphases were characterized by XPS and low-angle X-ray diffraction.     

Formation of nano-rod and nano-particles of polyaniline using Langmuir–Blodgett technique

We present the formation of nano-structures especially nano-rod and nano-particles of polyaniline (PANI) using Langmuir–Blodgett (LB) technique of molecular deposition. Decrease in the pH of the sub-phase of LB trough increases level of doping (protonation) of polyaniline emeraldine base to emeraldine salt and causes doping induced nano-structure formation. High resolution transmission electron microscopy reveals that anisotropic rod like nano-structures of PANI of diameter less than 50 nm are formed at pH 1 while pH 3 induces the formation of dispersed nano-particle of diameter 15 nm. On the contrary, connected lump (aggregation) type nano-structures of PANI are formed at a higher value of pH 6.     

Transition from split streamlines to dip-coating during Langmuir–Blodgett film deposition

Mono-molecular films of arachidic acid were deposited on glass slides using the Langmuir–Blodgett (LB) technique. The liquid subphases were dilute solutions of ZnSO₄ at different pH. Glass slides were treated to create contact angles (θ) ranging from approximately 15° for clean glass slides, to contact angles greater than 120° for slides treated with ferric stearate. Intermediate contact angles were created by immersing slides in solutions of Sigmacote^® of varying concentration. Very small contact angles, θ≈0° were obtained with clean glass slides at high pH values. LB deposition data and transfer ratios (TR) were recorded for up-stroke and down-stroke operation. During upstroke, TR increase with decreasing contact angles reaching a maximum TR close to 100% when the receding contact angle is approximately 15–20°. This is typical of the split-ejection flow pattern found during up-stroke. For very small contact angles, i.e. less than 10°, TR suddenly become zero indicating a transition to a dip-coating flow pattern. During down-stroke operation, TR is zero or negative for small contact angles, reaching a maximum TR approximately 100% for contact angles larger than 120°.     

Information storage based on photochemical effects in mixed Langmuir–Blodgett films

Mixed Langmuir–Blodgett (LB) films of two novel thiophene-spaced N-alkylpyridinium malononitrile zwitterionic dyes have been prepared. The LB films present two sharp, non-overlapping charge-transfer absorption bands which can be selectively photobleached in a irreversible fashion. The former could have potential application in multifrequency optical data storage.     

X-ray photoelectron spectroscopy study of Langmuir–Blodgett films of N-octadecyl-8-hydroxy-2-quinoline carboxamide deposited from subphases containing metal ions

The Langmuir–Blodgett films of N-octadecyl-8-hydroxy-2-quinoline carboxamide (HOQ) deposited from subphase containing metal ions were investigated by X-ray photoelectron spectroscopy (XPS). The amphiphilic HOQ with its complexing head group in contact with the aqueous phase can form metal complexes with the metal ions present in the aqueous phase. The formation of HOQ–metal complexes leads to the appearance of new XPS peaks assigned to the metal ions. The information on stoichiometry provided by XPS indicates that a metal ion is coordinated by one HOQ molecule for transition metal ions of the fourth period, but by two HOQ molecules for the metal ions after the fourth period.     

Surface characterization of the monolayer and Langmuir–Blodgett films of tetra-tert-butyl-copper phthalocyanine

The relaxation and hysteresis phenomena of the tetra-tert-butyl-copper phthalocyanine (ttb-CuPc) monolayer were investigated. The monolayer was then transferred to a hydrophilic glass surface to prepare one monolayer of Langmuir–Blodgett (LB) films. The uniformity, stability and molecular arrangement of the LB films were studied by measurements of dynamic contact angle (DCA), and were compared with the information obtained by transmission electron microscopy (TEM) and atomic force microscopy (AFM). The results show that the monolayer of ttb-CuPc is generally stable. The limiting area of a molecule is smaller than those reported in the literature, which is attributed to the aggregation of ttb-CuPc molecules into multilayer domains. The advancing and receding contact angles of water on these LB films are much smaller than those on a homogeneous film prepared by vacuum deposition. The wettability analysis on the LB films suggests that ttb-CuPc molecules are not arranged uniformly and continuously, and the LB film of ttb-CuPc contains a high ratio of exposed glass substrate. The surface morphology inspected by TEM and AFM shows the formation of separated domains of ttb-CuPc molecules, which is consistent with the surface condition evaluated from the surface wettability.     

Solid polymerization and supramolecular chirality formation of azobenzene substituted diacetylene Langmuir–Blodgett films

An azobenzene mesogen-substituted diacetylene (NADA) monolayer has been transferred onto the solid substrate by the traditional Langmuir–Blodgett (LB) method. Solid-state polymerization of NADA LB films can be sensitized in visible light region. In situ UV–vis absorption measurement enables us to study polymerization kinetics of NADA LB films. The polymerization process can be described as a first order rate equation and polymerization rate constants are characterized in detail. Furthermore, achiral NADA molecules can form chiral LB films through overcrowded packing of the azobenzene moiety.     

Hybrid Langmuir and Langmuir–Blodgett films composed of amphiphilic cyclodextrins and hydrophobic azobenzene derivative

Hybrid Langmuir and Langmuir–Blodgett (LB) films consisting of amphiphilic cyclodextrins (CDs) and hydrophobic azobenzene were fabricated. Due to the larger cross-sectional area of the CD core compared with the sum of the cross-sectional areas of the attached alkyl chains, the films had free space in the hydrophobic regions. Azo(p-Hexyl) having hydrophobic terminal chains was accommodated in the free space, whereas the usage of an azobenzene derivative bearing hydrophilic groups led to the phase separation. The average tilt angle of Azo(p-Hexyl) gave minima when the free space was just filled with Azo(p-Hexyl). Photoisomerization of azobenzenes in the hybrid LB films was studied.     

The gas sensitivity of a metal-insulator-semiconductor field-effect-transistor based on Langmuir–Blodgett films of a new asymmetrically substituted phthalocyanine

Langmuir–Blodgett (LB) films of an amino-tri-tert-butyl-phthalocyanine (AmBuPc) were fabricated as the semiconductor thin layer for a metal-insulator-semiconductor field-effect-transistor (MISFET). The gas sensitivity of the low-conducting LB films MISFET was measured in a NO₂ atmosphere at different concentration. The results showed that the gas concentration and the drain-source current of the AmBuPc gas sensor satisfy Langmuir adsorption isotherm.     

Langmuir–Blodgett films of substituted bis(naphthalocyaninato) rare earth complexes: structure and interaction with nitrogen dioxide

Ordered molecular assemblies of novel alkylthio-substituted bis(naphthalocyaninato) rare earth complexes M[2,3-Nc(SC₁₂H₂₅)₈]₂ (M=Gd, Er) have been fabricated by Langmuir–Blodgett (LB) technique and characterized by surface pressure-area isotherm measurements, electronic absorption and polarized electronic absorption spectroscopy and low-angle X-ray diffractometry. The interaction between the thin films and NO₂ gas was investigated. The experimental results indicate that the bis(naphthalocyaninato) rare earth molecules form well-ordered stable monolayers with face-to-face orientation for the macrocycles and edge-on configuration for the molecules at the air–water interface and lamellar multilayers on solid substrates. The orientation angles of naphthalocyanine rings with respect to the quartz plate surface in the LB films for M[2,3-Nc(SC₁₂H₂₅)₈]₂ with M of Gd and Er have been determined based on the polarized absorbance and found to be 50° and 54°, respectively. The adsorption–desorption process of NO₂ on LB films of M[2,3-Nc(SC₁₂H₂₅)₈]₂ has been monitored by electronic absorption spectroscopy. A process of gas desorption was found to obey the Elovich equation.