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The process of formation of a Langmuir-Schaefer (LS) matrix based on a mixed monolayer of arachidic acid (AA) and 8 nm CdSe/CdS/ZnS quantum dots (QDs) stabilized by molecules of trioctylphosphine oxide (TOPO) was investigated. The change in the morphology, monolayer compressibility, and area per elementary cell of the created mixed monolayers, depending on the ratio of the components, was studied. It is shown that the change in the morphology of Langmuir-Blodgett (LB) monolayers begins to occur at a ratio between the number of QDs and AA molecules of 1:24. Dendrimeric structures with a thickness of the order of 30-40 nm appear in the mixed monolayer when LB film deposition was carried out above the collapse surface pressure of a Langmuir film from only TOPO-covered QDs. Information on the dependence of the morphology of such structures on the molar ratio of the components is necessary for the production of ordered 2D nanostructures containing 0D and 1D objects with quantum bonds. Such nanostructures can be used in nanoelectronic and optoelectronic devices as a sensitive sensor element. The obtained results would be relevant for any type of spherical shape nanoparticles.

Amphiphilic biomembrane structures determine significant biological functions and are extensively used as structure models to learn from and study nature. Many biomimetic amphiphilic membranes have been established to connect natural and artificial substances. In this paper, taking advantage of the intercalation and assembly properties of the layered double hydroxides (LDHs), the amphiphilic LDHs/arachidic acid (AA) nanocomposite Langmuir–Blodgett (LB) ultrathin films (UTFs) were fabricated by the LB technology. The CdTe quantum dots (QDs) were incorporated into the LB monolayers via a layer-by-layer (LbL) method based on the electrostatic interaction between LDHs and CdTe QDs. The amphiphilic (CdTe QDs@LDHs/AA)n nanocomposite LB UTFs were composed of CdTe QDs@LDHs hydrophilic segments and hydrophobic layers formed by the long alkyl chain of AA. Because of the spacing effect of amphiphilic AA, the fluorescence intensity of CdTe QDs was enhanced about 10-fold, and the fluorescence lifetimes (38.96 ns vs 17...

Synchrotron-based X-ray scattering measurements of phase-separated surfactant monolayers at the air-water interface provide molecular-level structural information about the packing and ordering of film components. In this work, grazing incidence X-ray diffraction (GIXD) and X-ray reflectivity (XR) measurements were used to collect crystallographic structural information for binary mixed monolayers of arachidic acid (AA, C19H39COOH) with perfluorotetradecanoic acid (PA, C13F27COOH), a system that has previously been investigated using a variety of thermodynamic and micron-scale structural characterization methods. GIXD measurements at surface pressures of π = 5, 15, and 30 mN/m indicated that AA in pure and mixed films forms a rectangular lattice at π = 5 and 15 mN/m but a hexagonal lattice at π = 30 mN/m. PA formed hexagonal lattices under all conditions, with films being highly ordered and crystalline (as determined by Bragg peak width) at even the lowest surface pressures investigated. Phase separation occurred for all mixed monolayer film compositions and surface pressures, manifesting as diffraction peaks characteristic of the individual components appearing at different in-plane scattering vector qxy. For both pure and mixed films, the molecular tilt angle of the AA hydrocarbon chain toward the nearest-neighbor was substantial at low pressures but decreased with increasing pressure. The PA fluorocarbon chain showed negligible molecular tilt under all conditions, and was oriented normal to the subphase surface regardless of surface pressure or the presence of AA in the films. In all cases, the two components in the mixed film behaved entirely independently of film composition, which is exactly the expected result for a fully phase-separated, immiscible system. XR measurements of film thickness at the air-water interface supported these results; overall film thickness approached the calculated ideal surfactant tail lengths with increasing surface pressure, indicating nearly normal oriented surfactants. The overall surfactant packing and crystallographic features of the mixed monolayers are discussed in terms of the lipophobic nature of the perfluorinated surfactant as well as in context of thermodynamic miscibility and domain structure formation reported elsewhere in the literature for these mixed monolayer systems.

In the present Article, a reversible transition behavior from J-aggregates to excimer of an indocarbocyanine dye 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate (DiI) in Langmuir–Blodgett (LB) films was reported. Surface pressure–area (π–A) isotherms, UV–vis, and fluorescence spectroscopies as well as atomic force microscopy (AFM) were used for characterizations of the films. π–A isotherms suggest a balance of interactions between DiI and fatty acids in the mixed monolayer at DiI mole fraction XDiI = 0.4, resulting in a stable and ideally mixed monolayer. It has been observed that pure DiI formed excimer in LB films, whereas both J aggregates and excimer were formed in LB films when DiI was mixed with long chain fatty acids, viz., stearic acid or arachidic acid. In fatty acid matrix at XDiI = 0.4, only J aggregates were formed in the LB films. This has been confirmed using deconvolution of spectroscopic results as well as using excitation spectroscopy. The coherent size of the J aggrega...

This study proposes a rapid magnetic solid-phase extraction (MSPE) based on monodisperse magnetic single-crystal ferrite (Fe(3)O(4)) nanoparticles (NPs) for determining the quantities of eight free fatty acids (FFAs), including palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:1), linoleic acid (C18:2), linolenic acid (C18:3), arachidic acid (C20:0), eicosenoic acid (C20:1), and behenic acid (C22:0) in oil. The amine-functionalized mesoporous Fe(3)O(4) magnetic NPs were applied as a sorbent for MSPE of FFAs from oil samples in a process that is based on hydrophilic interaction. The extraction can be completed rapidly in a dispersive mode with the aid of vigorous vortex. Additional tedious processing steps such as centrifugation and evaporation of organic solvent were not necessary with this procedure. Furthermore, esterification of FFAs can be accomplished during the desorption procedure by using methanol/sulfuric acid (99:1, v/v) as the desorption solvent. Several parameters affecting the extraction efficiency were investigated, including the matrix solvent for extraction, the desorption solvent and desorption time, and the amount of sorbent and extraction time. The pretreatment process was rapid under optimal conditions, being accomplished within 15 min. When coupled with gas chromatography-flame ionization detection (GC-FID), a rapid, simple, and convenient MSPE-GC-FID method for the determination of FFAs in oil samples was established with a total analysis time within 25 min. The limits of detection for the target FFAs were found to be 7.22-26.26 ng/mL. Recoveries in oil samples were in the range of 81.33-117.75%, with RSDs of

Plasmon-enhanced Raman scattering and plasmon-enhanced fluorescence of the two molecules N,N′-dimethylquinacridone (DMQA) and N,N′-diisoamylquinacridone (DIQA) used as codopants in OLEDs (with improved stability) are reported. The work includes a complete vibrational characterization using Raman and infrared spectra supported by DFT calculations. Plasmon enhancement is achieved using silver and mixed Ag/Au nanostructures: colloids and metal island films, supporting localized surface plasmon resonances (LSPR). However, fine-tuning of the experimental conditions is necessary to attain surface-enhanced (resonance) Raman scattering (SERS/SERRS) of the two molecules with similar structures. SERRS spectra of DMQA are obtained on silver colloids and from a Langmuir–Blodgett (LB) monolayer deposited onto silver island films (SIF). High quality SERRS spectra of DIQA were only obtained from LB layers on mixed Ag/Au island films. Using spacer LB layers of arachidic acid (AA) to separate the fluorophore from the meta...

Ordered two-dimensional (2D) arrays of β-HgS nanocrystal aggregates were prepared successfully at the air/water interface through the interfacial reaction between Hg(2+) ions in the subphase and H(2)S in the gaseous phase under the direction of liquid-expanded monolayers of arachidic acid (AA). These 2D arrays are composed of hexagonal or quasi-hexagonal aggregates with the size of several hundreds of nanometers that consist of several tens of HgS nanocrystals with the size of several nanometers. The formed HgS nanocrystals together with AA molecules self-assembled into round aggregates due to the interactions between the species, and the aggregates self-assembled into 2D arrays further due to the attractions between them. During the self-assembly process, the soft round aggregates transformed into hexagonal or quasi-hexagonal ones. The experimental conditions, especially the phase states of the AA monolayers and temperature, have great influences on the formation of the 2D arrays. To the best of our knowledge, this is the first case to get 2D ordered arrays at the air/water interface through a one-step synthesis and assembly process.

We have investigated the structure of the mixed Langmuir-Blodgett (LB) film of a merocyanine dye derivative (MO(18))-deuterated arachidic acid (C(20)-d) binary system and the influence of successive hydrothermal treatment in the liquid phase (HTTL) on the mixed LB film by means of polarized UV-visible and IR absorption spectroscopy. The visible absorption band with in-plane anisotropy at 503 nm before HTTL transforms into an absorption band with in-plane isotropy at 557 nm after HTTL for 16-18 min through a peak maximum near 520 nm after HTTL for 2-12 min. The degree of total MO(18) intramolecular charge transfer for the 503 nm band is the largest among those for all of the bands. Therefore, the 503 nm band is ascribed to the MO(18) H-like aggregation, based on its shape, peak height, and in-plane anisotropy, the subsequent change to two kinds of visible peaks by successive HTTL, and the most degree of MO(18) intramolecular charge transfer among all of the aggregation states. While the MO(18) hydrocarbon chain takes the all-trans conformation before HTTL, its conformation and orientation are most disarranged after HTTL for 2 min. Subsequently, the original conformation and orientation are recovered by degrees with successive HTTL, except after final HTTL for 18 min, when the orientation is again changed. On the other hand, the C(20)-d hydrocarbon chain maintains the all-trans conformation before and after HTTL. The orientation of the C(20)-d hydrocarbon chain after HTTL for 2 min is more ordered than that before HTTL, with the nature of the C(20)-d subcell packing changing from hexagonal to orthorhombic. During successive HTTL from 2 to 18 min, the C(20)-d orientation is gradually disorganized but with the orthorhombic nature remaining constant. Thus, the variations in the conformation and orientation of the MS(18) hydrocarbon chain and in the orientation of the C(20)-d hydrocarbon chain tend to change from ordered and disordered structures and turn to more disordered and ordered ones, respectively, where the former is mainly caused by the priority action of thermal energy and the latter by hydrophobic effect due to the presence of warm water. Consequently, it is suggested that there is a correlation between the degree of structural order for both hydrocarbon chains and the preferential action that takes place during HTTL.

Our recently developed multiple transmission−reflection infrared (MTR-IR) spectroscopy method was applied to measure arachidic acid Langmuir−Blodgett films on hydrophilic and hydrophobic silicon substrates. High-quality MTR-IR spectra at both s and p polarizations were obtained. The MTR-IR absorption intensity at different incident angles was found to be linearly correlated with the transmission times (N) for arachidic acid monolayers on a hydrophilic silicon substrate. Significant differences in polarization-dependent intensities were observed for some specific vibration modes, for example, CH3 and CH2 stretching, carboxylic acid stretching, and CH2 bending, on different types of monolayer and multilayer films. By means of polarization-dependent spectra, the molecular orientation was numerically calculated, and the molecular structures such as the crystalline packing of hydrocarbon chains and the trans and cis configurations of carboxylic acid species were deduced. Obvious and repeatable intensity differ...

Triangular single-crystalline nanorings of PbS were prepared at the air/water interface and characterized by transmission electron microscopy (TEM), high-resolution TEM (HRTEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), and UV−vis spectroscopy. The nanorings were transformed from triangular PbS nanopyramids that were formed under Langmuir monolayers of arachidic acid (AA) through interfacial reactions between Pb2+ ions in the subphases and H2S in the gaseous phase. The basal plane of the pyramids is a (111) face of PbS crystals with rock salt crystal structure, which is parallel to the air/water interface. The tips of the pyramids beneath the interface dissolved gradually due to selective etching of Pb2+ in the nanocrystals by Cl− ions in the subphase because of their higher surface energy, resulting in the formation of the rings. The size of the rings could be tuned by changing the experimental conditions, and the optical properties changed when the rings formed.

We have investigated the thermal behavior of H-aggregate in a mixed Langmuir-Blodgett (LB) film of the merocyanine dye (MS18)-arachidic acid (C20)- n-octadecane (AL18) ternary system by means of UV-visible and IR absorption spectroscopy in the range from 25 to 250 degrees C with a continuous scan. The results of both UV-visible and IR spectra indicate that the temperature-dependent variation in MS 18 aggregation state is linked not only with the degree of intramolecular charge transfer and the behavior of packing, orientation, conformation, and thermal mobility of the MS18 hydrocarbon chain but also with the presence and absence of AL18. The H-aggregate dissociates from 25 up to 50 degrees C, which is caused by the AL18 evaporation from the mixed LB film and the increment of thermal mobility of the MS18 hydrocarbon chain. From 110 to 160 degrees C, blue-shifted bands, attributed to the oligomeric MS18 aggregation, appear near 515 nm in the MS18-C 20-AL18 ternary system as well. The temperature at which the 515 nm band occurs is identical for both present ternary system and previously investigated MS18-deuterated arachidic acid (C20- d) binary system, and it is in good agreement with the melting point (110 degrees C) of cadmium arachidate (CdC20). Therefore, it is indicated that the driving force which induces the 515 nm band comes from the melting phenomenon of CdC20 molecules which are phase-separated from MS 18 molecules in as-deposited LB films.

We have investigated the influence of heat treatment in an air atmosphere (HT) and hydrothermal treatment in the liquid phase (HTTL) on the H-aggregate in a mixed Langmuir-Blodgett (LB) film of merocyanine dye with an octadecyl group (MS(18))-arachidic acid (C(20))-n-octadecane (AL(18)) ternary system by means of polarized visible and IR absorption spectroscopy. HT causes the variation from the H-aggregate to the monomer, the increment in the number of gauche conformers in the MS(18) hydrocarbon chain, the slight orientation change in the C(20) hydrocarbon chain, and the complete evaporation of AL(18). The dissociation of MS(18) is probably ascribed to the complete evaporation of AL(18) from the mixed LB film and the increase in thermal mobility of the long axis of the MS(18) hydrocarbon chain during HT. However, HTTL can easily and rapidly induce the conversion of the MS(18) aggregation state from H- to J-aggregates, the modification of the C(20) subcell packing from hexagonal to orthorhombic, and the removal of most of the AL(18) molecules. The conversion of the MS(18) aggregation state can be interpreted to consist of two processes from the H-aggregate to the monomer and from the monomer to the J-aggregate. In the initial stage of HTTL, the MS(18) aggregation state changes from the H-aggregate to the monomer, which is caused by the removal of almost all of the AL(18) molecules from the mixed LB film to warm water via the thermal energy of warm water. Then, the large relative permittivity of warm water is expected to relate strongly to the subsequent variation from the monomer to the J-aggregate. This transformation results in the decrease in the total value of the electrostatic energy based on the MS(18) permanent dipole interaction. Moreover, the modification of the C(20) subcell packing is possibly due to the hydrophobic effect, where the C(20) hydrocarbon chains cohere again in the warm water during HTTL. Consequently, it has been found that HTTL is quite effective to reorganize the chromophore alignment of MS(18), to modify the subcell packing of C(20) and to erase the majority of AL(18) molecules in the mixed LB film of the MS(18)-C(20)-AL(18) ternary system in a short time.

The nanomechanical properties of Langmuir−Blodgett monolayers of arachidic acid extracted at surface pressures of 1, 15, and 35 mN/m and deposited on mica were investigated by atomic force microscopy, force spectroscopy, and lateral force microscopy. It was experimentally demonstrated that the arachidic acid molecular orientation depends on the extraction pressure. According to this, tilting angles of 50, 34, and 22° with respect to the surface perpendicular were detected and identified as conformations that maximize van der Waals interactions between the arachidic acid alkyl chains. The vertical force needed to puncture the monolayers with the AFM tip strongly depends on the molecular tilting angles attained at different monolayer extraction surface pressures, obtaining values that range from 13.07 ± 3.24 nN for 50° to 22.94 ± 5.49 nN for 22° tilting angles. The different molecular interactions involved in the monolayer cohesion are discussed and quantitatively related to the experimental monolayer break...

We have investigated the thermal behavior of J-aggregates in the mixed Langmuir-Blodgett (LB) films composed of the merocyanine dye (MS18)-deuterated arachidic acid (C20-d) binary system in the temperature range from 25 to 250 degrees C by means of UV-visible and IR transmission absorption spectroscopy. The temperature-dependent variations in both UV-visible and IR absorption spectra indicate that the MS18 aggregation states are linked with the MS18 intramolecular charge transfer and the behavior of the packing, orientation, conformation, and thermal mobility of the MS18 hydrocarbon chain. The J-aggregate formed at 25 degrees C in the mixed LB films dissociates in the temperature range from 25 to 110 degrees C, which is mainly ascribed to the increase in the thermal mobility of MS18 hydrocarbon chain and the dissociation of the chelation by a cadmium ion to the MS18 keto group. A thermally induced blue-shifted band appears at around 515 nm from 110 to 160 degrees C. This band is attributed to oligomeric aggregation with side-by-side alignment of the MS18 transition dipole moments on the basis of the shift to a higher-energy side, broadening, and temporary increment of the MS18 intramolecular charge transfer of the band. Consequently, the appearance of the thermally induced blue-shifted band indicates the possibility that the MS18 aggregation states can be controlled from the red shift to the blue shift by the annealing method adopted in the present study.

The Langmuir-Blodgett (LB) monolayers offer a unique system to study molecular interaction at the air-water interface with reduced dimensionality. In order to develop this further to follow macromolecular interactions at equilibrium, we first characterized the Ni (II)-arachidate (NiA) monolayer at varying conditions. Subsequently, the interaction between NiA and histidine-tagged RNA polymerase (HisRNAP) were also studied. LB films of arachidic acid-NiA and NiA-RNAP with different mole fractions were fabricated systematically. Surface pressure versus area per molecule (P-A) isotherms were registered, and the excess Gibbs energy of mixing was calculated. The LB films were then deposited on solid supports for Fourier transform infrared (FTIR) spectroscopic measurements. The FTIR spectra revealed the change in the amount of incorporated Ni (II) ions into the arachidic acid monolayer with the change in pH and the increasing mole fraction of RNAP in the NiA monolayer with its increasing concentration in the subphase. The system developed here seems to be robust and can be utilized to follow macromolecular interactions.

Experimental and theoretical studies of the equilibrium and dynamics of the penetration of the soluble cationic surfactant cetyltrimethylammonium bromide (CTAB) into arachidic acid monolayers are reported. The experimental studies of the system are performed at different pH values in acidic, alkaline, and neutral media. The penetration of CTAB from the alkaline subphase into the arachidic acid monolayer is shown to result in a significant increase of the surface pressure of the mixed monolayer, whereas the surface pressure jump for the penetration from the acidic subphase does not differ from that corresponding to the adsorption from the single CTAB solution with the same concentration onto the pure aqueous surface. This phenomenon is explained by the fact that the dissociation degrees of arachidic acid are different (the dissociation is the largest in the alkaline subphase, and nearly no dissociation exists in the acidic subphase), and in the alkaline subphase, strong Coulombic interaction exists between...

A hydrotalcite clay/dendrimer nanocomposite prepared by the ionic exchange process was adsorbed from suspension of the nanocomposite on a Langmuir monolayer of arachidic acid at the air/water interface, followed by compressing and transferring onto an arachidic acid monolayer Langmuir-Blodgett (LB) film on mica. For comparison, the hydrotalcite-adsorbed hybrid film was also prepared. The morphology of hydrotalcite and the nanocomposite studied by transmission electron microscopy indicated the layered structures with respectively 1.2 +/- 0.3 and 3.2 +/- 0.5 nm repeating distances. The hybrid Langmuir films displayed the occupied surface area of 0.24 nm2 for both hydrotalcite and the nanocomposite. The formation of hybrid Langmuir films was confirmed by Brewster angle microscopy. Atomic force microscopic images of hybrid LB films revealed the formation of plateau domains with the height difference of 6 nm for hydrotalcite and 12 nm for the nanocomposite and the presence of dendrimers adsorbed on the clay surface of the nanocomposite.

Here, we report a system we have developed where long double-stranded DNAs (dsDNAs) are immobilized on a monolayer of Zn-arachidate. We have applied the Langmuir-Blodgett technique to form the monolayer of Zn-arachidate where Zn(II) is bound to arachidic acid through charge neutralization. Because tetrahedral Zn(II) participates in DNA recognition through coordination, we have been able to layer DNA over the Zn-arachidate monolayer. The DNA layer shows a typical compression and expansion cycle in a concentration-dependent fashion. Interestingly, the DNA monolayer is available for enzymatic degradation by DNaseI. The detection of DNA and its accessibility towards biological reaction is demonstrated by imaging through fluorescence microscopy. The conformation of the DNA, immobilized on the monolayer, was studied with the help of atomic force microscopy (AFM). We observed that the dsDNAs were aligned in a stretched manner on the surface. To investigate further, we also demonstrate here that the small single-stranded DNA (ssDNA) immobilized on the air-water interface can act as a target molecule for the complementary ssDNA present in the subphase. The study of DNA hybridization done with the help of fluorescence spectroscopy clearly supports the AFM characterization.

Three kinds of Langmuir monolayers formed by dipalmitoylphosphatidylcholine (DPPC), arachidic acid (AA), and octadecylamine (ODA) were used as templates to study the initial stage of nucleation and crystallization of calcium phosphates. It was demonstrated that the combination of calcium ions (or phosphates) to the monolayer/subphase interface is a prerequisite for subsequent nucleation. It was found that calcium phosphate dihydrate (DPCD) formed at 25.0 degrees C for 12 h has a biphasic structure containing both amorphous and crystalline phases. These results showed that calcium phosphates were formed through a multistage assembly process, during which an initial amorphous phase DPCD was followed by a phase transformation into a crystalline phase and then the most stable hydroxyapatite (HAp). This provided new insights into the template-biomineral interaction and a mechanism for biomineralization.

We investigate the making of semiconductor nanorods using well-defined molecular templates. The films are characterized by AFM and XPS. The spin-coated monolayer of arachidic acid assembles on graphite as 1D nanostripes with bilayer periodicity. The copper arachidate film shows curved stripes, which become straight after reacting with hydrogen sulfide. The new template scheme may facilitate the fabrication of nanorod arrays of a variety of inorganic and semiconducting materials.

Interaction between an anionic polyelectrolyte, poly(acrylamido)methylpropanesulfonate (PAMPS), and anionic fatty acid, arachidic acid (AA), has been studied at the air−water interface. Although si...

Langmuir and Langmuir−Blodgett (LB) films of neat titanyl(IV) phthalocyanine (TiOPc) and mixed (TiOPc)−arachidic acid (AA) films were studied. The surface pressure−area isotherms (π−A) were recorded, and an unusual expansion of the surface area per molecule was detected for mixed TiOPc−AA Langmuir monolayers. The expansion is attributed to the TiOPc molecular orientation in the neat films being different from that in the mixed films with arachidic acid. The molecular orientation in LB films was monitored using reflection−absorption infrared spectroscopy (RAIRS). It was found that the TiOPc molecules are tilted with respect to the substrate in the neat film, changing to a preferential face-on orientation in the TiOPc−AA mixed films. Complementary information about molecular organization and film structure was obtained using UV−visible absorption and micro-Raman imaging.

The structure of the mixed Langmuir and Langmuir−Blodgett (LB) films of arachidic acid (AA) and perfluorotetradecanoic acid (PA) are investigated. Surface pressure−area isotherms of the mixed Langmuir films of AA and PA fall between those of pure AA and pure PA, indicating that the additivity rule holds in this system. This shows that the two components are phase-separated or are ideally mixed. The results of transmission and reflection−absorption IR spectroscopic measurements of the mixed LB films reveal that the composition of the LB films is the same with that in the spreading solution and that the orientation of the two components does not change with mixing. Molecular axes of AA and PA are almost perpendicular to the film surface. AFM and FFM show that AA forms distinct monolayer domains that are surrounded by monolayer PA. These results indicate that AA and PA are phase-separated in the mixed LB films. On the other hand, rather different results were reported for the mixed Langmuir and LB films of A...

The nucleation and growth rate of an amorphous mineral film at a Langmuir monolayer interface has been observed in situ with X-ray scattering techniques for the first time. We present measurements of a calcium carbonate film, nucleating at a fatty acid monolayer from a supersaturated calcium carbonate subphase containing a dilute poly(acrylic acid) additive, in emulation of biogenic mineralizing systems. The arachidic acid molecules were observed to self-assemble on the subphase into an untilted structure, with one bound Ca2+ ion per 14−25 surfactant molecules, and with a two-molecule planar centered rectangular unit cell with lattice constants a = 4.38 A and b = 8.51 A. Subsequently, an amorphous mineral phase forms beneath the monolayer, growing at a rate of 22 A/h to a thickness of 300 A after about 15 h. The electron density of the film was 0.7 times that of crystalline calcium carbonate hexahydrate, suggesting that the precursor is a hydrated phase with an open structure. During film growth, no chang...

The formation of CdS nanoparticles by reacting mixed Langmuir-Blodgett films of arachidic acid and either octadecylamine or dimethyldioctadecylammonium nitrate on a cadmium-containing subphase with hydrogen sulfide gas has resulted in the identification of a number of structural changes, observed using grazing incidence X-ray diffraction. In the case of octadecylamine, the structure after reaction is a hexagonal close-packed array of surfactant-stabilized nanoclusters, with a lattice constant of a = 17.65 Angstrom. In both octadecylamine and dimethyldioctadecylammonium nitrate films, the presence of a unit cell tilted at 38degrees to the plane of the substrate was found. Despite these changes, the average nanoparticle size was unaffected by the addition of either second component to the film.

We have previously studied the electrostatic entrapment of the heme proteins cytochrome c (Cyt c) and hemoglobin in thermally evaporated fatty lipid films (Gole et al. Langmuir 2001, 17, 5646−5656). It was observed that the diffusion of Cyt c from solution into thermally evaporated arachidic acid films was extremely slow requiring ca. 40 h for protein equilibration in 500 A thick films thus marking this out as a disadvantage of the protocol. Preliminary attempts to enhance the diffusion rate of Cyt c in arachidic acid films organized in a lamellar structure by Pb2+ ion intercalation were promising. In this paper, we examine the use of stearic acid films organized in a lamellar c axis oriented structure in greater detail and demonstrate that such films grown either by the Langmuir−Blodgett technique or by thermal evaporation followed by metal ion intercalation enhances the diffusion rate of Cyt c by over an order of magnitude. The entrapment of the protein molecules in the lamellar hydrophilic regions of t...

For the first time, the thickness and refractive index of monolayers at the air/water interface have simultaneously been determined by null ellipsometry. Separation of refractive index from film thickness has been achieved by highly precise measurements of the two ellipsometric angles Ψ and Δ. In the solid state, film thicknesses of arachidic acid and valine gramicidin A obtained by ellipsometry are comparable with those obtained by the X-ray techniques. For arachidic acid in the condensed state, our results suggest that only the thickness of the hydrophobic moiety is measured. When highly hydrated, the thickness of the polar headgroup is not detected. This is presumably due to its refractive index being the same as that of the bulk water; hence, the calculated film thickness corresponds to the thickness of the hydrophobic part only. As molecular area is reduced, the polar headgroup gradually loses hydration water molecules causing its refractive index profile to become different from that of the bulk wat...

Monolayer and multilayer Langmuir−Blodgett (LB) films of the endohedral metallofullerene Dy@C82 mixed with arachidic acid (Dy@C82/AA) were deposited onto ITO substrates from the N2/water interface....

Intercalation of the heme proteins, cytochrome c (Cyt c) and bovine hemoglobin in thermally evaporated fatty lipid films under protein-friendly conditions by a novel beaker-based diffusion mechanism is described. An attractive electrostatic interaction between charged groups on the protein surface and ionized lipid molecules in the film is primarily responsible for the diffusion of the proteins from the solution into the lipid matrix. To highlight the generality of the approach, Cyt c (cationic at a pH of ca. 7) and hemoglobin (anionic at pH = 9) have been incorporated into thermally evaporated arachidic acid (anionic at pH = 7) and octadecylamine (cationic at pH = 9) films, respectively, by simple immersion of the films in the respective protein solutions. Quartz crystal microgravimetry measurements were used to follow the kinetics of protein diffusion into the films and was found to be strongly dependent on the protein solution pH. The electrostatic nature of coordination between the proteins and matrix...

Mixed insoluble monolayers of bis(N-ethyl,N-octadecyl)rhodamine perchlorate (RhC18) and arachidic acid (ArAc) at the air−water interface were characterized by surface pressure−area isotherm, second...

Unimolecular rectification was detected between oxide-free Au electrodes for a Langmuir−Blodgett (LB) monolayer of the zwitterionic D+-π-A- molecule hexadecylquinolinium tricyanoquinodimethanide, C16H33Q−3CNQ. The top gold pad was deposited by a process that cools the metal vapor before deposition. The maximum rectification ratio is 27.5 at 2.2 V (the average rectification ratio is 7.55). The currents are as large as 9.04 × 104 electrons molecule-1 s-1. The result reinforces previous work with oxide-bearing Al electrodes, but the currents with Au electrodes are larger by 3−5 orders of magnitude. Rectification was also seen for a nine-monolayer Z-type LB film between similar Au electrodes but not for a monolayer of arachidic acid. The direction of enhanced electron current is from the negatively charged dicyanomethylene end of C16H33Q−3CNQ to the quinolinium ring, as predicted by the Aviram−Ratner analysis. However, there is a good fit to the behavior expected for quantum conduction dominated by a single m...

Monolayers of simple fatty acids exhibit a rich polymorphism with at least seven solid phases. The reason for such a variety of phases is not known yet and therefore is the object of the current investigation. In the present work the pH of the subphase is varied between 2 and 10.5 and the influence of the degree of dissociation on phase transition pressures and temperatures of arachidic acid monolayers is investigated in detail in the range from 2 to 45 °C by means of Brewster-angle microscopy and surface pressure−area isotherms. The shift of phase boundaries is ascribed to the change in the steric, electrostatic, and bonding interactions between the lipid headgroups. The impressive correlation between the L2/Ov nearest neighbor to next nearest neighbor (NN/NNN) transition pressure and the position correlation length as functions of the pH value suggests that the L2/Ov NN/NNN transition in fatty acid monolayers is strongly influenced or even originates in headgroup bonding interactions. The influence of h...

Mixed Langmuir−Blodgett (LB) films of arachidic acid (AA) and [Ru(L)(totpy)(OH2)](ClO4)2 (L = Ph2AsCH2CH2AsPh2; 4-totpy = 4‘-(4-tolyl-2,2‘:6‘,2‘ ‘-terpyridine)) complex (2:1) were used in the prepa...

trans-Parinaric acid, a polyene fatty acid, is widely used as a fluorescent membrane probe in photophysical and biophysical studies. We have worked on the orientational order of this molecule in Langmuir−Blodgett multilayer films of both gel-phase dipalmitoylphosphatidylcholine and arachidic acid at room temperature. Namely, orientational density probability functions were calculated using the maximum entropy method. Because liquid-crystal lipids do not deposit forming multilayers by Langmuir−Blodgett techniques, we have used Brownian dynamics methods to simulate a trans-parinaric acid molecule in a liquid-crystal bilayer environment. Orientational density probability functions are also achieved under the ergodic hypothesis. In the gel phase, trans-parinaric acid is highly ordered (narrow density probability function) and almost perpendicular (78°) to the multilayer planes. In the liquid-crystal phase, the density probability function broadens and the average orientation is not so close to the multilayer ...

The influence of substituents on the adsorption and aggregation of the anionic 3,3‘-disulfopropyl-5,5‘-dichloro-9-ethylthiacarbocyanine (THIATS) and its cationic analogue 3,3‘-diethyl-5,5‘-dichloro-9-ethylthiacarbocyanine (TDC) was investigated in Langmuir films at the air−water interface. Dioctadecyldimethylammonium bromide (DODAB) and octadecylammonium chloride (ODACl) were used to adsorb THIATS. Arachidic acid (AA) and dihexadecyl phosphate (DHP) were used to adsorb TDC. J-aggregate formation has been observed for the four different combinations of dyes and surfactants. The absorption and emission spectra of THIATS at the air−water interface revealed one narrow intense J-band which was not influenced by the chemical structure of the amphiphiles or by the concentration of THIATS in the subphase. Fluorescence microscopy experiments suggest that, depending on the subphase dye concentration, aggregation of dye molecules leads either to a layer of J-aggregates distributed homogeneously on the scale of a few...

The thermodynamic and morphological properties of arachidic acid monolayers at high pH values (pH 11−13) and temperatures (10 °C ≤ T ≤ 35 °C) are studied. The two-phase coexistence region of the su...

The structures of mixed monolayers of cadmium arachidate (CdAr) with tetrakis(3,5-di-tert-butylphenyl)porphinatocopper(II) (TDBPC) (0.13 mole fraction) at the air/water interface have been studied by grazing incidence synchrotron X-ray diffraction (GIXD) and specular X-ray reflectivity. Only the hexagonal structure of CdAr was observed in the GIXD measurements, with d(11) = 4.16 Angstrom, giving an area per chain of 20.0 Angstrom(2). The chains are perpendicular to the subphase surface and the positional correlation length is 45 Angstrom. For comparison, GIXD measurements of CdAr alone show a hexagonal in-plane structure with d(11) = 4.13 Angstrom and an area per chain of 19.7 Angstrom(2). The acyl chains in the film are perpendicular to the surface of the subphase and have a correlation length of 140 Angstrom. Reflectivity measurements on the monolayer of arachidic acid on a CdCl(2) solution confirm that the chains are normal to the surface of the subphase and suggest that the headgroups have the composition -COOCdOH. For the mixed film reflectivity measurements indicate that, at a surface pressure of 25 mN m(-1), the porphyrin rings have a diameter of about 15.2 Angstrom and are perpendicular to the surface. At 2 mN m(-1) the rings are either tilted from the normal by about 28 degrees, or normal to the surface leaving some areas of low density in the film. The two compounds are immiscible in the mixed monolayer, but the formation of CdAr domains is hindered by the presence of the porphyrin.

The point-by-point mapping of the surface-enhanced resonance Raman scattering (SERRS) and surface-enhanced Raman scattering (SERS) spectra obtained from Langmuir−Blodgett (LB) monolayers of bis(n-butylimido)perylene (BuPTCD) on silver island films are reported. Wide field global images of the SERRS signal are also discussed. The mapping and global Raman images of the LB-coated silver surfaces, obtained using the 514.5 nm and the 780 nm laser lines, give a visual picture of the variation of the intensity of the SERRS/SERS signal on the rough metal surface with ca. 1 μm2 spatial resolution. Neat and mixed LB monolayers of BuPTCD with arachidic acid of 20% and 1% molecular concentration of the analyte were used as samples in the SERRS and SERS experiments. This is the first report of SERS and SERRS mapping and imaging of single Langmuir−Blodgett monomolecular layers. The use of BuPTCD is particularly important, since the molecules are not chemically bound to the surface. SERRS spectra with large signal-to-no...

As a potential material for use in optical fiber fluorescence sensors for rapid detection of saxitoxin, 9-(monoaza-18-crown-6-methyl)-10-hexadecylanthracene (CAC16) was synthesized, and the interfacial and spectroscopic properties of the Langmuir monolayers and Langmuir−Schaefer films of CAC16 were studied. The surface pressure−area and surface potential−area isotherms of CAC16 on different subphases were obtained. An increased limiting molecular area was observed on a pH 2 subphase. In situ fluorescence emission spectra (λex = 366 nm) of the CAC16 monolayer showed a broad fluorescence band on a pH 2 subphase but none on a pure water subphase. Mixed monolayers of CAC16/C20 (arachidic acid) on a pure water subphase showed an increased fluorescence emission intensity of anthracene with an increase in the proportion of C20. This suggests that the low fluorescence activity of the pure CAC16 monolayer could be caused by self-quenching due to the high concentration of CAC16 at the interface. In a mixed monolaye...

The miscibility and phase behavior of mixed monolayers of Ru(dpphen)32+ (dpphen = 4,7-diphenyl-1,10-phenanthroline) (abbreviated as Ru(II)) and arachidic acid (AA) with different molar proportions ...

Arachidate Langmuir−Blodgett (LB) films of different chemical composition and number of monomolecular layers deposited on silylated silica glass substrates were studied by means of positron annihilation spectroscopy. The applied methods included the measurement of the Doppler broadening of the annihilation photopeak with variable energy positron beams and bulk positron lifetime measurements. The studied samples were 58 monomolecular layers (MML) thick Mg- and Cd-arachidate, arachidic acid (50 MML) and a series of Pb-arachidate samples with 4, 10, 20, 40, and 58 MML. The investigation showed that the variable energy positron beam technique is capable of measuring the thickness of the deposited LB films. The measured positron annihilation parameters are sensitive to the chemical composition of the films and the behavior of the films in a vacuum. The results confirmed the stability of salt base LB films in high vacuum conditions and showed the desorption of pure acid films. These investigations have also sho...

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 cor...

The method of X-ray reflectometry with electron density “labeling” of polyampholytes by heavy counterions has been demonstrated for measuring the adsorption profiles of gelatin at both hydrophobic ...

The luminescent enhancement effect of Y(TTA)3Phen (TTA = thenoyltrifluoroacetone; Phen = 1,10-phenanthroline) on Eu(III) in Langmuir−Blodgett (LB) films of rare earth complexes mixing with arachidic acid (AA) in a molar ratio of 1:1 and the intermolecular energy transfer from Y(TTA)3Phen to Eu(TTA)3Phen in the films were investigated in this paper. The compositions of studied films follow the formula of [x% Eu(TTA)3Phen + (100 − x)% Y(TTA)3Phen]:AA = 1:1 (x = 0, 0.05, 0.1, 0.2, 0.3, 0.5, 30, 50, 80, and 100; in molar percentage). Luminescence intensities of Eu(III) in the films, compared with those that are regulated to no Y(TTA)3Phen, were enhanced in varying degrees. They also reveal that the lower the molar percentage of Eu(TTA)3Phen that exists in the films, the higher the efficiency of luminescent enhancement that is observed. Meanwhile, the monolayer and multilayer films were characterized by Brewster angle microscopy (BAM), electron diffraction (ED), and UV−vis spectra. The experimental results of ...

Langmuir-Blodgett (LB) films of surface-active azodye, YOPE, were prepared at different surface pressures and observed by atomic force microscopy. The surface structure was compared with that of LB films of the arachidic acid/YOPE hybrid. The two-dimensional phase separation was observed in hybrid LB films. The molecular arrangement of YOPE on Langmuir films was inferred from the AFM observation of LB films and the surface pressure-area (π-A) isotherms. At lower surface pressures, the dye chromophores of YOPE molecules were lying along the air-water interface. The arithmetic additivity of π-A isotherms was substantiated for hybrids.

The adsorption process of the recombinant human growth hormone on organic films, created by self-assembly of octadecyltrichlorosilane, arachidic acid, and dipalmitoylphosphatidylcholine, is investigated and compared to adsorption on silica and methylated silica substrates. Information on the adsorption process of human growth hormone (hGH) is obtained by using total internal reflection fluorescence (TIRF). The intensity, spectra, and quenching of the intrinsic fluorescence emitted by the growth hormone's single tryptophan are monitored and related to adsorption kinetics and protein conformation. For the various alkylated hydrophobic surfaces with differences in surface density and conformational freedom it is observed that the adsorbed amount of growth hormone is relatively large if the alkyl chains are in an ordered structure while the amounts adsorbed are considerably lower for adsorption onto less ordered alkyl chains of fatty acid and phospholipid layers. Adsorption on methylated surfaces results in a relatively large conformational change in the growth hormone's structure, as displayed by a 7 nm blue shift in emission wavelength and a large increase in the effectiveness of fluorescence quenching. Conformational changes are less evident for hGH adsorption onto the fatty acid and phospholipid alkyl chains. Adsorption kinetics on the hydrophilic head groups of the self-assembled monolayers are similar to those on solid hydrophilic surfaces. The relatively small conformational changes in the hGH structure observed for adsorption on silica are even further reduced for adsorption on fatty acid head groups.

A planar microcavity using mixed a Langmuir-Blodgett film of a europium complex HDP-Eu(NTA) 4 (where HDP = cetylpyridinium and NTA = α-naphthyltrifluoroacetone) and arachidic acid (AA) as fluorescence working material, and vacuum evaporated silver films as reflective mirrors was fabricated for the first time. Using the traditional Langmuir-Blodgett (LB) technique, the mixed Langmuir film of the Eu complex and AA on a water subphase containing 0.20 mM of Eu(ClO 4 ) 3 was finely transferred onto a lipophilically pretreated silver mirror to form a multilayer LB film microcavity with a λ/2 optical length (where λ is the emission wavelength). The optical length of the microcavity was measured by a multibeam interference method. The fluorescence spectrum of the λ/2 resonant microcavity coincides with that of the LB film of the complex, and microcavity effects such as fluorescence intensity enhancement and lifetime shortening have been observed.

By using a composite subphase, the atypical amphiphilic Tb(acac)3Phen (where acac denotes acetylacetone and Phen denotes 1,10-phenanthroline) molecules without long hydrophobic chains were deposited onto solid substrates. The results of UV−vis spectra and fluorescence emission spectra show the Tb(acac)3Phen/arachidic acid (1:1 molar ratio) Langmuir−Blodgett (LB) film to be homogeneous in direction normal to the substrate. A periodic layer structure of the LB film is demonstrated by low-angle X-ray diffraction results, the average layer spacing being 5.40 nm. The LB film containing Tb(acac)3Phen can emit strong green fluorescence, and the fluorescence signal can be detected from a single layer. The wavelengths of fluorescence emission are not altered in the ordered molecular film; however, the fluorescence intensities of some emission peaks are increased.

The structure and morphology of the three-dimensional aggregates of arachidic acid were studied by atomic force microscopy (AFM) after transfer onto a silicon wafer and by synchrotron grazing incidence X-ray diffraction (GID) at the helium/water interface. The 3D aggregates on the wafer observed by AFM are islands of granulelike and platelike shapes. The plate islands consist of terraces of different heights. The crystal structure of the plate islands was determined through molecular resolution by AFM. They have the C-crystal structure of arachidic acid at the beginning of the relaxation. During further relaxation the B-crystal structure becomes apparent. The islands with B-crystal structure dominate at the end of the relaxation process. Regions with a disordered molecular structure are found beside the ordered crystal structures. In all ordered regions of a single island the same crystal structure is observed. Using GID, the B- and C-crystal structures of the 3D aggregates of arachidic acid were also found at the helium/water interface. No peaks of any crystal structure are observed until 20% of the monolayer material is transformed into 3D aggregates. Then first the peaks of the B-crystal structure appear, which increase with the relaxation time. Additionally small peaks corresponding to the C-crystal structure are found.

A series of calix[6]arene-based surfactants have been synthesized, which contain amide oxime head groups on their upper rim and 5,5-dimethylhexyl (I), n-octyl (II), n-dodecyl (III), and n-hexadecyl (IV) groups on their lower rim. Composite membranes that were fabricated from Langmuir−Blodgett (LB) multilayers derived from each surfactant plus poly[1-(trimethylsilyl)-1-propyne] (PTMSP) cast film showed a significant increase in their selectivity toward helium and nitrogen, relative to bare PTMSP. In sharp contrast, analogous composites that were prepared with LB multilayers of conventional single chain surfactants [arachidic acid (AA), cadmium arachidate (AA/Cd2+), and stearoamideoxime (SA)] exhibited permeation properties that were identical with those of bare PTMSP. When a polymeric surfactant [poly(1-octadecene-co-maleic anhydride), POM] was used for LB film construction, a modest increase in selectivity was observed. These findings, together with an analysis of representative composites by X-ray photoe...