Dissertations / Theses on the topic 'Fluoropolymere'

Modern three-dimensional integrated circuit design is rapidly evolving to more complex architecture. With continuous downscaling of devices, there is a pressing need for metrology tool development for rapid but efficient process and material characterization. In this dissertation work, application of a novel multiple internal reflection infrared spectroscopy metrology is discussed in various semiconductor fabrication process development. Firstly, chemical bonding structure of thin fluorocarbon polymer film deposited on patterned nanostructures was elucidated. Different functional groups were identified by specific derivatization reactions and model bonding configuration was proposed for the first time. In a continued effort, wet removal of these fluorocarbon polymer was investigated in presence of UV light. Mechanistic hypothesis for UV-assisted enhanced polymer cleaning efficiency was put forward supported by detailed theoretical consideration and experimental evidence. In another endeavor, plasma-induced damage to porous low-dielectric constant interlayer dielectric material was studied. Both qualitative and quantitative analyses of dielectric degradation in terms of increased silanol content and carbon depletion provided directions towards less aggressive plasma etch and strip process development. Infrared spectroscopy metrology was also utilized in surface functionalization evaluation of very thin organic films deposited by wet and dry chemistries. Palladium binding by surface amine groups was examined in plasma-polymerized amorphous hydrocarbon films and in self-assembled aminosilane thin films. Comparison of amine concentration under different deposition conditions guided effective process optimization. A time- and cost-effective method such as current FTIR metrology that provides in-depth chemical information about thin films, surfaces, interfaces and bulk layers can be increasingly valuable as critical dimensions continue to scale down and subtle process variances begin to have a significant impact on device performance.

The work described in this thesis was concerned with the synthesis and metathesis ring .opening polymerization of some fluorinated norbornenes and norbornadienes. The objectives of the work were to synthesise some new stereoregular fluoropolymers.This thesis is divided into five chapters. In the first chapter the background of the olefin metathesis reaction is reviewed. Chapter Two gives details of the synthesis of some fluorinated norbornenes and norbornadienes. The third chapter discusses the ring opening metathesis polymerization of a series of relatively simple monomers, and the characterization of the polymers produced, by (^13)C n.m.r. and infrared spectroscopy. In the fourth chapter the polymerization of a series of more complicated monomers is described. The final chapter details some of the physical properties of the polymers.

The aim of the project was to gain a better understanding of the factors that affect adhesion of fluoropolymers. This was achieved by employing various analytical techniques to the treated and untreated polymers. The effects of novel pretreatments, and established treatments, on Polytetrafluoroethylene, PTFE, Poly (vinyl fluoride), PVF, and poly (vinylidene fluoride) PVdF, were characterised using: adhesion tests, X-ray photoelectron spectroscopy (XPS), including derivatisation reactions, Fourier Transform Infrared (FTIR), contact angles and scanning electron microscopy (SEM) For untreated PVF and PTFE it was found that a certain degree of adhesion improvement was achievable without any chemical modification of the surfaces. This was observed when the substrates were repeatedly bonded. It is proposed that weakly cohesive material was present in the polymers and these acted as weak boundary layers when bonded. Removal of weak boundary layers alone was found to be insufficient to obtain high adhesion with PTFE. Surface functionality, increased wettabiIity and favourable topography all contributed to the high bond strengths observed with 'Tetra-Etch' treated PTFE. 'Tetra-Etch' treatment is used commercially on PTFE but prior to this programme was unreported on PVF and PVdF. The treatment was effective at promoting adhesion for PVF though at a much slower rate than for PTFE. Additional mechanisms to that for PTFE (Le. electron transfer) are proposed for the action of 'Tetra-Etch' on PVF. These are dehydrohalogenation through electron transfer and an elimination reaction. The same mechanisms are proposed for PV dF. Flame and low pressure plasma treatments were carried out on PVF and PTFE. Flame was found to be ineffective for PTFE but with PVF chemical modification (oxidation) occurred at the carbon/hydrogen sites. No defluorination was observed; this was in contrast to the mechanism of oxidation via plasmas on PVF, where defluorination, oxidation, ablation, and crosslinking may have all contributed to the high bond strength obtained. Certain plasma treatments were effective at improving the adhesion of PTFE but were slower and caused less modification. Removal of weak boundary layers was proposed as the major factor since oxidation was often slight. Reaction with solutions of potassium hydroxide (KOH), sodium hydroxide (NaOH) and lithium hydroxide (LiOH) were effective as adhesion pretreatments for PVF and PVdF but not for PTFE. For PVF and PVdF rates of reaction and chemical modification varied with time, temperature, molarity of solution and the nature of the solution i.e. aqueous or alcoholic. The greatest improvement in rate and effectiveness of the treatment for adhesion improvement was on the addition of a phase transfer catalyst to the aqueous solution. It was found for PVF that substantial surface oxidation could be achieved without improving the adhesion. It was suggested that oxidation occurred at sites present in a weakly cohesive layer. Mechanisms of the reactions were considered in terms of neucloephilic substitution and elimination; for PVF and PV dF both are likely. The mechanism of the phase transfer catalyst was investigated and found to be complex. It was found not to be simply a wetting agent but had inherent reactivity on its own. A combination of mechanisms was proposed.

The work herein covers the complete process for development, production and testing of a melt processable pyrotechnic composition, with the goal of using the composition as a printing material in a fused deposition modelling (FDM) type 3D printer. 3D printing is fast becoming an area of interest for energetic materials research. This is due to the role that geometry can play in combustion performance of a composition and 3D printing’s ability to produce a variety of complex designs. Melt processable fluoropolymers were selected as oxidisers. The polymers selected for the study were FK-800® and Dyneon 31508®. Both are co-polymers of vinylidene fluoride (VDF) and chlorotrifluoroethylene (CTFE). Aluminium was the choice fuel in this instance as it had better energetic performance than the alternatives investigated. It was also deemed to be a safer fuel when considering the combustion products. Hazardous combustion products like hydrofluoric and hydrochloric acid could be suppressed by increasing the fuel loading to 30 wt.%, thereby reducing the risks associated with burning the composition. Preliminary differential thermal analysis (DTA) analysis indicated that the compositions would only ignite above 400 °C which was well above the suggested processing temperature of 230 °C as determined from thermogravimetric (TGA) analysis. These thermal analysis techniques indicated that the reactions were most likely a gas-solid reactions due to ignition temperatures being significantly lower than those associated with phase changes occurring in the fuels tested, yet above the decomposition temperatures for the oxidisers. ii Extrusion of the compositions proceeded with addition of LFC-1® liquid fluoroelastomer. This addition was made in order to order to lower the melt viscosity, thereby improving the quality of the filament produced. Compositions were extruded with an aluminium loading of 30 wt.%. Oxidiser and LFC-1® made up the rest of the mass with the LFC-1® contributions being either 7 wt.% or 14 wt.%. Burn rates, temperatures and ignition delays were all influenced by the addition of LFC-1® to the system. FK-800® was found to be a better oxidiser in this instance since its burn rates were consistent especially when compared to erratic nature of the Dyneon 31508® burns. Linear burn rates for the FK-800® increased from 15.9 mm·s−1 to 18.9 mm·s−1 with the increase in LFC-1® loading. Combustion temperature also increased by approximately 180 °C from 794 °C. Printing with the material was achieved only after significant alterations were made to the hot end used. Printing proceeded in a staged, start-stop manner. After each new layer of material was deposited the printer was cleared of material and the hot end was allowed to cool. If this procedure was not followed it led to significant preheating of the material within the feeding section of the extruder. This premature heating caused feeding problems due to softening and swelling of the material within the cold side of the hot end which led to blockages, leading to the conclusion that the composition was not compatible with the off-the-shelf hot end used in this study. Low quality printing could be achieved with both FK-800® and Dyneon 31508® compositions. This would suggest that slight compositional changes paired with the alterations made to the hot end could improve the quality of the prints to an extent that would be comparable to that of more commonplace printing materials.
Dissertation (MEng)--University of Pretoria, 2017.
Chemical Engineering
MEng
Unrestricted

The contact lens is an undoubtedly important optical correction medium for many visual defects. Materials used in contact lens applications must exhibit specific properties which are determined by the physiological conditions of the eye. Polymethyl methacrylate became a popular hard lens material because of its toughness, excellent optical clarity, acceptable surface properties, and biocompatibility. Its rigidity and virtual impermeability to oxygen led to the development of alternative materials such as rigid gas permeable contact lenses of which fluoropolymers have long been considered as desirable materials. As an introduction to this thesis, the eye and its defects are discussed briefly with methods for their correction. A concise review of the property requirements of a contact lens precedes a detailed discussion of the history and development of contact lenses and their materials. Perfluoropolymers, well known for their extraordinary resistance to chemical and thermal attack, and low surface energy deterring deposition, have potential utility in ophthalmic applications due to their oxygen permeability and biocompatibility. Partially fluorinated hydrocarbon materials are also promising, among which are fluoroacrylates and fluoromethacrylates related to polymethyl methacrylate. A range of simple fluoroacrylates and fluoromethacrylates with increasing fluoroalkyl side chain length were synthesised alone and together with methyl methacrylate in various formulations to assess their structural-property relationship. Reaction kinetics were studied using differential scanning calorimetry to determine optimum polymerisation conditions, and gel permeation chromatography was used to evaluate reactivity ratios and hence the distribution of the different components throughout the polymer chain. As experienced with past and present contact lens materials, it became apparent that to acquire desired properties, for example high oxygen permeability, a compromise had to be made with other properties, for example low wettability. This problem has constantly plagued the experts working in this field, and looks as if it will continue to do so for some time. In conclusion, the polymers investigated were discovered to be only suitable as contact lens materials as components in formulations with other monomers providing the necessary balance of properties.

Fouling is a chronic problem in many heat transfer systems and results in the need for frequent heat exchanger (HEX) cleaning. In the dairy industry, the associated operating cost and environmental impact are substantial. Antifouling coatings are one mitigation option. In this work, the fouling behaviour of fluoropolymer, polypropylene and stainless steel heat transfer surfaces in processing raw milk and whey protein solution are studied. Methodologies to assess the economics of antifouling coatings are developed and applied. Two experimental apparatuses were designed and constructed to study fouling at surface temperatures around 90 °C. A microfluidic system with a 650 x 2000 µm flow channel enables fouling studies to be carried out by recirculating 2 l of raw milk. The apparatus operates in the laminar flow regime and the capability to probe the local composition of delicate fouling deposit $\textit{in-situ}$ with histological techniques employing confocal laser scanning microscopy. A larger bench-scale apparatus with a 10 x 42 mm flow channel was built to recirculate 17 l of solution in the turbulent flow regime which is more representative of conditions in an industrial plate HEX. Experimental results demonstrate that fluoropolymer coatings can reduce fouling masses from raw milk and whey protein solution by up to 50 %. Surface properties affect the structure and composition of the deposit. At the interface with apolar surfaces raw milk fouling layers are high in protein, whereas a strongly attached mineral-rich layer is present at the interface with steel. Whey protein deposits generated on apolar surfaces are more spongy and have a lower thermal conductivity and/or density than deposits on steel. The attraction of denatured protein towards apolar surfaces and the formation of a calcium phosphate layer on steel at later stages of fouling are explained with arguments based on the interfacial free energy of these materials in water. The financial attractiveness of coatings is considered for HEX subject to linearly and asymptotically increasing fouling resistance and using a spatially resolved fouling model. An explicit solution to the cleaning-scheduling problem is presented for the case of equal heat capacity flow rates in a counter-current HEX. Scenarios where the use of coatings may be attractive or where there is no financial benefit in cleaning a fouled exchanger are identified. Finally, experimental data are used to estimate the economic potential of fluoropolymer coated HEXs in the ultra-high-temperature treatment of milk. In the considered case, the value of a fluoropolymer coating inferred from the reduction in fouling is estimated to be around 2000 US$/m².

The objectives of this research project were to synthesize and investigate the chemistry of model compounds related to the hexafluoropropene/vinylidene fluoride copolymer system. A number of compounds of this type were prepared which underwent a series of reactions in order to obtain definitive information about the chemical processes occurring during the cross-linking of the copolymer system with bis-nucleophiles. Further studies with the model compounds also indicated potential sites in the cured copolymers through which chemical degradation could take place, during their use in aggressive environments. Other investigations with the model compounds, together with unsaturated compounds derived from these systems, led to the observation of some very unusual chemistry. Lewis acid induced dehydrofluorination reactions with antimony pentafluoride led to the formation of a number of observable carbocations and a unique contiguous dication. This methodology was further developed in the treatment of saturated homopolymers, in which dehydrohalogenation by antimony pentafluoride led to formation of polyacetylene derivatives displaying intense colouration. In order to circumvent the formation of potential sites of chemical instability during the curing process with nucleophiles, a methodology was investigated in which cross-linking could occur via a free radical mechanism involving hemolytic bond cleavage of sterically demanding groups. A number of monomers containing a bulky pendant group were prepared and were investigated in order to determine their suitability to undergo copolymerisation with vinylidene fluoride. Copolymers obtained in this way were then examined to determine whether polymer radicals could be produced by thermally induced hemolytic bond scission of sites involving the sterically crowded groups. The results obtained clearly demonstrated that this type of cross-linking process is entirely feasible.

This thesis focused on comparing various levels of a coagent (bismaleimide, BMI) within an unfilled fluoroelastomer (FKM) in both the cured and uncured states, and determining whether high levels of coagent could still produce an elastomer with acceptable mechanical properties. Further, to determine any links between morphology, cure chemistry/kinetics, and the mechanical properties of the material. Adding BMI as a coagent, even at higher than normal loadings, was shown to produce a material with acceptable mechanical properties (as per ASTM D2000). This conclusion is different to that drawn from literature, where it is suggested that materials with high levels of coagent are brittle and cannot form ‘useful’ products. In the uncured state, the BMI powder acts as a filler of low structure. In the cured state, the BMI coagent also acts as a filler, with SEM and EDX analysis demonstrating that any domains of coagent acting as a filler were below the resolution of the microscope, even though DSC analyses indicated that the two materials were immiscible. The effectiveness of the reinforcement using BMI as a coagent at high loadings has shown to be very high; potentially greater than that of some carbon blacks in other elastomers. With increasing levels of BMI coagent, it was also shown that the molecular weight between cross-links decreased. This occurs even though the elastomer chains can only be cross-linked at the chain ends. Therefore, it is proposed that the BMI is forming filler-like domains. However, these interact with the elastomer molecules, restricting chain mobility. Following progression of the cure process was possible using infrared analyses and by rheometer studies, with infra-red analysis shown not to be as reliable as utilising the rheometer. The cure reactions associated with increasing BMI content were non-linear with regards to Arrhenius plots. This demonstrates different competing reactions when curing the material.

Les polymères fluorés sont des macromolécules intéressantes qui, en raison de leurs propriétés uniques, sont souvent utilisées dans des applications spéciales dans les industries du bâtiment, de l'aérospatiale, du génie chimique, du traitement des textiles, optiques et de la microélectronique. Cette thèse se concentre sur le développement de polymères fluorés fonctionnels à base de phosphore et de silane par la co/terpolymérisation radicalaire conventionnelle de monomères fonctionnels avec le fluorure de vinylidène (VDF). Ces monomères fonctionnels ont été préparés à partir de la modification de l'acide 2- (trifluorométhyl) acrylique (MAF) pour préparer des MAF-ester avec le groupement fonctionnel souhaité. Tout d'abord, une étude fondamentale concernant la cinétique de polymérisation du VDF avec MAF-TBE a montré que ces paires de monomères ont une tendance à se propager de manière croisée, ce qui donne des copolymères alternés. On a ensuite préparé du MAF avec une fonction phosphonate (MAF-DMP) et sa copolymérisation avec du VDF a permis d'obtenir du PVDF à fonctionnalité phosphonate qui, après l'hydrolyse consécutive du groupe phosphonate en acide phosphonique, avait des propriétés anticorrosion sur l'acier. De façon similaire, un monomère de MAF porteur une fonction carbonate cyclique (MAF-cyCB) a également été copolymérisé avec du VDF. Les groupes carbonate cycliques dans le copolymère de PVDF obtenu ont ensuite été ouverts par 1'aminopropyltriéthoxysilane pour introduire un groupe silane, qui, par son hydrolyse, a permis au copolymère d'adhérer fortement sur les substrats. Enfin, un terpolymère à base de PVDF fonctionnel porteur à la fois un groupe phosphonate et un groupe triéthoxysilane a été préparé. Le groupe silane a ensuite été hydrolyse et réticulé pour obtenir un réseau 3D de polymères. Enfin, l'hydrolyse du groupe phosphonate en acide phosphonique a conduit à une matière pouvant être utilisée dans l'extraction des ions Eu (III) de l'eau
Fluorinated polymers are intresting macromolecules which due to their unique properties are often used in special applications in building industries, aerospace, chemical engineering, optics, textile treatment and microelectronics. This thesis focusses on the development of phosphorous and silane functional fluorinated polymers through the conventional radical co/terpolymerization of functional monomers with vinylidene difluoride (VDF). These functional monomers were prepared from the modification of 2-(Trifluoromethyl)acrylic acid (MAF) to prepare MAF-esters with the desired functional group. First a fundamental study regarding the kinetics of polymerization of VDF with MAF-TBE revealed that these monomer pair tends to cross propagate resulting in an alternating copolymer. Phosphonate functional MAF (MAF-DMP) was then prepared and its copolymerization with VDF led to phophonate functional PVDF, that after the consequent hydrolysis of the phosphonate group into phosphonic acid showed anticorrosion properties to steel. Following the same concept, a cyclic carbonate functional MAF monomer (MAF-cyCB) was also copolymerized with VDF. The cyclic carbonate groups in the obtained PVDF copolymer was then opened by aminopropyltriethoxysilane to introduce a silane group, that by its hydrolysis allowed the copolymer to adhere strongly onto substrates. Finally, a terpolymer based on PVDF functional with both a phosphonate and a triethoxysilane group is prepared. The silane group was then hydrolyzed and crosslinked to obtain a 3D network of polymers. Finally, the hydrolysis of the phosphonate group into phosphonic acid led to material that can be employed in Eu(III) ion extraction from water

This thesis describes research on the effects of using carbon nanotubes (CNTs) and fluoropolymer based interlayers on the performance of organic devices. Photoelectron spectroscopy showed that the insertion of acid oxidised CNTs can improve the work function of indium-tin-oxide transparent electrodes. No significant changes of the HOMO level of triphenyldiamine (TPD) indicated that the equilibrium condition was met at the interfaces. Device I-V characteristic indicated that high density of trap levels had been introduced throughout the triphenyldiamine layer. This hypothesis is supported by Atomic Force Microscopy (AFM) and by high contrast current mapping using conductive AFM measurements. The broadening and featureless spectrum for the modified triphenyldiamine provides further confirmation. The high density of traps in TPD results in a high current density with lower luminance in the organic) light-emitting diode (OLED) device due to the imbalance of charge injection from positive and negative electrodes. The insertion of CNTs into polymer LEDs shows that the direct contact between the nanotube with the electroluminescencing polymer could induce significant quenching effect of the photoluminescence at the interface. However, the insertion of a hole-transport interlayer which also acts as an electron-blocking layer between the CNT and the polymer can reduce the quenching effect by shifting the recombination zone away from the anode/CNT interface. The effects of insertion of a polytetrafluoroethylene (PTFE) interlayer deposited via thermal evaporation in OLED and organic photovoltaic (OPV) devices are studied. The PTFE interlayer can improve the work function of PEDOT:PSS and reducing the electrochemical process in-between the PEDOT:PSS/polyfluorene. A remarkable improvement on the device lifetime and colour purity are found by incorporating PTFE to prevent the de-doping of the PEDOT:PSS. In the OPV devices, the PTFE and ultraviolet (UV) treated PTFE buffer layers at the anode/organic interface can improve the short-circuit current, open-circuit voltage and power conversion efficiency due to the reduction of the hole extraction barrier.

This research project investigates a new technique to efficiently mix crystalline solid additives with polymers by gentle ball milling with steel balls in the presence of carbon dioxide (C02) at 17 to 30°C and 1300 to 2500 psig. As the ball milling system is agitated, the steel balls transfer mechanical energy to the fluoropolymer and additive thereby converting them to powders. C02 is added into the chamber to expand the polymer and make it amenable to impregnation by the additive. At the end of the mixing process, a free flowing powder is produced consisting of the additive coated with fluoropolymer. The additives were extracted from the powders and intrinsic viscosity measurements were done on the remnant fluoropolymer. Viscosity studies showed that the virgin and post-ball milled fluoropolymers had similar intrinsic viscosities, hence similar molecular weights within experimental error limits. This implies that most of the polymer chains were simply disentangled during the mixing process and not broken. Differential Scanning Calorimetry (DSC) and Thermal Gravimetric Analysis (TGA) were done on the virgin polymer, the additives and the fabricated powders to determine the loading levels and to ascertain if there were any changes to the physical properties of the polymer. Scanning electron micrographs showed that some of the powder particles had additive particles stuck on the surface, but when these additives were washed off the surface of the powders with a suitable solvent that did not dissolve the polymer, DSC analysis showed the presence of additive incorporated into the polymer matrix.

This thesis describes studies directed to the ring opening metathesis polymerisation (ROMP) of some fluorinated compounds using a range of well-defined initiators. Chapter 1 reviews some general aspects of olefin metathesis and ring opening metathesis polymerisation of relevance to the work described in this thesis. Topics such as piezo- and pyro-electricity and optical and electrical properties of conjugated polymers are introduced and these receive more detailed attention later in the thesis. Chapter 2 describes the synthesis, characterisation and properties of . poly(bis(trifluororaethyl)norbomadiene) in detail. The use of various initiating systems that have been used previously and the effect they have on the tacticity of the resulting polymer raicrostructure are discussed. The latter part of this chapter reviews some of the current thinking concerning the detailed mechanistic aspects of this polymerisation. Chapter 3 reviews attempts directed to an improvement in tacticity control in the synthesis of poly(bis(trifluoromethyl)norbomadiene). The synthesis and activity of the new well-defined initiators used in these studies are reported. It is shown that varying the nature of the ancillary Ligands surrounding the metal centre can have a dramatic influence on the tacticity of the resulting polymer. Chapter 4 reports studies directed to an examination of the limits of the well controlled synthesis of poly(bis(trifluoromethyl)norbornadiene). The syntheses of high trans and high cis, highly tactic poly(bis(trifluoromethyl)norbornadiene samples using well-defined initiating systems are described. It is shown that by varying the monomerinitiator ratio, samples with a wide range of molecular weights can be achieved and these are reported. Chapter 5 describes experiments concerning the ROMP of fluorinated monomers containing six membered rings. In particular ROMP studies of the monomers, 2,3-bis(trifluoromethyl)bicyclo[2.2.2]octa-2,5-diene . and 2,3- (tetrafluorobenzo)bicyclo[2.2.2]octatriene are described finally, Chapter 6 provides a summary of the work reported and outlines some ideas for future studies.

Cette thèse s'inscrit dans le cadre d'un projet de l'Agence National de Recherche (ANR) dans lequel participent deux sociétés et deux laboratoires universitaires. L'objectif de ce projet consiste à améliorer les propriétés mécaniques (résistance à l'abrasion) et thermiques (température de dégradation) de revêtements fluorés antiadhésifs en y intégrant des nanoparticules de silice. Or, la silice est une charge hydrophile qui se disperse difficilement dans une matrice fluorée. C'est pourquoi nous avons envisagé de modifier sa surface avec des réactifs fluorés, et la nature des divers précurseurs a une influence sur l'amélioration de la dispersion des nanoparticules. Ainsi, nous avons, dans un premier chapitre, étudié la miscibilité et la compatibilité des polymères fluorés entre eux. Les polymères fluorés sont réputés pour leur inertie chimique, hydrophobie et leurs propriétés thermiques très avantageuses. Mais les très bonnes propriétés des polymères fluorés entraînant parfois des difficultés de mise en œuvre, nous avons choisi de travailler avec deux copolymères fluorés, le poly(TFE-co-HFP), un copolymère statistique à base de tétrafluoroéthylène (TFE, -CF2-CF2-) et d'hexafluoropropène (HFP, -CF(CF3)-CF2-) voisin du PTFE utilisé pour les revêtements, et le poly(VDF-co-HFP), un copolymère composé de fluorure de vinylidène (VDF, -CH2-CF2) et d'hexafluoropropène. Ils présentent de bonnes propriétés et sont faciles à employer à l'état fondu de par leurs faibles températures de fusion (respectivement de 140 et 275°C pour le poly(VDF-co-HFP) et le poly(TFE-co-HFP)). Des mélanges binaires à l'état fondu ont été réalisés puis caractérisés entre ces deux copolymères semi-cristallins mais également avec un polyéther fluoré, composé de plusieurs unités d'oxyde d'hexafluoropropène (HFPO, -CF(CF3)CF2O-) totalement amorphe. Les résultats obtenus suite à ces mélanges ont indiqué les trois types de précurseurs fluorés à employer lors des modifications de surface et ce en fonction de la matrice fluorée : composés à base de TFE (-CF2-CF2-), de VDF (-CH2-CF2-) et de l'HFPO (-CF(CF3)CF2O-). Ainsi, le second chapitre est consacré aux stratégies de synthèse de ces précurseurs fluorés contenant des motifs VDF et HFPO. Deux méthodes de polymérisation ont été réalisées : 1) La polymérisation radicalaire par transfert d'iode (ITP) du VDF conduisant à CnF2n+1-[CH2-CF2]m-I ; 2) La polymérisation anionique par ouverture de cycle de l'HFPO permettant la synthèse C3F7O-[CF(CF3)CF2O]-CF(CF3)-COX avec X : groupements fonctionnels. Ces produits ont été caractérisés par spectroscopies RMN du 19F et du 1H, IR, GPC, DRX, ATG et DSC. Les oligomères du TFE (CnF2n+1-I ou CnF2n+1-C2H4-SH avec n= 4 ou 6) n'ont pas été préparés du fait des risques encourus lors de la manipulation du TFE (gaz explosif). Après leurs synthèses, fonctionnalisations et caractérisations, nous les avons greffés à la surface de silices submicroniques. La principale méthode de greffage employé est le « grafting onto » qui permet de modifier la surface des particules inorganiques avec des macromolécules (oligomères ou polymères) et le troisième chapitre présente trois méthodes de greffage : 1) L'addition radicalaire de RFI ou RFC2H4SH sur une double liaison (vinylique ou allylique) ; 2) La condensation d'un oligomère à base d'HFPO fonctionnalisé ester méthylique sur une silice possédant des fonctions amine ; 3) La méthode la plus communément, utilisée l'hydrolyse-condensation, à partir d'oligo(HFPO) fonctionnalisés alkoxysilane. Les méthodes d'analyses employées afin de caractériser ces nanohybrides fluorés sont les spectroscopies RMN 1H et 29Si à l'état solide, IR, les analyses élémentaires et thermogravimétriques. Nous avons utilisé ces différentes stratégie de modifications de surface afin d'obtenir une large gamme de silices modifiées avec des groupements fluorés tout en tenant compte de la miscibilité des chaînes fluorées entre elles (Chapitre 1)
This thesis is part of a project of the National Research Agency (ANR) which involved two companies and two university laboratories. The objective of this project is to improve the mechanical properties (abrasion resistance) and thermal (degradation temperature) nonstick fluorinated coatings by incorporating silica nanoparticles. However, silica is a hydrophilic filler which is hardly dispersed in a fluoridated matrix. Therefore, we planned to modify its surface with fluorinated reagents, and the nature of various precursors has an influence on improving the nanoparticles dispersion. Thus, we, as a first chapter, studied the miscibility and compatibility of the fluoropolymers. Fluoropolymers are known for their very attractive properties like chemical inertness, hydrophobicity and thermal. But these very good properties of fluoropolymers sometimes cause difficulties application, we chose to work with two fluorinated copolymers, poly (TFE-co-HFP), a copolymer based on tetrafluoroethylene (TFE,-CF2-CF2-) and hexafluoropropylene (HFP,-CF(CF3)-CF2-) neighbor of PTFE used for coatings, and poly (VDF-co-HFP), a copolymer composed of vinylidene fluoride (VDF, -CH2-CF2) and hexafluoropropylene. They have good properties and are easy to use in blend due to their low melting temperatures (140 and 275° C for poly (VDF-co-HFP) and poly (TFE-co-HFP), respectively). Blends have been realized and characterized between two semi-crystalline copolymers but also with a fluorinated polyether composed of several units of hexafluoropropylene oxide (HFPO,-CF(CF3)CF2O-) which is completely amorphous. The results obtained from these blends indicated that the three types of precursors can be used for fluorinated surface modifications and in function of the fluoropolymer : compounds are based on TFE (-CF2-CF2-), VDF (-CH2-CF2-) and HFPO (-CF(CF3)CF2O-). Thus, in the second chapter, the synthesis of these fluorinated precursors containing VDF and HFPO units are shown for this, two polymerization methods were carried out : 1) The iodine transfer polymerization (ITP) of VDF ; 2) The anionic polymerization by ring opening of HFPO. These products were characterized by 19F and 1H NMR spectroscopy, FTIR, GPC, XRD, TGA and DSC. Oligomers of the TFE (CnF2n+1-I or CnF2n+1-C2H4-SH with n = 4 or 6) have not been prepared because of the risks incurred during the handling of TFE (explosive gas). After their synthesis, functionalization and characterization, we have grafted them on the surface of silica nanoparticles. The main method used is the "grafting onto" which allows to modify the surface of inorganic particles with macromolecules (oligomers or polymers) and the third chapter presents three methods of grafting : 1) The radical addition of RFI and/or RFC2H4SH on a double bond (vinyl or allyl) ; 2) The condensation of an oligomer based HFPO functionalized methyl ester on a silica with amine functions ; 3) The most commonly used hydrolysis-condensation, using oligo (HFPO) functionalized alkoxysilane. The analysis methods used to characterize these fluorinated nanohybrids are the 1H and 29Si solid state NMR, FTIR, elemental and thermogravimetric analysis. We used these different surface modification to obtain a wide range of modified silica with fluorinated groups. After their characterization, these fluorinated silica are introduced by blend into two fluorinated matrices poly (VDF-co-HFP) and poly (TFE-co-HFP). The fourth is dedicated to the study of nanocomposite poly (VDF-co-HFP) / silica. Initially, a state of the art is presented as this type of composite has been widely discussed in the literature contrary to nanocomposites poly (VDF-co-HFP) or poly (TFE-co-HFP) with fluorinated nanoparticles

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2007.
Includes bibliographical references.
Initiated chemical vapor deposition (iCVD) is a one-step, soventless process that can be used to produce polymeric thin films. The iCVD technique has been used to polymerize a wide variety of vinyl monomers such as glycidyl methacrylate (adhesive) and 2-hydroxyethyl methacrylate (hydrophilic). The proposed polymerization mechanism is the classical free radical polymerization mechanism of vinyl monomers. Monomer and initiator gases are fed into a vacuum chamber where resistively heated wires are used to thermally decompose the initiator molecules into free radicals. The free radicals then attack the vinyl bonds of the monomer molecules. Propagation occurs on the surface of a cooled substrate. This thesis presents an in-depth mechanistic study of the iCVD deposition of low surface energy poly(1H,1H,2H,2H-perfluorodecyl acrylate) (PPFDA) thin films. PPFDA films have many uses due to their hydrophobic and oleophobic properties. Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy of the iCVD PPFDA films showed complete retention of the fluorine moieties. Deposition rates as high as 375 nm/min were achieved. It was found that the deposition rate and molecular weight increases with decreasing substrate temperature and increasing monomer partial pressure.
(cont.) Quartz crystal microbalance measurements showed that these effects correlated with an increased monomer concentration at the surface. Dimensionless analysis was used to scale up this iCVD polymerization to a custom modified roll-to-roll reactor. The roll-to-roll process allows for the fast production of realistic size samples. The use of liquid solvents in membrane coating processes often creates a blanket coating in which the pores are clogged due to surface tension problems and wettability. These problems do not exist for solventless processes such as iCVD. This thesis presents the use of the iCVD technique to functionalize electrospun fiber mats and polymeric capillary pore membranes in order to make water-repellent, self-cleaning membranes. X-ray photoelectron microscopy data confirmed the presence of the PPFDA coating on the topside and the backside of the membranes and electron microprobe analysis confirmed the presence of the coating along the pore wall. It was found that the iCVD process can be used to functionalize membranes with very high aspect ratio (-80:1) pores.
by Malancha Gupta.
Ph.D.

The effect of processing on the properties of three transfer moulding grades of perfluoroalkoxy was investigated. There is anecdotal evidence to suggest exposure to high shear rates and residence time at processing temperature detrimentally affect the polymer, however there is a lack of information published in this area. This work set out to provide a better understanding of the material behaviour under various processing conditions. A bespoke capillary rheometer was used to determine flow characteristics at various temperatures between 5-400s-1. The materials were found to be shear thinning, with the virgin grades exhibiting Newtonian behaviour at low shear rates. The viscosity of the carbon black filled PFA was found to have a higher viscosity than the virgin materials, despite it having a higher Melt Flow Rate. Spectroscopy was found to be unsuitable for investigation of polymer containing carbon black due to laser heating. However changes due to residence time at processing temperature in the virgin material could be detected using statistical analysis of Near Infrared spectra. Whether the mechanical properties of the virgin material changed following exposure to high shear rates or residence time varied on manufacturer, with Dyneon 6502TZ appearing to be more process stable than Chemours 350TJ. This information can be used to optimise the transfer moulding process, and assist in meeting the requirements of the Chemical Processing Industry for larger and more complex lined piping components.
Innovate UK and CRP Ltd

The polymer bonded explosive TCV is analogous to PBX compositions used in some nuclear weapons where the PBX will be exposed to high energy ionising gamma radiation. It is therefore important to study how gamma radiation affects the mechanical and chemical properties of the PBX. In this study 60Co was used to irradiate samples of the TCV, its FK-800 binder and TATB explosive filler, at 37.5 °C, to total doses up to 200 kGy in air and under vacuum. Post irradiation analysis consisted of mechanical, thermal and chemical analysis of the irradiated materials. Results from the radiolysis of the FK-800 showed predominant main chain scission taking place, these results in the release of volatile fluorine containing products and an increase in the polymer’s crystallinity. The changes to the FK-800’s structural properties result in an increase in Young’s modulus and yield stress whilst reducing both ultimate tensile strength and elongation at maximum stress. Dynamic mechanical analysis shows the material softening initially upon irradiation, then stiffening as crystallinity increased. TATB was found to turn green and have increased sensitiveness to impact and electric spark discharge with gamma radiation. Analysis by HPLC and LC-MS identified a decomposition product with a mass of 240 g mol-1. No significant changes to the mechanical properties of TCV were identified; however, its sensitiveness to impact and electric spark discharge were found to increase similar to TATB’s. In conclusion, gamma irradiation of TCV has identified significant changes to the mechanical and chemical properties of the FK-800 binder, have little to no effect on mechanical properties of PBX up to 100 kGy. The predominant radiolytic effects on TCV were to its hazard characteristics caused by changes in the TATB. A mono-furazan derivative of TATB has been suggested as the decomposition product identified, and as a possible cause for the increase in sensitiveness of TATB upon gamma irradiation.

Scratch recovery is a desirable property of many polymer systems. The reason why some materials have demonstrated excellent scratch recovery while others do not has been a mystery. Explaining the scratch resistance based upon the hardness of a material or its crosslink density is incorrect. In this thesis, novel polymers were tested in an attempt to discover materials that show excellent scratch recovery - one of the most important parameters in determining the wear of a material. Several hypotheses were developed in an attempt to give an accurate picture of how the chemical structure of a polymer affects its scratch recovery. The results show that high scratch recovery is a complex phenomenon not solely dependent upon the presence of electronegative atoms such as fluorine.

Cette these decrit les effets de la fonctionnalisation de thiophenes en position 3 par des groupements fluoroalkoxy et fluoro sur les proprietes electriques et electrochimiques des polymeres resultants. Les 3-fluoroalkoxythiophenes sont obtenus par la reaction de substitution nucleophile aromatique catalysee par le cuivre. Le 3-fluorothiophene est obtenu par une reaction de transhalogenation sur thiophenique active par un groupement nitrile. Les poly(3-fluoroalkoxythiophenes) presentent des proprietes interessantes telles que : la solubilite dans les solvants organiques, la stabilite sous cyclage et une conductivite satisfaisante. La synthese et l'electropolymerisation du 3-fluorothiophene montre que l'halogene affecte le potentiel d'oxydation des 3-halogenothiophenes par son effet electronique ; et que le potentiel d'oxydation des polymeres est a la fois controle par son effet electronique et sterique. La preparation et la caracterisation de composites conducteurs a base de p. V. D. F. Et de poly(thiophene), poly(3-methylthiophene) et de poly(3-octylthiophene) sont decrits

Cette thèse décrit le développement d'une plateforme d'amplification d'ADN dans des microgouttes transportées par une huile fluorée. Dans la première partie du projet nous avons mis au point des protocoles pour la production des puces microfluidiques en utilisant un nouveau matériau (Dyneon THV). Ce polymère fluoré est très hydrophobe, transparent et présente une température de fusion faible. Ces puces sont adaptées au transport de gouttes d'eau dans les huiles fluorées, ainsi qu'à la manipulation des solvants organiques et à la détection par fluorescence. Nous avons ensuite couplé ces puces avec un système pour la production des gouttes à partir des réactifs stockés dans une plaque microtitre. Cette approche permet d'utiliser un système de chauffage planaire, plus adapté pour la détection en temps réel. Ce système nous a permis de valider l'amplification par PCR dans des gouttes de 60 nanolitres, et représente une première étape vers la réalisation d'une plateforme automatisée

Thesis (Ph. D.)--University of North Carolina at Chapel Hill, 2006.
Title from electronic title page (viewed Oct. 10, 2007). "... in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Chemistry." Discipline: Chemistry; Department/School: Chemistry.

Piezotech, une start-up rachetée en 2010 par le leader français de la chimie, Arkema, développe et commercialise des copolymères fluorés électroactifs (EAPs). Ces copolymères présentent un grand intérêt pour des applications dans l’électronique imprimée, les capteurs, les actionneurs, les muscles artificiels, et le stockage de l’énergie. Les copolymères à base de fluorure de vinylidène (VDF) et de trifluoroéthylène (TrFE) possèdent les meilleures propriétés piézoélectriques et ferroélectriques (FE) parmi les polymères existants. L’introduction d’un termonomère, tel que le 1,1-chlorotrifluoroéthylène (CFE) ou le chlorotrifluoroéthylène (CTFE), modifie la conformation de la chaine polymère et change le comportement du matériau en relaxeur ferroélectrique (RFE). Le travail de thèse s’inscrit dans la recherche de nouveaux EAPs fluorés et la compréhension des relations structure-propriétés de ces matériaux. Après l’étude de la cinétique de copolymérisation avec le VDF et le TrFE de différents termonomères porteurs de groupements CF3, les terpolymérisations ont été examinées. Dans une première partie, le trans-1,3,3,3-tetrafluoropropène (1234ze), un termonomer qui n’homopolymérise pas, a été étudié. Des terpolymères de composition homogène ont été synthétisés. Ensuite, le 3,3,3-trifluoropropène (TFP) et le 2,3,3,3-tetrafluoropropène (1234yf) ont été terpolymérisés avec le VDF et le TrFE. Bien que les terpolymérisations batch amènent à une forte dérive de composition, un procédé de polymérisation en suspension en semi-continu a permis d’obtenir une meilleure homogénéité. Les propriétés thermiques et électroactives de tous les terpolymères ont été caractérisées. Dans une dernière partie, l’introduction d'une faible quantité d’un monomère fonctionnel (2-(trifluorométhyl) acide acrylique, MAF), dans les chaines du copolymère poly(VDF-co-TrFE), a permis une amélioration des propriétés d’adhésion sur le verre et le métal sans altérer les propriétés électroactives. L’étude des terpolymérisations avec le VDF, le TrFE et un termonomère porteur d’un groupement CF3 a contribué l’amélioration de la compréhension des relations structure-propriété dans les EAPs fluorés. En particulier, il a été montré que la réduction de la taille des cristaux n’est pas une condition suffisante pour obtenir un caractère RFE
Piezotech, a start-up acquired in 2010 by the French leader in Chemistry, Arkema, develops and commercializes fluorinated electroactive copolymers (EAPs). These copolymers arouse a significant interest in printed electronics, printed memories, sensors, actuators, artificial muscles, and energy storage devices. Vinylidene fluoride (VDF) and trifluoroethylene (TrFE) -based copolymers are the polymers exhibiting the highest piezoelectric and ferroelectric (FE) properties. The introduction of a third slightly bulkier termonomer such as 1,1-chlorofluoroethylene (CFE) or chlorotrifluoroethylene (CTFE) was shown to modify the polymer chain conformation and change their electroactive behaviors into those of relaxor ferroelectric (RFE) materials. This PhD work aimed to discover new fluorinated EAPs and to better understand their structure-properties relationships. After the study of the kinetics of copolymerization of various CF3-bearing termonomers with VDF and TrFE; the terpolymerizations were investigated. First trans-1,3,3,3-tetrafluoropropene (1234ze), a non-homopolymerizable termonomer, was studied. Terpolymers with homogeneous compositions were synthesized. Then, 3,3,3-trifluoropropene (TFP) and 2,3,3,3-tetrafluoropropene (1234yf) were terpolymerized with VDF and TrFE. Although batch terpolymerizations resulted in terpolymers with strong compositional drift, the semi-continuous suspension process afforded better homogeneity. The thermal and electroactive properties of all the terpolymers were characterized. Finally, the introduction into poly(VDF-co-TrFE) copolymer chains of small amounts of a functional monomer (2-(trifluoromethyl)acrylic acid, MAF) allowed an increase of the adhesion properties onto glass and metal substrates without altering the electroactive properties. The study of the terpolymerizations of VDF, TrFE and a CF3-bearing termonomer contributed to a better understanding of the structure-properties relationships in fluorinated EAPs. Notably, the reduction of the crystal size was shown to be insufficient to afford RFE properties

Fluoropolymers are a versatile and attractive group of compounds having an interesting mix of properties that make them highly useful for various applications. Because of strong bonding between the carbon and fluorine atom, they exhibit unique physical and chemical properties such as high thermal stability, increased chemical resistance, low refractive index, enhanced inertness towards many solvents and hydro-compounds. These characteristics have led them to be widely used in aerospace, aeronautics, optics, microelectronics, paints and coatings, and engineering structures and as biomaterials. Amphiphilic copolymers possess unique solution and solid-state properties due to their well-defined molecular architecture. These properties arise as the result of covalently combining two thermodynamically different polymer blocks that phase separate on the nanoscale. Amphiphilic copolymers based on a fluoro-monomer will combine the favourable physiochemical properties of the desired fluorine segment in combination with complementary hydrophilic segments. Such fluorinated amphiphilic copolymers are potentially useful for drug delivery vehicles and membrane applications. This project is aimed at making fluorinated amphiphilic block copolymers of hydrophobic 2, 3, 4, 5, 6 –pentafluorostyrene (PFS) and hydrophilic methacrylic acid (MAA). A controlled radical polymerization mechanism, nitroxide mediated polymerization (NMP) using NHS-BlocBuilder as the initiator was employed. The advantage of using NMP is that it facilitates the synthesis of copolymers with well-controlled narrow molecular weight distribution. However, methacrylate homopolymerization by NMP is challenging due to the high dissociation equilibrium constant therefore, the use of PFS as a controlling comonomer was explored. We established that to obtain a controlled copolymerization, a minimum of 70 mol% PFS was required, which is significantly greater than other copolymerization systems such as using as little as 4.5-8 mol% styrene to control the copolymerization of MAA. We surmise that this lack of control is due to the unfavourable reactivity ratios (Appendix I) which favour the addition of MAA rather than PFS (rPFS = 0.012, rMAA = 8.12). However, these unique reactivity ratios suggest that a semi-batch approach can be utilized to synthesize almost pure block copolymers in one pot. Therefore, poly(PFS)–b-(PFS-ran-MAA) block copolymers were synthesized and characterized by a semi batch addition of MAA. While successful, the concentration of irreversibly terminated chains was evident and greater care in reducing these unwanted reactions needs to be addressed.

Le couplage transport-réaction est l'une des voies possibles pour accroître la per sélectivité d'une membrane ionique vis-à-vis d'espèces non ioniques. L'objet de cette étude est de mettre en évidence et de modéliser le transport facilité du Zwitterion S de deux acides aminés à travers une membrane perfluorosulfonique sous forme acide. L'accent a été mis sur les phénomènes de polarisation. Dans ce but, nous avons expérimenté un système membranaire ou une fibre creuse Nafion 811x est placée au centre d'un dispositif à symétrie cylindrique. Ce montage est particulièrement adapté au contrôle des conditions hydrodynamiques. Ses performances sont comparées à celui constitué par une membrane plane au contact de deux solutions agitées. Nous présentons tout d'abord les relations qui sont à la base du modèle et identifions les paramètres a caractériser. Ceux-ci sont déterminés par partages entre phase externe et membrane sous différentes formes ioniques, puis par diffusion passive, diffusion de traces et auto diffusion. Ces différentes données nous ont permis de prévoir quantitativement le transport facilite de l'alpha alanine dont le coefficient apparent de protonation est constant. Une étude complémentaire, effectuée sur la phénylalanine, nous suggère d'élargir le modèle au cas de réactions où les coefficients apparents du produit formé varient suivant une loi de type Harned

L'alternance de deux groupes de polarités très différentes, CH2 et CF2, permet au poly fluorure de vinylidène (PVDF) d’être un polymère industriellement très intéressant. Cependant, cette spécificité mène aussi à d’importantes inversions du monomère lors de la polymérisation vinylique. Pendant la polymérisation, en complément de la propagation tête-queue, CH2CF2CH2CF2, les monomères inversés conduisent à l’addition en queue-queue, CF2CH2CH2CF2, et tête-tête, CH2CF2CF2CH2. Le taux de transformation de polymère se trouve expérimentalement entre 3 et 7%. Ce pourcentage élevé entraine sans aucun doute la modification de propriétés macroscopiques. En utilisant la dynamique moléculaire, cette thèse a pour but de montrer l'effet de ces défauts sur la température de transition vitreuse (Tg), la dynamique locale et sur la température de fusion (Tm) du PVDF. En phase amorphe, le PVDF avec différents pourcentages de régio-défauts a été étudié : 3.6, 4.1, 9.3 et 23%. Cette étude permet de prédire le comportement de polymères qui ne sont pas synthétisés. Étant donné que les Tg simulées et expérimentales concordent avec précision, les motifs moléculaires qui donnent lieu à l'effet plastifiant de l'inversion de monomères peuvent être envisagés. En plus d'accentuer leur effet de plastifiant, la conclusion significative est que la relaxation de la chaîne peut être révélée en abordant explicitement des mouvements locaux. Car cette procédure ne peut pas être déduite de la connaissance du Tg, nous avons basé notre analyse sur le fait cela : 1) Nous avons démontré que des relations linéaires directes entre Tg et l'énergie d'activation conformationnelle de transition (Ea) extraite à partir d'un graphe d'Arrhenius, existent. Ce diagramme correspond au logarithme naturel des taux de transition entre les états rotameriques contre l'inverse de la température. La pente de cette courbe rapporte directement à cet Ea efficace. Un tel lien a été seulement spéculé dans la littérature. 2) Nous avons calculé des relations d'Arrhenius pour différents genres de torsions le long de la chaîne d'épine dorsale. En conséquence, une barrière d'énergie potentielle, ea, est associée à la rotation d'un lien dans un environnement spécifique. L'addition de ces énergies pesées par le pourcentage de chaque lien le long de l'épine dorsale, donne un ea moyen qui est équivalent à l'ea efficace. À l'aide de cette procédure, nous avons maintenant accès au mouvement local de la chaîne entière. 3) Nous avons vérifié cette procédure pour calculer une valeur pour le Tg du copolymère alternatif du l'éthylène-tétrafluoroéthylène (E-TFE), qui possède les segments qui sont présents le PVDF changé. L'ambiguïté concernant la valeur de la Tg du copolymère E_TFE peut être résolue grâce à cette approche, puisque le PVDF avec 50% de défauts régio-isomériques conduit à l'E_TFE. D'ailleurs, nous avons étudié les temps de relaxation pour la fonction d'autocorrélation de torsion au-dessus d'un large éventail de température. La dynamique locale est alors spécifiquement étudiée. L'équation Vogel-Fulcher-Tammann (VFT) est utilisée pour décrire le processus de relaxation associée aux mouvements coopératifs des segments le long de la chaîne. Nous avons également étudié le possibilité d'utiliser le Kohlrausch-Williams-Watts (KWW), fonction exponentielle étirée, afin de décrire la dépendance temporelle du processus de relaxation, ce travail a été effectué à différentes températures. Les résultats concordent bien avec les données expérimentales. L'objectif principal de cette section est d'étudier conjointement la fréquence des transitions conformationnelles et le temps de relaxation obtenu par la fonction d’autocorrelation de torsion, sur une plage importante de température, afin d’établir un entre les fréquences des transitions conformationnelles et le comportement de type VFT. Nous montrons pour la première fois qu’une relation linéaire peut être établie entre la barrière de transition conformationnelle et l’énergie d’activation effective. Nous montrons pour la première fois qu'une relation linéaire peut être établie entre la barrière de transition conformationnelle, Ea et l'énergie d'activation effective, B, responsables de la dynamique locale. Parmi les cinq phases cristallines que présente le PVDF, les cristaux α et ß présentent des propriétés particulières intéressantes et ont fait l'objet d'une attention significative. Ces deux structures cristallines sont celles que l’on rencontre le plus souvent, la phase α est la plus thermodynamiquement stable le cristal β possède des propriétés ferroélectriques. Toutefois, le comportement lors de la fusion de ces deux phases cristallines n’est pas encore totalement compris. Certains chercheurs pensent que la température de fusion de la phase β est supérieure à la phase alpha . D'autres affirment que le pic endothermique vu sur le thermogramme obtenue par calorimétrie différentielle à balayage (DSC) a été attribué par erreur à la phase β, cela à cause d’une confusion dans les références . À cet égard, le comportement de la Tm des cristaux α et β par rapport à leur épaisseur est obtenu par la dynamique moléculaire. Différents types de nanocristaux composés de chaînes de PVDF, sans ou avec 10% de régio-défauts, ayant des longueurs différentes ont ainsi été simulées dans les phases α et β. On applique l'équation de Gibbs-Thomson (G-T) afin de déterminer l'énergie de surface et l’enthalpie de fusion des nanocristaux. Les valeurs déterminées sont en accord avec les données expérimentales. Nous avons montré que le PVDF en phase β pur a une température de fusion inférieure à celle du PVDF en phase α pur. Cependant, en insérant des défauts à l'intérieur du cristal, la phase α modifiée présente une température de fusion inférieure à celle de la phase β modifiée.
Abstract : Alternating two groups, CH2 and CF2, of very different polarities along the backbone chain of polyvinylidene fluoride (PVDF) leads to very interesting properties, such as ferroelectricity. However, these properties are affected by the presence of regioisomerism defects (monomer inversion) that appear during the synthesis. During the polymerization, in addition to the Head-to-Tail (HT) sequences, CH2CF2CH2CF2, the reversed monomer units lead to formation of Tail-to-Tail (TT), CF2CH2CH2CF2, and Head-to-Head (HH), CH2CF2CF2CH2, links. The rate of this chain alteration experimentally lies between 3 and 7 %. This percentage undoubtedly brings changes in macroscopic properties. The aim of this thesis is to reveal the impact of these defects on the glass transition temperature (Tg), local dynamics and melting temperature (Tm) of PVDF by using Molecular Dynamics (MD) simulation. In amorphous phase, PVDF chains with different percentages of regiodefects were investigated: 0, 3.6, 4.1, 9.3, and 23 %. This study makes it possible to predict the experimental behavior of polymers which have not yet been synthesized. Once Tg is acquired, the relaxation of the chain can be investigated through the calculation of the activation energy (Ea) of the conformational transition. The significant conclusion is that the relaxation of the chain can be revealed by addressing the local motions. More specifically: a) We demonstrate a direct linear relationship between Tg and Ea extracted from an Arrhenius plot. This diagram corresponds to the natural logarithm of transition rates between rotameric states versus the inverse of the temperature. The slope of this curve yields directly Ea. Such a link was only speculated in the literature. b) A significant finding of this work is that the mobility of the chain can be associated with different types of bonds in PVDF with regiodefects. c) Based on the analysis of Ea for the different bond contributions, we proposed a value for the Tg of ethylene-tetrafluoroethylene (E-TFE), an isomeric polymer of PVDF with 50% regiodefects. Experimentally, the available data for the Tg of E-TFE are limited and highly variable. For example, it has been reported as varying from -108 °C to 145 °C. The ambiguity of Tg for this copolymer can be resolved with this approach. Furthermore, we studied the relaxation time associated with the torsional autocorrelation function (TACF) over a wide temperature range. The Vogel-Fulcher-Tammann (VFT) equation was used to describe the temperature dependence of the relaxation time. The Kohlrausch Williams Watts (KWW) stretched exponential function is then applied to fit the time dependence of the relaxation process at various temperatures. The results obtained from this work were found to be in good agreement with the experimental data. A particular interest in this study is the question of how the non-Arrhenius VFT of relaxation process is related to the Arrhenius behavior of conformational jump rates near the glass transition. In both cases, the energies (the conformational transition energy (Ea) and the effective activation energy (B) in VFT equation), were very close to the value of a single torsional barrier. However, in contrast to the relaxation time associated with TACF, the rates of conformational jumps show the activation energy higher than the single barrier value. We have shown that a linear relationship can be established between the conformational transition energy and the effective activation energy. In crystalline PVDF, among the five typical phases, the α and β crystals are of particular interest. The α phase is the most thermodynamically stable form and the β crystal possesses ferroelectric properties. The melting behaviour of these two crystal phases is not so clear. Some researchers believe that the melting temperature of the β phase is higher than that of the α phase. Others have claimed that the higher melting temperature of the peak in Differential Scanning Calorimetry (DSC) has been mistakenly attributed to β phase melting, due to confusion in the referencing of literature sources. In this regard, the melting temperatures of α and β crystals (with and without regiodefects) with respect to their thickness are captured by MD simulation. We then applied the Gibbs-Thomson (G-T) equation to determine the melting temperature, as well as the surface energy and enthalpy of fusion, for α and β nanocrystals. We have shown that pure β phase PVDF has a lower melting temperature than pure α phase PVDF. However, by inserting regiodefects randomly inside the crystal, the α phase with regiodefects shows a lower melting temperature than that of the β phase with regiodefects. We attributed this behaviour to the different structures of the two phases.

This dissertation details research aimed at designing a small batch distillation column to purify tetrafluoroethylene and hexafluoropropylene from a mixture containing tetrafluoroethylene, hexafluoropropylene and octafluorocyclobutane. As no vapour-liquid equilibrium data are available for these chemicals in this mixture, new vapour-liquid equilibrium data were experimentally generated and modelled for use in the design of the batch distillation column. The data were fitted to the Peng-Robinson equation of state, utilizing the Mathias-Copeman alpha function. The model was used with the Wong- Sandler mixing rules alongside the NRTL alpha function. The model was fitted with mean relative deviations lower than 1.2 %, indicating an acceptably accurate description of the VLE data gathered by the model. The experimental data and the model also passed the thermodynamic consistency test for all the systems and isotherms. The design simulations were completed by means of the Aspen Batch Distillation, a module of the Aspen Technologies package. The results show that the optimum design for recovering high-purity products requires six equilibrium stages in the column. The batch column should consist of a still pot, also functioning as a reboiler, a packed column section and a total condenser. The total condenser and the reboiler both count as equilibrium stages. Using this design, a TFE product purity of 99.999 % is predicted with a recovery of 96 %. An HFP product purity of 99 % is predicted at a recovery of 68 %. The recovery of the HFP product can be increased, but entails a significant loss of product purity. The minimum column diameter required to achieve the flow rates suggested in the simulation is 29 mm. The column diameter was selectedas 1¼ ″ (or 31.75 mm) on the basis of the standard pipe diameters available in the industry. Pall ring packing is suggested for use in the column, with an estimated maximum HETP of 0.5 m. As there are five equilibrium stages in the column itself, the column has to be at least 2.5 m high. Copyright
Dissertation (MEng)--University of Pretoria, 2011.
Chemical Engineering
unrestricted

Cette etude s'inscrit dans le cadre general de la realisation et de la caracterisation de polymeres hemocompatibles susceptibles d'etre utilises en tant que protheses vasculaires de diametre inferieur a 4 mm. La synthese de ces nouveaux materiaux repose d'une part sur le radiogreffage de styrene dans des films de fluoropolymeres (polyfluorure de vinylidene: pvdf, et son copolymere avec l'hexafluoropropylene: p(vdf - hfp)) a la suite d'irradiations avec des ions lourds rapides, et d'autre part sur la fonctionnalisation des noyaux aromatiques du styrene par des groupements heparin - like (sulfonates et sulfonamides d'acide aspartique). La determination de la nature des groupements fonctionnels presents dans le volume (spectroscopie infrarouge a transformee de fourier: ftir) et a la surface (spectroscopie de photoelectrons: xps) des polymeres permet de demontrer la faisabilite des differentes etapes de synthese (radiogreffage et fonctionnalisation). Par l'analyse des variations d'intensite des raies composant les spectres xps, une estimation quantitative raisonnable de la composition moleculaire de la surface du materiau, apres chaque phase du traitement, a pu etre realisee. Une influence des conditions de radiogreffage sur la quantite et la repartition du polystyrene (ps) a la surface du polymere substrat a egalement ete mise en evidence par xps. L'optimisation des parametres caracteristiques des diverses etapes de la synthese a ete realisee de facon a obtenir un materiau dont la surface soit recouverte de maniere homogene par du polystyrene fonctionnalise majoritairement par des groupements sulfonamides. L'existence d'un gradient de concentration en ps dans l'epaisseur du film est clairement mise en evidence par la determination de la quantite de ps presente dans differentes epaisseurs de l'echantillon (xps, atr (spectroscopie infrarouge par reflection totale attenuee) et ftir)