Characterization Of Langmuir Research Articles

Formation and characterization of Langmuir and Langmuir-Blodgett films of Newkome-type dendrons in presence and absence of a therapeutic compound, for the development of surface mediated drug delivery systems

Organic macromolecules with dendrimeric architectures are polymeric materials potentially useful as nanocarriers for therapeutic drugs. In this work, we evaluate a series of Newkome-type dendrons in Langmuir and Langmuir-Blodgett films as platforms capable of interacting with a potential antitumoral agent. The nanocomposite is proposed as model for the development of surface mediated drug delivery systems. We were successful in the formation and characterization of pure (dendrons) and composite (drug-dendron) stable and reproducible monolayers, and their transfer to solid substrates. A detailed study of topographic characteristics of the generated surfaces by atomic force microscopy was conducted. Furthermore, we probed dendron monolayer films as anchorage surfaces for mammalian cells. Normal cell attachment and proliferation on the surfaces were observed. No evident cytotoxic effects were detected, demonstrating the adequate biocompatibility of the surfaces.

Characterization of Langmuir and Langmuir–Blodgett films of an octasubstituted zinc phthalocyanine

In this work we report the fabrication of Langmuir and Langmuir–Blodgett (LB) films of a substituted ZnPc (octakis(oxyoctyl)phthalocyanine of zinc), and their characterization by means of several techniques. These characterization techniques include surface pressure (π-A) and surface potential (ΔV-A) isotherms as well as UV–vis Reflection spectroscopy and Brewster Angle Microscopy (BAM) for the films at the air–water interface together with UV–vis absorption and IR spectroscopies and Atomic Force Microscopy (AFM) for the LB films. The π-A and ΔV-A isotherms and BAM images indicate a phase transition at a surface pressure of ca. 9mN/m and a multilayer formation at surface pressures around 19–20mN/m; at a surface pressure around 27mN/m a disordered collapse of the film occurs. In addition, AFM images of LB films at π=10mN/m and π=20mN/m show a monomolecular and a multilayered film, respectively. The comparison of the UV–vis spectrum of ZnPc in solution, the reflection spectra of the Langmuir films and UV–vis spectra of LB films reveals a significant reduction in the Q band intensity for the films, indicative of an organization of ZnPc in the Langmuir and LB films versus the random distribution in solution. The UV–vis Reflection spectra are also consistent with multilayer formation at surface pressures around 19–20mN/m. The relative intensities of the IR spectrum bands change from the KBr pellet to the LB film which is also attributable to orientation effects in the film. Cyclic voltammetric experiments of LB films incorporating the ZnPc derivative show peaks that can be correlated with redox processes occurring in the phthalocyanine ring. A small but significant influence of the surface pressure and the number of deposited layers in the electrochemical behaviour is observed. The electrochemical response of cast films exhibits some differences with respect to that of LB films which have been attributed to their different molecular organizations.

Optically anisotropic and photoconducting Langmuir–Blodgett films of neat poly(3-hexylthiophene)

Among the several types of conjugated polymers used in recent investigations, polythiophene and its derivatives have attracted considerable attention over the past 20 years due to their high mobility and other remarkable solid-state properties. They have potential applications in many fields, such as microelectronic devices, catalysts, organic field-effect transistors, chemical sensors and biosensors. There are two critical parameters that determine the polymer-based device performance: chemical structure and nanostructure of the conjugated polymer in solid state. Langmuir–Blodgett (LB) films may be an interesting alternative for producing the films used in the devices since they can be obtained with high degree of thickness control, low number of defects, and some degree of organization at the molecular scale. However, most of the polythiophene derivatives have poor film forming properties by LB method and need the use of film form aiding materials. In this work, we report on the fabrication and characterization of Langmuir and Langmuir–Blodgett films of neat poly(3-hexylthiophene). Although the LB technique is not suitable to obtain LB films with a great number of layers, good quality films, with thicknesses suitable for fabrication of opto-eletronic devices could be easily built by using the proper deposition conditions.

J-aggregates of thiacyanine dye organized in LB films: Effect of irradiation of light

In the present communication we report the preparation and characterizations of Langmuir and Langmuir–Blodgett films of a thiacyanine dye N,N′-dioctadecyl thiacyanine perchlorate (NK) mixed with Octadecyl trimethyl ammonium bromide (OTAB). The relationship between the molar ratio of OTAB and NK and the orientation of molecules at the air–water interface was investigated using surface pressure-area per molecule ( π–A) isotherm. UV–vis absorption and fluorescence spectroscopic investigations reveal that prominent J-aggregation of NK molecule was observed in the LB films lifted at higher surface pressure. This J-aggregation can be controlled by diluting the NK molecules with OTAB. It was observed that the J-aggregates of NK decayed to monomer and H-aggregates when the NK-LB film was exposed to a monochromatic light of wavelength 460 nm ( λ max of J-aggregates).

Preparation and characterization of Langmuir and Langmuir–Blodgett films from a pyridine-terminated stilbene

Langmuir and Langmuir–Blodgett films of a pyridine-terminated stilbene derivative, namely 4-hexyloxy-4′-[N-(4-pyridilmethylene)amine] stilbene (abbreviated as HPAS), have been fabricated and characterized at various surface pressures, with surface pressure and Brewster Angle Microscopy being used to map the different phases of the stilbene monolayer at the air–water interface. UV–vis reflection spectroscopy showed a strong blue shift of 48 and 93 nm of the reflection spectrum of the Langmuir film with respect to the spectrum of a solution of HPAS, which indicates that two dimensional H-aggregates are formed at the air–water interface. These structures represent a minimum free energy conformation for the system, as they are observed even before the compression process starts. The sequential transfer of monolayers of HPAS onto solid substrates results in a Y-type deposition. Single layer LB films transferred at several surface pressures onto mica substrates have been analyzed by means of atomic force microscopy, from which it can be concluded that 20 mN/m is an optimum surface pressure of transfer, giving well-ordered homogeneous films without three dimensional defects and a low surface roughness. The optical properties of the LB films have been determined, with significant blue-shifted absorption spectra suggesting that the two dimensional H-aggregates at the air–water interface are transferred undisturbed onto the solid substrates. In addition, absorption and emission spectra are indicative of a strongly coupled excitonic interaction between the HPAS H-aggregates. X-ray reflectivity (XRR) experiments yielded a film thickness consistent with one monolayer in which the molecules are tilted 73° with respect to the solid substrate.

Characterization of Langmuir−Blodgett Film Using Differential Charging in X-ray Photoelectron Spectroscopy

Characterization of Langmuir−Blodgett Film Using Differential Charging in X-ray Photoelectron Spectroscopy

Preparation and Characterization of Langmuir−Blodgett Films of Wheel-Shaped Cu-20 Tungstophosphate and DODA by Two Different Strategies

A novel surfactant-encapsulated organic-inorganic hybrid compound (DODA)(24)Li[Cu(20)Cl(OH)(24)(P(8)W(48)O(184))] x 18 H(2)O (DODA-Cu20) has been prepared from the wheel-shaped tungstophosphate salt K(12)Li(13)[Cu(20)Cl(OH)(24)(H(2)O)(12)(P(8)W(48)O(184))] x 22 H(2)O (Cu20) and dimethyldioctadecylammonium bromide (DODA), and it has been characterized by elemental analysis (EA), thermogravimetric analysis (TGA), (1)H NMR, Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD) measurements. Monolayer and multilayer films of DODA-Cu20 were fabricated on different substrates by the Langmuir-Blodgett (LB) technique using H(2)O as the subphase. Another type of organic-inorganic hybrid film, DODA/Cu20, was also deposited on the same substrates as used for the film containing DODA-Cu20 under the same conditions by the LB technique using a Cu20 aqueous solution as the subphase and DODA as the cationic amphiphile for comparison. Both thus-prepared organic-inorganic hybrid films were characterized by UV-vis spectroscopy, XRD, transmission and polarized FT-IR spectroscopy, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The results indicate that stable monolayers at the air-water interface for DODA-Cu20 and at the air-Cu20 solution interface for DODA can be formed and that two LB films containing DODA-Cu20 and DODA/Cu20 constructed by two different methods both exhibit well-ordered lamellar structures. It is proposed that Cu20 exhibits different packing modes in the two LB films depending on the deposition strategy used.

Characterization of Langmuir−Blodgett Film Using Differential Charging in X-ray Photoelectron Spectroscopy

Differential charging is often regarded as a problem in X-ray photoelectron spectroscopy (XPS) studies, especially for insulating or partially conducting samples. Neutralization techniques have been developed to circumvent this effect. Instead of neutralizing the positive charge, which is often the technique to obtain good quality data, it is possible to exploit this phenomenon to get useful information about the sample. An attempt is made here to use this differential charging to study the mono- and multilayer Langmuir-Blodgett (LB) films of cadmium arachidate on silicon substrate. The surface potential was probed by measuring XPS line shift with respect to their neutral position and was found to have correlation with the thickness of the films. No differential charging was observed in the monolayer LB film where there was only one layer of cadmium headgroup. Significant differential charging was observed for multilayer films, the total charging as well as the differential charging in these films increase with increasing number of layers. Angle-resolved XPS measurements were performed to obtain additional information about the structure of the films. Charging of the upper layer of the films close to the vacuum interface was found to be less compared to that of the interior. The discrete cadmium layers were found to be more differentially charged compared to the continuous hydrocarbon stacks in the multilayer LB films. Charging of the discrete cadmium layers has been utilized to obtain quantitative information of the multilayer LB films.

Preparation of Ordered Films Containing a Phenylene Ethynylene Oligomer by the Langmuir−Blodgett Technique

This paper reports the fabrication and characterization of Langmuir and Langmuir-Blodgett (LB) films incorporating an oligo(phenylene-ethynylene) (OPE) derivative, namely, 4-[4-(4-hexyloxyphenylethynyl)-phenylethynyl]-benzoic acid (HBPEB). Conditions appropriate for deposition of monolayers of HBPEB at the air-water interface have been established and the resulting Langmuir films characterized by a combination of surface pressure and surface potential versus area per molecule isotherms, Brewster angle microscopy, and ultraviolet reflection spectroscopy. The Langmuir films are readily transferred onto solid substrates, and one-layer LB films transferred at several surface pressures onto mica substrates have been analyzed by means of atomic force microscopy, from which it can be concluded that 14 mN/m is an optimum surface pressure of transference, giving well-ordered homogeneous films without three-dimensional defects and a low surface roughness. The optical and emissive properties of the LB films have been determined with significant blue-shifted absorption spectra indicating formation of two-dimensional H aggregates and a Stokes shift illustrating the effects of the solid-like environment on the molecular chromophore.

Preparation and Characterization of Langmuir and Langmuir−Blodgett Films from a Nitrile-Terminated Tolan

Langmuir and Langmuir−Blodgett films of a nitrile-terminated tolan, namely 4-[4‘-decyloxyphenylethynyl]benzonitrile, have been fabricated and characterized at various surface pressures, with surface pressure and surface potential isotherms together with Brewster angle microscopy being used to map the different phases of the tolan monolayer at the air−water interface. The Langmuir films have been characterized by UV−vis spectroscopy, with quantitative analysis of the reflection spectra supporting an organizational model in which compression of the film leads to change in the tilt angle of the tolan molecules from an initial value of ca. 35° to one of ca. 60° before collapse of the monolayer. Moreover, a blue shift in the reflection spectrum of the Langmuir film of 30 nm with respect to the spectrum of a chloroform solution of the nitrile tolan indicates that two-dimensional H-aggregates are formed at the air−water interface. These structures represent a minimum free-energy conformation for the system, as t...

Characterization of Langmuir and Langmuir–Blodgett films of a thiomacrocyclic ionophore by surface pressure and AFM

The new synthesized thiomacrocyclic ionophore 4-phenyl-4-sulfide-11-(1-oxodecyl)-1,7-dithia-11-aza-4-phosphacyclotetradecane has proven to form Langmuir and Langmuir–Blodgett (LB) films. This ionophore shows a large affinity for copper(II) ions. Thus, the influence of the subphase composition on the surface pressure–area isotherms has been studied. The LB films have been observed by AFM and the effect of the subphase composition and the deposition surface pressure on the LB films is discussed. AFM image morphology has been correlated to the ionophore molecular structure. Surface pressure–area isotherms and AFM images show that the presence of copper(II) ions has an important role in the film structure.

Characterization of Langmuir−Blodgett Films of a Ferroelectric Liquid Crystal

Molecular orientation, structure, and phase transition behaviors in Langmuir-Blodgett (LB) and cast films of a ferroelectric liquid crystal of sec-butyl 6-(4-(nonyloxy)benzoyloxy)-2-naphthoate (FLC-1) are determined by ultraviolet (UV) spectroscopy, X-ray diffraction, and infrared (IR) spectroscopy. It is found that the orientation angle of chromophores theta in LB films is 41 degrees from the surface normal. The tilt angle of the chromophore changes at 56, 70, and 88 degrees C, respectively, which denotes the presence of phase transitions. Two kinds of layered or isomeric crystal structures of the LB films with layer spacings of 3 and 3.5 nm at room temperature have been found while the latter disappears above 45 degrees C, as confirmed by measurement of temperature-dependent IR spectra.

Langmuir and Langmuir-Blodgett films of organophosphorus acid anhydrolase.

In this paper, we describe the preparation and characterization of Langmuir and Langmuir-Blodgett (LB) monolayers of the enzyme organophosphorus acid anhydrolase (OPAA). Langmuir films of OPAA were characterized on different subphases, such as phosphate, ammonium carbonate, and bis-tris-propane buffers. Monolayers at the air-water interface were characterized by measuring the surface pressure and surface potential-area isotherms. In situ UV-vis absorption spectra were also recorded from the Langmuir monolayers. The enzyme activity at the air-water interface was tested by the addition of diisopropylfluorophosphate (DFP) to the subphase. LB films of OPAA were transferred to mica substrates to be studied by atomic force microscopy. Finally, a one-layer LB film of OPAA labeled with a fluorescent probe, fluorescein isothiocyanate (FITC), was deposited onto a quartz slide to be tested as sensor for DFP. The clear, pronounced response and the stability of the LB film as a DFP sensor show the potential of this system as a biosensor.

Preparation and characterization of Langmuir–Blodgett‐type arachidate films

AbstractMetal arachidate Langmuir–Blodgett (LB) films with Pb2+ and Cd2+ cations and varying numbers of monomolecular layers (2 and 4 monolayers, ML) were deposited on trimethylsilylated glass substrates. The arachidate salt formation was commenced during the film deposition from a water‐based solution. The extent of salt formation and the build‐up of the LB layer were evaluated by quantitative XPS.The completeness of the salt formation was assessed by the atomic ratio of the carboxylic (‐COO‐)‐type carbon component with C 1s binding energy at ∼288.5 eV to that of the selected line of the actual cation.The surface coverage of the glass substrate by the LB film was assessed by calculations based on a substrate–overlayer model using the XPS MultiQuant program. According to this model, the attenuation of the Si 2p photoelectron signal from the substrate by the 2 and 4 ML LB films (with 56 and 112 Å thickness, respectively) was calculated and compared with the measured intensities, enabling the completeness of the layer to be evaluated. The layer thickness values calculated from the measured intensity of the layer constituents reflected accurately the thickness derived from the geometry of the arachidate molecule, confirming both the adequacy of the model and the accuracy of the measurement.In agreement with earlier results it was confirmed that salt‐based LB films are fairly stable under high vacuum conditions, although slow decomposition of lead arachidate films was detected during prolonged x‐ray irradiation. Copyright © 2002 John Wiley & Sons, Ltd.

Electron spin resonance characterization of Langmuir–Blodgett films containing functional molecules

The role of electron spin resonance (ESR) spectroscopy in the characterization of Langmuir–Blodgett (LB) films containing functional molecules is discussed. Unpaired electrons in LB films are associated with radical molecules produced by charge transfer, paramagnetic metallic ions such as Cu2+ and so on. ESR parameters such as g-value and hyperfine coupling provide information of local molecular orientation and electronic states. ESR can unambiguously determine the orientation distribution function of molecules through g-value anisotropy. The case of mixed LB films of a merocyanine dye and arachidic acid is discussed as a typical example. The analysis of the anisotropic ESR spectra of stable radicals existing in these films has revealed detailed in-plane orientation of radicals, which led to the discovery of flow orientation effect during LB dipping process. Light-induced ESR (LESR) is introduced to directly detect the dye radicals generated by photoinduced charge transfer. Observed LESR spectra, associated with a resolved 14N hyperfine structure, uniquely probe the orientation and electronic states of dye molecules forming the J-aggregates in highly ordered LB matrix. AFM observation of dye domains in these films is also discussed.

Specific approach of generalized ellipsometry for the determination of weak in-plane anisotropy: application to Langmuir–Blodgett ultrathin films

We report on a procedure of generalized ellipsometry for the determination of the optical constants of stratified samples that present a weak in-plane anisotropy. We first derive the analytical expressions of the Jones reflection matrix and of the detected intensity for a rotating-polarizer ellipsometer configuration. These expressions show that the in-plane birefringence and the orientation of the principal axes of the dielectric tensor can be obtained from a measurement of the normalized off-diagonal terms of the reflection matrix as a function of the sample azimuth, followed by a Fourier analysis and a wavelength-by-wavelength inversion of these experimental data. We apply this method to the optical characterization of Langmuir–Blodgett molecular films deposited on silicon substrates. The obtained results show that even for transparent and ultrathin films it is possible to accurately determine very weak in-plane birefringence and axis orientations.

Structural and Optical Nonlinear Characterizations of Langmuir−Blodgett Films of 1-Benzyl-9-hydrofullerene-60

The structural and optical nonlinear features of the condensed layers at the air-water interface and Langmuir-Blodgett (LB) films of the substituted fullerene 1-benzyl-9-hydrofullerene-60 (C{sub 60}-Be) were investigated by {pi}-A isotherm, small angle X-ray diffraction (SAXD), and optical measurements. Pure C{sub 60}-Be molecules existed at the air-water interface in a bulk phase. A new type of two-chain amphiphilic molecule, 1, 10-bistearyl-4, 6, 13, 15-tetraene-18-nitrogen-crown-6 (NC), was used as an inert material to construct mixed C{sub 60}-Be/NC LB films of much better quality than the pure C{sub 60}-Be LB films. Our {pi}-A, UV-visible absorption, and SAXD measurements show that the structural improvement in the mixed C{sub 60}-Be/NC LB films was realized by insertion of the C{sub 60}-Be molecules between the two hydrophobic chains of the NC molecules. The relatively large third-order nonlinear susceptibility {Chi}{sup (3)}{sub {chi}{chi}{chi}{chi}}(-3{omega}; {omega},{omega},{omega}) = 2.1 x 10{sup -11} esu was deduced by measuring third-harmonic generation in the mixed C{sub 60}-Be/NC LB films. 13 refs., 7 figs.

The Influence of Depositing Velocity on Polyamic Acid Salt Langmuir–Blodgett Alignment Films for Nematic Liquid Crystal

Abstract The characterization of Langmuir–Blodgett (LB) orientation films in terms of the optical retardation as a function of the LB depositing velocity has been studied, and the surface anchoring strength of the LB films for a nematic liquid crystal has been estimated. The optical retardation decreases as the LB depositing velocity increases. In contrast, the anchoring strength increases as the LB depositing velocity increases. The macroscopic anchoring strength may not have a positive correlation with the optical retardation which reflects the microscopic orientational order. Furthermore, we succeeded in generating the high pretilt angle by only using the LB method. The pretilt angle gradually decreases with increasing the depositing velocity.

Preparation of Langmuir-Blodgett multilayers with differently substituted poly(3-alkylthiophenes)

It has been reported (I. Watanabe, K. Hong and M. F. Rubner, Langmuir, 6 (1990) 1164) that polyalkylthiophenes are not suitable for multilayer formation owing to the lack of suitable interaction with the water surface. Therfore it seems that, in order to obtain polymer useful for the preparation of mulltilayers, this class of polymer should be subjected to chemical modifications that improve the polarity of the macromolecules. We have mainly modified the side chain of the polymers by introducing an oxygen atom in different positions on the alkyl side chain. This modification has the advantage that the polyenic backbone is unperturbe by the change in chemical structure. The aim of this work is to report on some data concerning the preparation and the characterization of Langmuir- Blodgett multilayers prepared with this new class of polymer.