Polyurea Thin Film Research Articles

Effects of chitosan and piperazine on surface morphology and mebeverine hydrochloride removal in polyurea thin film composite membranes

Effects of chitosan and piperazine on surface morphology and mebeverine hydrochloride removal in polyurea thin film composite membranes

Nitrate removal studies on polyurea membrane using nanofiltration system – membrane characterization and model development

Abstract Desalination of nitrates from brackish water is prominent in the coastal areas due to excessive disposal of pesticides by agricultural industries. Nowadays, membrane processes are growing tremendously for the desalination of brackish water. In this context, polyurea (PU) could be a useful membrane material for the treatment of brackish water. The present work deals with the removal of nitrates from synthetic water using PU membranes by nanofiltration (NF) process. Polyurea thin film composite (PU-TFC) membranes were prepared by interfacial polymerization followed by thermal crosslinking and characterized using Fourier transformed infrared spectral (FTIR), X-ray diffraction (XRD), scanning electron microscopy– energy dispersion X-ray spectroscopy (SEM–EDS), Atomic force microscopy (AFM), thermogravimetric (TGA), and universal testing machine (UTM) for structural analysis, crystallinity, morphological, compositional, thermal and mechanical properties, respectively. Experimental studies were conducted on an NF pilot plant by varying operating pressure from 2 to 10 bar and feed nitrate concentration from 60 to 200 mg/L for evaluating PU membrane performance. Experimental observations revealed a maximum water flux of 30.6 L/m2 h and nitrate rejection of 97.2% at a pressure of 10 bar for feed containing 140 mg/L of nitrate. A mass transfer model was developed on the basis of solution–diffusion mechanism for a semi-batch NF process by considering cake enhanced concentration polarization model, for laminar flow with feed recycle, using a plate and frame membrane module. A generic semi-batch NF process model was integrated taking into account concentration polarization and fouling layer resistance. The integrated model was successfully compared with existing data in literature and could be used for process scale-up. Due to the merits of hydrophilicity, negative charge, high thermal and mechanical resistance, the PU membrane can be termed as a low cost, commercially viable and ecofriendly barrier for separation of nitrates.

Understanding the influence of graphene and nonclay on the microcracks developed at cryogenic temperature

This research examines reduction of microcracks in polyurea by addition of graphene and nanoclay on account of potential improvement in barrier properties. Graphene and nanoclay were added in different wt. fractions to polyurea followed by thin film preparation. The prepared thin film samples were characterized using scanning electron microscopy. Surface images before and after exposure to cryogenic temperature indicate that controlled addition of graphene and nanoclay to polyurea thin film can lead to a reduction in microcracking caused by thermal shocks.

Solution-Processable, Thin, and High-κ Dielectric Polyurea Gate Insulator with Strong Hydrogen Bonding for Low-Voltage Organic Thin-Film Transistors.

We developed a solution-processable, thin, and high-dielectric polyurea-based organic gate insulator for low-voltage operation and high performance of organic thin-film transistors (OTFTs). A 60 nm-thick polyurea thin film exhibited a high dielectric constant of 5.82 and excellent electrical insulating properties owing to strong hydrogen bonding. The hydrogen bonding of the synthesized polyurea was confirmed using infrared spectroscopy and was quantitatively evaluated by measuring the interactive force using atomic force microscopy. Moreover, the effect of hydrogen bonding of polyurea on the insulating properties was systematically investigated through the combination of various monomers and control of the thickness of the polyurea film. The dinaphtho[2,3- b:2',3'- f]thieno[3,2- b]thiophene-based OTFTs with the polyurea gate insulator showed excellent thin-film transistor (TFT) performance with a field-effect mobility of 1.390 cm2/V·s and an on/off ratio of ∼105 at a low operation voltage below 2 V. In addition, it is possible to fabricate flexible polymer organic semiconductor (OSC)-based TFT devices using a solution process, owing to excellent solvent stability in various organic solvents. We believe that the solution-processable polyurea gate insulator with a high dielectric constant and good insulation properties is a promising candidate for low-voltage-operated OTFTs using various OSCs.

Polyurea spin-coated thin films: Pyro- and piezoelectric properties and application to infrared sensors

We have investigated the pyro- and piezoelectric properties of polyurea spin-coated films with thermal and chemical stability and their performance as infrared sensors. The piezoelectric coefficient d33 was measured by a laser Doppler vibrometer to be 23.5 pC/N. This coefficient increased with the poling electric field up to around 75 MV/m, suggesting that the polyurea dipole is aligned by applying an electric field greater than 75 MV/m. When a triangular thermal wave was applied, a square-wave pyroelectric current was observed and the pyroelectric coefficient measured to be 5.11 µC/(m2·K). The infrared sensor performance of the polyurea thin film was examined by measuring the voltage sensitivity to infrared irradiation. The obtained result of 70.4 V/W at 1 Hz is consistent with the results calculated from the measured pyroelectric coefficient. Our findings suggest that the performance of the sensor may be improved by increasing the pyroelectric coefficient of the polyurea films.

Electric power generation using vibration of a polyurea piezoelectric thin film

An energy harvesting system is proposed, in which mechanical energy is converted to electrical energy through the piezoelectric effect of a polymer polyurea film on the device. Electrical energy harvesting methods that use piezoelectric elements have been reported by several groups, and lead zirconate titanate (PZT) is predominantly employed as the piezoelectric material. An energy harvesting device with a polyurea thin film formed through vapor deposition polymerization with 4,4′-diphenylmethane diisocyanete (MDI) and 4,4′-diamino diphenyl ether (ODA). The conversion efficiency from mechanical to electrical energy was calculated using finite elemental analysis (FEA) of the cantilever configuration. Higher conversion efficiency was obtained using a thinner and shorter cantilever configuration with increased resonance frequency of the device. Experiments were conducted using an electric power generation device with a 3 μm thick polyurea thin film attached to a 0.1-mm-thick, 18-mm-long beryllium copper cantilever. Vibration in the vertical direction, which induces the bending vibration on the cantilever, was applied to the device and the output voltage was measured by connecting load resistances. The output power was measured with a change in the load resistance from 10 kΩ to 10 MΩ, and an optimum output was obtained at 1 MΩ, which corresponds to the value calculated using FEA. The conversion efficiency was improved by changing the cantilever length and an efficiency of 0.233% was obtained with a 4-mm-long cantilever .

Measurement of Surface Acoustic Wave Velocity Using a Variable-Line-Focus Polyurea Thin-Film Ultrasonic Transducer

This paper presents the novel measurement method of the surface acoustic wave velocity by the variable-line- focus transducer using a polyurea piezoelectric ultrasonic transducer. First, a multiresonant polyurea thin-film ultrasonic transducer is fabricated by the vapor deposition polymerization process using 2 monomers. Second, the measurement system of surface acoustic wave velocity modified from the V(z) curve method is established. The system uses the fabricated polyurea thin film as a variable-line-focus transducer at the 30-MHz resonance frequency. The focal length is changed by varying the radius of curvature of the film transducer. To estimate the surface acoustic wave velocities from the measured data theoretically, the photographs of the transducer bent shapes are taken by using a digital microscope, and the bent transducer curvature is modeled by the 7th-order polynomial. To examine the performances of the variable-line-focus transducer, the surface acoustic wave velocities of an aluminum and a synthesized silica glass specimen have been measured. The measured surface acoustic velocities showed good agreement with the reference values.

Homogeneous Immobilization of Probe DNAs on DNA Chip Using Polyurea Thin Film

We propose a method to attach probe DNAs with a homogeneous population for quantitative measurement of a minimum number of target DNA/RNA for the next generation of DNA chip. To control the homogeneous population of DNA probes, polymer films having neighboring reactive groups at the same distance, i.e., aromatic polyurea film formed with 3,5-diaminobenzonic acid (DBA) and methylenedi(p-phenylene) diisocyanate (MDI) and aliphatic polyurea film formed with DBA and hexamethylene diisocyanate (HDI), were polymerized directly on the surface of a chip substrate by vapor deposition polymerization. The spatial arrangement and homogeneity of the reactive groups on the surfaces of the substrates were examined by observing the immobilization of DNA fragments bound to 20-nm gold nano-particles on the polymer films. The results showed that physical adsorption of the DNA was effectively inhibited on the DBA/HDI film in contrast to the DBA/MDI film and the conventional aminosilane surface. Moreover, the distribution of the particles was homogeneous on the DBA/HDI film, unlike on the other surfaces. These results indicate that the aliphatic polyurea film could be used to control the selectivity and uniformity of reactive groups on the surface of substrates for more precise quantitative measurement of DNA chip technology. [DOI: 10.1380/ejssnt.2009.728]

Relationship between Film Deposition Rate and Exhaust Speed in Aliphatic Polyurea Thin Film Prepared by Vapor Deposition Polymerization

1,12-Diaminododecane (DAD) and 1,3-bis(isocyanatomethyl)cyclohexane (H6XDI) are the raw materials of the aliphatic polyurea that we studied. These materials are prepared by vapor deposition polymerization (VDP). The setting of the temperatures of the chamber, substrate and raw material monomers is important in depositing monomer gas efficiently on the substrate. Generally, films are formed in the VDP equipment, while the conductance valve is released. However, multiple problems related to the trouble of the equipment occur in this method, when the vapor pressure is high, similar to that in the case of an aliphatic group monomer. Thus, we developed a new method of preventing these problems. In this method, the conductance valve is closed to make the exhaust speed zero, and it is also proven that the film deposition rate increases.

Polyurea Thin Film Ultrasonic Transducers for Nondestructive Testing and Medical Imaging

Ultrasonic transducers using polyurea piezoelectric thin film are studied in this paper. Aromatic polyurea thin films, prepared by vapor deposition polymerization, have useful characteristics for use as an ultrasonic transducer. This paper presents the fabrication and experimental evaluation of ultrasonic transducers formed using polyurea films. First, the vapor deposition polymerization process using two monomers is briefly reviewed, and the temperature conditions for higher piezoelectric constants are explored. Second, in order to test the fundamental characteristics of this material as a high-frequency, ultrasonic transducer, a polyurea film of 2.5 microm thickness was deposited on a silicon substrate. In the pulse/echo experiment results, a resonant frequency of about 100 MHz was observed. Third, we fabricated a concave point focus transducer and a cylindrical line focus transducer. To examine the performances of the focus transducers, two-dimensional images of a coin and V(z) curve measurements for an aluminum surface were demonstrated.

Multilayered high‐performance transducer using polyurea thin film

Polyurea thin film exhibits useful characteristics as a high‐frequency ultrasonic transducer such as a low acoustic impedance of 70% of that of PVDF, considerably high piezoelectric constants compatible with conventional piezoelectric polymers, and a higher Curie temperature. A polyurea thin film transducer working at over 100 MHz can be made on any surfaces through vapor deposition polymerization with a high controllability of thickness. To enhance the transducer performance, a multilayered configuration is studied in this study. A special twin‐vacuum‐chamber is used for laminating the polyurea layers and the aluminum electrodes alternately. We fabricate two‐ and three‐layered transducers with 1.5‐μm polyurea thin films as well as single‐layer transducers. To evaluate the transducer performances, we measure the capacitances, the electrical admittances, the coupling factors, and the Q values. The pulse/echo measurements are also conducted to determine the transmission and receiving characteristics of the transducers using a glass plate as a reflector. The results of the pulse/echo experiments show that the received voltage amplitude of the multilayered transducer is higher than that of the single‐layer transducer.

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2P322 均一なプローブ固定化用表面としての蒸着重合によるポリ尿素膜の評価(計測))

Influence of Poling Field on Polymerization in Polyurea Thin Films for Second-Harmonic Generation Prepared by Vapor Deposition Polymerization

Using 4,4′-diphenylmethane diisocyanate and 1,4-diamino-2-nitrobenzene (DNB), an aromatic polyurea thin film (PU(DNB)) was fabricated by vapor deposition polymerization. In PU(DNB), although the enhanced optical nonlinearity due to the introduction of the NO2 groups was achieved, a drastic decay of second-harmonic intensity was observed immediately after the poling field was turned off at 200° C. The structural analysis revealed that the polymerization proceeded during heat treatment, but not during the poling process. This was attributed to the reduction of the reactivity of DNB monomers under the poling field due to possible interaction between the NO2 group (electron acceptor) and the NH2 group (electron donor) through the π-electron system.

FT-IR observation on orientation of dipolar urea bonds in polyurea prepared by vapor deposition polymerization

Abstract Polyurea thin films from 4,4-diaminodiphenyl methane and 4,4-diphenyl methane diisocyanate were prepared by vapor deposition polymerization method. Polyureas include urea bonds, which contain NH and CO dipolar groups. In this report, the orientation of dipoles, which was caused by corona poling treatment, was observed by FT-IR reflectance. In the process of diode corona poling, an electric field is applied between a needle electrode and a planar electrode just under the polyurea thin film. The dipoles align best at the area right below the needle electrode, and the degree of dipole orientation decreases in proportion to the distance from the needle electrode. Surface potential is also highest at the area just below the needle electrode, and decreases with distance away from the electrode. In the triode corona poling, a grid electrode is set up between the needle electrode and the planar electrode. In this case, uniform orientation was accomplished over the entire surface. FT-IR spectra of the sam...