Littérature scientifique sur le sujet « Sol-Gel/Centrifugation »

Stimulated human submandibular/sublingual (HSMSL) and whole saliva were separated into sol and gel phases and mucins were isolated by density-gradient centrifugation in CsCl/4M guanidinium chloride. MUC5B and MUC7 were identified using anti-peptide antisera raised against sequences within the MUC5B and MUC7 apoproteins respectively. MUC7 was found mainly in the sol phase of both HSMSL and whole saliva, but some MUC7 was consistently present in the gel phase, suggesting that this mucin may interact with the salivary gel matrix. In HSMSL saliva, MUC5B was found in the gel phase; however, most of the material was ‘insoluble’in guanidinium chloride and was only brought into solution by reduction. In whole saliva, the MUC5B mucin was present both in the sol and gel phases although some material was again ‘insoluble’. Rate-zonal centrifugation of whole saliva showed that MUC5B mucins in the sol phase were smaller than those in the gel phase, suggesting differences in oligomerization and/or degradation. Antibodies against IgA, secretory component, lysozyme and lactoferrin were used to study the distribution of non-gel-forming proteins in the different phases of saliva. The majority of these proteins was found in the sol phase of both HSMSL and whole saliva. However, a significant fraction was present in the gel phase of whole saliva, suggesting a post-secretory interaction with the salivary gel matrix. A monoclonal antibody against a parotid salivary agglutinin was used to show that this protein is present mainly in the gel phase of both whole saliva and parotid secretion.

To investigate the genetic identities of the mucins secreted in cystic fibrosis (CF) airways, sputum was collected from five individuals. Samples were separated into gel and sol phases by high-speed centrifugation and the gel phase was extracted in 6 M guanidinium chloride. The ‘insoluble’ residue remaining after extraction of the gel phase was brought into solution by reduction/alkylation. Density-gradient centrifugation in CsCl revealed polydisperse distributions of sialic acid-containing mucins in the gel phase, insoluble residue and sol phase fractions and the degree of variation between the different individuals was low. Antibodies recognizing MUC5AC and MUC5B identified these mucins in each of the fractions. MUC2, however, was present only as a component of the insoluble residue from the gel which accounted for less than 4% by mass of the total mucins. MUC5B and MUC5AC from the gel phase were large oligomeric species composed of disulphide-bond linked subunits and MUC5B was present as two populations with different charge densities which are likely to correspond to MUC5B ‘glycoforms’. The sol phase contained, in addition to MUC5AC and MUC5B, mainly smaller mucins which did not react with the antisera and which were probably degraded. MUC5AC appeared to be enriched in the sol, suggesting that this mucin may be more susceptible to proteolytic degradation than MUC5B. The mucins present in sputum remained broadly similar during acute exacerbation and following antibiotic treatment, although the relative amount of an acidic MUC5B glycoform was decreased during infection.

Mucus glycoproteins (mucins) were isolated from sputum of patients with cystic fibrosis (CF) after separation into sol and gel phases. The mucus gel was solubilized with gentle stirring in 6 M-guanidinium chloride supplemented with proteinase inhibitors, and purification of mucins was subsequently achieved by isopycnic density-gradient centrifugation in CsCl/guanidinium chloride. Density-gradient centrifugation also revealed a heterogeneity of the macromolecules, the pattern of which varied between individuals, and mucins from the gel phase was pooled as ‘heavy’ and ‘light’ fractions. Gel chromatography on Sepharose CL-2B showed that the heavy fraction contained a larger proportion of smaller species than the ‘light’ fraction and that the gel phase mucins were much larger than those from the sol. An apparently homogeneous high-Mr mucin population from one individual contained approx. 70% (w/w) carbohydrate, the major sugars being N-acetylglucosamine (17.8%), N-acetylgalactosamine (6.7%), galactose (20.7%), fucose (13.2%) and sialic acid (11.4%). These mucins had an S020.w of 47 S, and an Mr of 15 x 10(6) -20 x 10(6), and rate-zonal centrifugation revealed a polydisperse size distribution [range (5-30) x 10(6)] with a weight-average Mr of 17 x 10(6). The whole mucins were visualized with electron microscopy as linear and apparently flexible threads, disperse in size. Reduction produced subunits which were included on Sepharose CL-2B, and subsequent trypsin digestion yielded high-Mr glycopeptides which were further retarded. The size distributions and fragmentation patterns of mucin from two other CF patients were the same, as studied by gel chromatography, rate-zonal centrifugation and electron microscopy. We conclude that CF mucins are heterogeneous in both size and buoyant density and that the various populations, though differing in buoyant density, share the same architecture and macromolecular properties and are, in this respect, similar to mucins from normal respiratory secretions [Thornton, Davies, Kraayenbrink, Richardson, Sheehan & Carlstedt (1990) Biochem. J. 265, 179-186] and human cervical mucus [Carlstedt & Sheehan (1989) SEB Symp. XLIII 289-316].

Bovine respiratory secretions were separated into gel and sol phases to allow the identification of the gel-forming mucins. Mucins were subsequently isolated from the surface epithelium and submucosal tissue to investigate the tissue origins of the species in the secretions. Density-gradient centrifugation revealed ‘high-density’ and ‘low-density’ mucins in the gel phase of the secretions. The ‘high-density’ mucins were large, composed of subunits joined by disulphide bonds and contained two highly glycosylated domains of apparently different lengths, whereas the ‘low-density’ mucins were smaller and monomeric. The sol also contained both ‘high-density’ and ‘low-density’ species. A ‘high-density’ mucin similar to that in the gel was isolated from the surface epithelium, suggesting that the goblet cells produce large, gel-forming mucins. A second ‘high-density’ species was released from the submucosal tissue after reduction/alkylation, indicating that large mucins from the submucosal glands may also be a component of the mucus gel. In addition, two small, ‘low-density’ mucins were obtained from the submucosal tissue. One species was associated with the gel phase but was also present in the sol, whereas the other was present only in the sol. Bovine respiratory-tract secretions thus comprise a complex mixture of large gel-forming mucins originating from the goblet cells and submucosal glands, and smaller ‘soluble’ species from the submucosal glands which may interact with the gel.

Mucous secretions were obtained from cat tracheas that had received [3H]glucose and [35S]sulphate to radiolabel mucus glycoproteins biosynthetically. Samples were collected under resting (‘basal’) conditions as well as after pilocarpine stimulation and were separated into gel and sol phases by centrifugation. Macromolecules were partially purified by using gel chromatography on Sepharose CL-4B, and the species that were eluted with the void volume were then separated into two major populations with isopycnic density-gradient centrifugation in CsCl. The major component from the gel phase of pilocarpine-induced secretions had a buoyant density typical of mucins and was observed as linear and apparently flexible chains by electron microscopy. Reduction of disulphide bonds gave subunits that could be further cleaved by trypsin digestion into components of approximately the same size as the high-Mr glycopeptides obtained from other mucins after this treatment. In contrast, the dominant species in the gel phase of the ‘basal’ secretion had a significantly higher buoyant density than expected for mucins and was largely unaffected by reduction, as studied by gel chromatography. The macromolecules were fragmented by trypsin, suggesting that they contain a polypeptide backbone. This more dense component also predominated in the sol phase both from the ‘basal’ secretions and from the pilocarpine-released secretions. Digestion with DNAase, chondroitin ABC lyase or heparan sulphate lyase had no effect, which shows that this component is not DNA, a dermatan sulphate/chondroitin sulphate or a heparan sulphate proteoglycan. In contrast, endo-beta-galactosidase and keratanase caused some fragmentation, suggesting that the molecules contain some linkages of the poly-(N-acetyl-lactosamine) type, although the degradation was not as extensive as expected for keratan sulphate. Treatment with alkaline borohydride resulted in extensive fragmentation of the high-Mr glycopeptides from both components, indicating that the glycans were oligosaccharides that were probably O-linked. The monosaccharide compositions of both components were consistent with that expected for mucins. The data are in keeping with the major component from the pilocarpine-stimulated gel secretions being a mucus glycoprotein and the more dense component being a mucin-like molecule, possibly related to the keratanase-sensitive material isolated from canine trachea by Varsano, Basbaum, Forsberg, Borson, Caughey & Nadel [(1987) Exp. Lung Res. 13, 157-184].

N-doped TiO2 nanoparticle powders were prepared efficiently by the sol-gel method using triethylamine and ammonium hydroxide as composite N precursor. The as-prepared N-doped TiO2 precursor powders were calcined at 300°C in air for 3 h and subsequently annealed at 300°C in air for 2.5 h. The samples were characterized by X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, thermo-gravimetric analysis, and X-ray photoelectron spectroscopy. The visible light photocatalytic activities of as-prepared samples were evaluated by photodecomposition of methyl orange (MO). The results show that the as-prepared samples have high visible light photocatalytic activities. Triethylamine produces the N-species doped in TiO2 lattice responsible for the high visible light photocatalytic activity. Ammonium hydroxide makes the gel of the TiO2 nanoparticles nitrided by triethylamine gelate further and facilitates significantly the centrifugation of the gel. An annealing treatment can eliminate effectively the outer N species caused by ammonium hydroxide and the surface organic residues, improve effectively crystallinity, and retain the N species caused by triethylamine.

Core–shell nanoparticles consisting of La 0.75 Sr 0.25 MnO 3 cores covered by silica were synthesized by a procedure consisting of several steps, including the sol–gel method in the presence of citric acid and ethylene glycol, thermal and mechanical treatment, encapsulation employing tetraethoxysilane and final separation by centrifugation in order to get the required size fraction. Morphological studies revealed well-separated particles that form a stable water suspension. Magnetic studies include magnetization measurements and investigation of the ferromagnetic–superparamagnetic–paramagnetic transition. Magnetic heating experiments in ‘calorimetric mode’ were used to determine the heating efficiency of the particles in water suspension and further employed for biological studies of extracellular and intracellular effects analysed by tests of viability.

Electrorheological (ER) polishing is a novel polishing technology having flexible and tunable characteristics. At present, ER polishing uses ER particles to drive abrasive particles to polish the material surface. Under the action of high-speed centrifugation, the abrasive particles are easily separated from ER particles due to their significantly different ER effect, and this can easily cause the degradation of polishing ability. In this work, alumina-doped titanium dioxide ER polishing particles were developed via a sol-gel method. As a classical abrasive, alumina has higher hardness and can improve the ER effect of titanium dioxide by doping. Thus, alumina-doped titanium dioxide particles simultaneously possess high ER effect and high hardness. No phase separation appears in the polishing process and the result shows that alumina-doped titanium dioxide has a good polishing efficiency for materials with Mohs hardness of 3 and below.

Thin films of copper oxide were fabricated by sol-gel method. For the preparation of CuO thin films, a sol-gel method based on copper acetate (Cu(CH3COO)2•H2O), isopropyl alcohol (C3H8O) and diethylamine ((CH3CH2 )2NH) was used. The film was applied by centrifugation at a speed of 1500 rpm for 75 seconds. The films were applied in 2, 4, 8 layers with drying between layers for 10 minutes at 250 °C. The thermal probe method was used to determine the p-type of conductivity of the films. The films were annealed at temperatures of 300, 400, 500, 600 °C. By method of X-ray phase analysis, it was found that the main phase in the films is CuO. On films without additional annealing, a single reflex corresponding to CuO (110) 31.7° is observed. After annealing the films at 400 and 500 °C, crystallization occurs and reflexes manifest: (110) by 31.7°, (–111) by 35.5°, (111) by 38.8°, corresponding to CuO. It was found that with an increase in the annealing temperature, the grain size decreases, which indicates the crystallization of the film and contributes to the improvement of gas-sensitive properties. The transparency of the films in the visible range has values T = 30—67 %. The width of the gap is estimated to be 1.9 eV. According to AFM data, the films have a fine-grained structure and with an increase in the annealing temperature from 300 °C to 400 °C, the size of the roughness decreases. The films have high gas sensitivity values (resistance change of 30 %) and low temperature values of maximum gas sensitivity (180—190) °C to ethanol, acetone, ammonia vapors in the air.

Les enjeux énergétiques ont pris une importance considérable dans notre vie quotidienne. Ils doivent répondre en effet au double défi du besoin croissant d'énergie et des considérations environnementales et écologiques. Bien que l'énergie fossile présente des avantages indéniables, ses défauts poussent constamment la recherche vers des solutions alternatives. Dans cette course, des matériaux écologiques et performants sont toujours recherchés en vue du développement des condensateurs de stockage d'énergie et des dispositifs de refroidissement électrocalorique (EC). On outre, le contexte de la miniaturisation nécessite la fabrication des matériaux de taille de plus en plus réduite allant de céramiques aux films minces nanostructurés (1D) ayant des structures hiérarchiques en passant par les films minces (2D) denses et continus. La présente thèse a pour objectif de mieux cerner l'apport de la dimensionnalité, l'architecture, la géométrie et l'orientation des grains au sein des céramiques et des films minces élaborés afin d'augmenter la densité d'énergie stockée et l'effet électrocalorique de ces matériaux. Nous avons développé dans un premier temps des céramiques de Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) par deux méthodes de synthèse (sol-gel : BCZT-SG et électrofilage : BCZT-ES). Une optimisation de temps de frittage a été menée sur ces céramiques. Les analyses effectuées nous ont permis de caractériser l'effet de la méthode de synthèse et le temps de frittage sur les propriétés diélectriques, électrocaloriques et de stockage d'énergie des céramiques de BCZT. Les caractérisations physico-chimiques ont révélé d'une part que les céramiques de BCZT frittées pendant 6h présentent des propriétés microstructurales, diélectriques, électrocaloriques et de stockage d'énergie améliorées. D'autre part, les céramiques préparées par la méthode d'électrofilage (BCZT-ES) sont plus performantes que celles préparées par le procédés sol-gel (BCZT-ES). Cela pourrait être attribué à la finesse des grains des poudres de BCZT-ES et au rapport important des proportions des phases tétragonale (T) et orthorhombique (O) coexistantes dans ces céramiques. En effet, la céramique de BCZT-ES-6h présente une densité d'énergie récupérée intéressante de 233,69 mJ/cm3 et une efficacité énergétique élevé de 72,17% à E = 40 kV/cm, au voisinage de la transition ferroélectrique-paraélectrique. Ainsi, cette céramique montre un coefficient électrocalorique atteignant une valeur élevée de ζ ≈ 0,523 K.mm/kV. L'utilisation de BCZT sous forme de couche mince au lieu de la céramique nous a permis d'appliquer des champs électriques plus forts favorisant des propriétés de stockage d'énergie intéressantes. Une optimisation des paramètres expérimentaux (liant utilisé, mode et température de recuit de cristallisation) a été faite sur les films minces de BCZT déposés par la méthode sol-gel combinée à la technique de revêtement par centrifugation. Le film BCZT-850 cristallise dans une structure pérovskite pure présentant une microstructure granulaire relativement dense. Il présente une valeur élevée de Wr = 1,211 J/cm2 avec une efficacité énergétique intéressante de 72,31% à un champ appliqué de 372 kV/cm. Afin de comprendre l'effet de la forme et de l'orientation des grains sur les propriétés diélectriques des films minces, une synthèse hydrothermale des films nanostructurés (1D) verticalement alignés de BaTiO3/TiO2 a été menée. Une étude systématique des différents paramètres de synthèse a permis de déterminer les conditions optimales d'élaboration de ce type de films présentant une structure hiérarchique 1D avec une orientation préférentielle des nanotiges suivant l'axe c, un pourcentage élevé de la phase de BaTiO3 (94%), et une permittivité diélectrique (εr′ ) très élevée de ≈ 16085. À la lumière de ces résultats, ce travail de thèse peut contribuer à la conception de matériaux écologiques ayant un effet électrocalorique et des performances de stockage d'énergie électrique
Energy issues have taken on considerable importance in our daily lives. They have to address the dual issue of the expanding energy demand as well as environmental and ecological concerns. Although, fossil fuels have undeniable advantages, their drawbacks are constantly driving the search for alternative solutions. In this regard, eco-friendly and effective materials are always being investigated for the development of energy storage capacitors and electrocaloric (EC) refrigeration devices. Additionally, the context of miniaturization requires the fabrication of smaller and smaller material sizes, ranging from ceramics to dense and continuous (2D) thin films to nanostructured (1D) thin films exhibiting hierarchical structures. The goal of this thesis is to understand how the dimensionality, architecture, geometry, and grain orientation of the ceramics and thin films intend to enhance the electrocaloric effect and stored energy density of these materials. By using two synthesis techniques: sol-gel (SG) and electrospinning (ES), we first synthesized BCZT ceramics (BCZT-SG and BCZT-ES) which underwent a sintering time optimization process. Then, the bulk ceramics were subjected to studies in order to evaluate how the synthesis technique and sintering time influenced the dielectric, electrocaloric, and energy-storage properties of BCZT ceramics. The physico-chemical characterisations revealed that on the one hand, BCZT ceramics sintered for 6h had improved microstructural, dielectric, electrocaloric and energy storage properties, on the other hand, the ceramics prepared by the electrospinning method (BCZT-ES) are more efficient than those prepared by the sol-gel process (BCZT-ES) which could be attributed to the fineness of the grains of the BCZT-ES powders and to the significant ratio of the coexisting tetragonal (T) and orthorhombic (O) phases in ceramics.. Indeed, the BCZT-ES-6h ceramic showed an interesting recovered energy density of 233.69 mJ/cm3 and a high energy efficiency of 72.17% at E = 40 kV/cm, around the ferroelectric-paraelectric transition. Thus, this ceramic shows an electrocaloric coefficient reaching high value of ζ ≈ 0.523 K.mm/kV. Instead of using ceramic, using BCZT thin layers produced using the sol-gel process coupled with the spin coating technique, allowed us to apply higher electric fields, which promoted interesting energy storage properties. For these BCZT thin films, experimental parameters (binder, mode and temperature annealing) were optimized. the BCZT-850 film crystallises in a pure perovskite phase with relatively dense granular microstructure. It exhibits a high value of Wr = 1.211 J/cm3 with an interesting energy efficiency of 72.31% at an applied field of 372 kV/cm. In addition, a hydrothermal synthesis of vertically aligned (1D) nanostructured BaTiO3 (BT) films was conducted to better understand the effect of grain shape and orientation on the dielectric properties of thin films. The optimal conditions for the synthesis of these types of films were established by a methodical analysis of the various hydrothermal synthesis parameters. A 1D BaTiO3 lattice with nanorods preferentially aligned along the c-axis exhibiting a high aspect ratio of ≈ 9.27, and a very high dielectric constant of ≈ 16539 were produced by using the optimal parameters

La tendance generale a la miniaturisation des dispositifs conduit de plus en plus a focaliser les recherches sur les materiaux fonctionnels en couches minces. Parmi ces materiaux, les ferroelectriques prennent une place de plus en plus importante notamment dans le domaine des memoires non volatiles. Si les pzt ont deja fait l'objet de nombreux travaux, les recherches sur les composes ferroelectriques a couches de bismuth ou phases d'aurivillius sont en plein essor en raison de leur resistance a la fatigue et de leur aptitude a conserver leur polarisation apres de nombreux cycles de fonctionnement. Dans le cadre general, et compte tenu de l'experience acquise au spcts dans ce domaine, le travail presente concerne une des phases d'aurivillius parmi les plus prometteuses, srbi 2nb 2o 9 (sbn), pour laquelle persistent encore des zones d'ombre concernant a la fois la fabrication, la nature des defauts structuraux, son epitaxie sur divers substrats monocristallins, ce dernier point etant etroitement lie a son utilisation dans les memoires (possibilite d'obtenir des couches ferroelectriques avec des orientations choisies de la polarisation par rapport au substrat). Sbn a ete prepare par voie sol-gel selon une technique deja utilisee au spcts. La cristallisation des xerogels, puis son orientation et l'epitaxie de couches deposees par centrifugation (spin-coating) ont ete etudiees a la fois par diffraction des rayons x et par microscopie electronique en transmission. La fabrication de la phase sbn cristallisee passe toujours par la formation d'une phase intermediaire de type fluorine de composition inconnue, certainement riche en bismuth, qui pourrait etre le precurseur des feuillets bi 2o 2 caracteristiques des phases d'aurivillius

The two oil sands plants operated by Syncrude Canada Ltd. and Suncor Canada Ltd. near Fort MacMurray, Alberta, use a hot water process for the separation of bitumen from oil sands. In brief, hot water and oil sands, with caustic soda as dispersing agent, are mixed thoroughly, and bitumen is floated to the top of the resulting slurry by streams of air. After secondary bitumen recovery, the remaining tailings are carried to ponds, where the coarse sands are used to form dikes, the fine tails are left to settle, and freed water is recycled. Typical production figures for the Syncrude plant are 390 000 barrels of diluted bitumen per day produced from 325 000 tonnes of oil sand. One complicating factor is that the fine tails dewater only to a solids content of ~30%, requiring ponds of ever increasing size (the Syncrude pond is 22km2) to store the resulting sludge. As the ponded material is toxic to wildlife, it poses a considerable local environmental hazard. In addition, there is the potential hazard of contamination of surface water and a major river system as a result of seepage or potential dike failure. The work reported here was carried out as part of a major project initiated to address the problem of the existing tailings ponds, and also to modify the currently used separation process so as not to produce sludge. Starting with the recognition that the very stable fine tails, consisting of water, silt, clay and residual bitumen, have gel-like properties, we employed the strategy of fractionating the fine tails with the hope of identifying a specific fraction which might show gel-forming propensity. This was done by breaking the gel, and collecting fractions according to sedimentation behavior during centrifugation. Fractions consisting of the coarser solids (>0.5μm) settled rapidly, whereas fractions with smaller particle sizes (termed ultrafines) gave suspensions which set into stiff, thixotropic gels on standing. Gel formation and the sol-gel transition in colloidal clay suspensions are classical problems which have received much attention over the years; however, much remains to be learned. NMR techniques have shown considerable promise in understanding clay-water interactions at a microscopic level.