Langmuir-Blodgett Multilayers Research Articles

Structural Insights into Phycocyanin Langmuir–Blodgett Multilayers via Serial Femtosecond Crystallography with X-ray Free-Electron Laser

Structural Insights into Phycocyanin Langmuir–Blodgett Multilayers via Serial Femtosecond Crystallography with X-ray Free-Electron Laser

First Direct Gravimetric Detection of Perfluorooctane Sulfonic Acid (PFOS) Water Contaminants, Combination with Electrical Measurements on the Same Device—Proof of Concepts

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are pollutants of concern due to their long-term persistence in the environment and human health effects. Among them, perfluorooctane sulfonic acid (PFOS) is very ubiquitous and dangerous for health. Currently, the detection levels required by the legislation can be achieved only with expensive laboratory equipment. Hence, there is a need for portable, in-field, and possibly real-time detection. Optical and electrochemical transduction mechanisms are mainly used for the chemical sensors. Here, we report the first gravimetric detection of small-sized molecules like PFOS (MW 500) dissolved in water. A 100 MHz quartz crystal microbalance (QCM) measured at the third harmonic and an even more sensitive 434 MHz two-port surface acoustic wave (SAW) resonator with gold electrodes were used as transducers. The PFOS selective sensing layer was prepared from the metal organic framework (MOF) MIL-101(Cr). Its nano-sized thickness and structure were optimized using the discreet Langmuir–Blodgett (LB) film deposition method. This is the first time that LB multilayers from bulk MOFs have been prepared. The measured frequency downshifts of around 220 kHz per 1 µmol/L of PFOS, a SAW resonator-loaded QL-factor above 2000, and reaction times in the minutes’ range are highly promising for an in-field sensor reaching the water safety directives. Additionally, we use the micrometer-sized interdigitated electrodes of the SAW resonator to strongly enhance the electrochemical impedance spectroscopy (EIS) of the PFOS contamination. Thus, for the first time, we combine the ultra-sensitive gravimetry of small molecules in a water environment with electrical measurements on a single device. This combination provides additional sensor selectivity. Control tests against a bare resonator and two similar compounds prove the concept’s viability. All measurements were performed with pocket-sized tablet-powered devices, thus making the system highly portable and field-deployable. While here we focus on one of the emerging water contaminants, this concept with a different selective coating can be used for other new contaminants.

Chloroform sensing properties of Langmuir-Blodgett thin films of Zn(II)phthalocyanine containing 26-membered tetraoxadithia macrocycle groups

A zinc(II)phthalocyanine containing 26-membered tetraoxadithia macrocycle moiety (ZnPc-26) was prepared for the fabrication of multilayered Langmuir-Blodgett (LB) thin films. The LB thin film fabrication procedure is given in detail with the isotherm and the transfer graph where the transfer ratio was calculated as 0.95. LB thin film quality is monitored by the UV-Vis and SPR with respect to the increasing number of layers with linear regressions of 0.998 and 0.979 respectively. 8, 12 and 20 layered ZnPc-26 LB thin films are selected to investigate the chloroform sensing properties. The response times between 2 and 6 s are observed with reproducible and reversible responses. Limit of detection value of 3.76 ppm was calculated with a sensitivity of 0.797 × 10−3 ppm−1 for the 20 layered ZnPc-26 LB thin film. A reduction of approximately 20% in the response rate was observed after 5 weeks from the first investigation. ZnPc-26 molecule has a potential for the gas sensing applications.

Enhanced luminescence and electrical conductivity of polymer ultrathin films doped with TiO2 nanoparticles

The chemical polymerization method was used to prepare nanocomposite materials of polyaniline (PANi) and Titanium dioxide (TiO2) nanoparticles. Ultrathin films were deposited by using the Langmuir Blodgett (LB) Technique. Surface Pressure vs mean molecular area isotherms of nanocomposite materials showed an increase in maximum attained surface pressure with variation in nanoparticle doping concentration. Photoluminescence (PL) spectra were taken for LB multilayers deposited on a quartz substrate, an increase in the intensity of PL peaks with increasing doping concentration of TiO2 nanoparticles. The topography of LB monolayer film under atomic force microscopy (AFM) revealed that films were uniformly and densely deposited on the substrate. Phase imaging ensured the presence of nanoparticles in the polymer matrix. Conductive atomic force microscopy (C-AFM) was used to investigate the local electrical properties of nanocomposite LB films. Current-voltage characteristics showed variation in current with changing doping concentrations of TiO2 nanocomposite in PANi matrix. The work presents new insights in analyzing uniformly deposited ultrathin films of the composites which can be probed by C-AFM to reveal local electric properties by understanding topography-current correlation at the nanoscale. The conductive data analysis could be useful for understanding the current flow through the nanostructure surface.

Sensor application and mathematical modeling of new Zn(II) phthalocyanine containing 26-membered tetraoxadithia macrocycle moieties

A novel phthalonitrile containing 26-member tetraoxadithia macrocycle moiety was synthesized in a multistep reaction sequence. New zinc(II) phthalocyanine was obtained by the cyclomerization reaction of this macrocyclic phthalonitrile. The novel phthalocyanine and the precursor compounds have been characterized by a combination of 1H and 13C NMR, FT-IR, UV–vis, elemental analysis and MALDI-TOF mass spectral data. 26-membered phthalocyanine was used to fabricate multilayered Langmuir-Blodgett (LB) thin films dedicated to investigating the gas sensing properties of these novel phthalocyanine materials. SEM images of the uncoated substrate, 8-layered and 16-layered LB thin films were compared to observe the successfully transferred layer by layer onto the solid substrates. Sensor parameters such as selectivity, reproducibility, thickness effect, recovery and response rates were examined for highly toxic benzene and toluene vapors using the mass sensitive Quartz Crystal Microbalance (QCM) technique. The first time the thickness effect on the gas sensing mechanism for selected material was also investigated. Validation of the experimental measurements of QCM kinetic was implemented using nonlinear autoregressive with exogenous input neural network for modelling using the frequency shift value. Comparison of these frequency shift of artificial neural network with real-experimental data showed the accuracy of the artificial neural network model.

Mesoscale Ordering of Phycocyanin Molecules in Langmuir-Blodgett Multilayers.

Phycocyanin molecules, which are part of light-harvesting complexes in cyanobacteria, can be assembled into mesoscale multilayer nanofilms by the Langmuir-Blodgett technique. Results obtained by quartz crystal microbalance and atomic force microscopy confirm the homogeneity and reproducibility of phycocyanin Langmuir-Blodgett multilayer deposition. We show by cryo-electron microdiffraction that amorphous phycocyanin Langmuir-Blodgett multilayers form, after annealing at 150 °C and cooling to room temperature, a layered nanofibrillar lattice with rotational disorder. Scanning X-ray nanodiffraction suggests that structural transformation is not homogeneous through the film but limited to patches of up to about 10 μm diameter.

Multilayer Langmuir-Blodgett thin films studies for chemical sensors development

This paper presents the study of the development of complex organic materials deposited by the Langmuir Blodgett technique. We have synthetized Langmuir Blodgett multilayers for the recognition of toxic chemicals in the air and / or ultraviolet radiation. The sensitive materials are based on multilayers of stearic acid metal salts combined with nanocarbon and metalloporphyrin structures. We prepared and obtained by the Langmuir Blodgett method films with nano-metric thicknesses combined in different concentrations of metal salts of fatty acids, Nano carbon structures and metalloporphyrins. Further we have characterized and tested the materials obtained for the sensitivity and selectivity of multilayers under the influence of various toxic gases and / or ultraviolet radiation obtaining high results in the field of sensors.

Characterization of Molecular Arrangement of Long‐chain Ferrocenyl Derivatives Having Asymmetric Carbon by Method of Organized Molecular Films and Formation of Its Helical Nanofibers

AbstractFormation of organized molecular film and helical nanofibers of ferrocene derivatives having R‐12‐hydroxystearyl chains with asymmetric carbon was investigated. The 12‐hydroxystearyl chain, which induces “thixotropy” due to the formation and breakage of intermolecular hydrogen bonds, was introduced into the ferrocenyl unit. The structure of this derivative as a monolayer on the water surface and its Langmuir‐Blodgett (LB) film properties were analyzed. The monolayer showed a two‐dimensional phase transition, corresponding to the formation of fibrous morphology. In the LB multilayers, intermolecular hydrogen bonding between hydroxyl groups at the 12‐position of the chain and crystalline packing was observed. Raman mapping revealed the difference in surface morphology of each derivative depending on the number of 12‐hydroxystearyl chains. The derivative having the single chain showed a right‐handed helical morphology in the film and this behavior is similar to those having two and three chains. In circular dichroism spectra, the film showed a positive Cotton effect. Since the helical chains easily entangle with each other to form a sponge‐like organization, it was expected that the solvent uptake was the origin of gelation induction to its contact solvent.

Additive and subtractive modification of butterfly wing structural colors

The modification of photonic nanoarchitectures occurring in butterfly wing scales with different nanostructures was investigated experimentally and by modeling. Single crystalline, polycrystalline, simple thin film, and pepper-pot-type photonic nanoarchitectures in the wing scales of different butterflies were investigated. By atomic layer deposition (ALD) (additive) the color of all nanoarchitectures was red shifted and by plasma etching (subtractive) the color of all nanoarchitectures was blue shifted in a controllable way. Langmuir-Blodgett multilayers of silica nanospheres were used as physical models. ALD produced color shifts similar to those for butterfly wings. In the case of a simple thin film, a theoretical calculation reproduced the spectral alterations well. For the more complex photonic nanoarchitectures, the general trends of the modifications were well reproduced by more sophisticated models, but differences in the magnitude of the alterations were found, attributed to the complex, random porous structures of the pepper-pot-type structures.

Tracking and Recovery of Metal Desorption from Organized Films of Polyguanamine Derivatives having Cyclic Moieties

AbstractMetal desorption behavior of polyguanamine derivatives having cyclic moieties (c‐PGs), with metal‐scavenging abilities, organized into molecular films was investigated, and a recovery technique was realized. Cadmium (a toxic metal), palladium (a precious metal), and neodymium (a rare earth metal) were studied, along with sodium (a cationic metal). A monolayer of c‐PGs forming on an aqueous metal solution surface effectively scavenges cations from the subphase owing to the relative basicity of the cyclic moiety. X‐ray photoelectron spectroscopy revealed that cadmium and palladium (both divalent cations) were desorbed by simple 30–60 min ultrasonication of their Langmuir–Blodgett multilayers. Conversely, the desorption of neodymium, a trivalent cation, was very slow. Sodium, a monovalent cation, was difficult to collect. Its valence and monolayer condensation on the aqueous sodium buffer were remarkable, indicating that coordinated sodium ions escape during the monolayer condensation.

Titania Nanofilms from Titanium Complex-Containing Polymer Langmuir-Blodgett Films.

This paper proposes a method of fabricating low-dimensional TiO2 nanofilms at room temperature under ambient pressure conditions. The titanium-containing polymer complex Ti-p(DDA/acac) was synthesized by reacting an amphiphilic copolymer (p(DDA/acac)) with a titanium complex. Its ultrathin films were prepared using the Langmuir-Blodgett (LB) technique. The monolayer was found to be free from hydrolysis and cross-linking side reactions, even at the air-water interface. The transferred LB films (nanosheets) were oxidized by ultraviolet irradiation at room temperature. The photo-oxidized material has an amorphous and porous structure with subnanometer-scale controllability (0.18 nm per layer). Photocatalytic performance was demonstrated by converting multilayered LB films of Ti-(DDA/acac) and the silicon-containing polymer p(DDA/SQ) into ultrathin hetero-multilayers of TiO2 and SiO2 under UV-O3 treatment. The scalability affords a uniform photopattern formation of photo-oxidized TiO2 films over several hundreds of micrometers.

Evidence of 2D anti-ferromagnetic ordering in rare-earth Langmuir–Blodgett films

In recent years the ordering of spins in two-dimensions has received considerable attention due to both the fundamental physics interest and for the possible technological applications. Langmuir–Blodgett (LB) films with magnetic ions are ideal systems to study two-dimensional (2D) magnetic ordering as the distances of the magnetic-ions along the out-of-plane and in-plane directions differ by almost an order of magnitude and the effect of the substrate can be neglected. In particular, vortex formation in ferro and antiferro 2D magnetic structures are of current interest and LB films are ideal to study this evolving physics. We show here that 2D magnetic ordering along the in-plane direction of multilayered LB films changes from ferromagnetic to anti-ferromagnetic as the rare-earth magnetic ion is changed from Gadolinium (Gd) to Holmium (Ho). The in-plane magnetization results have shown that Gd based LB films exhibit a temperature dependent saturation moment due to the existence of a vortex structure. The results of the magnetization study presented here show that the Ho based LB films exhibit an in-plane anti-ferromagnetic ordering and the saturation moment is found to be almost independent of temperature indicating the absence of spin vortex structures. From a 1/χ − T plot the asymtotic Curie point θa and the Neel temperature θN of the Ho-St LB film were found to be 66 K and 42 K respectively.

Electrical properties of alternating acid and amino substituted calixarene Langmuir-Blodgett thin films

The Langmuir-Blodgett (LB) alternate layer fabrication technique provides one of the most effective methods to fabricate organic thin films in the nanoscale. The structure of these thin films could be controlled at the molecular scale by spreading a monolayer on an air-water interface followed by sequential transferring of this layer onto a selected solid substrate. These films can be utilized within optical, electrical and biological applications in many different fields. Within this paper, two calix[4]arenes containing either carboxylic acid or amino substituents were utilised to prepare multilayer LB films and to study the electrical characteristic of these films using I–V and C-f measurements. The resultant calix[4]acid/amine multilayers demonstrated a highly non-linear I–V behaviour which obeys a Schottky conduction mechanism.

Low temperature processable ultra-thin WO3 Langmuir-Blodgett film as excellent hole blocking layer for enhanced performance in dye sensitized solar cell

The hole-blocking and electron- transporting layer is an important component of third-generation solar cells. This layer is responsible for both hindering the hole recombination from the hole-transport layer and collecting photo-generated electrons; that in turn impact photon-to-current conversion efficiency (ɳ) of devices. Conventionally, WO3 is being used as hole-transport layer owing to high work function and carrier mobility; and excellent thermal stability. In this paper we report ultra-thin WO3 films, prepared by UVO-treatment of WO3-octadecylamine Langmuir-Blodgett multilayers, for use as blocking layers in dye sensitized solar cells (DSSCs). For the first time, it is observed that ɳ of DSSCs with optimized WO3 blocking layer improved significantly (21%) as compared to those based on conventional TiO2 blocking layers. The improvement in ɳ is the result of improved short-circuit current density which is obtained without any accompanying reduction in open-circuit potential and fill factor. This is attributable to the dense and uniform morphology, excellent hole-blocking properties, crystallinity and proper position of Fermi level. The analyses not only reveal that ɳ of DSSCs can be enhanced by employing ultra-thin WO3 LB films as blocking layers but also suggest that the films can possibly be extended further for perosvskite and polymer solar cells.

Effects of Cu(II) on the Formation and Orientation of an Arachidic Acid Langmuir-Blodgett Film.

The influence of the copper(II) ion on the formation, morphology, and organization of an arachidic acid monolayer was investigated using Langmuir-Blodgett (LB) monolayers, Π-A isotherms, and Brewster angle microscopy (BAM). Our findings indicate that a Cu2+-complexed LB film exhibits an order that depends on the subphase pH, analogous to other metal ions. Yazdanian , M. ; et al. Ionic Interactions of Fatty Acid Monolayers at the Air-Water Interface . Langmuir 1990 , 6 , 1093 - 1098 . Kurnaz , M. L. ; et al. Morphology of Microphase Separation in Arachidic Acid-Cadmium Arachidate Langmuir-Blodgett Multilayers . J. Phys. Chem. 1996 , 100 , 11113 - 11119 . The metal ion facilitates the formation of solid-phase films at surface pressures as low as 5 mN/m. The films exhibit a rigid, ordered phase, evidenced by the absence of a collapse point and an increase in surface pressure rather than the typical sharp decrease in surface pressure, indicative of film failure. Amphiphile ionic charge vs pH (i.e., the extent of arachidic acid protonation) plays a role in the observed absence of collapse and the ability of the films to maintain order and cohesion at high surface pressures (ca. 65 mN/m). Additionally, film thickness data suggest that the incorporation of Cu2+ ions induces a change in orientation of the aliphatic chains of the amphiphiles and that amphiphile solubility in the subphase may play a role in the observed film behavior at low surface areas and high pH.

Structural and optical properties of two-dimensional gadolinium stearate Langmuir monolayer

Langmuir-Blodgett (LB) films having large stack of amphiphilic-fatty-acids bearing rare-earth-ions are ideal two-dimensional magnetic systems to study spin-vortex ordering as the distances of the magnetic-ions along the out-of-plane and in-plane directions differ by an order of magnitude. Here we present results of in-situ X-ray scattering measurements on Langmuir monolayer of the amphiphilic stearic acid on the water surface containing Gadolinium ions to understand the formation process of monolayer and multilayer LB films on the substrates. Infrared spectroscopy and microscopy measurements were also carried out to understand the growth and transfer mechanism of the LB films.

Improvement of signal-to-noise ratio in oxygen sensitive emission from hybrid Langmuir–Blodgett films of amphiphilic iridium complexes with the exfoliated nanosheets using a metal layer

Cyclometalated Ir(III) complexes are attracting extensive attention due to their high emission properties in the visible region. Oxygen sensitive photoluminescence (PL) emissions from single- and multi-layered Ir(III) Langmuir–Blodgett (LB) films are measured. The single-layered LB film on a non-aluminum coated glass substrate shows oxygen sensitive PL emission but its intensity is very weak. In contrast, the multi-layered LB film shows higher intensity but their oxygen sensitivity is lower than that of the single-layered sample. To break the trade-off between intensity and sensitivity, PL characteristics from the LB film on an aluminum-coated glass substrate are investigated. The PL emission from the LB film on the metal layer show higher intensity and good oxygen sensitivity. The mechanism of the emission enhancement is also discussed in this paper.

Controlled deposition of functionalized silica coated zinc oxide nano-assemblies at the air/water interface for blood cancer detection

We report results of the studies relating to controlled deposition of the amino-functionalized silica-coated zinc oxide (Am-Si@ZnO) nano-assemblies onto an indium tin oxide (ITO) coated glass substrate using Langmuir-Blodgett (LB) technique. The monolayers have been deposited by transferring the spread solution of Am-Si@ZnO stearic acid prepared in chloroform at the air-water interface, at optimized pressure (16 mN/m), concentration (10 mg/ml) and temperature (23 °C). The high-resolution transmission electron microscopic studies of the Am-Si@ZnO nanocomposite reveal that the nanoparticles have a microscopic structure comprising of hexagonal assemblies of ZnO with typical dimensions of 30 nm. The surface morphology of the LB multilayer observed by scanning electron microscopy shows uniform surface of the Am-Si@ZnO film in the nanometer range (<80 nm). These electrodes have been utilized for chronic myelogenous leukemia (CML) detection by covalently immobilizing the amino-terminated oligonucleotide probe sequence via glutaraldehyde as a crosslinker. The response studies of these fabricated electrodes carried out using electrochemical impedance spectroscopy show that this Am-Si@ZnO LB film based nucleic acid sensor exhibits a linear response to complementary DNA (10−6–10−16 M) with a detection limit of 1 × 10−16 M. This fabricated platform is validated with clinical samples of CML positive patients and the results demonstrate its immense potential for clinical diagnosis.

Stability of J-aggregated species in an indocarbocyanine dye in Langmuir–Blodgett Films

Here, the stability behaviour of J-aggregate of an indocarbocyanine dye 1,1′-Dioctadecyl-3,3,3′,3′-Tetramethylindocarbocynine perchlorate (DiI) in fatty acid mixed (XDiI=0.4) Langmuir–Blodgett (LB) films under different condition was reported. Surface pressure–area per molecule (π–A) isotherm measurement suggest that the molecular interaction between the constituent molecules changes with subphase temperature. UV–vis absorption and fluorescence spectroscopy and Atomic Force Microscopy (AFM) were used to study the stability behaviour. It has been observed that prominent J-aggregate of DiI occurred in the mixed films at subphase temperature 15°C. With the passage of time as well as post heat treatment DiI J-aggregate decayed to excimer in both mono- and multilayer LB films. Total transition from J-aggregate to excimer occurred in monolayer films, whereas, the transition was partial in multilayer films. The stability of DiI J-aggregate in monolayer films was increased by two ways – (i) depositing the DiI-SA mixed LB films at higher surface pressure, (ii) exposing the films at 50°C for 5min. It has been observed that after heat treatment the DiI J-aggregate remained almost stable even after 200 days. AFM investigations gave the compelling visual evidences of the same.

Topological “interfacial” polymer chemistry: Dependency of polymer “shape” on surface morphology and stability of layer structures when heating organized molecular films of cyclic and linear block copolymers ofn-butyl acrylate-ethylene oxide

The “topological polymer chemistry” of amphiphilic linear and cyclic block copolymers at an air/water interface was investigated. A cyclic copolymer and two linear copolymers (AB-type diblock and ABA-type triblock copolymers) synthesized from the same monomers were used in this study. Relatively stable monolayers of these three copolymers were observed to form at an air/water interface. Similar condensed-phase temperature-dependent behaviors were observed in surface pressure–area isotherms for these three monolayers. Molecular orientations at the air/water interface for the two linear block copolymers were similar to that of the cyclic block copolymer. Atomic force microscopic observations of transferred films for the three polymer types revealed the formation of monolayers with very similar morphologies at the mesoscopic scale at room temperature and constant compression speed. ABA-type triblock linear copolymers adopted a fiber-like surface morphology via two-dimensional crystallization at low compression speeds. In contrast, the cyclic block copolymer formed a shapeless domain. Temperature-controlled out-of-plane X-ray diffraction (XRD) analysis of Langmuir–Blodgett (LB) films fabricated from both amphiphilic linear and cyclic block copolymers was performed to estimate the layer regularity at higher temperatures. Excellent heat-resistant properties of organized molecular films created from the cyclic copolymer were confirmed. Both copolymer types showed clear diffraction peaks at room temperature, indicating the formation of highly ordered layer structures. However, the layer structures of the linear copolymers gradually disordered when heated. Conversely, the regularity of cyclic copolymer LB multilayers did not change with heating up to 50 °C. Higher-order reflections (d002, d003) in the XRD patterns were also unchanged, indicative of a highly ordered structure. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015