Langmuir-Blodgett Thin Films Research Articles

Catalytically Active Gold Nanoparticles on Star Block Co-polymer Matrix: Synthesis of Nanocomposite Film Exploring the Langmuir-Blodgett Technique.

Nanocomposites with metal nanoparticles and block copolymers distributed in a stable and robust thin film are preferred for various applications. Here, synthesis of such a nanocomposite is reported, which is composed of gold nanoparticles (AuNPs) embedded in a tetronic 701 (T701) and 90R4 (T90R4) thin film matrix generated using the Langmuir-Blodgett (LB) thin film technique. Tetronics contain a monoprotonated central ethylenediamine group at pH 5 due to the presence of chloroauric acid (HAuCl4) in the subphase, along with poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) blocks, both of which have the capacity to serve as the reducing agent toward chloroaurate anion (AuCl4-). Calorimetric experiments have shown that T90R4 has a better interaction with AuCl4-, probably due to its better electrostatic interaction with AuCl4- ions due to the higher % of the hydrophilic PEO group. On the other hand, the T701-AuNP interaction turned out to be more spontaneous due to the higher hydrophobicity of T701 (higher PPO/PEO ratio). The optical properties and structure/morphology of these nanocomposites are characterized by UV-vis spectroscopy, FTIR spectroscopy, XRD, and TEM. The composite thin film has the ability to catalyze the organic electron transfer process between p-nitrophenol and p-aminophenol in the presence of sodium borohydride. A clear correlation has been found between the reaction rates and the kind of tetronic present in the nanocomposite, which acted as a matrix and stabilizer toward AuNPs.

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.

Red-Ox front propagation in polyaniline-polymer electrolyte system as a basis for spiking and rate-based neural networks and multibit ReRAM

We observed and studied the phenomenon of the redox front propagation in different polyaniline (PAni) deposited samples interfaced with liquid or solid polymeric electrolyte. The front of electrochemical conversion, in which the insulator and the conductor parts of PAni are interfaced, is studied observing the temporal evolution of the conductivity of PAni samples. The propagation of redox front was studied in electrochemically obtained thick (2 µm) and in thin (50 nm) polyaniline films, obtained using Langmuir-Blodgett (LB) method. In the configuration that we tested, the speed of the red-ox front propagation for the thin LB films was found to be 200 µm/sec opening the way for the manufacturing large neural networks, realized using PAni based memristive devices, in which the memristance can be quickly changed in the programmable manner. The prototypes of the spiking neuron connections were manufactured on the basis of lithographically developed gold contacts, bridged by electrochemically grown polyaniline and placed under polymer electrolyte layer with only one counter electrode (gate) for the whole manifold of pseudo-two-terminal memristor bridges. The spike propagation was studied in such gold-polyaniline systems. The research opens the possibility of miniature spike or rate-based neural network circuits manufacture, based on metal pads and polyaniline.

A new approach for the adsorption kinetics using surface plasmon resonance results

This work is focused on a new approach to determine the adsorption kinetics of Surface Plasmon Resonance (SPR) measurement data yielded from Calix[4]arene Langmuir-Blodgett (LB) thin films upon exposure to a range of volatile organic vapors such as benzene, chloroform, toluene and ethyl acetate. Experimental results were analyzed using the well known Pseudo first-order and second-order, Ritchie and Elovich adsorption models. The validity of these models was assessed by using the correlation coefficient (R2) as an indicator of the conformity between the model prediction and experimental adsorption data. Sorption capacity, adsorption rate constant and the amount of vapor molecules were calculated and discussed. The values of R2 = 0.96, R2 = 0.94, and R2 = 0.98 for chloroform vapor were calculated for Pseudo-first order, Pseudo-second order and Elovich models respectively. Pseudo-second order model gave the best fit values for benzene (R2 =0.9991), toluene (R2 =0.999) and ethanol (R2 =0.993).

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.

Sensing behaviors of lipophilic calix[4]arene phosphonate based Langmuir-Blodgett thin films for detection of volatile organic vapors

This study concentrates on the lower rim effect of calix[4]arenes based lipophilic phosphonate (CTPO4 and CPO4) with and without tert-butyl group Langmuir-Blodgett (LB) thin films in the volatile organic vapors (VOCs) sensing applications. Surface plasmon resonance (SPR) technique was employed to determine optical parameters and to investigate VOCs sensor properties of thin films. The thicknesses of 3 layered CTPO4 and CPO4 thin films were estimated as 1.9 ± 0.02 and 2.6 ± 0.02 nm. Atomic force microscope (AFM) and contact angle (CA) analysis were taken for the morphological study. Both thin film surfaces showed a uniform distribution, the surface roughness of CTPO4 thin film (23.04 nm) was found to be higher than the CPO4 thin film (10.53 nm). The equilibrium contact angle values of 58.96° ± 0.43° for CTPO4 and 44.23° ± 2.25° for the CPO4 thin film surface were determined. CTPO4 and CPO4 LB thin films were exposed to various VOCs gas in real time. Ficks’ second law of diffusion was adopted to explain the sorption process of VOCs into the thin films, and the diffusion is interpreted as a two-region interaction. The diffusion coefficients were determined between 2.7 × 10−22–63.19 × 10−22 cm2 s−1 and 2.7 × 10−24–63.19 × 10−24 cm2 s−1 for the first and second region of the interaction respectively. The responses of CTPO4 are higher than CPO4 due to the upper rim tert-butyl groups onto CTPO4 molecule. Both films were highly affiliated by the chlorinated VOCs compared with the aromatic compounds. The presence of tert-butyl group has improved sensing properties and these new calix[4]arenes are good candidates for sensor applications.

Sensor application of pyridine modified calix[4]arene Langmuir-Blodgett thin film

5,11,17,23–5,11,17,23-Tetra-(tert-butyl)− 25,27-di-(2-aminomethyl pyridine acetamide)− 26,28-dihydroxy calix[4]arene (C4P2T) molecule was transferred to gold coated glass substrate for the first time as a sensor active layer for the detection of volatile organic compounds (VOCs) such as acetone, benzene, chloroform, ethyl acetate and methanol. UV–visible spectroscopy and surface plasmon resonance (SPR) techniques were employed to monitor Langmuir-Blodgett (LB) thin film layer during the fabrication process of each sensor layers. In order to determine film thickness and refractive index values of C4P2T LB film, SPR measurements were performed using a Kretschmann’s prism configuration set-up system. Thickness and the refractive index values for the C4P2T LB thin films were determined to be 1.01 nm/layer and 1.59, respectively, by fitting the SPR curves using WINSPALL software based on the Fresnel formula. For the VOCs sensor application of the C4P2T LB thin film, reflected light intensity was recorded as a function of time by using SPR system. These measurements indicated that C4P2T LB thin film sensor layer was suitable for multiple usage with a fast response time (~ 3 s) and a recovery time (~ 3 s). The amount of C4P2T LB sensor responses against VOCs were followed by decreasing order acetone, chloroform, methanol, ethyl acetate and benzene. As a result, C4P2T LB film sensor has a sensitive and selective character and is suitable for VOCs sensor applications.

The aggregation of 1,3,4-thiadiazole based Hockey stick shaped Mesogen in Langmuir-Blodgett thin film in comparison to that of 1,3,4-oxadiazole

Bent Core Mesogens are remarkably interesting achiral Liquid Crystals. These grab attention for their utility. The compound, taken for investigation, is a Schiff base addition product, composed of 2-(4β-aminophenyl)-5-(4?β-butyloxyphenyl)-1,3,4- thiadiazole and 4-n-hexadecyloxy salicylaldehyde. The property of this imine derivative is in accordance with liquid crystal and is a Bent Core Mesogen (BCM). The thin layers were prepared with the help of Langmuir-Blodgett apparatus. The morphology and photo-physical characteristics of thin films were examined in comparison to similar BCM derivative of 1,3,4-Oxadiazole. The expectation was the formation of monolayer of molecules on the substrate. Practically there were layer of clusters on the substrate. Both molecules form nano clusters. The typically different aggregates by the thiadiazole moiety in comparison to oxadiazole moiety are revealed. Cluster formation is also supported by the Atomic Force Microscopic (AFM) images.

Carbon Dioxide Sensing with Langmuir–Blodgett Graphene Films

Graphene has become a material of choice for an increasing number of scientific and industrial applications. It has been used for gas sensing due to its favorable properties, such as a large specific surface area, as well as the sensitivity of its electrical parameters to adsorption processes occurring on its surface. Efforts are ongoing to produce graphene gas sensors by using methods that are compatible with scaling, simple deposition techniques on arbitrary substrates, and ease of use. In this paper, we demonstrate the fabrication of carbon dioxide gas sensors from Langmuir–Blodgett thin films of sulfonated polyaniline-functionalized graphene that was obtained by using electrochemical exfoliation. The sensor was tested within the highly relevant concentration range of 150 to 10,000 ppm and 0% to 100% at room temperature (15 to 35 °C). The results show that the sensor has both high sensitivity to low analyte concentrations and high dynamic range. The sensor response times are approximately 15 s. The fabrication method is simple, scalable, and compatible with arbitrary substrates, which makes it potentially interesting for many practical applications. The sensor is used for real-time carbon dioxide concentration monitoring based on a theoretical model matched to our experimental data. The sensor performance was unchanged over a period of several months.

Synthesis, characterization and chemical sensor properties of a novel Zn(II) phthalocyanine containing 15-membered dioxa-dithia macrocycle moiety

The issue of utilizing organic materials in chemical sensing devices has recently received considerable critical attention. Phthalocyanines (Pcs) and metal phthalocyanines (MPcs) have been identified as promising materials thanks to their outstanding properties reported in this study. A novel zinc(II) phthalocyanine containing four 15-membered dioxa-dithia macrocyclic moieties was synthesized via the reaction of anhydrous Zn(II) acetate and 13,14-dihydro-6H,12H,20H-tribenzo[f,j,n][1,5]dioxa[9,12] dithiacyclopenta-decine-2,3-dicarbonitrile which was prepared from 1,3-di(2-thio-methylphenoxy) propane and 4,5-dichloropthalonitrile. In order to synthesize and characterize this novel compound, elemental analysis, MS, FT-IR, 1H, 13C NMR, and UV–vis spectral techniques were utilized. To create a Quartz Crystal Microbalance (QCM) sensor, zinc(II) phthalocyanine-based macrocyclic molecules were deposited onto a quartz crystal using the Langmuir-Blodgett (LB) thin film technique. The sensing ability of this chemical sensor was examined by recording the interaction between this novel material as a QCM-sensor and selected chemical vapors such as carbon tetrachloride, chloroform, benzene and toluene. The interaction results for this zinc(II) phthalocyanine based macrocyclic material indicated that this material can be used as a QCM chemical sensor element for chloroform sensing devices with a low detection limit, fast response and recovery times, selectivity, and high sensitivity.

Preparation of Zinc (II) phthalocyanine-based LB thin film: Experimental characterization, the determination of some optical properties and the investigation of the optical sensing ability

Zinc(II) phthalocyanine (Zn(II)Pc) molecule was the first time prepared onto three different substrates utilizing Langmuir-Blodgett (LB) deposition technique to investigate its vapor sensing abilities and some optical properties. We utilized five different and well-known techniques to control monolayer quality of Zn(II)Pc LB film. The obtained the thickness and refractive index values for Zn(II)Pc LB film with coated at different layers vary from 3.2 to 10.9 nm and from 1.42 to 1.71, respectively. The sensing properties were investigated by exposing the Zn(II)Pc-based mass or optical sensor to some organic vapors. Kinetic results presented that this Zn(II)Pc material is a good candidate as a sensor element with a fast and reversible response for dichloromethane sensing devices.

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.

Aromatik hidrokarbonların dedekte edilmesi için kaliksaren bazlı diamid kimyasal sensor çiplerinin geliştirilmesi

In the present work, a new macrocycle materials (SB77) was selected and Langmuir-Blodgett thin films of this macrocycle compounds were examined for its vapor sensing capabilities against vapor of aromatic BTX hydrocarbons (benzene, toluene, xylene) through Quartz Crystal Microbalance (QCM) technique. In accordance with this aim, the calix[4]arene LB thin films were prepared onto quartz crystal substrates. The characterization of SB77 LB thin film was performed for nine LB layers fabricated onto the quartz crystal. The frequency shifts and the mass changes for monolayer of these LB thin films were obtained as 32.35 Hz / per layer and 2206.65 ng (8.32 ng mm-2), respectively. All QCM results indicated that SB77 LB thin film chemical sensors exhibits high response, a good sensitivity and selectivity for benzene vapor at saturated or different concentrations than other aromatic hydrocarbon vapors. These LB thin film sensors with SB77 calix [4]arene macrocycle materials have been potential candidates for organic vapor sensing applications with simple and low cost preparation at room temperature.

The unique asymmetric nano-cluster formation by the uneven hockey-stick-shaped mesogen based on 1,3,4-oxadiazole in Langmuir–Blodgett thin film

Achiral Bent Core Mesogens (BCMs) are an exciting class of potentially useful material that catch special attention in the last decade. The newly synthetic compound 5-hexadecyloxy-2-[(E)-({4-[5-(4-octyloxyphenyl)-1,3,4-oxadiazol-2-yl] phenyl}imino)methyl]phenol, named as ABC, is a Schiff base derivative. Having both flexible hydrophobic and rigid hydrophilic part it shows a surface-active liquid crystalline property. This study is based on the Langmuir–Blodgett (LB) thin film fabricated with this molecule. The spectral study, showing intense bathochromic shift of characteristic peaks, reveals that the J-aggregation of molecules in the film in comparison to its solution. Atomic force microscopic (AFM) and scanning electron microscopic (SEM) images reveal the occurrence of unique unsymmetrical nano-size cluster formation in pure ABC thin film as well as mixed thin film with Behenic acid (BA) as supporting matrix.

Grafen Kaplı Kimyasal Sensörlerin Şişme Davranışları ve Matematiksel Modelleme

Bu çalışmada, grafen kaplı Langmuir-Blodgett (LB) ince filmlerin şişme davranışları Kuartz Kristal Mikrobalans (KKM) tekniği kullanılarak incelenmiştir. Bu filmler, bazı organik buharların (aseton, etanol ve metanol) difüzyon katsayı değerlerinin hesaplanması (Fick’in erken-zaman difüzyon kanunu kullanılarak) için oda sıcaklığında etkileşmeye bırakılmıştır. Difüzyon katsayı değerleri sırası ile aseton, etanol ve metanol için 20.43 x 10−16, 1.30 x 10−16 ve 0.91 x 10−16 cm2 s−1 olarak hesaplanmıştır. Benzer sıralama grafen kaplı KKM sensörünün tepkisi (frekans değişimi, Δf) için de aseton (342 Hz) > etanol (76 Hz) > metanol (51 Hz) olarak elde edilmiştir.

Fabrication of picoline amide-based calix[4]arene Langmuir-Blodgett thin film for volatile organic vapor sensing application

Picoline amide-based calix[4]arene molecule was the first time deposited onto gold substrate as an active layer by using Langmuir-Blodgett (LB) coating technique. UV-visible, atomic force microscopy, and surface plasmon resonance (SPR) technique were used to control monolayer quality. The sensing properties were investigated by exposing the LB thin film to different percentage of organic VOCs vapors such as acetone, benzene, chloroform, ethyl acetate, and methanol in air-VOCs mixture. SPR results showed that this calix[4]arene molecule is a good candidate with a fast and reversible sensor response for VOCs sensing applications.

A macrocyclic tetra-undecyl calix[4]resorcinarene thin film receptor for chemical vapour sensor applications

This work demonstrates the fabrication of chemical vapour sensors using Langmuir–Blodgett (LB) thin films, describing the thin film properties of a tetra-undecyl calix[4]resorcinarene molecule along with a discussion of their sensing performance. Atomic Force Microscopy and Surface Plasma Resonance (SPR) methods were used for the characterization of the deposited thin films. As evidenced by these characterization methods, high quality and uniform Langmuir monolayers were formed on the water surface and can be transferred onto glass and gold-coated glass substrates with a transfer ratio of over 95%. The gas sensing properties towards the vapours of four volatile organic compounds were also examined by the SPR technique. Tetra-undecyl calix[4]resorcinarene LB thin film is sensitive to organic vapours (benzene, chloroform, ethanol and toluene) with rapid response and recovery times, demonstrating promise towards future vapour detection applications, especially for the rapid detection of leaks or spillage.

Interaction of N,N'-Di(4-chlorophenyl)diimide 1,1'-Binaphtyl-4,4',5,5',8,8'-hexacarboxylic Acid with Thiourea Dioxide in Solution and Thin Film

The reactions of interaction of N,N'-di(4-chlorophenyl)diimide 1,1'-binaphtyl-4,4',5,5',8,8'-hexa-carboxylic acid (cubogen red) with thiourea dioxide in a water-alkaline solution and a Langmuir–Blodgett thin film, obtained on quartz and silicon substrates, have been investigated. Electron absorption spectroscopy have revealed that the reaction of reductive cyclization of cubogen with formation of perylenetetracarboxylic acid diimide derivatives occurs in a water-alkaline solution. At the same time, the interaction of thiourea dioxide with a cubogen thin film does not lead to the formation of cyclization products; nevertheless, it changes the film structure. One might suggest that soluble leuco forms of J aggregates are formed in this case, whereas H aggregates remain intact in the structure.

An Aminopyridine Bearing Pillar[5]arene-Based QCM Sensor for Chemical Sensing Applications: Design, Experimental Characterization, Data Modeling, and Prediction

This study presented that deca pyridin-2-amine bearing Pillar[5]arene (P5-PA) was designed in an appropriate cavity, which acts a part significant role in host–guest interactions of the macrocyclic molecules. P5-PA monolayer was deposited onto suitable substrates as an active layer by using Langmuir-Blodgett (LB) coating technique to examine its vapor sensing capabilities against vapor of some aliphatic hydrocarbons through Quartz Crystal Microbalance (QCM) technique. The kinetic vapor studies were occurred by exposing the P5-PA/LB thin film to different percentage of organic VOCs vapors such as dichloromethane, chloroform and carbon tetrachloride in air-VOCs mixture. The early-time Fick’s diffusion law was handled to extract the diffusion coefficients by utilizing QCM data depending real time. It is observed that there were two different regions with two slopes indicating that one belongs to slow surface diffusion and another fast for bulk diffusion into LB thin film. The collected experimental data with 1 Hz sampling frequency was modelled with deep learning models (NARNET and LSTM) which could get satisfactory results on small datasets. The models were trained with 83% samples of data; the remaining 17% data is used to evaluate the developed models prediction performance. The predicted values of models were compared with the original (measured) data in the results section. It is observed from the results; the developed deep learning models have higher than 0.98 correlation coefficient for each vapor, which is satisfactory for prediction applications.

Developing of N-(4-methylpyrimidine-2-yl)methacrylamide Langmuir-Blodgett thin film chemical sensor via quartz crystal microbalance technique.

In the present work, the characterization and gas sensing properties of newly synthesized N-(4-methylpyrimidine-2-yl)methacrylamide (N-MPMA) monomer Langmuir-Blodgett (LB) thin films were investigated. The UV-visible spectroscopy, quartz crystal microbalance (QCM), and atomic force microscopy were utilized to characterize N-MPMA LB thin films. The surface behavior of N-MPMA monolayer was stable and allowed an effective transfer at a surface pressure of 14 mN/m. The mass change/unit area value of the N-MPMA LB thin film deposited quartz crystal surfaces was investigated. The amount of N-MPMA LB thin film deposited on the substrate for bilayer was calculated as 228.72 ng (86.31 ng/mm2 ) and 12.5 Hz frequency shift was observed for each layer of the N-MPMA film. The kinetic responses of N-MPMA LB film against chloroform, dichloromethane, benzene, and toluene were measured via QCM system at room temperature. N-MPMA QCM sensor results displayed that chloroform has the largest frequency shifts compared with the other vapors used in the present work and these results can be illuminating in terms of physical properties of organic vapors.