Hierarchical Porous TiO2 thin films by soft and dual templating: A quantitative approach of specific surface and porosity

Poster (2013, March)

Hierarchical porous structures, with different pore sizes, constitute an important field of research for many applications. However, increasing the pore size results in the decrease of specific surface ... [more ▼]

Hierarchical porous structures, with different pore sizes, constitute an important field of research for many applications. However, increasing the pore size results in the decrease of specific surface. There is a need to quantify and predict the resulting porosity and specific surface. We have prepared hierarchical porous TiO2 thin films either by surfactant templating (soft) or dual surfactant/microspheres templating (soft/hard). They all show narrow, bimodal distribution of pores. Soft templating route leads to very thin films showing high specific surface and bimodal porosity with diameters of 10 nm and 54 nm. Dual templating route combines a Pluronic surfactant-based precursor solution with polystyrene (PS) microspheres (diam. 250 nm) in a one-pot simple process. This gives thicker films with a bimodal distribution of pores (8 nm and 165-200 nm). The dye loading of hierarchical films is compared to pure Pluronic-templated TiO2 films and shows a relative decrease of 29% for Single Templating (ST) and 43% for Dual Templating (DT-250). Finally, a geometrical model is proposed and validated for each system, based on the agreement between calculated specific surfaces and experimental dye loading with N719 dye. [less ▲]

YBCO SUPERCONDUCTING THICK FILMS: ELECTROPHORETIC DEPOSITION (EPD) ON NON-PLANAR SILVER SUBSTRATES

Scientific conference (2013, January 30)

A new formulation of a stable YBa2Cu3O7-δ (YBCO) suspension is proposed in which butanol is preferred to the commonly-used acetone as the suspension medium. Appropriate surfactant has been used to develop ... [more ▼]

A new formulation of a stable YBa2Cu3O7-δ (YBCO) suspension is proposed in which butanol is preferred to the commonly-used acetone as the suspension medium. Appropriate surfactant has been used to develop the superficial charge on the YBCO particles in order to promote migration during the process of electrophoresis. YBCO thick films were deposited on silver tubes and half-tubes by electrophoretic deposition (EPD). The EPD parameters (deposition voltage, deposition time, number of layers etc.) were optimized with respect to the microstructural properties of the YBCO layers after an intermediate heat treatment at 920°C. An essential criterion is the minimization of macrocracks after the 920°C heat treatment, since it was found to favour good superconducting properties after the final heat treatment. This final heat treatment involves (i) partial melting above the peritectic temperature, (ii) peritectic recombination at lower temperature and (iii) reoxygenation at 500°C. Finally, the superconducting properties of the best films are discussed. A uniformly coated 55μm-thick YBCO film on a curved Ag substrate showed excellent superconducting properties with the onset of critical temperature at 92.2 K and an associated sharp resistive transition with transition width < 1 K. [less ▲]

Lithium transition metal (Ti, Nb, V) oxide mesoporous thin films: contrasting results when attempting direct synthesis by evaporation-induced self assembly

in Microporous & Mesoporous Materials (2013), 172

This work investigates the possibility to prepare mesoporous thin films of Li-Ti, Li-Nb, Li-Nb-V and Li-V oxides through a direct sol-gel EISA route by dissolving a lithium salt in the precursor solution ... [more ▼]

This work investigates the possibility to prepare mesoporous thin films of Li-Ti, Li-Nb, Li-Nb-V and Li-V oxides through a direct sol-gel EISA route by dissolving a lithium salt in the precursor solution. Experimental conditions involve a hydrolysis molar ratio H2O/TM ~10 (TM = Ti,Nb,V) and the common Pluronic structuring agent P123 (EO20-PO70-EO20). Systematic formation of lithium-containing oxides as first-crystallizing phases points to a significant intermixture of lithium and transition metal ions in the inorganic network. In the case of Ti-based and Nb-based oxide films, addition of lithium to the precursor solution is compatible with the formation of amorphous mesoporous films at 350°C. On the contrary, addition of lithium has a detrimental effect on the notoriously difficult formation of vanadium-based mesostructured films: even when replacing half of the vanadium by niobium as a stabilizer, formation of mesostructured films has not been possible in the investigated range of experimental conditions. [less ▲]

YBa2Cu3O7-x thick films on silver tubes for magnetic shielding applications

Scientific conference (2012, December 07)

YBa2Cu3O7-x (YBCO) thick films are investigated for magnetic shielding applications at low frequencies (< 1 kHz). This requires deposition of YBCO on curved substrates such as tubes, half-tubes or even ... [more ▼]

YBa2Cu3O7-x (YBCO) thick films are investigated for magnetic shielding applications at low frequencies (< 1 kHz). This requires deposition of YBCO on curved substrates such as tubes, half-tubes or even more complex shapes. Electrophoretic Deposition (EPD) is an efficient method to achieve this goal: positively-charged YBCO particles suspended in a non aqueous medium drift towards the substrate, used as negative electrode for the application of the electric field. A crucial point is then to optimize the heat treatment of the as-deposited layers in order to achieve suitable superconducting properties. In the present work, we have developed a new suspension formulation in butanol, using a suitable surfactant to stabilize the suspension of YBCO powder (grain size < 2 µm). The EPD parameters (deposition voltage, deposition time, number of layers,...) have been selected to provide uniform layers of YBCO on silver substrates of various shapes. In the proposed communication, we shall discuss in detail the optimization of the heat treatments to achieve densification, peritectic recombination and oxygenation of the YBCO thick films deposited on silver. Scanning electron microscopy coupled with energy dispersive analysis was extensively used to characterize the (i) density / porosity, (ii) presence of macro-cracks, (iii) thickness uniformity, (iv) secondary phase content. We shall then present the characterization of the superconducting properties of the best films. Typically, a uniformly coated 55μm-thick YBCO film on a curved Ag substrate shows a magnetic Tc onset at 92.2 K and sharp resistive transition (< 1K). [less ▲]

Measuring the flowing properties of powders and grains

in Powder Technology (2012), 224

A granular material is a complex system which exhibits non-trivial transitions between the static, the quasi-static and the dynamical states. Indeed, an assembly of grains can behave like a solid or a ... [more ▼]

A granular material is a complex system which exhibits non-trivial transitions between the static, the quasi-static and the dynamical states. Indeed, an assembly of grains can behave like a solid or a fluid according to the applied stress. In between solid and fluid granular states, very slow dynamics are observed. When a complete macroscopic characterization of a powder is needed, all these granular states have to be precisely analyzed. In this paper, we show how three measurement techniques can be used to measure the physical properties of a powder. The measurements are based on classical tests modified to meet the recent fundamental researches on granular materials. The static properties of the powder are analyzed through the shape of a heap. The quasi-static behavior is studied with the analysis of the compaction dynamics. Finally, the dynamical regime is monitored through the flow in a rotating drum. In order to illustrate how these measurements can be used in practical cases, analyses are performed with three types of granular materials: silicon carbide abrasives, flours and rice. These selected materials allow to show the influence of the different parameters (grain size, grain size distribution, grain shape) on the macroscopic properties of the assembly. Moreover, these studies show the pertinence of the parameters obtained with the proposed techniques for the rheological characterization of powders and grains. [less ▲]

Material Aspects of Bone Tissue Engineering

Diverse speeche and writing (2012)

Bone tissue engineering is a highly studied topic in material science in the recent decades. Basic principles of chemistry and biology along with advanced material science techniques should be used in ... [more ▼]

Bone tissue engineering is a highly studied topic in material science in the recent decades. Basic principles of chemistry and biology along with advanced material science techniques should be used in order to elucidate the parameters which may influence the bone tissue growth on artificial implants. Progress has been made to an advanced level but still there is room for improvements. Especially in case of large bone defects, finding a ‘universal’ replacement implant is difficult. Patient specific data have to be taken in to account to get a good osteointegration. Metal and ceramic implants are commonly tested in case of large bone defects, but a good mimic of natural bone is hard due to various reasons. However fine tuning these materials and combination of these materials are finding good results. Addition of polymer materials in such implants is a recent effective attempt. Different combinations of these materials along with functionalisation using bioactive molecules make the bone tissue engineering nearly perfect. This presentation will discuss about the recent trends in the materials used in bone tissue engineering. [less ▲]

ZnO Nanowire Arrays with Higher Surface Area and Reversible Wetting Properties Manufactured by Combined Nanosphere Lithography and Hydrothermal Growth

Poster (2012, April 10)

Development of  mesoporous tungsten oxide WO3 thin films for electrochromic applications

Poster (2012)

Systematic processing of β – tricalcium phosphate for efficient protein loading and in vitro analysis of antigen uptake

in Advanced Engineering Materials (2012)

Microparticulate calcium phosphate (CaP) powders are promising drug carriers because of their biocompatibility and degradability under physiological conditions. The adsorption capability of CaP ... [more ▼]

Microparticulate calcium phosphate (CaP) powders are promising drug carriers because of their biocompatibility and degradability under physiological conditions. The adsorption capability of CaP microparticles makes them interesting candidates, within the inorganic carrier materials, for delivering protein antigens to professional antigen presenting cells (APC) for vaccination purpose. However, in order to bind and deliver a sufficient amount of protein, the challenge is to effectively increase the binding capacity of this material. In this study, b-tricalcium phosphate (b-TCP) powder is engineered to obtain microparticles with increased protein loading, using bovine serum albumin as a model antigen. The decrease in particle size and increase in specific surface area of carrier is shown to strongly affect protein adsorption. Finally, we demonstrate that the processed b-TCP is capable of delivering its protein payload in vitro to dendritic cells, which are professional APCs and the target cell population for microparticulate vaccines. [less ▲]

Nanosphere Lithography and Hydrothermal Growth : How to Increase Surface Area and Control Reversible Wetting Properties of ZnO Nanowire Arrays ?

in Journal of Materials Chemistry (2012), 22(33), 17086-17093

Due to their large surface-area-to-volume ratio as well as their interesting intrinsic optical and electronic properties, ZnO 1D nanostructures are part of the few dominant materials for nanotechnology ... [more ▼]

Due to their large surface-area-to-volume ratio as well as their interesting intrinsic optical and electronic properties, ZnO 1D nanostructures are part of the few dominant materials for nanotechnology. In this article, we compare two different routes of using the nanosphere lithography for the manufacturing of well-aligned, density-controlled ZnO nanowires by low-temperature hydrothermal growth. The first route uses the colloidal mask as a template for the patterned growth of the nanowires, while in the second route, the nanospheres act as a mask to pattern the seed layer. SEM and XRD characterizations are performed on samples manufactured by both routes and evidence patterned well-aligned nanowires with high c-axis texturing in the first synthetic route. Oriented growth is less pronounced in the second route, as well as the ability to adsorb dye. However, for the first route the dye loading measurements reveal that the amount of N-719 adsorbed is higher than on unpatterned ZnO nanowires films, highlighting an increased interface area. Reversible hydrophobicity to superhydrophilicity transition was observed and intelligently controlled by alternation of UV illumination and dark storage. This promising synthetic route opens exciting perspectives for the production of ZnO nanowire arrays with tunable density, wetting properties and enhanced adsorption properties. [less ▲]