Rheology and Dispersion Behavior of Ethylene‐Vinyl Acetate Copolymers/TiO2 Masterbatches Prepared by Melt‐Compounding

The rheology and dispersion behavior of ethylene‐vinyl acetate (EVA) copolymer/TiO₂ masterbatches prepared by melt‐compounding were investigated. The pure EVA exhibits obviously pseudoplastic behavior and the apparent viscosity decreases remarkably at experimental temperatures, especially in the range of 100–500 s^?1. The EVA/TiO₂ masterbatches exhibit similar shear rheology behavior with pure EVA and the apparent viscosities are obviously higher than that of pure EVA when the TiO₂ content is above 10 wt.%. Field‐emission scanning electron microscopy (FE‐SEM) and energy dispersive x‐ray spectroscopy (EDX) show that relatively low TiO₂ loading and moderate shear rate are helpful for the improvement of dispersion behavior of TiO₂ nanoparticles; moreover, the dispersion behavior of TiO₂ greatly influences the melt viscosity. The extensional rheology of pure EVA decreases with increasing extension rate, especially at low melt temperatures. EVA/TiO₂ masterbatches have similar extensional rheology behavior as pure EVA and the TiO₂ loading has almost no influence on the extensional viscosity of materbatches.     

In situ Radical Copolymerization in Presence of Surface‐Modified TiO2 Nanoparticles: Influence of a Double Modification on Properties of Unsaturated Polyester (UP) Nanocomposites

In the preparation of nanocomposites, there is competition between the dispersion of nanoparticles and the formation of agglomerates. In this study, radical copolymerization of ethyl acrylate and methyl methacrylate initiated by 2,2‐azobis (isobutyro) nitrile (AIBN) was performed, in the presence of titanium oxide (TiO₂) nanoparticles modified in a new approach; a good dispersion of the nanoparticles in the unsaturated polyester (UP) matrix was obtained. The TiO₂ nanoparticles were exposed to 3‐(methacryloxy) propyl trimethoxy silane as the coupling agent. The presence of coupling agent‐grafted TiO₂ nanoparticles in the copolymerization process resulted in the formation of a polymeric layer on the surface of the TiO₂ nanoparticles (doubly modified‐TiO₂). The grafting of coupling agent molecules and consequently copolymer macromolecular chains onto the surface of TiO₂ nanoparticles was investigated using Fourier transform infrared (FTIR) analysis. It found that the formation of an acrylate layer on the surface of nanoparticles was successful. Then, unsaturated polyester (UP)/TiO₂ nanocomposites were prepared. The morphology was studied using transmission electron microscopy (TEM). Mechanical properties and ultraviolet visible (UV/VIS) spectroscopy of various samples, including the doubly modified‐TiO₂ nanoparticles, with different nanoparticle inclusions and the unmodified‐TiO₂ nanoparticles, were also investigated. The results showed the doubly modified‐TiO₂ nanoparticles, compared to those of unmodified‐TiO₂, had better nanoparticle dispersion causing improvement in the mechanical properties and UV shielding.     

Investigations of Pulse‐Plasma‐Polymer Coating on TiO2 Nanoparticles and Their Dispersion

An amorphous acrylic acid (AA) polymer coating was generated on TiO₂ nanoparticles through pulse radio frequency (RF) plasma polymerization. The AA plasma synthesis mechanism was studied by its optical emission spectrum. The chemical structures of AA–plasma‐polymer were carefully investigated by Fourier transform infrared spectroscopy (FTIR). The dispersion behaviors of AA‐coated and uncoated TiO₂ nanoparticles in glycol solution were characterized by ultraviolet absorbency and particle size distribution measurements. The results showed that the aggregation of TiO₂ nanoparticles in glycol solution was effectively lowered and the dispersion was improved a lot after AA–plasma‐polymer coating. The pulse plasma coating parameters played an important role in the dispersion enhancement of TiO₂ nanoparticles. By properly regulating the pulse discharge parameters, the system could gain the highest radical–monomer reactions rate, the most compatible functional groups on the nanoparticles, and the best dispersion in the background media.     

Amplification of Solar Energy Conversion in Quantum‐Confined CdSe‐Sensitized TiO2 Photonic Crystals by Trapping Light

Photonic effects amplifying solar energy conversion are reported in titania inverse opals sensitized with quantum‐confined CdSe films. TiO₂ inverse opals (i‐TiO₂‐o) and unstructured nanocrystalline TiO₂ (nc‐TiO₂) films are sensitized with CdSe deposited via successive ionic layer adsorption and reaction (SILAR) by generating Se^2? in situ under inert atmosphere, and the film absorbance is tuned by the number of SILAR cycles. Photonic effects are investigated while varying the i‐TiO₂‐o stop band position relative to CdSe films’ absorbance. i‐TiO₂‐o films with stop band at 700 and 560 nm are sensitized with CdSe having absorption edges at 600 and 650 nm thus tuning absorbance to the red and the blue of the stop band. Significant amplification in photon‐to‐current conversion efficiency is measured when CdSe films prepared via two cycles are adsorbed on i‐TiO₂‐o with a stop band at 700 nm, with a maximum average enhancement factor equal to 6.7 ± 1.6 at 640 nm, 60 nm to the blue of the stop band center, relative to nc‐TiO₂ sensitized with comparable CdSe amounts. The gain is observed over a wide frequency range to the blue of the stop band and is greatest when film absorbance was low. The photocurrent gain is not a result of differences in the rates of charge separation or charge transport, and occurs in the same frequency range where absorbance amplification is measured to the blue of the 700‐i‐TiO₂‐o stop band, and is thus attributed to slow light effects enhancing absorbance in the photonic crystal environment.     

Characterization of TiO2 Smoke Prepared Using Gas‐Phase Hydrolysis of TiCl4

The formation of submicron TiO₂ smoke (a gas‐phase suspension) from titanium tetrachloride in a low‐pressure hydrolysis reaction in a simple reactor configuration has been studied. Particle size distribution, particle morphology and degree of crystallinity have been characterized as a function of reaction conditions. Highly crystalline anatase TiO₂ particles with narrow size distribution and smaller particle size were formed at high reactor temperature, while larger, amorphous particles were found at lower reactor temperatures. These results are consistent with literature studies. At 817 °C, small (450 nm), spherical, unagglomerated particles could be produced. A gas‐phase dispersion of these particles is intended for use as seeds in subsequent kinetic studies of titanium dioxide formation reactions involving a rapid compression methodology.     

Characterization of TiO<Subscript>2</Subscript> nanoparticle suspensions for electrophoretic deposition

The rheology of suspensions is critically important for the successful achievement of defect-free TiO₂ deposits by electrophoretic deposition (EPD). The rheological behaviour of TiO₂ nanoparticle suspensions in acetylacetone with and without iodine was investigated over a broad solid-concentration range (0.3–2.5 wt.%) and at different shear rates ( = 10–250 s⁻¹). The influence of these parameters on the quality of TiO₂ films obtained by EPD on stainless steel substrates was assessed. The pure solvent and the 1 wt.% TiO₂ nanoparticles suspension without iodine exhibited shear-thickening flow behaviour. For other concentrations, the suspensions showed shear-thinning behaviour followed by an apparent shear-thickening effect at a critical shear rate (100 s⁻¹). For the suspension with 1 wt.% TiO₂ containing iodine, a shear-thickening flow behaviour was observed over the whole shear rate range investigated. The maximum solids fraction (ϕ_m) was experimentally determined from a linear relationship between solid concentration and viscosity. The estimated value was ϕ_m = 7.94 wt.% for this system. Using a suspension with 1 wt.% concentration, good-quality TiO₂ deposits on stainless steel planar substrates were obtained by EPD at constant voltage condition. The influence of pH on suspension stability was determined in the range pH = 1–9, being pH ≈ 5 the optimal value for this system in terms of EPD results.     

Evidences for charge‐transfer complex formation in the benzene adsorption on sulfated TiO2–a resonance Raman spectroscopy investigation

Benzene adsorbed on highly acidic sulfated TiO₂ (S‐TiO₂) shows an intriguing resonance Raman (RR) effect, with excitation in the blue‐violet region. There are very interesting spectral features: the preferential enhancement of the e_2g mode (1595 cm⁻¹) in relation to the a_1g mode (ring‐breathing mode at 995 cm⁻¹) and the appearance of bands at 1565 and 1514 cm⁻¹. The band at 1565 cm⁻¹ is probably one of the components of the e_2g split band, originally a doubly degenerate mode (8a, 8b) in neat benzene, and the band at 1514 cm⁻¹ is assigned to the 19a mode, an inactive mode in neat benzene. These facts indicate a lowering of symmetry in adsorbed benzene, which may be caused by a strong interaction between S‐TiO₂ and the benzene molecule with formation of a benzene to Ti (IV) charge transfer (CT) complex or by the formation of a benzene radical cation species. However, the RR spectra of the adsorbed benzene cannot be assigned to the benzene radical cation because the observed wavenumber of the ring‐breathing mode does not have the value expected for this species. Moreover, it was found by ESR measurements that the amount of radicals was very low, and so it was concluded that a CT complex is the species that originates the RR spectra. The most favorable intensification of the band at 1595 cm⁻¹ in the RR spectra of benzene/S‐TiO₂ at higher excitation energy corroborates this hypothesis, as an absorption band in this energy range, assigned to a CT transition, is observed. Copyright © 2008 John Wiley & Sons, Ltd.     

Preparation of N-doped TiO<Subscript>2</Subscript> photocatalyst by atmospheric pressure plasma process for VOCs decomposition under UV and visible light sources

The nitrogen doped (N-doped) titanium dioxide (TiO₂) photocatalyst was prepared by the atmospheric-pressure plasma-enhanced nanoparticles synthesis (APPENS) process operated under normal temperature, i.e. the dielectric barrier discharge plasma process. The N₂ carrier gas is dissociated in the AC powered nonthermal plasma environment and subsequently doped into the TiO₂ photocatalyst that was capable of being induced by visible light sources. The APPENS process for producing N-doped TiO₂ showed a higher film deposition rate in the range of 60–94 nm/min while consuming less power (<100 W) as compared to other plasma processes reported in literatures. And the photocatalytic activity of the N-doped TiO₂ photocatalyst was higher than the commercial ST01 and P25 photocatalysts in terms of toluene removals in a continuous flow reactor. The XPS measurement data indicated that the active N doping states exhibited N 1s binding energies were centered at 400 and 402 eV instead of the TiN binding at 396 eV commonly observed in the literature. The light absorption in the visible light range for N-doped TiO₂ was also confirmed by a clear red shift of the UV-visible spectra.     

The dispersion study of TiO2 nanoparticles surface modified through plasma polymerization

In this study, the surface of TiO₂ nanoparticles was modified through plasma polymerization, which is a dry coating method at room temperature. The surface morphology of TiO₂ nanoparticles was characterized by high-resolution transmission electron microscope (HRTEM). The dispersion behavior of TiO₂ nanoparticles in water and ethyl glycol was investigated by laser size distribution and ultraviolet–visible absorption spectrum. TiO₂ nanoparticles were coated with a thin film through plasma polymerization, which prevents the agglomeration and improves the dispersion behavior of TiO₂ nanoparticles.     

Preparation and Characterization of Nano‐TiO2 Doped Polystyrene Materials by Melt Blending for Inertial Confinement Fusion

Abstract

Nano‐TiO₂ doped polystyrene (PS) materials (TiO₂‐d‐PS) used for inertial confinement fusion (ICF) targets were prepared by means of melt blending. The effect of the pretreatment process, including coupling agents and ultrasonic dispersion on nano‐TiO₂, was studied. Tensile tests were conducted to evaluate the mechanical properties of the TiO₂‐d‐PS materials. Scanning electron microscopy (SEM) combined with energy dispersive spectroscopy (EDS) was used to characterize the degree of dispersion of nano‐TiO₂ in the PS matrix. Transmission electron microscopy (TEM) and dynamic contact angle (DCA) measurements were introduced to demonstrate the surface state of untreated and pretreated nano‐TiO₂. The results showed that coupling agents improved the interfacial adhesion between the PS matrix and dopants; ultrasonic dispersion contributed to the increase in the tensile properties of the TiO₂‐d‐PS materials. The dispersion stability of nano‐TiO₂ powder and the stability of the TiO₂‐d‐PS materials were significantly enhanced through pretreatment, which was supported by the increase in the DCA when the nano‐TiO₂ was pretreated by the coupling agent. The results of SEM and EDS indicated that the nano‐TiO₂ dispersed homogeneously in the PS matrix. The pretreatment process is an effective way to break the aggregation of nano‐TiO₂, which was confirmed by TEM results. Melt blending is a feasible method to prepare PS doped high Z element ICF target materials.     

Temperature dependence of pre‐edge features in Ti K‐edge XANES spectra for ATiO3 (A = Ca and Sr), A2TiO4 (A = Mg and Fe), TiO2 rutile and TiO2 anatase

XANES (X‐ray absorption near‐edge structure) spectra of the Ti K‐edges of ATiO₃ (A = Ca and Sr), A₂TiO₄ (A = Mg and Fe), TiO₂ rutile and TiO₂ anatase were measured in the temperature range 20–900 K. Ti atoms for all samples were located in TiO₆ octahedral sites. The absorption intensity invariant point (AIIP) was found to be between the pre‐edge and post‐edge. After the AIIP, amplitudes damped due to Debye–Waller factor effects with temperature. Amplitudes in the pre‐edge region increased with temperature normally by thermal vibration. Use of the AIIP peak intensity as a standard point enables a quantitative comparison of the intensity of the pre‐edge peaks in various titanium compounds over a wide temperature range.     

Effect of annealing on TiO2 nanoparticles

TiO₂ nanoparticles have been prepared by simple chemical precipitation method and annealed at different temperatures. The as-prepared TiO₂ are amorphous, and they transform into anatase phase on annealing at 450 °C, and rutile phase on annealing at 900 °C. The X-ray diffraction results showed that TiO₂ nanoparticles with grain size in the range of 21–24 nm for anatase phase and 69–74 nm for rutile phase have been obtained. FESEM images show the formation of TiO₂ nanoparticles with small size in structure. The FTIR and Raman spectra exhibited peaks corresponding to the anatase and rutile structure phases of TiO₂. Optical absorption studies reveal that the absorption edge shifts towards longer wavelength (red shift) with increase of annealing temperature.     

Room‐Temperature Synthesis of High Surface Area Anatase TiO2 Exhibiting a Complete Lithium Insertion Solid Solution

The synthesis of highly divided anatase TiO₂ nanoparticles displaying 300 m² g^?1 surface area is achieved by following a two‐step synthetic process at room temperature. The particles exhibit a needle‐like morphology composed of self‐assembled 4 nm nanoparticles. The crystallization process from amorphous TiO₂.1.6H₂O to oriented aggregation of anatase TiO₂ proceeds according to a slow solid dehydration process taking place in a large range of pH in deionized water (1 < pH < 12) or alternatively when including a low amount of NH₄F_(aq) in solution. Driven by their high surface area enhancing the chemical/electrochemical reactivity, it is reported in the case of the anatase TiO₂ that a modification in the lithium insertion mechanism is no longer attributable to a two‐phase reaction between the two‐end members Li_εTiO₂ and Li_0.5±αTiO₂ when downsizing the particle size, but instead through a complete solid solution all along the composition range.     

Preparation and Characterization of Poly(Methyl Methacrylate) Coated TiO2 Nanoparticles

Titanium dioxide (TiO₂) nanoparticles were modified with poly(methyl methacrylate) (PMMA) to improve the dispersion stability of the nanoparticles in a dielectric medium and to reduce the density mismatch between TiO₂ and a dielectric medium for a microcapsule‐type electrophoretic display application. Nanoparticles were coated with PMMA by in situ dispersion polymerization. The PMMA‐coated TiO₂ nanoparticles were characterized by fourier transform‐infrared spectrometrey (FT‐IR), electrophoretic light scattering (ELS), and scanning electron microscopy (SEM). Density of PMMA‐coated TiO₂ nanoparticles was found to be dependent on the thickness of the PMMA coating on the nanoparticles. An increase of thermal stability of the PMMA layer and the contents of PMMA on the surface of the nanoparticles were measured via thermogravimetric analysis (TGA).     

The Sharkskin Onset and Stability Diagram

The onset of sharkskin extrudate was investigated in terms of molecular structure, molecular weight, temperature, and die geometry. The recoverable shear S_R or the ratio of wall shear stress over the storage modulus was determined and found to be independent of molecular weight, temperature, and die geometry for linear low-density polyethylenes (LLDPEs), but it depended critically on these factors and the molecular weight distribution for high-density polyethylenes (HDPEs). The plot of S_R versus λ _s /? _s , or the sharkskin wavelength roughness amplitude ratio, constituted a sharkskin marginal stability curve common for all molecular weights, temperatures, and die geometry investigated; it is unique for each polymer type or molecular structure. Sharkskin instability occurred without hysteresis effect.     

Control of optical absorption edge of TiO2 through co-doped acceptors: The chemical trend

Tuning the optical adsorption edge of TiO₂ is attracting increasing attention as a potential solution to the worldwide energy shortage. A possible strategy to achieve high efficiency photocatalysis with TiO₂ is through dopants to modulate chemical composition. Based on first-principles calculations, we propose a hole-strain-mediated coupling mechanism between co-doped acceptors in anatase TiO₂. When the dopant complex on neighboring oxygen sites contains a large radius atom, and the doped system has at least one net hole, the dopants will strongly couple to form a pair through the local lattice strain induced by the large dopant. The coupling results in bandgap narrowing due to the appearance of the fully occupied mid-gap states, leading to a much more effective band gap reduction than that induced by mono-doping or conventional donor–acceptor codoping. The calculated absorption spectra show that acceptor–acceptor codopings could shift the absorption edge to the visible light region.     

Optical properties of in situ doped and undoped titania nanocatalysts and doped titania sol-gel nanofilms

In this paper we present spectroscopic properties of doped and undoped titanium dioxide (TiO₂) as nanofilms prepared by the sol-gel process with rhodamine 6G doping and studied by photoacoustic absorption, excitation and emission spectroscopy. The absorption spectra of TiO₂ thin films doped with rhodamine 6G at very low concentration during their preparation show two absorption bands, one at 2.3 eV attributed to molecular dimmer formation, which is responsible for the fluorescence quenching of the sample and the other at 3.0 eV attributed to TiO₂ absorption, which subsequently yields a strong emission band at 600 nm. The electronic band structure and optical properties of the rutile phase of TiO₂ are calculated employing a fully relativistic, full-potential, linearized, augmented plane-wave (FPLAPW) method within the local density approximation (LDA). Comparison of this calculation with experimental data for TiO₂ films prepared for undoped sol-gels and by sputtering is performed.     

A New Insight of the Photothermal Effect on the Highly Efficient Visible‐Light‐Driven Photocatalytic Performance of Novel‐Designed TiO2 Rambutan‐Like Microspheres Decorated by Au Nanorods

Photocatalyst‐assisted degradation of organic pollutants, which exhibits a novel strategy for solar‐energy utilization, possesses enormous potential in various applications. Extending the light‐absorption range in the spectrum of sunlight and improving light‐conversion efficiency are always primary issues to enhance the catalytic performance of these photocatalysts. Herein, a new structure of gold‐nanorod‐decorated TiO₂ rambutan‐like microspheres is designed, which exhibits superior photocatalytic ability toward Rhodamine B in the range of visible light due to the 3D distribution of the TiO₂ branches on the surface of the microspheres, which prompts the multireflection of photons. The absorption rate of photons is thereby tremendously enhanced. This is beneficial for the generation of hot electrons originating from the localized surface plasmonic resonance of Au nanorods, which can be used to both initiate the reaction and produce the photothermal effect. Hot electrons generated by a single Au nanorod in microspheres to initiate the degradation reaction can be as high as 2.5 times of those in the nanowires' counterpart. Moreover, the heating power of a single Au nanorod in microspheres reaches up to 4.4 times higher than that in nanowires, which further accelerates the degradation rate. The reaction pathway of visible‐light‐assisted RhB degradation catalyzed by Au/TiO₂ microspheres goes through an initial N‐deethylation process instead of the complete cycloreversion catalyzed by pure TiO₂ microspheres under UV irradiation. This strategy of structure design for improved photon absorption, which achieves high degradation rate and photothermal effect, is promising for the development of novel photocatalysts.     

Influence of Particle Morphology and Flow Conditions on the Dispersion Behavior of Fumed Silica in Silicone Polymers

The dispersion behavior of agglomerates of several grades of fumed silica in poly(dimethyl siloxane) liquids has been studied as a function of particle morphology and applied flow conditions. The effects of primary particle size and aggregate density and structure on cohesivity were probed through tensile and shear strength tests on particle compacts. These cohesivity tests indicated that the shear strength of particle compacts was two orders of magnitude higher than the tensile strength at the same overall packing density. Experiments carried out in both steady and time‐varying simple‐shear flows indicate that dispersion occurs through tensile failure. In the steady‐shear experiments,enhanced dispersion was obtained at higher levels of applied stress and, at comparable levels of applied stress, dispersion was found to proceed faster at higher shear rates. Experiments conducted in time‐varying flows further corroborated the results obtained in tensile cohesivity tests. Experiments in which the mean and maximum stresses in the time‐varying flows were matched to the stresses produced in steady shear flows highlight the influence of flow dynamics on dispersion behavior.     

Enhanced Photoelectric and Photothermal Responses on Silicon Platform by Plasmonic Absorber and Omni‐Schottky Junction

Recent progresses in plasmon‐induced hot electrons open up the possibility to achieve photon harvesting beyond the fundamental limit imposed by band‐to‐band transitions in semiconductors. To obtain high efficiency, both the optical absorption and electron emission/collection are crucial factors that need to be addressed in the design of hot electron devices. Here, we demonstrate a photoresponse as high as 3.3mA/W at 1500nm on a silicon platform by plasmonic absorber (PA) and omni‐Schottky junction integrated photodetector, reverse biased at 5V and illuminated with 10mW. The PA fabricated on silicon consists of a monolayer of random Au nanoparticles (NPs), a wide‐band gap semiconductor (TiO₂) and an optically thick Au electrode, resulting in broadband near‐infrared (NIR) absorption and efficient hot‐electron transfer via an all‐around Schottky emission path. Meanwhile, time and spectral‐resolved photoresponse measurements reveal that embedded NPs with superior absorption resembling plasmonic local heating sources can transfer their energy to electricity via the photothermal mechanism, which until now has not been adequately assessed or rigorously differentiated from the photoelectric process in plasmon‐mediated photon harvesting nano‐systems.