Arachidic Acid Monolayers Research Articles

Regular Stripe Patterns in Skeletonized Langmuir−Blodgett Films of Arachidic Acid

Regular stripe patterns are formed in skeletonized LB films of two arachidic acid monolayers deposited on Si wafers from Cd2+-containing aqueous subphase after monolayer transfer at pH 5.7. These stripe patterns are very different from those less regular patterns observed at lower or higher pH values of the aqueous subphase. Atomic force microscopy (AFM) and phase shift interference microscopy (PSIM) studies have shown that these stripes are grooves aligned in definite distances along the meniscus and perpendicular to the dipping direction of the monolayer transfer. There exist deep straight grooves of about 6 nm depth in a regular distance and between them less marked stripelike defect lines. These regular stripe patterns occur only in the skeletonized LB films, but they are already preformed during the monolayer transfer onto the solid substrate. The formation of the regular stripe patterns is decisively affected by the arachidic acid/cadmium arachidate ratio but also by the dipping rate. The direct correlation to the autooscillations of the meniscus suggests an electrohydrodynamic instability mechanism as cause for the nonuniform ordering and composition of the LB film.

Effect of subphase Ca++ ions on the viscoelastic properties of Langmuir monolayers

It is known that the presence of cations like Ca++ or Pb++ in the water subphase alters the pressure-area isotherms for fatty acid monolayers. The corresponding lattice constant changes have been studied using x-ray diffraction. Reflection-absorption spectroscopy has been used to probe the chemical composition of the film. We report on the first measurements of the time evolution of the shear viscosity of arachidic acid monolayers in the presence of Ca++ ions in the subphase. We find that the introduction of Ca++ ions to the water subphase results in an increase of the film’s viscosity by at least three orders of magnitude. This increase occurs in three distinct stages. First, there is a rapid change in the viscosity of up to one order of magnitude. This is followed by two periods, with very different time constants, of a relatively slow increase in the viscosity over the next 10 or more hours. The corresponding time constants for this rise decrease as either the subphase pH or Ca++ concentration is increased.

Oriented Crystallization of KH2PO4 under a Compressed Langmuir Monolayer

Oriented growth of KH2PO4 (KDP) under a compressed Langmuir monolayer of arachidic acid (AA) has been studied by using π−A isotherms, X-ray diffraction (XRD), Brewster angle microscope (BAM), and atomic force microscopy (AFM) techniques. All produced crystals are almost connected with the monolayer by the crystal face (100), epitaxial forming multilayer structures along the vertical direction. BAM observation shows that KDP crystals induced by the Langmuir monolayer are nearly homogeneous and uniform in crystal size. Crystallization induction time is reduced evidently. The optical second harmonic generation (SHG) experiment indicates that the SHG signal of the sample of 25 layers deposited in Z type is better than that of the crystals in the absent of a monolayer, which demonstrates that oriented KDP crystals are homogeneous with a uniform orientation.

Conformations of poly(dihexylsilane) embedded in Langmuir-Blodgett multilayers of arachidic acid

Poly(dihexylsilane) (PDHS) and arachidic acid (AA) were co-spread onto a cadmium-containing water subphase and transferred onto a solid substrate as multilayers by the Langmuir-Blodgett method. The structure of these films was evaluated by means of UV-visible absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray diffractometry, and film thickness measurements. The results indicated that the PDHS ultrathin film is incorporated into a well-structured AA multilayer matrix without appreciable destruction of the layer structure. The conformational behavior of PDHS embedded within this film was evaluated by UV-visible absorption spectroscopy. The phase transition temperature of the ordered (all-trans zigzag) to the disordered (helical gauche) state on the AA monolayer at the air-water interface is lowered and the conformational state is virtually maintained in the as-deposited multilayers during storage at room temperature at least for a month. PDHS in the AA multilayer on heating showed a substantially broadened transition around 40°C, which clearly reflects a geometrical restriction effected by the AA multilayer matrix.

Conformations of poly(dihexylsilane) embedded in Langmuir-Blodgett multilayers of arachidic acid

Poly(dihexylsilane) (PDHS) and arachidic acid (AA) were co-spread onto a cadmium-containing water subphase and transferred onto a solid substrate as multilayers by the Langmuir-Blodgett method. The structure of these films was evaluated by means of UV-visible absorption spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray diffractometry, and film thickness measurements. The results indicated that the PDHS ultrathin film is incorporated into a well-structured AA multilayer matrix without appreciable destruction of the layer structure. The conformational behavior of PDHS embedded within this film was evaluated by UV-visible absorption spectroscopy. The phase transition temperature of the ordered (all-trans zigzag) to the disordered (helical gauche) state on the AA monolayer at the air-water interface is lowered and the conformational state is virtually maintained in the as-deposited multilayers during storage at room temperature at least for a month. PDHS in the AA multilayer on heating showed a substantially broadened transition around 40°C, which clearly reflects a geometrical restriction effected by the AA multilayer matrix.

Subphase pH effect on composition and structure of Fe(III) arachidate monolayers

The arachidic acid monolayers on Fe(III) subphase surfaces with various pH values have been studied. The π– A isotherms of monolayers and Fourier transform infra-red (FTIR) spectra of Langmuir–Blodgett (LB) films show that the films obtained on different pH subphases with a concentration of Fe(III) 5×10 −5 M have different compositions. At low pH (2.4), the film appears to be almost 100% acid. The content of Fe(III) arachidate increases with increasing pH, at pH 3.7, the film appears to be 100% salt; and the content of salt decreases with pH larger than 3.7. The transmission electron microscope (TEM) observations show that the monolayer structures changed from patch aggregates formed by Fe(III) arachidate at low pH to a network or dotted structures formed by hydrolysates of Fe(III) at high pH. The Brewster angle microscopy (BAM) experiments show the different monolayer behaviors at various pH. These results indicate that the subphase pH greatly influenced the arachidic acid monolayers.

Fabrication of nano-sized particles of metallic copper and copper sulfide in Langmuir–Blodgett films

Langmuir monolayers of arachidic acid on a subphase of 0.3 mM CuSO 4/17 mM NH 3 were transferred to hydrophobic glass and mica substrates to give Langmuir–Blodgett films of cupric arachidate (CuAr). Transfer ratios of close to 1 were observed and regular “Y”-type deposition was demonstrated with hydrophobic glass. With mica as the substrate, “Z”-type deposition occurred. The films were exposed to H 2S and hydrazine, and evidence for the formation of copper sulfide and metallic copper particles, respectively, was obtained by ultraviolet/visible spectrophotometry, X-ray photoelectron spectroscopy and atomic force microscopy.

Chemical sensor based on surface acoustic wave resonator using Langmuir-Blodgett film

A one-port surface acoustic wave (SAW) resonators incorporating Langmuir-Blodgett (LB) films has been investigated. SAW sensors are one potential applications of SAW devices. Most of the work reported on SAW sensor concerns delay lines. In this paper we characterize the mass loading effects of one-port resonators by depositing successive monolayers of LB films onto the surface. A 90 MHz SAW gas-phase sensor has been fabricated on an ST cut quartz substrate, and one-port resonator configurations have been used as the sensing element. Ultra thin monolayers of arachidic acid and arachidic acid ethyl ester have been deposited using the LB method. The resonant frequencies and the Q values have been measured as sensor response. Experimental results show that the Q values and the resonant frequencies of the one-port SAW resonator vary with film mass loading on the SAW device surface.

Europium and terbium carboxylate interactions in monolayers and Langmuir–Blodgett films

The interaction of trivalent europium and terbium ions with arachidic acid monolayers is reported. The ions are incorporated into the monolayer from the subphase solution, increasing the minimum area per molecule and modifying the pressure–area isotherms. Europium and terbium arachidate bonding in multilayer films transferred to solid supports is evidenced by FTIR and photophysical measurements. The luminescent films are `Y' type structures, as shown by the X-ray diffraction patterns.

Preparation and spectral characteristics of gold particles in Langmuir-Blodgett films

Langmuir-Blodgett films incorporating complex ions of gold(III) have been fabricated from air-water monolayers of arachidic acid, dimethyldioctadecylammonium bromide and dihexadecyl phosphate. The films, and their reactions with reducing agents to produce colloidal gold particles, have been characterised by surface pressure/area per molecule ( π- A) isotherms, UV-vis. and XPS spectroscopy, atomic force microscopy (AFM) and transmission electron microscopy (TEM). Colloidal gold particles, produced in films exposed to carbon monoxide, were examined by AFM and TEM. The gold particles, as determined by TEM, were of a mean size of 10 nm and were randomly distributed in the films. Solvent immersion studies were also conducted in order to investigate the effect of the dielectric medium on the position of the gold colloid plasmon band. The position of the wavelength maximum of the gold plasmon band of the gold-LB film in air was not consistent with a just a layer of surfactant surrounding the particles. From the position of the surface plasmon band peak an effective refractive index of 1.35 is calculated for the LB film, which is considerably lower than that of a dense surfactant film. Also, the band maximum did not shift to any measurable extent when the films were immersed in water. We suggest that the reason for these observations is that air is trapped in the film and this lowers the refractive index of the film and prevents water penetration into the film. Immersion of a gold-LB film in the high refractive index liquid CS 2 resulted in a redshift in the gold plasmon band, which was a consequence of the aggregation of the gold particles due to the dissolution of the surfactant film in the surrounding liquid.

Determination of the Tilt Angle of Langmuir Monolayers with Brewster Angle Autocorrelation Spectroscopy and Quantitative Image Analysis in Brewster Angle Microscopy: A Comparison between Two Different Methods

We have developed a method to determine the tilt angle of the aliphatic molecule chains of Langmuir monolayers on the water surface by combination of Brewster angle microscopy (BAM) and autocorrelation technique (Brewster angle autocorrelation spectroscopy). In this paper measurements of the surface pressure dependent tilt angle of stearic acid and arachidic acid monolayers on water will be presented. We compare our technique and the results with another previously presented method of quantitative image analysis in BAM. The comparison with X-ray diffraction data show that Brewster angle autocorrelation spectroscopy is an efficient tool for measuring the tilt angle in Langmuir monolayers with high accuracy.

Distribution of a water-soluble porphyrin in mixed monolayers evaluated by energy transfer

Mixed monolayers of a water-soluble tetra-anionic porphyrin (PO) with dioctadecyldimethylammonium bromide (DOMA) and methyl stearate (SME) have been formed by co-spreading, with the aim of achieving molecular recognition. The lateral distribution of PO in such monolayers has been investigated by Förster energy transfer from the amphiphilic oxacyanine dye S9 in a mixed monolayer of methyl arachidate (AME) and arachidic acid (AA). Mixed monolayers of PO:DOMA:SME, mixing ratios 1:4: X ( X = 32, 64, 160, 240, 320 and 480) were transferred to hydrophobic glass plates coated with S9:AME:AA = 1:2:18 by vertical dipping. The system was excited with ultraviolet radiation (λ = 366 nm). The excitation energy of S9 is transferred to PO and the relative fluorescence intensity I d I ∞ ( I d in the presence and I ∞ in the absence of PO) of S9 at 420 nm was measured. The results indicate a homogeneous lateral distribution of PO i.e. no cluster formation, for low densities of PO in mixed monolayers with DOMA and SME.

In-situ measurement of lead(II) ion binding to an arachidic acid langmuir monolayer using a quartz crystal microbalance

A quartz crystal microbalance (QCM) was used to measure the in situ binding of lead (II) ions to a Langmuir monolayer of arachidic acid (ArH) at the air-water interface. A horizontally oriented QCM was lowered onto an ArH monolayer and an analiquot of a Pb 2+ solution was injected beneath the monolayer. A decrease in the QCM frequency was observed, consistent with Pb 2+ binding to the ArH monolayer. Models for a fatty acid to divalent metal ion ratio ( F: M) of 2 and 1 were considered. The experimental data was consistent with 2:1 binding.

Bending Energy of Amphiphilic Films at the Nanometer Scale

The diffuse scattering of x rays by the thermally excited out-of-plane fluctuations of different amphiphilic films was measured for in-plane wavelengths down to the nanometer range, giving access to nontrivial bending effects. The Helfrich Hamiltonian applies on pure water and in the solid phase of an arachidic acid monolayer a large bending rigidity constant was measured. When formed on a subphase containing divalent cadmium ions, the height-height fluctuation spectrum $〈z(q)z(\ensuremath{-}q)〉$ is greatly modified: no longer consistent with a ${q}^{\ensuremath{-}4}$ law at large wavelengths but rather with a ${q}^{\ensuremath{-}3.3\ifmmode\pm\else\textpm\fi{}0.2}$ law, revealing a very different physical mechanism whose origin is discussed.

Effect of Ionic Repulsion among Hydrophilic Groups on Aggregation Structure of Fatty Acid Monolayer on the Water Surface

The effect of ionic repulsion among hydrophilic groups of arachidic acid molecules on the aggregation structure of the arachidic acid monolayer on the water surface was investigated on the basis of surface pressure−surface area (π−A) isotherm measurements, Fourier transform infrared spectroscopic (FT-IR) measurements, and transmission electron microscopic (TEM) observations. π−A isotherm and FT-IR measurements revealed that the degree of ionic dissociation of hydrophilic groups in the monolayer drastically changed in a pH range of 10−12. The arachidic acid monolayer in a slightly dissociated state of hydrophilic groups (pH = 5.8) did not exhibit the phase transition from an amorphous state to a crystalline one during compression. On the other hand, the monolayer in a highly dissociated state (pH = 12.6) showed the phase transition from an amorphous state to a crystalline one by surface compression at the subphase temperature, Tsp, below the melting temperature, Tm, of the monolayer, and also, the monolaye...

Poly(di-n-hexylsilane) Ultrathin Films Assisted on an Arachidic Acid Monolayer

A 1:1 mixture of poly(di-n-hexylsilane) (PDHS) and arachidic acid (AA) was spread on pure water. UV absorption spectroscopy and Brewster angle microscopy on the water surface as well as X-ray diffractometry and Fourier-transform infrared spectroscopy of the deposited films all supported the concept that an ultrathin film of PDHS is formed on the top of lipophilic ends of the AA monolayer by this simple cospreading method. The PDHS film on the AA monolayer exhibited some characteristic conformational behaviors. The disordered to crystalline conformational change of PDHS was epitaxially induced by the compressive phase transition from the liquid condensed (L2) to state the crystalline solid (S) state of the AA monolayer. The crystalline state of PDHS became particularly unstable at temperatures above 15 °C, which is substantially lower than the phase transition temperature of bulk materials (ca. 40 °C).

Spectroscopic and electrochemical studies of N, N′-bis(decamethylcarboxylic)-3,4,9,10-perylene-bis(dicarboxyimide)

The vibrational and electronic characterization of N, N′-bis(decamethylcarboxylic)-3,4,9,10-perylene-bis(dicarboxyimide) prepared by the Langmuir-Blodgett (LB) technique was accomplished, and the average molecular orientation in LB films was calculated from the transmission and RAIRS data. It was found that the short and long chromophore axes are tilted to the perpendicular by about 70° and 28°, respectively. Using electronic spectra together with steady state fluorescence, it was concluded that the packing behavior of perylene tetracarboxylic diimide is mainly determined by II-II aromatic interactions. The electrochemical measurements show the presence of a non-negligible amount of pinhole defects in the prepared films. Monolayers of arachidic acid were used as spacer layers on silver island films, and resonance Raman scattering from the molecules was studied as a function of their spacing from the rough silver layer. A long range SERRS effect with an enhancement dropping off between 11 and 13 nm was obtained.

Langmuir-Blodgett films of three new biferrocene derivatives and their electrocatalysis

Monolayers of three new biferrocene derivatives (BiFc) containing an α, β-unsaturated carbonyl group have been investigated and a stable Langmuir monolayer of each BiFc was formed at the air-water interface. The mixed monolayer of each BiFc with arachidic acid (AA) is easily assembled to Langmuir-Blodgett (LB) films. The UV-Vis spectra indicate that an H-aggregate is formed in mixed LB films. The surface morphology of each kind of mixed LB monolayer has been detected by scanning electron microscopy and phase separation has been observed. The electrochemical redox reaction of Fe(CN) 3− 6 Fe(CN) 4− 6 could be catalyzed by the indium tin oxide electrodes modified with the mixed monolayer of BiFc and AA.

The conformational state and phase transition of polysilane in arachidic acid LB film matrix

Langmuir-Blodgett (LB) films containing a mixture of poly(di- n-hexylsilane) (PDHS) and arachidic acid were prepared. The surface pressure-area curves indicate that PDHS is positioned between the lipophilic ends of arachidic acid monolayers in the LB films. The Si backbone of PDHS is present in both the trans-zigzag planar and disordered states in the LB films. The ratio of the two states is dependent on the deposition number and temperature of the water subphase. The phase transition temperature (approximately 25 °C) in the floating monolayer is reduced compared with that in the cast bulk film (42 °C).

A trough with radial compression for studies of monolayers and fabrication of Langmuir-Blodgett films

A new type of Langmuir trough with radial compression is reported for studies of monolayer properties and fabrication of Langmuir-Blodgett (LB) films. The trough included twenty curved diaphragms, which form a circular shape on water and compress monolayers. Typical monolayers of arachidic acid, DL-α-phosphatidylcholine dipalmitoyl, cellulose tridecanoate, and poly (butyl methacrylate) showed reproducible surface pressure-area isotherms with radial compression. Flow profiles were studied of monolayers on cellulose tridecanoate and poly(butyl methacrylate) and suggested that the monolayers are radially compressed with no particular film disturbance. A Wilhelmy glass plate preserved no deflection in the subphase surface from low to high surface pressures during the film compression and decompression; no pressure excess causing the deflection, which is frequently observed in the case of the film compression with a sliding barrier, was found on both sides of the Wilhelmy plate. Application of the radial compression enabled to do a symmetrical deposition for the fabrication of LB films.