Characterization of hydrophobin proteins at interfaces and in solutions using x rays

Hydrophobins are a group of particularly surface active proteins. The surface activity is demonstrated in the ready adsorption of hydrophobins to hydrophobic/hydrophilic interfaces such as the air/water interface. Adsorbed hydrophobins self-assemble into ordered films, lower the surface tension of water, and stabilize air bubbles and foams. Hydrophobin proteins originate from filamentous fungi. In the fungi the adsorbed hydrophobin films enable the growth of fungal aerial structures, form protective coatings and mediate the attachment of fungi to solid surfaces. This thesis focuses on hydrophobins HFBI, HFBII, and HFBIII from a rot fungus Trichoderma reesei. The self-assembled hydrophobin films were studied both at the air/water interface and on a solid substrate. In particular, using grazing-incidence x-ray diffraction and reflectivity, it was possible to characterize the hydrophobin films directly at the air/water interface. The in situ experiments yielded information on the arrangement of the protein molecules in the films. All the T. reesei hydrophobins were shown to self-assemble into highly crystalline, hexagonally ordered rafts. The thicknesses of these two-dimensional protein crystals were below 30 Å. Similar films were also obtained on silicon substrates. The adsorption of the proteins is likely to be driven by the hydrophobic effect, but the self-assembly into ordered films involves also specific protein-protein interactions. The protein-protein interactions lead to differences in the arrangement of the molecules in the HFBI, HFBII, and HFBIII protein films, as seen in the grazing-incidence x-ray diffraction data. The protein-protein interactions were further probed in solution using small-angle x-ray scattering. Both HFBI and HFBII were shown to form mainly tetramers in aqueous solution. By modifying the solution conditions and thereby the interactions, it was shown that the association was due to the hydrophobic effect. The stable tetrameric assemblies could tolerate heating and changes in pH. The stability of the structure facilitates the persistence of these secreted proteins in the soil.

Large negative magnetoresistance and metal-insulator transition observed in MnO/C composite coatings grown on ceramic alumina by metalorganic chemical vapor deposition

MnO/C composite coatings were grown by the metalorganic chemical vapor deposition process on ceramic alumina in argon ambient. Characterization by various techniques confirms that these coatings are homogeneous composites comprising nanometer-sized MnO particles embedded in a matrix of nanometer-sized graphite. Components of the MnO/C composite coating crystalline disordered, but are electrically quite conductive. Resistance vs. temperature measurements show that coating resistance increases exponentially from a few hundred ohms at room temperature to a few megaohms at 30 K. Logarithmic plots of reduced activation energy vs. temperature show that the coating material undergoes a metal-insulator transition. The reduced activation energy exponent for the film under zero magnetic field was 2.1, which is unusually high, implying that conduction is suppressed at much faster rate than the Mott or the Efros-Shklovskii hopping mechanism. Magnetoconductance us. magnetic field plots obtained at various temperatures show a high magnetoconductance (similar to 28.8%) at 100 K, which is unusually large for a disordered system, wherein magnetoresistance is attributed typically to weak localization. A plausible explanation for the unusual behavior observed in the carbonaceous disordered composite material is proposed. (C) 2010 Elsevier Ltd. All rights reserved.

Ultrasonic spray pyrolysis of CZTS solar cell absorber layers and characterization studies

CZTS (Copper Zinc Tin Sulphide) is a wide band gap quartnery chalcopyrite which has a band gap of about 1.45 eV and an absorption coefficient of 10(4) cm(-1); thus making it an ideal material to be used as an absorber layer in solar cells. Ultrasonic Spray Pyrolysis is a deposition technique, where the solution is atomized ultrasonically, thereby giving a fine mist having a narrow size distribution which can be used for uniform coatings on substrates. An Ultrasonic Spray Pyrolysis equipment was developed and CZTS absorber layers were successfully grown with this technique on soda lime glass substrates using aqueous solutions. Substrate temperatures ranging from 523 K to 723 K were used to deposit the CZTS layers and these films were characterized using SEM, EDAX and XRD. It was observed that the film crystallized in the kesterite structure and the best crystallites were obtained at 613 K. It was observed that the grain size progressively increased with temperature. The optical band gap of the material was obtained as 1.54 eV.

A General Route to Nanoparticle Thin Films and Coatings

Nanoparticles thin films have wide range of applications such as nanoelectronics, magnetic storage devices, SERS substrate fabrication, optical grating and antireflective coating. Present work describes a method to prepare large area nanoparticles thin film of the order of few square centimeters. Thin film deposition has been done successfully on a wide range of conducting as well as non conducting substrates such as carbon-coated copper grid, silicon, m-plane of alumina, glass and (100) plane of NaCl single crystal. SEM, TEM and AFM studies have been done for microstructural characterization of the thin films. A basic mechanism has been proposed towards the understanding of the deposition process.

Microwave ECR Plasma Assisted MOCVD of Y(2)O(3) Thin Films Using Y(tod)(3) Precursor and Their Characterization

Yttrium oxide (Y(2)O(3)) thin films were deposited by microwave electron cyclotron resonance (ECR) plasma assisted metal organic chemical vapour deposition (MOCVD) process using indigenously developed metal organic precursors Yttrium 2,7,7-trimethyl-3,5-octanedionates, commonly known as Y(tod)(3) which were synthesized by an ultrasound method. A series of thin films were deposited by varying the oxygen flow rate from 1-9 sccm, keeping all other parameters constant. The deposited coatings were characterized by X-ray photoelectron spectroscopy, glancing angle X-ray diffraction and infrared spectroscopy. Thickness and roughness for the films were measured by stylus profilometry. Optical properties of the coatings were studied by the spectroscopic ellipsometry. Hardness and elastic modulus of the films were measured by nanoindentation technique. Being that microwave ECR CVD process is operating-pressure-sensitive, optimum oxygen activity is very essential for a fixed flow rate of precursor, in order to get a single phase cubic yttrium oxide in the films. To the best of our knowledge, this is the first effort that describes the use of Y(tod)(3) precursor for deposition of Y(2)O(3) films using plasma assisted CVD process.

Wear behavior of plasma electrolytic oxidation (PEO) and hybrid coatings of PEO and laser on MRI 230D magnesium alloy

Wear resistant coatings were produced on a permanent mould cast MRI 230D Mg alloy by (a) PEO in silicate based electrolyte, (b) PEO in phosphate based electrolyte, (c) hybrid coatings of silicate PEO followed by laser surface alloying (LSA) with Al and Al(2)O(3), and (d) hybrid coatings of phosphate PEO followed by LSA with Al and Al(2)O(3). Microstructural characterization of the coatings was carried out by scanning electron microscopy (SEM) and X(ray diffraction. The tribological behavior of the coatings was investigated under dry sliding condition using linearly reciprocating ball-on-flat wear test. Both the PEO coatings exhibited a friction coefficient of about 0.8 and hybrid coatings exhibited a value of about 0.5 against the AISI 52100 steel ball as the friction partner, which were slightly reduced with the increase in applied load. The PEO coatings sustained the test without failure at 2 N load but failed at 5 N load due to micro-fracture caused by high contact stresses. The hybrid coatings did not get completely worn off at 2 N load but were completely removed exposing the substrate at 5 N load. The PEO coatings exhibited better wear resistance than the hybrid coatings and silicate PEO coatings exhibited better wear resistance than the phosphate PEO coatings. Both the PEO coatings melted/decomposed on laser irradiation and all the hybrid coatings exhibited similar microstructure and wear behavior irrespective of the nature of the primary PEO coating or laser energies. SEM examination of worn surfaces indicated abrasive wear combined with adhesive wear for all the specimens. The surface of the ball exhibited a discontinuous transfer layer after the wear test. (C) 2011 Elsevier B.V. All rights reserved.

Reactive pulsed laser deposition and characterization of niobium nitride thin films

We present a systematic study to explore the effect of important process variables on the composition and structure of niobium nitride thin films synthesized by Reactive Pulsed Laser Deposition (RPLD) technique through ablation of high purity niobium target in the presence of low pressure nitrogen gas. Secondary Ion Mass Spectrometry has been used in a unique way to study and fix gas pressure, substrate temperature and laser fluence, in order to obtain optimized conditions for one variable in single experimental run. The x-ray diffraction and electron microscopic characterization have been complemented by proton elastic backscattering spectroscopy and x-ray photoelectron spectroscopy to understand the incorporation of oxygen and associated non-stoichiometry in the metal to nitrogen ratio. The present study demonstrates that RPLD can be used for obtaining thin film architectures using non-equilibrium processing. Finally the optimized NbN thin films were characterized for their hardness using nano-indentation technique and found to be similar to 30 GPa at the deposition pressure of 8 Pa. (C) 2011 Elsevier B.V. All rights reserved.

Enhancement of Corrosion Resistance of Zinc Coatings Using Green Additives

In the present work, morphology, microstructure, and electrochemical behavior of Zn coatings containing non-toxic additives have been investigated. Zn coatings were electrodeposited over mild steel substrates using Zn sulphate baths containing four different organic additives: sodium gluconate, dextrose, dextrin, and saccharin. All these additives are ``green'' and can be derived from food contents. Morphological and structural characterization using electron microscopy, x-ray diffraction, and texture co-efficient analysis revealed an appreciable alteration in the morphology and texture of the deposit depending on the type of additive used in the Zn plating bath. All the Zn coatings, however, were nano-crystalline irrespective of the type of additive used. Polarization and electrochemical impedance spectroscopic analysis, used to investigate the effect of the change in microstructure and morphology on corrosion resistance behavior, illustrated an improved corrosion resistance for Zn deposits obtained from plating bath containing additives as compared to the pure Zn coatings.

Development And Characterization Of Composite Ni-Cr-C-Caf2 Laser Cladding On Gamma-Tial Intermetallic Alloy

A process of laser cladding Ni-CF-C-CaF2 mixed powders to form a multifunctional composite coatingd on gamma-TiAl substrate was carried out. The microstructure of the coating was examined using XRD, SEM and EDS. The coating has a unique microstructure consisting of primary dendrite or short-stick TiC and block Al4C3 carbides reinforcement as well as fine isolated spherical CaF2 solid lubrication particles uniformly dispersed in the NiCrAlTi (gamma) matrix. The average microhardness of the composite coatings is approximately HV 650 and it is 2-factor greater than that of the TiAl substrate. (C) 2008 Elsevier B.V. All rights reserved.

Modified porous silica antireflective coatings with laser damage resistance for Ti:sapphire

Porous SiO2 antireflective (AR) coatings are prepared from the colloidal silica solution modified with methyltriethoxysilane (MTES) based on the sol-gel route. The viscosity of modified silica suspensions changes but their stability keeps when MTES is introduced. The refractive indices of modified coatings vary little after bake treatment from 100 to 150 Celsius. The modified silica coatings on Ti:sapphire crystal, owning good homogeneity, display prominent antireflective effect within the laser output waveband (750-850 nm) of Ti:sapphire lasers, with average transmission above 98.6%, and own laser induced damage thresholds (LIDTs) of more than 2.2 J/cm2 at 800 nm with the pulse duration of 300 ps.

Preparation and characterization of La2Zr2O7 coating with the addition of Y2O3 by EB-PVD

Thermal barrier coatings (TBCs) of La2Zr2O7 (LZ) with the addition of 3 wt.% Y2O3 (LZ3Y) were deposited by electron beam-physical vapor deposition (EB-PVD). The phase stabilities, thermophysical and mechanical properties, and chemical compositions of these ceramics and coatings were studied in detail. The phase stability and thermal expansion behavior of LZ3Y bulk material are identical to those of LZ bulk material, but the mechanical properties of the former are superior to those of the latter. Elemental analysis and X-ray diffraction indicate that compositional deviation of LZ coating can be optimized after doping by 3 wt.% Y2O3, Y2O3 acts as a dopant as well as a process regulator. The optimal composition of LZ3Y coating could be effectively achieved by the addition of excess Y2O3 into the ingot and by properly controlling the current of electron beam (i.e. similar to 650 mA).

A facile synthesis and characterization of monodisperse spherical pigment particles with a core/shell structnre

In this paper, a facile sol-gel process for producing monodisperse, spherical, and nonaggregated pigment particles with a core/shell structure is reported. Spherical silica particles (245 and 385 nm in diameter) and Cr2O3, alpha-Fe2O3, ZnCo2O4, CuFeCrO4, MgFe2O4, and CoAl2O4 pigments are selected as cores and shells, respectively. The obtained core/shell-structured pigment samples, denoted as SiO2@Cr2O3 (green), SiO2@alpha-Fe2O3 (red), SiO2@MgFe2O4 (brown), SiO2@ZnCo2O4 (dark green), SiO2@CoAl2O4 (blue), and SiO2@CuFeCrO4 (black), are well characterized by using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and UV-vis diffuse reflection, as well as by investigating the magnetic properties. The results of XRD and high-resolution TEM (HRTEM) demonstrate that the pigment shells crystallize well on the surface Of SiO2 Particles. The thickness of the pigment shell can be tuned by the number of coatings, to some extent. These pigment particles can be well dispersed in some solvents (such as glycol) to form relatively more stable suspensions than the commercial products.

Modulating the selectivity for CO and butane oxidation over heterogeneous catalysis through amorphous catalyst coatings

The preparation of porous films directly deposited onto the surface of catalyst particles is attracting increasing attention. We report here for the first time a method that can be carried out at ambient pressure for the preparation of porous films deposited over 3 mm diameter catalyst particles of silica-supported Pt-Fe. Characterization of the sample prepared at ambient pressure (i.e., open air, OA) and its main structural differences as compared with a Na-A (LTA) coated catalyst made using an autoclave-based method are presented. The OA-coated material predominantly exhibited an amorphous film over the catalyst surface with between 4 and 13% of crystallinity as compared with fully crystallized LTA zeolite crystals. This coated sample was highly selective for CO oxidation in the presence of butane with no butane oxidation observed up to 350 degrees C. This indicates, for the first time, that the presence of a crystalline membrane is not necessary for the difference in light off temperature between CO and butane to be achieved and that amorphous films may also produce this effect. An examination of the space velocity dependence and adsorption of Na+ on the catalysts indicates that the variation in CO and butane oxidation activity is not caused by site blocking predominantly, although the Pt activity was lowered by contact with this alkali.

Voltammetric characterization of the ferrocene vertical bar ferrocenium and cobaltocenium vertical bar cobaltocene redox couples in RTILs

Ferrocene, Fc, and cobaltocenium hexafluorophosphate, CcPF(6), have been recommended for use as internal reference redox couples in room-temperature ionic liquids (RTILs), as well as in more conventional aprotic solvents. In this study, the electrochemical behavior of Fc and CcPF(6) is reported in eight commonly used RTILs; [C(2)mim][NTf2], [C(4)mim][NTf2], [C(4)mim][BF4], [C(4)mim][PF6], [C(4)mim][OTf], [C(4)mim][NO3], [C(4)mpyrr][NTf2], and [P-14,P-6.6,P-6][FAP], where [C(n)mim](+) = 1-butyl-3-methylimidazolium, [NTf2](-) = bis(trifluoromethylsulfonyl)imide, [BF4](-) = tetrafluoroborate, [PF6](-) = hexafluorophosphate, [OTf](-) = trifluoromethylsulfonate, [NO3](-) = nitrate, [C(4)mpyrr](+) = N-butyl-N-methylpyrrolidinium, [P-14,P-6,P-6,P-6](+) = tris(ri-hexyl)-tetradecylphosphonium and [FAP](-) = trifluorotris(pentafluoroethyl)phosphate, over a range of concentrations and temperatures. Solubilities and diffusion coefficients, D, of both the charged and neutral species were determined using double potential-step chronoamperometry, and CcPF(6) (36.5-450.0 mM) was found to be Much more Soluble than Fc (27.5-101.8 mM). It was observed that classical Stokes-Einstein diffusional behavior applies for Fc and CcPF(6) in all eight RTILs. Diffusion coefficients of Fc and CcPF(6) were calculated at a range of temperatures, and activation energies calculated. It was also determined that D for Fc and CcPF(6) does not change significantly with concentration. This supports the use of both Fe and CcPF(6) to provide a well-characterized and model redox couple for use as a voltammetric internal potential reference in RTILs contrary to previous literature reports in the former case.

Physicochemical Characterization of Poly(ethylene glycol) Plasticized Poly(methyl vinyl ether-co-maleic acid) Films

The influence of the poly(ethylene glycol) (PEG) plasticizer content and molecular weight on the physicochemical properties of films cast from aqueous blends of poly(methyl vinyl ether-co-maleic acid) (PMVE/MA) was investigated with tensile mechanical testing, thermal analysis, and attenuated total reflectance/Fourier transform infrared spectroscopy. Unplasticized films and those containing high copolymer contents were very difficult to handle and proved difficult to test. PEG with a molecular weight of 200 Da was the most efficient plasticizer. However, films cast from aqueous blends containing 10% (w/w) PMVE/MA and either PEG 1000 or PEG 10,000 when the copolymer/plasticizer ratio was 4 : 3 and those cast from aqueous blends containing 15% (w/w) PMVE/MA and either PEG 1000 or PEG 10,000 when the copolymer/plasticizer ratio was 2 : 1 possessed mechanical properties most closely mimicking those of a formulation we have used clinically in photodynamic therapy. Importantly, we found previously that films cast from aqueous blends containing 10% (w/w) PMVE/MA performed rather poorly in the clinical setting, where uptake of moisture from patients' skin led to reversion of the formulation to a thick gel. Consequently, we are now investigating films cast from aqueous blends containing 15% (w/w) PMVE/MA and either PEG 1000 or PEG 10,000, where the copolymer/plasticizer ratio is 2 : 1, as possible Food and Drug Administration approved replacements for our current formulation, which must currently be used only on a named patient basis as its plasticizer, tripropylene glycol methyl ether, is not currently available in pharmaceutical grade