Third-order nonlinear optical properties of an ultrathin film containing a porphyrin derivative

An ultrathin nanoscopic multilayer film has been fabricated through the electrostatic layer-by-layer self-assembly of negatively charged 5,10,15,20-tetrakis(3,4,5-trihydroxyphenyl)porphyrin (DHP) and oppositely charged polyethylenimine (PEI). UV-vis spectra showed a continuous and uniform deposition process of PEI and DHP. The film structure was characterized by small-angle X-ray diffraction measurement and AFM images. The nonlinear optical properties of ultrathin film were studied by Z-scan technique with laser duration of 8 ns at a wavelength of 532 nm. The film sample exhibited strong nonlinear saturated absorption and a self-defocusing effect. The nonlinear absorption coefficient and refractive index of the self-assembly ultrathin film are -9.7 x 10(-5) m/W and -7.56 x 10(-12) m(2)/W, respectively.     

Free convection and mass transfer flow through a porous medium bounded by an infinite vertical limiting surface with constant suction

Steady two-dimensional free convection and mass transfer flow, of an incompressible viscous fluid through a porous medium bounded by a vertical infinite limiting surface (plane wall) is considered. Expressions for the velocity, temperature, concentration and the rate of heat transfer are obtained. Effects of Gr (Grashof number), Gm (modified Grashof number) and permeability K of the porous medium on the velocity and rate of heat transfer are discussed when the surface is subjected to a constant suction velocity.     

Hydrodynamics of nonlinear viscoplastic fluid in cylindrical hydrocyclone

A flow of non-linear viscoplastic fluid film in a cylindrical hydrocyclone was simulated. The distribution of the velocity component and also a dependence of a fluid film thickness on an axial coordinate were determined by numerical solution of a set of rheodynamic model equations for various rheological properties of the liquid and dimensionless quantities. An influence of plastic properties of the liquid on damping of the circumferential component of the velocity was examined. The results were physically substantiated.     

Double-diffusivity heat generation effects on bioconvection process embedded in a vertical porous surface with variable fluid properties

Journal of Thermal Analysis and Calorimetry - The present paper concerns the bioconvective flow, mass and heat transfer including motile microorganisms on a vertical surface saturated with porous...     

Electrochemical properties of a two-component DNA-polyaniline film at the surface of glassy carbon electrode

Aniline electropolymerization on a DNA-modified glassy carbon electrode gives rise to a stable composite DNA-polyaniline film possessing redox activity over a wide range of pH values. The heights and potentials of the redox peaks linearly depend on pH in the pH 3.0–8.0 range. It was established that the inclusion of DNA into the polyaniline composition enhances considerably the film conductivity and capacitance in the weakly acid and weakly alkaline pH regions; this effect is most pronounced for the reduced polymer form. The properties of the prepared DNA-polyaniline film point to its promise for the use in electrochemical biosensors.     

The structure and properties of n-octadecanol film present on the surface of a carbon-silica adsorbent

Summary The properties of the n-octadecanol film on carbon-silica adsorbent (Carbosil) were investigated. It was found that n-octadecanol forms an oriented film on the Carbosil's surface. If the surface of the basic silica gel is not completely covered with carbon, then the phase transition takes place in this film at a temperature higher than the melting temperature of n-octadecanol. One may distinguish two forms of this film, characterised by the different structures and the temperatures of the phase transitions. The first exists on the surface of silica gel unblocked by carbon. This part of the film is a monolayer, in which the alcohol molecules are vertically oriented. The solid compact-liquid expanded type phase transition at the well-defined temperature occurs in this film. In the second part of the film formed on the carbon surface, there is a multilayer of n-octadecanol. Its molecules are probably parallely oriented in relationship to the adsorbent surface. This film desintegrates progressively when the temperature increase. Maximum temperature of this phase transition is lower than the temperature of its analogue on pure silica gel surface.     

Studies with a derivatograph of the properties of a water film on a marble surface modified by tetradecylammonium chloride (TDACl)

The properties of water layers on bare marble and on marble samples covered with various amounts of tetradecylammonium chloride (TDACl) after flotation were investigated by thermal analysis methods. The dependences of the layer thickness, activation energy, enthalpy and entropy of the bonded watervs. the amount of TDACl previously deposited on the marble surface were determined. The results obtained and the literature data were used to propose an interpretation of the changes caused in these parameters by the coverage of the marble surface with TDACl molecules. A correlation between these parameters and the changes in water structure and marble flotatibility is also presented.

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Zusammenfassung Eigenschaften von Wasserfilmen auf unbeschichteten und mit Tetradecylammoniumchlorid (TDACl) in unterschiedlichen Mengen bedeckten Marmorproben wurden nach Flotation thermoanalytisch untersucht. Die Abhängigkeit der Schichtdicke, der Aktivierungsenergie und der Enthalpie und Entropie des gebundenen Wassers von der Menge des vorhergehend auf die Marmoroberfläche aufgebrachten TDACl wurden ermittelt. Die durch die Bedeckung der Marmoroberfläche mit TDACl verursachten Veränderungen dieser Parameter werden anhand der erhaltenen Resultate und von Literaturangaben interpretiert. Beziehungen zwischen diesen Parameters und Veränderungen der Wasserstrukturen und der Flotierbarkeit des Marmors werden angegeben.

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Ultrafast and large third-order nonlinear optical properties of CdS nanocrystals in polymeric film

We report the ultrafast and large third-order nonlinear optical properties of CdS nanocrystals (NCs) embedded in a polymeric film. The CdS NCs of 2 nm radius are synthesized by an ion-exchange method and highly concentrated in the two layers near the surfaces of the polymeric film. The two-photon absorption coefficient and the optical Kerr coefficient are measured with laser pulses of 250 fs duration at 800 nm wavelength. The one-photon and two-photon figures of merit are determined to be 3.1 and 1.3, respectively, at irradiance of 2 GW/cm(2). The observed nonlinearities have a recovery time of approximately 1 ps. The two-photon-generated free carrier effects have also been observed and discussed. These results demonstrate that CdS NCs embedded in polymeric film are a promising candidate for optical switching applications.     

New insight into surface properties of LB film of an amphiphilic terpolymer

Amphiphilic terpolymer(TPR) exhibits good film-forming behavior on pure water observed by means ofπ-A isotherms.To gain insight into physical properties of TPR,the films have been deposited on silicon substrates at different surface pressure by Langmuir-Blodgett(LB) technique.It was found that the increase in peak intensities of stretching mode was due to orderly packing of the films.The contact angles increased with increasing surface pressure,indicating an increase in hydrophobicity due to dense packing of chains of TPR.The cyclic voltammetric measurements indicated that TPR showed good current shielding effect for electron-transfer.In a word,LB films of TPR can produce a variety of structures with varied topography,enabling us to control not only the functionality of the surface,but also the interfacial transport characteristics.     

The CdS nanoparticle with capped surface and its nonlinear optical properties studied by hyper-Rayleigh scattering

The CdS nanoparticles synthesized in AOT (bis(2-ethylhexyl) sulfosuccinate, disodium salt) reverse micelle in addition of the electric neutral surface-capping agent of pyridine are characterized by XPS, TEM and the absorption spectra. The values of the first-order hyperpolarizability β for two kinds of nanoparticles, CdS/AOT^- and CdS/pyridine/AOT^-, have been experimentally measured in solution by the newly developed hyper-Rayleigh scattering technique. The values of β are larger than 10^-27 esu, which are among the largest values reported for solution species.     

Electroanalytical properties of aldehyde biosensors with a hybrid-membrane composed of an enzyme film and a redox Os-polymer film.

Aldehyde biosensors were constructed by cross-linking formaldehyde dehydrogenase (FDH) or aldehyde dehydrogenase (ADH) and bovine serum albumin on the surface of a redox Os-polymer-coated electrode. The prepared aldehyde biosensors responded rapidly (within 30 s) to aldehydes without the addition of a soluble mediator, because the inner redox Os-polymer film effectively mediated the electron transfer from NADH generated enzymatically into the outer enzyme film to a glassy carbon electrode. An FDH/Os-polymer electrode responded linearly over the concentration range of 2 x 10(-6)-5 x 10(-4) M for formaldehyde, while an ADH/Os-polymer electrode, though responding similarly to long chain aldehydes, such as propionaldehyde and butylaldehyde, responded linearly over the concentration range of 4 x 10(-6)-2 x 10(-4) M for acetaldehyde.     

Stability of thin stagnant film on a solid surface with a viscoelastic air-liquid interface

Linear stability analysis for a film on a solid surface with a viscoelastic air-liquid interface is presented. The interfacial dilatational and shear viscoelastic properties were described by Maxwell models. Dilatational and shear interfacial elasticity and viscosity were shown to improve film stability. When the interfacial rheological properties are extremely large or small, the maximum perturbation growth coefficient is shown to reduce to those for immobile and mobile interfaces respectively. Calculated values of maximum growth coefficient for thin film stabilized by 0.5% beta-lactoglobulin approached those of mobile films for thick (>2000 nm) and those for immobile films for thin (<100 nm) films respectively with the values lying between the two limits for intermediate film thicknesses.     

Molecular dynamics simulation of surface morphology and thermodynamic properties of polyaniline nanostructured film

To develop predictive models in nanostructured films, there is an ongoing research to validate molecular dynamics (MD) simulation results with experimental data. The morphology and surface topography of polyaniline (PANI) nanostructured film coated on a TiO₂ nanocrystalline surface were investigated by scanning electron microscopy and atomic force microscopy, respectively. The atomistic model of the simulated PANI was generated using energy minimization with a condensed‐phase optimized molecular potential for atomistic studies force field function to reach a thermodynamic equilibrium state. Various parameters of PANI such as density, energy, cavity size, and free volume distributions are calculated. MD simulation has also been used to obtain specific volume (V) as a function of temperature (T). It is demonstrated that this V–T curve can be used to determinate glass transition temperature T_g, reliably. Although experimental data available for the PANI film are very limited, simulation results such as density and T_g are in good agreement with the experimental values reported in the literature. Comparison of the surface topography of PANI demonstrates a reasonable trend between atomic force microscopy image analysis and the MD simulation results at various temperatures. Copyright © 2014 John Wiley & Sons, Ltd.     

Stable superhydrophobic surface via carbon nanotubes coated with a ZnO thin film

We report the formation of a stable superhydrophobic surface via aligned carbon nanotubes (CNTs) coated with a zinc oxide (ZnO) thin film. The CNT template was synthesized by chemical vapor deposition on an Fe-N catalyst layer. The ZnO film, with a low surface energy, was deposited on the CNT template by the filtered cathodic vacuum arc technique. Contact angle measurement reveals that the surface of the ZnO-coated CNTs is superhydrophobic with water contact angle of 159 degrees . Unlike the uncoated CNTs surface, the ZnO-coated CNTs surface shows no sign of water seepage even after a prolonged period of time. The wettability of the surface can be reversibly changed from superhydrophobicity to hydrophilicity by alternation of ultraviolet (UV) irradiation and dark storage.     

Preparation and properties of a thermo-sensitive latex film

Polymer particles with hydrophobic core and hydrophilic shell were prepared via a three-step method. First, poly(butyl methacrylate-co-methyl methacrylate) (p-(BMA-MMA)) latex was prepared through emulsion polymerization. Then, a shell of poly(glycidyl methacrylate) (p-GMA) was introduced around the p-(BMA-MMA) particles by using a redox initiation system under kinetically controlled conditions. Finally, part of the epoxy groups existing in the shell were converted into quaternary ammonium salts, resulting in an ionic hydrophilic shell. The core-shell particles could be redispersed in water to form a stable emulsion. The contact angle of the core-shell latex film with water was around 16° at 25 °C, which became larger than 90° after the film was heated at 150 °C for a short period of time. This showed that the latex film was completely switched from hydrophilicity to hydrophobicity by the action of heat. Additionally, the latex film before heat treatment could be easily washed away from the substrate with neutral water, but it could no longer be removed after the heat treatment. When an IR dye with the maximum absorption at 830 nm was incorporated into the film, it became sensitive to LD laser emitting at 830 nm and gave negative image after exposed by LD laser and developed with neutral water. This showed that the latex film might find uses in chemical-free thermal laser imaging applications.     

Laser studies of the reactivity of SiO with the surface of a depositing film

The reactivity of SiO produced in a SiCl₄/O₂ plasma with the surface of a depositing silicon oxide film has been measured to be near zero for surface temperatures of 25–500 °C using the IRIS technique (imaging of radicals interacting with surfaces). This method combines spatially resolved laser-induced fluorescence with molecular beam techniques. The SiO desorbs from the surface with a spatial distribution consistent with a cosine angular distribution.     

Transport and kinetics in electrocatalytic thin film biosensors: bounded diffusion with non-Michaelis-Menten reaction kinetics

In this paper, we describe the problem of describing the transport and catalytic kinetics at immobilized enzymes in an electronically conductive polymer thin film where substrate inhibition is important. Here, the enzyme kinetics are not well described by the Michaelis-Menten equation. We describe a mathematical procedure based on the recently developed Akbari-Ganji method (AGM) which facilitates a full analytical solution of the boundary value problem which is valid for all values of substrate concentration. Closed form expressions for both the substrate concentration in the film and the steady-state amperometric current response are presented. Limiting kinetic cases are identified and are expressed pictorially in parameter space using a kinetic case diagram.

     

Structural properties of opals grown with vertical controlled drying

We have grown thin opals of self-assembled silica colloids by the well-known vertically controlled drying method. The volume fraction at the start of the growth and the temperature were systematically varied. We have quantitatively characterized the lateral domain sizes by scanning electron microscopy. The sample thickness as a function of position was obtained from Fabry-Pérot fringes measured in optical reflectivity. We observe that the sample thickness strongly increases from top to bottom, independent of temperature, in agreement with a model that we propose. The inhomogeneity in thickness contrasts with earlier reports. The lateral domain shapes of the single-crystal domains are found to vary from irregular near the top to rectangular near the bottom. A surprising observation is that, grosso modo, the lateral domain extents increase linearly with thickness (i.e., thin crystals are small, and thick crystals are large). This behavior agrees qualitatively with results on completely different colloids such as disordered slurries. The consequence of our results for optical applications, including photonic crystals, is that unwanted scattering due to grain boundaries is reduced for large domains that are thick. Conversely, thin crystals will scatter relatively strongly from grain boundaries.