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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
111

L'utilisation des agents d'embolisation liquides dans les vaisseaux périphériques : mise au point, défis et futures perspectives : preuves de concept d'un nouvel agent sclero-embolique : Alconyx / The use of liquid embolic agents in peripheral vessels : current status, challenges and future perspectives : proof of concept of a new sclero-embolic agent Alconyx : Alconyx

Saeed Kilani, Mohammad Ali 07 December 2016 (has links)
Les agents d'embolisation liquides utilisés dans le traitement endovasculaire ont de nombreuses limitations. Des polymères, tels que l’Onyx et les cyanoacrylates sont disponibles. L’alcool est un agent puissant, mais non radio-opaque. Les cyanoacrylates entrainent une réaction inflammatoire significative. Leur polymérisation rapide est responsable d’un comportement mal prévisible.Il existe une possibilité de traitement incomplet.L’Onyx est efficace pour le traitement des MAV.Une pénétration plus distale est obtenue avec l’alcool, mais associée à un risque de migration systémique. Nous avons évalué les propriétés d'un nouvel agent embolique (Alconyx) composé d'un mélange d'alcool et d'Onyx. Cet agent devrait cumuler les avantages respectifs de l'alcool et de l'onyx avec une visualisation adéquate sous fluoroscopie, une meilleure pénétration distale que l'Onyx seul et moins de toxicité systémique liée à la réduction de quantité d’alcool injecté. Divers mélanges ont été testés avec différentes concentrations d'Onyx 18 et d’alcool absolu. Alconyx 25 (75% Onyx 18; 25% d'éthanol) est la formulation la plus prometteuse. Nous avons démontré sa facilité d'injection in vivo, sa nature cohésive sans fragmentation ainsi que sa bonne visualisation sous fluoroscopie. En raison de sa moindre viscosité démontrée in vitro, Alconyx a été capable de pénétrer profondément dans le lit artériel.. L'occlusion proximale par Alconyx 25 devrait permettre d'améliorer le contact entre l'éthanol et la paroi vasculaire et donc augmenter son pouvoir sclérosant et limiter son passage systémique. Les propriétés occlusives d’Alconyx 25 sont similaires à celle de l’Onyx 18 sous haute pression in vitro. / Commercially available liquid embolization agents used in endovascular treatment have many limitations. Polymeric agents as Onyx and cyanoacrylate are available. Ethanol also is a potent sclero-embolic agent. Cyanoacrylates are effective liquid embolic agents, however, their rapid polymerization makes their behaviour unpredictable with possibility of incomplete treatment. These properties render their use challenging.Onyx is easy to use. However, in very small arterial niduses, Onyx, is unable to penetrate deeply. Deep penetration is obtained with ethanol, associated with risk of systemic migration.Poor visualization of ethanol under fluoroscopy is major drawback. Mixing Onyx with ethanol had never been described in the literature till now. In this work, various mixtures have been tested with different concentrations of Onyx 18 and absolute ethanol. Alconyx 25 (75% Onyx 18; 25% ethanol) seems to be a promising product. We proved its ease of injection in vivo and in vitro, its cohesive nature showing no fragmentation or interruption of the injected column as well as its good visualization under fluoroscopy. It was able to penetrate deeply in the arterial bed. The occlusive properties of Alconyx 25 were rated as good as Onyx 18 under high pressure in vitro. Further investigation is needed to better understand the behavior of ethanol in the suspension and its effect on tissues compared to Onyx diluted simply with an equivalent amount of DMSO. Studies on other commercially available concentrations of Onyx would certainly be interesting.
112

Oxidative Copolymerization Of Vinylmonomers : Studies On The Microstructure And Reactivities Of The Copolyperoxides

Jayanthi, S 04 1900 (has links) (PDF)
No description available.
113

Developing of Germyldesulonylation and Thiodesulfonylation Reactions for the Synthesis of Novel Nucleoside Analogues. Efficient Synthesis of Novel (α-Fluoro)vinyl Sulfides

Sacasa, Pablo R, Jr 19 July 2010 (has links)
S-adenosyl-L-homocysteine (AdoHcy) hydrolase effects hydrolytic cleavage of AdoHcy to produce both adenosine and L-homocysteine and is a feedback inhibitor of S-adenosyl-L-methionine (SAM). Nucleoside analogues bearing an alkenyl or fluoroalkenyl chain between sulfur and C5′ utilizing Negishi coupling reactions were synthesized. Palladium-catalyzed cross-coupling between the 5′-deoxy-5′-(iodomethylene) nucleosides and alkylzinc bromides gives analogues with the alkenyl unit. Palladium-catalyzed selective monoalkylation of 5′-(bromofluoromethylene)-5′-deoxy-adenosine with alkylzinc bromide afford adenosylhomocysteine analogues with a 6′-(fluoro)vinyl motif. The vinylic adenine nucleosides produced time-dependent inactivation of the S-adenosyl-L-homocysteine hydrolases. Stannydesulfonylation reaction is a critical step in the synthesis of E-fluorovinyl cytidine (Tezacitabine) a ribonucleoside reductase inhibitor with a potent anticancer activity. The synthesis involves the removal of the sulfonyl group by a radical-mediated stannyldesulfonylation reaction using tributyltin hydride. In order to eliminate the toxicity of tin, I developed a radical-mediated germyldesulonylation utilizing less toxic germane hydrides. Treatment of the protected (E)-5'-deoxy-5'-[(p-toluenesulfonyl)-methylene]uridine and adenosine derivatives with tributyl- or triphenylgermane hydride effected radical-mediated germyldesulfonylations to give 5'-(tributyl- or triphenylgermyl)methylene-5'-deoxynucleoside derivatives as single (E)-isomers. Analogous treatment of 2'-deoxy-2'-[(phenylsulfonyl)methylene]uridine with Ph3GeH afforded the corresponding vinyl triphenylgermane product. Stereoselective halodegermylation of the (E)-5'-(tributylgermyl)-methylene-5'-deoxy nucleosides with NIS or NBS provided the Wittig-type (E)-5'-deoxy-5'-(halomethylene) nucleosides quantitatively. Radical-mediated thiodesulfonylation of the readily available vinyl and (α-fluoro) vinyl sulfones with aryl thiols in organic or aqueous medium to provide a bench and environmentally friendly protocol to access (α-fluoro)vinyl sulfides were developed. Methylation of the vinyl or (α-fluoro)vinyl phenyl sulfide gave access to the corresponding vinyl or (α-fluoro)vinyl sulfonium salts. These sulfonium ions were tested as possible methyl group donors during reactions with thiols, phenols or amino groups which are commonly present in natural amino acids.
114

Vliv okolních podmínek na recyklaci solárních modulů / The influence of environmental conditions of the recycling of solar modules

Langer, Filip January 2021 (has links)
This thesis is focused on experiments, goal of which is to separate protective glass apart from thin layer solar panel. This could lead to less expensive and more efficient recycling. We try to achieve the separation of the glass by thawing ethylene vinyl acetate layer, which serves as insulant and bonding material. Experiments are concluded in high temperature dryer and high temperature vacuum oven on samples of thin layer solar panel, which is for the purposes of experiments cut into same pieces by water jet cutting machine. The initiatory experiments in dryer and oven are to determine value of ethylene vinyl acetate thaw point in tested samples of panel. The thaw point is determined to be 340 °C. When exposed to this temperature, the ethylene vinyl acetate thaws enough for glass to be able to be extracted with minimal physical strength. The process is accompanied by fire destruction of tedlar layer and creation of exhaust gases. Following experiments in vacuum and nitrogen environment are to test their influence on thawing process. Exposing sample to temperature of 340 °C in vacuum led to no new results. Exposing sample to temperature of 340 °C in nitrogen environment prevented fire and achieved same level of thawing of ethylene vinyl acetate while creating less exhaust gases. Even though the fire was prevented, tedlar layer was still destroyed by the high temperature. Furthermore, particles of evaporated ethylene vinyl acetate condensed on surface of module in form of dust. Following experiments studied absorption of panel and influence of accessible solvents on thawing process. It was determined that panel is able to absorb approximately 2 % of acetone, 0,4 % of isopropyl alcohol and 0,11 % of distilled water in its own weight. Experiments with modules soaked in these solvents proved no new results in thawing process. By observing samples of ethylene vinyl acetate taken from module, thawed out of module after experiment in vacuum oven and dust condensed on surface of module after experiment in nitrogen environment, it was proven that the condensed dust is indeed ethylene vinyl acetate.
115

Understanding the Factors That Control Increased Photo-reactivity and Selectivity Of Vinylic And Aromatic Azides

Osisioma, Onyinye 22 October 2020 (has links)
No description available.
116

Den moderna vinylen : En studie av unga vuxnas relation till vinylskivor som lyssningsformat / The Modern Vinyl : the relation between young adults and vinyl as a listening format

Persson, Hampus January 2016 (has links)
Denna uppsats diskuterar fyra unga vuxnas, i Växjö, relation till vinylskivor som format för musiklyssning. Genom den kvalitativa intervjumetoden görs ett försök att beskriva hur informanterna motiverar användandet av vinylskivor, vilka egenskaper som de tillskriver skivorna och hur det förhåller sig gentemot digital musiklyssning. Materialet har analyserats med hjälp av teorier kring retrologier (skapandet av sätt att se tillbaka), affordance (vinylskivans polyvokala egenskaper) och rekontextualiseringsprocesser (vilka egenskaper tillskrivs formatet i en modern kontext). Studien visar på vinylskivans förmåga att frambringa en särskild känsla hos informanterna och hur detta skapas utifrån flertalet olika dimensioner, så som skivans fysikalitet, visuella egenskaper och inbjudan till ett aktivt lyssnande.
117

Studies On 2,3-Unsaturated Sugars : Reactivity Switching, Rearrangements And Conjugate Additions

Mukherjee, Arunima 09 1900 (has links) (PDF)
Unsaturated sugars constitute as an important category of carbohydrate precursors in synthesis. Specifically, 1,2- and 2,3-unsaturated glycosides are excellent intermediates to derivatize monosaccharides and as building blocks in organic synthesis. For example, a major utility of 1,2-unsaturated sugars, namely glycals, is the addition reactions to afford 2-deoxy glycosides under acidic conditions and rearrangement reactions to produce 2,3-unsaturated glycosides. Lewis acids favour the formation of 2,3-unsaturated glycosides, whereas, Brønsted acids lead to normal addition products. A mixture of both the product is obtained often, depending on the nucleophiles and the stereochemistry of glycal. Chapter 1 of the thesis describes (i) reactivities of glycals under acidic condition and (ii) a general survey of reactions involving on C2-C3 carbons of monosaccharides. Glycals are useful precursors to derive a number of functionalized monosaccharide derivatives. A well-known acid catalyzed reaction of glycals is their conversion to 2,3¬unsaturated glycosides, known as the Ferrier products. In a research programme, reactivity switching and selective activation of C-1 or C-3 of 2,3-unsaturated thioglycosides under acid catalyzed condition was undertaken. Thioglycosides are excellent glycosyl donors and can be activated easily. In identifying the reactivities of 2,3-unsaturated thioglycosides, obtained through Ce(IV)-mediated reaction of a glycal, it was intended to study the glycosylation reaction and also the reactivity control of C1-C3 carbons during a glycosylation reaction. Experiments showed that a reactivity switching was possible through activation of either C-1 or C-3. Thus, C-1 glycosylation with alcohol acceptors occurred in the presence of NIS/TfOH, without the acceptors reacting at C-3. On the other hand, reaction of 2,3-unsaturated thioglycosides with alcohols mediated by triflic acid alone led to a transposition of C-1 ethylthio-moiety to C-3 intramolecularly, to form 3-ethylthio-glycals. Resulting glycals underwent glycosylation with alcohols to afford 3-ethylthio-2-deoxy glycosides. However, when thiol was used as an acceptor, only a stereoselective addition at C-3 resulted, so as to form C-1, C-3 dithio-substituted 2-deoxypyranosides. Oxocarbenium ion is the reactive intermediate during activation of a glycosyl donor, and in the case of a 2,3-unsaturated thioglycosides, the oxocarbenium ion may stabilize further by the presence of a C2-C3 unsaturation. Reaction of a nucleophile with allylic oxocarbenium ion may lead to two regio-isomers. Initially, NIS/TfOH was attempted on 2,3–unsaturated sugar with various alcohols and it was found that C-1 was the preferred reactive centre (Scheme 1) Scheme 1 In order to optimize the reaction for selective nucleophilic attack at C-3, further study was continued by using stoichiometric TfOH, in presence of acceptors alcohols with the intension to activate the double bond. The reaction led to the formation of 2-deoxy O-glycosides with the concomitant transposition of C-1 ethylthio-moiety to C-3 (Scheme 2). Scheme 2 An important observation was that the transposition of thioethyl group from C-1 to C-3 was highly regioselective. For example, with thiocresol as the nucleophile, there was an addition across the C-2-C-3 double bond to afford C-1, C-3-dithio derivative (Scheme 2). Thus, hard-soft nature of the nucleophiles, as well as, carbon centres helped to rationalize the reactivites. It was also observed that the intramolecular transposition of thioethyl group is highly stereo-controlled by equatorial C-4 acetoxy group. Thus, thioethyl nucleophile approached selectively at C-3 and afforded trans-diequatorial products. This rationalization was further confirmed through (i) reaction of benzyl protected 2,3-unsaturated thioglycoside, wherein a C-3 epimeric mixture was observed in 1:1 ratio; (ii) galactosyl derivative under similar reaction condition afforded anomeric mixture of 3-(4-methylphenylthio)-O-glycosides, with trans-diaxial orientation of substituent at C-3 (Scheme 3). Scheme 3 These reactions confirmed the role of C-4 substituent on the carbocation at C-3, through the presence or absence of a neighbouring group participation. In summary, in Chapter 2 the selective activation of either anomeric carbon or C-3 with proper choice of activation and reactivity control at each carbon will be described. Thioglycosides are excellent glyosyl donor and their glycosylation reactions were well explored. Upon indentifying the intramolecular transposition of thioalkyl/aryl functionality from C-1 to C-3, further investigations was undertaken to utilize the newly formed carbon sulfur bonds at C-3. Realizing a potential for such 3-alkyl/aryl thio 2-deoxy sugar, the Pummerer rearrangement was investigated. For this purpose, the thioalkyl/aryl moiety at C-3 was oxidized first to a sulfoxide. The resulting sulfoxide was allowed to undergo Pummerer rearrangement to afford vinyl sulfide (Scheme 4), resulting from the elimination of HOAc in the thioacetal formed in situ. Having implemented Pummerer rearrangement on a sugar substrate, synthetic utility of the rearrangement product, namely vinyl sulfide was undertaken. An effort to implement conjugate addition reaction was undertaken, which required the conversion of vinyl sulfide to vinyl sulfoxide in the first step. The conjugate addition reactions were first conducted with alkoxide nucleophiles. The reaction showed that addition of nucleophiles occurred from axial face to furnish manno-configured derivatives as a single diastereomer at sulfinyl sulfur in a moderate yield along with O-deacetylated product. It was also found that O-benzyl protected sugar vinyl sulfoxide was totally resistant to the conjugate addition reaction (Scheme 4). Scheme 4 In order to find the influence of the substituents in sulfoxide moiety in the addition of nucleophiles, additional study was conducted in which a less hindered thioethyl moiety was installed in place of p-tolylthio moiety. To install ethylthio moiety, a similar sequence of reaction was undertaken as described previously in Scheme 4. Conjugate addition reaction with alkoxide nucleophiles was conducted and analysis of the reaction showed that the addition of alkoxides remained similar, leading to the formation of manno-configuration of substituents (Scheme 5). Scheme 5 The configuration of the Michael adducts were ascertained from 1H NMR, as well as 2D NMR spectroscopies. H-1 of all adducts appeared as an apparent singlet, consistent with very small J1,2 values. Aryl vinyl sulfoxide afforded conjugate addition product at much higher ratio than corresponding alkyl vinyl sulfoxide. Thus, among aryl and alkyl vinyl sulfoxides, conjugate addition occurred better with the aryl vinyl sulfoxide, indicating a strong electronic effect of aryl group in stabilizing the conjugate anion which would form in situ during nucleophilic addition with vinyl sulfoxide. Therefore, p-tolylthio substituted vinyl sulfoxide served as a more efficient Michael acceptor when compared to the thioethyl substituted vinyl sulfoxide. Asymmetric environment of vinyl sulfoxides play a vital role during the reaction. Vinyl sulfoxides can exist in two stereochemically distinct conformation which makes the vinyl group electronically dissimilar. In one of the conformer S-O and C-C bonds are coplanar, whereas in the other conformation, these two bonds are opposite to each other. It is agreed generally that vinyl sulfoxides generally try to adopt the most reactive conformer during the reaction in which the C-C and S-O bonds are syn to each other. Thus, the preference for an axial attack would originate from a face anti to the lone pair of electrons on the sulfur of sulfoxide functionality, leading to the formation of the product with manno-configuration. As O-deacetylated vinyl sulfoxide was obtained along with the Michael adducts, it was assumed that one of the epimers of vinyl sulfoxide appeared to be more reactive when compared to the other. Chapter 3 describes implementation of a Pummerer rearrangement in order to synthesize a sugar vinyl sulfoxide and its conjugate addition reactions with alkoxide nucleophiles. The nucleophilic addition reactions of vinyl sulfoxide with other nucleophiles were studied further. The effect of the substituents of chiral sulfoxides in conjugate addition reactions was also incorporated in the course of reactions. Reactions of amines, carbon and sulfur nucleophiles were undertaken with p-tolylthio-substituted vinyl sulfoxides. The reactions showed formation of the addition-elimination products (Scheme 6). All primary amines, carbon and sulfur nucleophiles afforded C-2 axial epimer, namely, threo-epimer exclusively, wherein secondary amines furnished the equatorial vs axial epimer in 3:1 ratio. Scheme 6 In order to assess the course of the reaction, vinyl sulfoxide presenting a p-cumenethio¬moiety was installed in place of p-tolylthio moiety. Conjugate addition reactions were performed with both primary as well as secondary amines that showed formation of the C-2 epimeric mixtures. With both the primary and secondary amines C-2 equatorial epimer was found to be as the major product (Scheme 7). Scheme 7 In conjugate addition of vinyl sulfoxides, nucleophiles approach the olefinic face preferentially, which is anti to the electron rich sulfur lone pair of electrons and syn to the bulky aryl group. Therefore, C-2 axial epimer was observed as most favourable product. However, secondary amines remarkably influenced the pattern as well as selectivity of the reaction. Steric considerations were likely to dictate the overall reactivity with secondary amines which was even more pronounced when using p-cumenethio-substituted vinyl sulfoxide. Chapter 4 describes the conjugate additions as well as remote effect of aryl substituent on the selectivity of addition of amines on sugar sulfoxide In summary, the Thesis establishes: A new reactivity of switching and a selective activation of 2,3-unsaturated thioglycoside; A Pummerer rearrangement route in order to synthesize sugar vinyl sulfide for the first time, which on selective oxidation furnish a sugar vinyl sulfoxide, a useful precursor for conjugate addition reactions; An assessment of the stereoelectronic, as well as, steric effect of the chiral vinyl sulfoxide with various nucleophiles in conjugate addition reactions; Influence of the protecting groups were also studied in conjugate addition reactions. Overall the study presented in the Thesis provides a new insight to unsaturated sugars. The salient features of the present findings also showed that the intermediates such as C-3 substituted thioalkyl/aryl glycosides, vinyl sulfides, a variety of new C-2 substituted vinyl sulfoxides are also the potential sites for many types of modifications in monosaccharides. (For structural formula pl see the pdf file)
118

Moisture Barrier Polymer Nanocomposites for Organic Device Encapsulation

Saravanan, S January 2016 (has links) (PDF)
The advancement in smart technologies for organic conducting polymers as flexible substrates in LEDs, PVs and solid state lighting necessitates the development of ultra-high barrier films to protect the devices from moisture and oxygen. The current encapsulation methodology of using layers of plastics and inorganic oxides has several deficiencies. Alternatively, the use of single layer of polymer nanocomposites is a promising substitute for these inorganic based encapsulation layers. The use of polymer materials have the advantage of flexibility, active electrodes printability and easy to make the devices for large area applications. The nano-fillers with high aspect ratio as nanocomposites ingredient in polymers reinforces its mechanical strength and also acts as a scavenging material for moisture and increases the residence time and/or for the penetrating moisture in the film. Chapter 1 gives the basic overview in the field of barrier technology films and coatings from polymers and inorganic oxide as either mono/multi layer hermetic encapsulation methods. The understanding of both chemistry and physics behind the moisture permeation and its interaction with the film material was discussed. The inclusion of functional nano-fillers as moisture trapping agents in the film provide better device protection achieved. The methods and instruments to measure such ultra-low permeation within the films are discussed. Finally, the advantage of polymer based nanocomposites for low-permeable films with existing materials are briefly discussed in this chapter. In this thesis, we employed both thermoplastic and thermoset polymer nanocomposites as encapsulation layer for device sealing. The use of ion-containing polymers (ionomers) as a sealant layer was also studied. Chapter 2 presents the detailed experimental procedures with materials and methods used in this thesis along with the synthesis methodologies to make films from the polymer. In chapter 3, we used cyclic olefin copolymer COC (copolymer of ethylene and norbornene) as an encapsulation layer with silica and layered silicate nano-fillers. The compatibility between hydrophilic silica and hydrophobic COC was achieved by maleic anhydride grafted PE with anchoring on COC as a compatibilizer and then silica filler was added to make the nanocomposite films. FTIR spectroscopy confirms the bond formation of silica with COC/MA-g-PE. The mechanical (tensile and DMA) and thermal studies (DSC) suggested that there is an improvement observed when adding silica/silicate layers in the polymer matrix with increased tensile strength, storage modulus and Tg. The calcium degradation test show enhanced performance towards moisture impermeation in the film. Chapter 4 deals with the synthesis of PVB based nanocomposite film with silica/layered silicate as nanofillers in the base matrix with varying degree of acetalization in the film. The FTIR and NMR spectroscopy show the evidence for acetal link formation in the in-situ synthesized PVB with silica/silicate nanofillers with three different acetyl contents. The tensile and DMA studies show the observed improvement in mechanical strength (increased tensile strength, storage modulus) were due to the intercalation of clay galleries during PVB formation and the interaction of silica particles interactive bond formation with –OH groups of PVA in PVB. The higher clay/silica particles show agglomerated nature and reduction in film strength. Thermal studies (DSC) show that there is an improvement observed in Tg when adding silica/silicate layers in the polymer matrix with moderate to low acetal content. The calcium degradation test show enhanced performance towards moisture impermeation in the film. Chapter 5 describes the inclusion of ionic groups (ionomers) in PVB and its effects on moisture permeation and mechanical properties. PVB ionomer was synthesized using formyl benzene 2-sulfonic acid sodium salt and 2-carboxy benzaldehyde (both sulfonic and carboxylic acid sources) as co-aldehyde with butyraldehyde and PVA. These acid groups were neutralized with potassium, magnesium and zinc ions. The level of acid content in the films was maintained between 6 to 28 mol percent. The sulfonic acid films with zinc and magnesium ions of 14 mol% exhibit good mechanical strength and low moisture permeation. Chapter 6 deals with the epoxy terminated silicone polymer nanocomposites as moisture barrier coatings for device encapsulation. Both silica and clay silicate layers were used to reinforce the silicone matrix. The silica nanoparticles were grafted with amino-silane groups, this would help in better mixing of silica particles in the silicone matrix due to the amine groups interaction in curing with epoxy groups. The calcium degradation test was used to determine the WVTR of the nanocomposites and device encapsulation was employed to estimate the degradation after exposure to ambient environment. Chapter 7 presents the concluding remarks of the results presented. The benefits as well as limitations of the polymer nanocomposite film and the future developmental work to be carried out are discussed in this chapter.
119

Probing the influence of bimetallic composition on the Pd/Au catalysed synthesis of vinyl acetate monomer

Haire, Andrew Richard January 2010 (has links)
Scanning Tunnelling Microscopy (STM) was utilised together with the high resolution depth-profiling capabilities of Medium Energy Ion Scattering (MEIS), a technique traditionally associated with single crystal substrates, to probe the mean size and depth dependent composition profile of bimetallic PdAu nanoparticles on planar oxide surfaces as functions of the starting composition and annealing temperature. In order to fit composition profiles to experimental MEIS data, a new analysis tool has been designed that models the particles as flat-topped structures with a hexagonal base which can be divided into a number of shells, each shell corresponding to a particular ion pathlength inside the material. The reliability of this method will be discussed in detail. Fitting results show that the surface layers are always significantly enriched in Au compared to the bulk alloy composition. By comparing MEIS data for clean surfaces data for modified surfaces it was found that Pd generally segregates towards the particle surface on adsorption of acetic acid. The interaction of potassium acetate with Au/Pd{111} alloy surfaces of varying composition has been investigated using Temperature Programmed Desorption (TPD) and Reflection Absorption Infra Red Spectroscopy (RAIRS). At lower coverage, potassium acetate reacts reversibly with the surface to form CO and carbonate. Formation of surface acetate is observed on Pd-rich surfaces only. At higher coverage, acetate is the major surface species formed on all samples examined.
120

Síntesse de novos estabilizantes poliméricos do tipo poli(álcool vinilico-co-neo decanoato de vinila) para utilização na copolimerização em miniemulsão do acetato de vinila (VAc) com o neo-nonanoato de vinila (VEOVA-9) / Synthesis of new poly(vinyl alcohol-co-vinyl neodecanoate) based polymeric stabilizers, to be used in the miniemulsion copolymerizatin of vinyl acetate (VAc) with vinyl neononanoate (VEOVA-9).

Oliveira, Mauricio Pinheiro de 30 April 2010 (has links)
Devido à importância industrial e tecnológica dos látices estabilizados com poli(álcool vinílico)/PVA e a dificuldade encontrada na etapa de polimerização em emulsão, na presença de monômeros hidrofóbicos e de PVA\'s com alto grau de hidrólise (>92%), a síntese de novos estabilizantes poliméricos derivados de PVA para utilização em reações de polimerização em emulsão e em miniemulsão se torna muito atraente e desafiadora. O objetivo principal deste trabalho foi sintetizar novos estabilizantes poliméricos do tipo poli(álcool vinílico-co-neodecanoato de vinila)/PVA-VV com alto grau de hidrólise e conseqüentemente com propriedades diferenciadas, para serem utilizados como estabilizantes nas reações de polimerização em emulsão e em miniemulsão do acetato de vinila (VAc) com o neo-nonanoato de vinila (VEOVA-9), visando a obtenção de adesivos com propriedades diferenciadas para colagem de madeiras. Os novos estabilizantes poliméricos foram obtidos em duas etapas: i) copolimerização em solução do VAc com o neo-decanoato de vinila (VEOVA-10); ii) hidrólise alcalina (NaOH/Metanol) do poli(acetato de vinila-coneodecanoato de vinila). As miniemulsões de VAc com VEOVA-9 com diferentes tipos de estabilizantes poliméricos foram preparadas em um homogeneizador de alta pressão do tipo \"Manton Gaulin\". Foi estudado o efeito dos estabilizantes poliméricos (PVA e PVA-VV) na etapa de emulsificação (diâmetro médio das gotas, polidispersão, estabilidade das miniemulsões) e na copolimerização em emulsão e em miniemulsão do VAc com o VEOVA-9, em processo batelada. O efeito do tipo de iniciador (persulfato de amônio/APS e hidroperóxido de tércio butila/TBHP e peróxido benzoato de tércio butila/TBPB, juntamente com o formaldeído sulfoxilato de sódio/SFS) na cinética da polimerização em miniemulsão do VAc com o VEOVA-9 foi estudado em processo semi-contínuo. A distribuição dos estabilizantes poliméricos (PVA e PVA-VV) entre a fase aquosa e a superfície das partículas de polímero (adsorvido/enxertado) foi determinada e correlacionada com a viscosidade e a estabilidade coloidal dos látices. Látices na condição ideal de cópia (1:1) das gotas de monômero para as partículas de polímero foram obtidos via polimerização em miniemulsão, apresentando propriedades diferenciadas, tais como, menores valores de viscosidade, menor concentração de coágulos e maior estabilidade de estocagem, em comparação com os látices obtidos em emulsão. / Due to the technological and industrial importance of latexes stabilized with poly(vinyl alcohol)/PVA and the difficulties related to the emulsion polymerization of hydrophobic monomers and the use of PVA having a high degree of hydrolysis (> 92%), the synthesis of new PVA based polymeric stabilizers for use in emulsion and miniemulsion polymerizations becomes very attractive and challenging. The aim of this work was to synthesize a new class of polymeric stabilizer, poly(vinyl alcohol-co-vinyl neo-decanoate)/PVA-VV, with a high degree of hydrolysis and differentiated properties to be used as stabilizers in the emulsion and miniemulsion copolymerization of vinyl acetate (VAc) with vinyl neo-nonanoate (VEOVA-9), that can be used as adhesive for wood bonding. New PVA based polymeric stabilizers with high degree of hydrolysis (94 - 98%) were synthesized in two steps: i) solution copolymerization of vinyl acetate (VAc) with vinyl neo-decanoate (VEOVA-10) and ii) alkaline hydrolysis (NaOH/Methanol) of poly(vinyl acetate-co-vinyl neodecanoate). Miniemulsions of VAc/VEOVA-9 were prepared using the different polymeric stabilizers in a \"Manton Gaulin\" high pressure homogenizer. The effect of different initiators (ammonium persulfate/APS or tert-butyl hydro peroxide/TBHP and tert-butyl peroxide benzoate/TBPB in the presence of sodium formaldehyde sulfoxylate/SFS) in the polymerization kinetic was evaluated. The effect of the type and concentration of polymeric stabilizer, in the emulsification step (average diameter of drops, stability of miniemulsions) as well in the polymerizations (rate of consumption of monomers, particle size and particles number) was investigated in this work. The partition of the polymeric stabilizers between the aqueous phase and the polymer particle surface (grafted/adsorbed) was determined and correlated with the viscosity and colloidal stability of latexes. Latexes with differentiated properties such as low-viscosity, lower grits content and improved storage stability, were obtained by miniemulsion polymerization with an ideal condition copy (1:1) of the monomer droplets to the polymer particles.

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