The mechanically compressive flow stress sensitivities of various polymers are investigated at high strain rates above 103 s-1. Temperatures near the glass transition temperature are investigated and the polymer stress-strain responses have been studied from ambient temperature to 100°C. Previous work has reported peaks in flow stress as a function of strain rate [Al-Maliky/Parry 1994, Al-Maliky 1997]. The analyses showed rapid increases of flow stress followed by a sudden drop at elevated strain rates, which is unlike the well known linear relationship documented at the low strain rates. The mechanics and stipulation of what bring about this phenomenon, or the types of polymers influenced are still unclear. Two fluoropolymers, polytetrafluoroethylene (PTFE) and polychlorotrifluoroethylene (PCTFE), and two vinyl polymers, polyvinylchloride (PVC) and polymethylmethacrylate (PMMA), are chosen for this study. PTFE, PCTFE and PVC are semi-crystalline polymers with different percentage of crystallinity contents, whereas PMMA is an amorphous polymer. The glass transition temperature, Tg, is the characteristic of the amorphous content in polymers, which has been suggested to influence the flow stress peaks [Swallowe/Lee 2003]. Tg of the semi-crystalline polymers are within the test temperature range. High strain rate compression tests have been carried out using the split Hopkinson pressure bar (SHPB). This is a well-established method for determining the stress, strain, and strain rate of materials. The strain rate range of interest is 103 s-1 to 105 s-1 where the strain rate sensitivity has previously been identified [Al-Maliky/Parry 1994, Al-Maliky 1997, Walley/Field 1994]. Two thermal analyses techniques are used to quantify the dependency of the viscoelastic behaviour in relation to time and temperature. Differential scanning calorimetry (DSC) measures the enthalpy of the polymers to show how the materials are affected by heat, and Dynamic mechanical analysis (DMA) is used to characterise the time-temperature dependence of the elastic storage and loss moduli of the polymers A total of 42 PCTFE, 44 PTFE, 45 PVC and 55 PMMA specimens were tested using the SHPB system, with the strain rate varying between 1600 s-1 and 6100 s-1. Initial results for PMMA have been reported [Forrester/Swallowe 2009]. The rate of strain where specimens begin to show crazing is identified. The value of yield stress increases with the increase of strain rate and the decrease in temperature. Large strain hardening can be seen in all three semi-crystalline polymers at higher strain rates. The temperature rise during plastic flow of compression is calculated by the stress-strain rate curves. In this thesis, the emphasis is on the relation of yield/flow stress to strain rate as the polymers deform under high strain compression. The mechanism behind the cause of high strain rate deformation responses for amorphous to semi-crystalline polymers in ductile state is discussed, with a view to understanding the sensitivity of yield/flow stresses as a function of strain rate. Also, the modelling of the polymers has been carried in order to alleviate doubts about the validity of the real experimental results that may arise due to the nature of the decomposition of the polymers. It has been shown that the strain energy density pulses through the sample in response to the compression wave in various circular intensities.

Thin films of Teflon AF have been directly patterned by electron-beam lithography without the need for post exposure chemical development. The relationship between pattern depth and exposure dose was found to be linear over a wide range of doses. Pattern depth was also observed to be dependent on initial film thickness. Teflon AF can be directly patterned at doses similar to typical e-beam resists. High resolution features as small as ~200 nm have been resolved. FTIR measurements revealed that CF3 and fluorinated dioxole groups play a significant role in the patterning mechanism. Teflon AF films also exhibited an increase in refractive index upon exposure to the electron-beam. This property has been exploited in waveguiding applications. Waveguides in Teflon AF were patterned using direct electron beam lithography technique. Waveguides were clearly visible to the naked eye. Characterization in the visible region showed evidences of light guiding through the waveguides. However light could not cross the entire chip. Characterization in the infrared region revealed the slab mode even though individual waveguides were not detected.

Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2005. / Morhan Srinivasarao, Committee Member ; CP Wong, Committee Member ; David M. Collard, Committee Chair ; Marcus Weck, Committee Member ; Laren Tolbert, Committee Member.

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.

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.

<p>The ignition of energetic materials, and specifically solid propellants, is a complex process</p> <p>that must be safe, consistent, and precisely controlled. There is a wide range of applications with</p> <p>specific ignition requirements for solid propellants including inflation of airbags, propulsion</p> <p>systems (including rockets), as well as arm and fire devices. Currently, electrical or percussion</p> <p>pyrotechnic igniters are most the commonly used ignition systems. These systems must be</p> <p>carefully designed to deliver the proper amount of energy to a specified surface area of the</p> <p>propellant. A photon light source (i.e. flash or laser-based, ranging from UV to IR wavelengths)</p> <p>can potentially be used to ignite energetic materials with lower input energy and more precise</p> <p>spatial and temporal control, thereby improving safety and reliability by eliminating electrical</p> <p>systems used in pyrotechnic igniters. In addition, they could be potentially safer from stray</p> <p>electrical charges causing unintentional ignition.</p> <p>The purpose of this work is to further explore the potential of optical ignition for energetic</p> <p>systems and identify ideal materials that can be used for optical ignition. In order to identify</p> <p>optically sensitive materials, we will study ignition energies, ignition delays, flame temperatures,</p> <p>and other combustion characteristics for possible energetic materials. This research addresses a</p> <p>gap in understanding of optical ignition for energetic materials, as finding and integrating materials</p> <p>that are optically sensitive while still being practical can be extremely challenging. These</p> <p>challenges include: (1) a lack of absorptivity to optical wavelengths in the UV to low-IR range,</p> <p>and subsequently, a very high sensitivity to input energy at the absorptive wavelengths that makes</p> <p>sustained ignition difficult, (2) a need for full density materials in practical energetic systems,</p> <p>while optically sensitive materials are exceedingly difficult to ignite as packing density increases</p> <p>due to heat transfer, and (3) the lack of research regarding novel fuels/oxidizers for the specific</p> <p>purpose of optical ignition.</p> <p>Metal/fluoropolymer energetic materials have been of interest to the energetic materials</p> <p>community for many years. Due to fluorine’s excellent oxidizing ability, they can be used in</p> <p>composite materials with metal fuels to produce energetic materials for a wide variety of</p> <p>applications. Polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polycarbon</p> <p>13</p> <p>monofluoride (PMF), and terpolymers such as tetrafluoroethylene, hexafluoropropylene, and</p> <p>vinylidene fluoride (THV) have already seen extensive use in applications ranging including</p> <p>protective coatings, strain gauges, and electronics. However, when combined with metals such as</p> <p>lithium, magnesium, aluminum, or titanium, they also present an opportunity for a wide variety of</p> <p>energetic materials. For this study, metal/fluoropolymer composites present a novel opportunity</p> <p>for exploring optical ignition of widely absorptive, full-density energetic materials. This work will</p> <p>characterize the combustion and sensitivity of metal/fluoropolymer composites to provide novel</p> <p>materials for optical ignition of energetics.</p> <p>Specifically, this work will begin with finding a suitable energetic composite that is optically</p> <p>sensitive. Once this material has been identified, research will be done to thoroughly characterize</p> <p>the optically sensitive composite by looking at additive manufacturability, flame temperatures, and</p> <p>ignition sensitivities from various methods and formulations. Once the material has been</p> <p>thoroughly characterized, it will be implemented into solid propellants to test the feasibility of the</p> <p>material in practical energetic systems. Finally, the lessons learned from this work will be applied</p> <p>to novel formulations to identify new optically sensitive energetic composites.</p>

No description available.

<p dir="ltr">Piezoelectric polymers and ceramics have applications throughout many fields, including their use as pressure sensors and transducers. Of the polymers, poly(vinylidene fluoride – trifluoroethylene) (P(VDF-TrFE)), has been the go-to for its high piezoelectric performance. With the addition of aluminum nanopowders (nAl), P(VDF-TrFE) acts as a binder and oxidizer, creating an energetic composite, a so-called piezoenergetic. However, this typically results in lower d₃₃ coefficients and can have lower reactivity since ideal mixtures may short when poled. Here, we develop and demonstrate single-layer and multilayer polymer composite films with high piezoelectric and energetic content. We prepared single-layer thin film piezoelectric energetic composites of nAl and P(VDF-TrFE) and a combination of thermal annealing and poling at elevated temperatures enabled full poling of 9 wt.% nAl/P(VDF-TrFE) films with d₃₃ of 22.7 pC/N that is comparable to P(VDF-TrFE) films. We also investigated the addition of barium titanate (BaTiO₃) particles as a piezoelectric ceramic to enhance the d₃₃ coefficient. In the neat polymer, BaTiO₃ had differing effects depending on the particle size, with 200 nm particles improving the d₃₃ coefficient more than the 1 μm particles. However, neither size of BaTiO₃ particle had a substantial effect on the piezoelectricity in the 9 wt.% nAl/P(VDF-TrFE) films. We also prepared hot-pressed, three-layer “sandwich” P(VDF-TrFE) – 30 wt.% nAl/P(VDF-TrFE) – P(VDF-TrFE) composites, which had marginally lower d₃₃ coefficients than the single-layer 9 wt.% nAl/P(VDF-TrFE) films. However, the 30 wt.% nAl/P(VDF-TrFE) sandwich films were far more energetic than the 9 wt.% nAl/P(VDF-TrFE) films, as confirmed by simultaneous differential scanning calorimetry and thermogravimetric analysis (DSC/TGA) and deflagration studies. The single films will often fail to fully sustain a deflagration, while the sandwich films burn completely. In addition, we can ignite the sandwich samples with an electrical discharge making these films also useful in ignition applications. To demonstrate the use of piezoenergetic films, 9 wt.% nAl/P(VDF-TrFE) single layer and 30 wt.% nAl/P(VDF-TrFE) sandwich films were calibrated as pressure gauges using a mini drop weight setup, and then demonstrated as a pressure gage. The improvements in the piezoelectric coefficient of the 9 wt.% nAl/P(VDF-TrFE) single layer films, as well as the energetic performance in the form of the 30 wt.% nAl/P(VDF-TrFE) sandwich films strongly amplify the existing potential of these multifunctional composites in energetic and pressure sensing applications.</p>

Tailored fluoropolymers remain the leading choice for a wide variety of advanced high-performance applications, including electronic/optical and energy conversion, owing to their unique blend of complementary high-performance properties. Amorphous semi-fluorinated polymers exhibit improved solubility and melt processability when compared to traditional perfluoropolymers. A leading class of semi-fluorinated aryl ether polymers includes perfluorocyclobutyl (PFCB), perfluorocycloalkenyl (PFCA), and fluoroarylene vinylene ether (FAVE) polymers. Monomers containing aromatic trifluorovinyl ethers (TFVE) are used to synthesize PFCB polymers via radical-mediated [2+2] cyclodimerization. On the other hand, FAVE and PFCA polymers are polymerized via base-mediated nucleophilic addition/elimination of bisphenols with TFVE monomers and decafluorocyclohexene respectively. The use of different monomer cores (aromatic, aliphatic, contorted, and renewable) should help to develop general structure/property relationships for this versatile and expanding approach to semi-fluorinated aryl ether polymers. The enchainment of polycyclic aromatic hydrocarbon (PAH) cores with functional fluorocarbon groups (or segments) recently afforded a new class of semi- fluorinated polymers in the continuing quest for novel organic materials for potential applications in optoelectronic, gas-separation, and advanced composites. Chapter 2 details the incorporation of commercially available acenaphthenequinone was achieved to afford PFCB aryl ether polymers with excellent solubility, high thermal stability, and film-forming capability. Chapter 3 represents base-promoted nucleophilic addition/elimination of commercial bisphenols with TFVE-triphenylene monomers affording FAVE aryl ether polymers possessing excellent solution processability, high thermal stability and photostability. In addition, triphenylene-enchained FAVE polymers exhibit extreme thermal-oxidative photostability and emit blue light after heating in air at 250 °C for 24 h. Further, time-dependent density functional theory (TD-DFT) computations were performed to understand electronic polymer structures. In one case, post-polymerization Scholl coupling converted the central triphenylene core to afford a hexabenzocoronene containing semi-fluorinated polymer with new optoelectronic properties. Chapter 4 demonstrates synthesis and characterization of renewable semi-fluorinated polymers obtained using aliphatic diol isosorbide. This renewable diol readily polymerizes with bis-TFVE derivatives of bisphenol A and 6F to provide high molecular weight thermoplastics exhibiting excellent solubility and tough, transparent film-forming capability. Finally, Chapter 5 presents synthesis of TFVE enchained corannulene which gave blue-light emission and outstanding processability. Synthesis and characterization, including the new materials' optical, thermal, and electronic properties, is presented.