This thesis is concerned with the development of methods and models to aid in optimization and development of new materials for Fused Filament Fabrication (FFF). We demonstrate a novel FFF nozzle design to enable the first measurements of in-situ rheology inside FFF nozzles, which is critical for part performance by ensuring that the polymer extrudate is flowing at an appropriate temperature and flow rate during the part build process. Testing was performed using Acrylonitrile butadiene styrene filament and a modified Monoprice Maker Select 3D printer. Tests using the default temperature control settings of the printer showed an 11 °C drop in temperature and significant fluctuations in pressure, during printing and while idle, of ± 2 °C and +/-14 kPa. These deviations were eliminated at lower flow rates with a properly calibrated proportional–integral–derivative (PID) system. At high flow rates, drops in temperature as high as 6.5 °C were observed even with a properly calibrated PID, providing critical input to the impact of flow rate and PID calibration on polymer melt temperature inside FFF nozzles. Pressure readings ranging from 140-6900 kPa were measured over the range of filament feed rates and corresponding extrusion flow rates. Theoretical predictions of pressure profiles, assuming a powerlaw fluid model, matched well with experimental results. Our nozzle prototype succeeded in measuring internal conditions of FFF nozzles for the first time, thereby providing several important insights into the printing process which are vital for monitoring and improving FFF printed parts. Furthermore, finite difference simulations based on first principles analysis are presented which are capable of quantifying the effect of processing conditions on the properties of semicrystalline parts made by FFF. Each layer was modelled as a rectangular cross section which was broken down into smaller elements for modelling. Crystallinity of each element was calculated using a parallel Avrami model which accounts for changes in crystallization rate due to temperature and multiple crystallization mechanisms. The amount of polymer diffusion, also referred to as the degree of healing, was calculated using a novel incremental diffusion model which accounted for not only changes in reptation time due to temperature but also restrictions to healing due to crystallinity. To the authors knowledge, this is the first healing model capable of accounting for the effect of crystallinity on healing and is relevant to any process involving healing of crystalline interfaces; not just FFF. Cumulative shear stresses between each layer and at the bottom of the part were also calculated for the first time using a force balance model by assuming constant shear strain throughout each layer. Simulations were performed using typical printing conditions for polyether ether ketone. In the first layer of a 24 layer part, the average degree of crystallinity, healing, and shear stress were 25.0%, 53.8% and 19.4 MPa respectively. The degree of crystallinity and healing at layer 22 (which represented the steady state values) were 18.4-25.0% and 51.4% respectively. When crystallinity was not accounted for, varying the printing parameters and material properties supported the use of high temperatures and specific heat in addition to a low printing speed, heat transfer coefficient, and thermal conductivity to maximize part properties. These conditions also supported crystallization, however, which led to a simultaneous reduction in the part properties when crystallinity was taken into account. These contradictory effects will need to be considered when optimizing the printing parameters, though the optimal balance will be highly dependent on the material used and the limitations of the printer. Experimental validation of the accuracy of the heat transfer and polymer diffusion models was performed using an amorphous polymer (polyether imide). Single road wide parts were printed at various nozzle temperatures, bed temperatures, and printing speeds and the results were compared to the simulated results. The predicted shear stress in the bottom of the part ranged from 2.3-3.8 MPa and correlated to warpages at the corners of each part of 1.2-2.4 mm. A linear increase in warpage with predicted shear stress was observed supporting the shear stress model. Predicted degrees of healing ranged from 2-90% but the experimental results ranged from 15-36%. Results of the healing model underpredicted strength at low printing speeds and over predicted strength at high printing speeds. The experimental validations showed the capabilities of the models, but the effect of printing speed will need to be investigated further to improve the accuracy of the healing model. / MS / This thesis is concerned with the development of methods and models to aid in optimizing a type of 3D printing known as Fused Filament Fabrication (FFF). We demonstrate a novel FFF nozzle design to enable the first measurements of the temperature and pressure within FFF nozzles, which is critical for ensuring that the printer is printing at the appropriate temperature and flow rate. Testing was performed using a material known as Acrylonitrile butadiene styrene and a modified Monoprice Maker Select 3D printer. Tests using the default temperature control settings of the printer showed an 11 °C drop in temperature and significant fluctuations in pressure, during printing and while idle, of ± 2 °C and +/-14 kPa. These deviations were eliminated at lower flow rates with a properly calibrated temperature control system. At high flow rates, drops in temperature as high as 6.5 °C were observed even with a properly calibrated temperature control system, providing critical input to the impact of flow rate and temperature control calibration on the temperature of the polymer melt inside FFF nozzles. Pressure readings ranging from 140-6900 kPa were measured over the range of extrusion flow rates tested. Theoretical predictions of the pressure within the nozzles matched well with the experimental results. Our nozzle prototype succeeded in measuring internal conditions of FFF nozzles for the first time, thereby providing several important insights into the printing process which are vital for monitoring and improving FFF printed parts. Furthermore, simulations of the FFF process are presented which can quantify the effect of processing conditions on the properties of FFF parts made from materials which can crystallize. Each layer was modelled as a rectangular cross section which was broken down into smaller elements for modelling. Crystallinity of each element was calculated using a model which can account for changes in the rate of crystallization due to temperature as well as multiple types of crystallization. The strength of the interlayer bonds was calculated using a novel model which accounts for the effects of temperature and crystallinity. To the authors knowledge, this is the first bonding model capable of accounting for the effect of crystallinity on bonding and is relevant to any process involving bonding of crystalline materials; not just FFF. The shear stress between each layer and at the bottom of the part was also calculated for the first time by balancing thermal and shear stresses of each layer. Simulations were performed using typical printing conditions for a high performance polymer (polyether ether ketone). In the first layer of a 24 layer part, the average amount of crystallinity, bonding, and shear stress were 25.0%, 53.8% and 19.4 MPa respectively. The degree of crystallinity and healing at layer 22 (which represented the majority of the part) were 18.4-25.0% and 51.4% respectively. When crystallinity was not accounted for, varying the printing parameters and material properties supported the use of high temperatures and specific heat in addition to a low printing speed, heat transfer coefficient, and thermal conductivity to maximize part properties. These conditions also supported crystallization, however, which led to a simultaneous reduction in the part properties when crystallinity was considered. These contradictory effects will need to be considered when optimizing the printing parameters, though the optimal balance will be highly dependent on the material used and the limitations of the printer. Experimental validation of the accuracy of the heat transfer and bonding models was performed using an amorphous polymer (polyether imide). Single road wide parts were printed at various nozzle temperatures, bed temperatures, and printing speeds and the results were compared to the simulated results. The predicted shear stress in the bottom of the part ranged from 2.3-3.8 MPa and correlated to the corners of each part peeling 1.2-2.4 mm from the printer. A linear increase in the experimental peeling with predicted shear stress was observed, supporting the shear stress model. Predicted bonding ranged from 2-90% of the strength of the material, but the experimental results ranged from 15-36%. Results of the bonding model underpredicted strength at low printing speeds and over predicted strength at high printing speeds. The experimental validations showed the capabilities of the models, but the effect of printing speed will need to be investigated further to improve the accuracy of the bonding model.

Small cantilevers with ultra-high resonant frequencies (1–3 MHz) have paved the way for high-speed atomic force microscopy. However, their potential for multi-frequency atomic force microscopy is unexplored. Because small cantilevers have small spring constants but large resonant frequencies, they are well-suited for the characterisation of delicate specimens with high imaging rates. We demonstrate their imaging capabilities in a bimodal frequency modulation mode in constant excitation on semi-crystalline polypropylene. The first two flexural modes of the cantilever were simultaneously excited. The detected frequency shift of the first eigenmode was held constant for topographical feedback, whereas the second eigenmode frequency shift was used to map the local properties of the specimen. High-resolution images were acquired depicting crystalline lamellae of approximately 12 nm in width. Additionally, dynamic force curves revealed that the contrast originated from different interaction forces between the tip and the distinct polymer regions. The technique uses gentle forces during scanning and quantified the elastic moduli Eam = 300 MPa and Ecr = 600 MPa on amorphous and crystalline regions, respectively. Thus, multimode measurements with small cantilevers allow one to map material properties on the nanoscale at high resolutions and increase the force sensitivity compared with standard cantilevers. / Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Ce travail est consacré à l’élaboration et à la caractérisation de couches minces de parylène D déposées par dépôt chimique en phase vapeur (CVD) sous forme de films de quelques microns d’épaisseur. L’objectif de l’étude est d’évaluer les potentialités de ce polymère en remplacement des parylènes de type N ou C pour des applications spécifiques ou encore pour l’intégrer dans de nouvelles applications. Une première étude a consisté à évaluer l’impact des paramètres des dépôts CVD (température de sublimation, température de pyrolyse, température du substrat d’accueil du film déposé) sur les changements physico-chimiques, structuraux et diélectriques du parylène D. Pour cela, nous nous sommes appuyés sur des analyses FTIR, XRD, DSC, TGA, AFM, SEM, DMA. Nous avons également appliqué des stress thermiques au parylène D dans le but d’évaluer leur performance à haute température (>200°C) ainsi que les changements opérés au niveau de la structure cristalline (taille des cristallites, pourcentage de cristallinité,…) ou encore la stabilité des propriétés thermiques (température de transition vitreuse, température de cristallisation, température de fusion) et diélectriques (constante diélectrique e’, facteur de dissipation tand et conductivité basse fréquence s’) Enfin, des analyses diélectriques en fréquence (de 0,1Hz à 100 kHz) sur une large plage de température de fonctionnement (-140°C – 350°C) ont permis de mettre en évidence la présence de trois mécanismes de relaxations (a, b, g), une polarisation d’interface de type Maxwell-Wagner-Sillars et une polarisation d’électrode. Les performances diélectriques sont également discutées par comparaison aux parylènes de type N et C plus couramment utilisés aujourd’hui dans les applications industrielles. Cette étude permet ainsi de disposer maintenant de paramètres de dépôt CVD bien contrôlés pour le dépôt de films de parylènes D aux propriétés souhaitées pour une application spécifique / This work is mainly focused on the elaboration and the characterization of parylene D thin films of few micrometers deposited by chemical vapor deposition (CVD). The goal of this study is to evaluate the potentialities of this polymer in order to replace the parylene N or C for specific applications or to integrate it in new applications. A first study consisted in evaluating the impact of the CVD process parameters (temperature of sublimation, temperature of pyrolysis, substrate temperature) on the surface morphology, the molecular structure and dielectric changes of parylene D. For that, we were based on several analyzes techniques as FTIR, XRD, DSC, TGA, AFM, SEM, DMA. Thermal stresses were applied to parylene D to evaluate their performance at high temperature (>200°C) and the changes on the crystal structure (size of crystallites, percentage of crystallinity,…) or the stability of the thermal properties (temperature of transition, temperature of crystallization, melting point) and dielectric properties (the dielectric permittivity, the dissipation factor, the electrical conductivity and the electric modulus). Dielectric and electrical properties of Parylene D were investigated by dielectric spectroscopy in a wide temperature ranges from -140°C to 350°C and frequency from 0.1 Hz to 1 MHz, respectively. (a, b and g)-relaxation mechanisms, interfacial polarization related to Maxwell-Wagner-Sillars and electrode polarization have been identified in this polymers. The dielectric performances of Parylene D have been also compared with parylenes N and C which are used in wide industrial applications. Optimized and controlled conditions of the CVD process of parylenes D are proposed in this work in relation to the properties. The obtained results open a new way for specific applications.

Proton exchange membrane fuel cells (PEMFCs) have been extensively studied as clean, sustainable and efficient power sources for electric vehicles, and portable and residential power sources. As one of the key components in PEMFC system, proton exchange membranes (PEMs) act as the electrolyte that transfers protons from the anode to the cathode. The state-of-art commercial PEM materials are typically based on perfluorinated sulfonic acid containing ionomers (PFSAs), represented by DuPont's Nafion®. Despite their good chemical stability and proton conductivity at high relative humidity (RH) and low temperature, several major drawbacks have been observed on PFSAs, such as high cost, high fuel permeability, insufficient thermo-mechanical properties above 80°C, and low proton conductivity at low RH levels. Therefore the challenge lies in developing alternative PEMs which feature associated ionic domains at low hydration levels. Nanophase separated hydrophilic-hydrophobic block copolymer ionomers are believed to be desirable for this purpose Three series of hydrophobic/hydrophillic, partially fluorinated/sulfonated multiblock copolymers were synthesized and characterized in this thesis. The hydrophilic blocks were based upon the nucleophilic step polymerization of 3, 3′-disulfonated, 4, 4′-dichlorodiphenyl sulfone (SDCDPS) with an excess 4, 4′-biphenol (BP) to afford phenoxide endgroups. The partially fluorinated hydrophobic blocks were largely based on 4, 4′-hexafluoroisopropylidenediphenol (6F-BPA) and various difluoro monomers (excess). These copolymers were obtained through moderate temperature (~130-150°C) coupling reactions, which minimize the ether-ether interchanges between hydrophobic and hydrophilic telechelic oligomers via a nucleophilic aromatic substitution mechanism. The copolymers were obtained in high molecular weights and were solvent cast into tough membranes, which had nanophase separated hydrophilic and hydrophobic regions. The performance and structure-property relationships of these materials were studied and compared to random copolymer systems. NMR results supported that the multiblock sequence had been achieved. They displayed superior proton conductivity, due to ionic, proton conducting channels formed through the self-assembly of the sulfonated blocks. The nano-phase separated morphologies of the copolymer membranes were studied and confirmed by transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). Through control of a variety of parameters, including ion exchange capacity and sequence lengths, performances as high, or even higher than those of the state-of-the-art PEM, Nafion®, were achieved. Another series of semi-crystalline hydrophobic poly(ether ether ketone)-hydrophilic sulfonated poly(arylene ether sulfone) (PEEK-BPSH100) multiblock copolymers was first synthesized and characterized. However due to their semi-crystalline structure, PEEK blocks are insoluble in most organic solvents at relatively low reaction temperatures, which prevents the coupling reaction between PEEK and BPS100. In order to facilitate the synthesis and processing, removable bulky ketimine was introduced to synthesize amorphous pre-oligomers poly(ether ether ketimine) (PEEKt). The synthetic procedure first involves the synthesis of hydrophobic poly(ether ether ketimine)-hydrophilic sulfonated poly(arylene ether sulfone) (PEEKt-BPS100) multiblock pre-copolymers via coupling reactions between phenoxide terminated hydrophilic BPS100 and fluorine terminated hydrophobic PEEKt blocks. The membranes cast from PEEKt-BPS100 were boiled in 0.5M sulfuric acid water solution to hydrolyze the amorphous PEEKt blocks to semi-crystalline PEEK blocks and acidify BPS100 blocks to BPSH100 blocks simultaneously. FT-IR spectra clearly showed the successful hydrolysis and acidification. The proton conductivity, water uptake and other membrane properties of the acidified semi-crystalline PEEK-BPSH100 membranes were then evaluated and compared with those of the state-of-the-art PEM, Nafion®. / Ph. D.

L’objectif de ce mémoire de thèse est de contribuer à la connaissance du comportement mécanique en grandes déformations du Polyéthylène à Haute Densité anisotrope obtenu par extrusion de plaques. Nous présentons le protocole et les résultats expérimentaux de traction séquencée, comportant des décharges, recharges et relaxations monotones et cycliques. Ces campagnes d’essais sont également centrées sur la mesure en temps réel de la variation de volume liée aux phénomènes d’endommagement. Les résultats sont présentés pour différentes orientations d’éprouvettes prélevées dans des plaques extrudées. La modélisation thermodynamique de l’ensemble des résultats, a fait l’objet d’un développement original conduisant à la prédiction unifiée de grandeurs en 3D : contrainte vraie axiale, déformations vraies transversales. Le modèle prévoit également le développement de l’endommagement et permet de mettre en évidence une variable tensorielle de dommage. L’identification des paramètres du modèle thermodynamique sur la base de données expérimentales conduit à des grandeurs physiques conformes aux caractéristiques de la microstructure. Ce travail ouvre la perspective d’un enrichissement de l’approche thermodynamique dans la direction de la prévision de l’anisotropie plastique induite des polymères semi-cristallins / The aim of this thesis is to contribute to the knowledge of the mechanical behavior in large strains of anisotropic High Density PolyEthylene (HDPE), obtained by extrusion of plates. We present the experimental procedure and the results for traction, with unloading, reloading and relaxation in monotonous and cyclic conditions. This work is also concerned with the measure in real time of the volume strain due to the phenomena of damage. The results are given for various orientations of specimen within the extruded plates. The thermodynamic modeling of the whole the results, is the subject of an original development leading to the unified prediction of measures in 3D: axial true stress, transverse true strains. The model also predicts the development of the damage and offer the possibility to introduce a tensorial damage variable. The identification of the model parameters on the basis of experimental data leads to physical quantities in conformity with the characteristics of the microstructure. This work opens the prospect for an enrichment of the thermodynamic approach in the direction of the prediction of the induced plastic anisotropy of semi-crystalline polymers

De nombreuses structures industrielles soumises à des chargements à long terme statique (fluage) ou cyclique (fatigue) sont constituées de matériaux polymères semi-cristallins. C’est le cas notamment des canalisations et réservoirs sous pression. Il est donc essentiel de traiter les problématiques de durabilité pour être capable d'anticiper et de contrôler leur fin de vie. Par ailleurs, elles présentent généralement des formes complexes et sont soumises à des états de contrainte multiaxiaux.Le matériau de l'étude est un polymère semi-cristallin : le Polyamide 6. Il est caractérisé par la coexistence d'une phase cristalline et d'une phase amorphe qui s'arrangent selon une microstructure sphérolitique.Dans un premier temps, les liens entre comportement mécanique à l'échelle globale de l'éprouvette et les micro-mécanismes de déformation sous-jacents conduisant à la rupture sont établis expérimentalement pour des sollicitations en traction monotone et en fluage qui présentent des résultats similaires puis en fatigue. L'influence de la multiaxialité de l'état de contrainte est étudiée à partir d’éprouvettes axisymétriques entaillées de différents rayons de fond d'entaille et d'éprouvettes « Compact Tensile ». Les phénomènes de cavitation sont caractérisés grâce aux techniques de tomographie et laminographie à rayonnement X synchrotron qui permettent d'observer et de quantifier les distributions spatiales de taux de porosité volumique et le caractère anisotrope des cavités. Et l'analyse des faciès de rupture a permis de mettre en évidence que les mécanismes de croissance et de coalescence de cavités étaient à l'origine de l’amorçage ductile de la rupture.Ensuite, un modèle poro-visco-plastique à deux mécanismes (permettant de différencier le comportement des phases amorphe et cristalline) a été utilisé. Ce modèle permet de reproduire à la fois le comportement global (courbes de chargement) en traction monotone et en fluage mais aussi les distributions spatiales de taux de porosité obtenues expérimentalement. De plus, les calculs par éléments finis permettent d'étudier les distributions spatiales du champ de contrainte et d'établir l'influence de l'état de contrainte sur l'état de cavitation. Les évolutions temporelles en cours de déformation de la pression hydrostatique (ou contrainte moyenne) ont été reliées aux distributions spatiales de taux de porosité volumique. Et l'anisotropie de cavitation (et donc la morphologie et les facteurs de forme des cavités) a été reliée aux évolutions des composantes du tenseur des contraintes de Cauchy. Enfin, la définition d'un critère de rupture en taux de porosité critique a permis de simuler l'amorçage et la propagation de fissures en traction monotone et fluage. / Many industrial structures subjected to quasi-static (creep) or cyclic (fatigue) long-term loadings are made of semi-crystalline polymers. Such is the case, for instance, of pressure vessels and pipes. It is therefore considered critical to study the issues related to their durability in order to be able to anticipate and control their end of life. Furthermore, they generally have complex designs and are subjected to multiaxial stress states.The material which has been studied was a semi-crystalline Polyamide 6. Its structure consisted of amorphous and the crystalline phases and a spherolitic microstructure.As a first step, the links between the mechanical behaviour at the global scale of the specimens and the underlying micro-mechanisms of deformation that lead to failure have been established experimentally for monotonic and creep loadings that show similar results and then for fatigue loadings. The influence of the multiaxiality of the stress state has been studied using circumferentially notched round bars with different notch root radii and Compact Tensile specimens. The cavitation phenomena were characterized using synchrotron radiation tomography and laminography techniques that enabled the observation and quantification of the spatial distributions of the voids and the anisotropy of the cavities. An analysis of the fracture surfaces has shown that the initiation of ductile failure resulted from void growth and coalescence mechanismsA poro-visco-plastic model with two mechanisms (that allow the behaviours of the amorphous and crystalline phases to be distinguished) has been used. Thanks to this model, the global behaviour (loading curves) under steady strain rates and steady loads but also the spatial distributions of the void volume fraction could be reproduced numerically. In addition finite element calculations have permitted the spatial distributions of the stress field to be studied and the influence of the stress state on the cavitation state to be investigated. The temporal evolutions during the deformation of the hydrostatic pressure have been linked to the spatial distributions of void volume fraction. The void anisotropy (and thus the void morphology and shape factors) has been related to the evolutions of the components of the Cauchy stress tensor. Finally, the definition of a rupture criterion based on a critical value of the void volume fraction has enabled crack propagation under steady strain rate and steady load to be simulated.

Le lien entre la structure semi-cristalline et les propriétés d’usage (mécaniques, diélectriques et électro-actives) de films de copolymères fluorés électro-actifs développés pour des applications en électronique organique imprimée a été étudié. Les matériaux investigués sont des copolymères poly(VDF-co-TrFE) et des terpolymères poly(VDF-ter-TrFE-ter-CTFE) à base de fluorure de vinylidène (VDF), trifluoroéthylène (TrFE) et chlorotrifluoroéthylène (CTFE).Les films de polymères obtenus par évaporation du solvant sont étudiés par diffraction des rayons X (SAXS-WAXS), DSC, FTIR, DMA, spectroscopie diélectrique et cycles de polarisation afin de mettre en évidence l’impact de la composition et de la mise en forme (recuit, polarisation) sur la structure et les propriétés finales du matériau. Nous montrons ainsi qu’au sein des films de copolymères, la phase ferroélectrique (FE) coexiste avec une phase ferroélectrique défective (DFE). La fraction croissante de cette phase DFE avec la teneur en TrFE permet d’expliquer l’évolution des propriétés thermiques dont la transition de Curie. Une transition structurale continue, de la phase DFE vers la phase paraélectrique (PE), en température a été mise en évidence.La teneur en termonomère CTFE influence fortement la structure cristalline et les propriétés électro-actives des films de terpolymères (disparition du caractère ferroélectrique au profit du caractère ferroélectrique relaxeur (RFE)). Nous prouvons pour la première fois l’existence d’une transition structurale continue entre la phase RFE et la phase PE au voisinage de la température ambiante. Cette transition permet d’expliquer les propriétés exacerbées de ces matériaux (constante diélectrique et déformation sous champ électrique). Enfin, des analogies de comportement entre les copolymères et les terpolymères sont discutées, notamment l’évolution des phases cristallines sous champ électrique, afin de mieux comprendre le fonctionnement de ces polymères électro-actifs pour leur futur développement au niveau industriel. / The relationship between semi-crystalline structure and properties of use (mechanical, dielectric and electroactive) of fluorinated copolymer films was studied for applications in organic electronics. Investigated materials are poly(VDF-co-TrFE) copolymers and poly(VDF-ter-TrFE-ter-CTFE) terpolymers based on vinylidene fluoride (TrFE), trifluoroethylene (TrFE) and chlorotrifluoroethylene (CTFE). Polymer films, obtained after solvent evaporation, are studied by X-ray diffraction (SAXS-WAXS), DSC, FTIR, DMA, dielectric spectroscopy and polarization cycles in order to highlight the impact of composition and processing (annealing, poling) on structure and final properties of material. We showed that the ferroelectric (FE) phase coexists with the defective ferroelectric (DFE) phase in copolymer films. The increasing fraction of DFE phase with TrFE content allows explaining the evolution of thermal properties. A continuous structural transition, from DFE phase to paraelectric (PE) phase was highlighted. The CTFE termonomer content highly influences the crystalline structure and the electro-actives properties of terpolymer films (loss of ferroelectric behavior in favor of relaxor ferroelectric (RFE) behavior).We proved for the first time the existence of a continuous structural transition between RFE phase and PE phase around room temperature. This transition allows explaining exacerbated properties of these materials (dielectric constant and deformation under electric field).Finally, analogies of behavior between copolymers and terpolymers are discussed, especially the evolution of crystalline phases under electric field, in order to better understand how these electro-active materials work for their future development at industrial level.

Small cantilevers with ultra-high resonant frequencies (1–3 MHz) have paved the way for high-speed atomic force microscopy. However, their potential for multi-frequency atomic force microscopy is unexplored. Because small cantilevers have small spring constants but large resonant frequencies, they are well-suited for the characterisation of delicate specimens with high imaging rates. We demonstrate their imaging capabilities in a bimodal frequency modulation mode in constant excitation on semi-crystalline polypropylene. The first two flexural modes of the cantilever were simultaneously excited. The detected frequency shift of the first eigenmode was held constant for topographical feedback, whereas the second eigenmode frequency shift was used to map the local properties of the specimen. High-resolution images were acquired depicting crystalline lamellae of approximately 12 nm in width. Additionally, dynamic force curves revealed that the contrast originated from different interaction forces between the tip and the distinct polymer regions. The technique uses gentle forces during scanning and quantified the elastic moduli Eam = 300 MPa and Ecr = 600 MPa on amorphous and crystalline regions, respectively. Thus, multimode measurements with small cantilevers allow one to map material properties on the nanoscale at high resolutions and increase the force sensitivity compared with standard cantilevers. / Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Multiphase systems provide an opportunity to develop both novel processing methods and create advanced materials through combining the properties of dissimilar phases in a synergistic manner. In this work, we detail the halogenation of poly(ether ether ketone) (PEEK) through both solution-state and gel-state functionalization methods. The multiphase gel-state chemistry restricts functionalization to the amorphous regions of the semi-crystalline parent homopolymer and generates a copolymer with a blocky microstructure. Solution-state functionalization yields random copolymers which provide matched sets to the blocky analogs for fundamental investigations into the effects of polymer microstructure on material properties. Halogenating PEEK using N-halosuccinimides allows for direct installation of pendant halogens along the polymer backbone with facile control of halogen identity. For both bromination and iodination, blocky halogenation of PEEK provides faster crystallization kinetics, higher glass transition (Tg) and melting temperatures as well as superior crystallizability than random halogenation. When comparing halogen identity, increasing halogen size results in increased Tgs, decreased backbone planarity, and for copolymers with blocky microstructures, an earlier onset of phase separation. Increasing halogen size also results in decreased crystallizability and crystallization kinetics, however, these deleterious effects are mitigated in blocky microstructures due to colocalization of the pristine repeat units. Iodination also results in greater flame resistance than bromination for PEEK-based copolymers, and preserved crystallizability allows for the generation of flame retardant aerogels. Direct halogenation of PEEK in the gel-state also provided a reactive microstructural template for subsequent functionalization. Through the use of copper mediated cross-coupling chemistries, the aryl halide functionalities were leveraged to decorate the polymer backbone with pendant perfluoroalkyl chains. The blocky perfluoro alkyl PEEK demonstrated preserved crystallizability and serves as a candidate for compatibilization of poly(tetrafluoroethylene)-PEEK polymer blends. Superacid-modified PEEK was synthesized through a similar methodology and demonstrated over 50,000% increased hygroscopicity relative to the parent homopolymer, and exhibited preserved crystallizability. Multiphase systems were also designed to additively manufacture reinforced elastomers through vat photopolymerization using a degradable scaffold approach that challenged the current paradigm that the scaffold only serves as a geometrical template in vat photopolymerization. The scaffold crosslinks were cleaved through a reactive extraction process that liberated the glassy photopolymer backbone and resulted in over 200% increased ultimate strain and 50% increased ultimate stress relative to a control that was subjected to a neutral extraction. Lastly, thermoresponsive micellar ligands were synthesized as a multiphase approach to environmental remediation of metal-contaminated aqueous systems. / Doctor of Philosophy / Multiphase systems, such as a mixture of oil and water, are of great interest due to their ability to exhibit a multitude of properties from one material. Minimizing the size of the phases, through a technique called compatibilization, often improves the properties of the material. A common example is salad dressing, where the oil phase is compartmentalized into microscopic particles using surface-active molecules known as surfactants. Surfactants, also known as amphiphiles, partition to the interface between different phases due to the surfactants being comprised of dissimilar molecular constituents. One way to generate polymeric amphiphiles, where a polymer is a large molecule comprised of a molecular chain of repeating units, is through synthesizing block copolymers. Block copolymers have blocks of different constituents that are colocalized through covalent bonds in the polymer backbone and often exhibit phase separated structures, allowing for enhanced transport properties such as is seen in membranes. Using semi-crystalline polymers in membranes allows for enhanced mechanical integrity, as the crystallites act as physical crosslinks, or tie points, similar to the knots in a 3D rope ladder. These molecular knots limit the distance that the linear segments of the rope ladder can stretch, which in membranes leads to reduced swelling and increased mechanical performance. In this work we use semi-crystalline polymers to generate blocky copolymers through the use of halogenation. Halogenation installs halogen moieties as pendant groups on the polymer backbone, which can then by used as a chemical handle for subsequent reactions to further incorporate functionality into the copolymer and achieve desired properties such as proton (hydrogen nuclei) transport in fuel cell membranes. Halogenation also allows for the generation of blocky semi-crystalline copolymers for compatibilizing polymer blends of materials like poly(tetrafluoroethylene) and poly(ether ether ketone). Also in this work, we discuss the additive manufacturing of mechanically reinforced elastomers. An elastomer is another type of crosslinked network, and a mechanically reinforced elastomer can be through of as a 3D rope ladder where some of the linear segments of rope are replaced with steel bars, thus increasing the amount of work required to deform the network. The last multiphase systems discussed are similar to salad dressing, where there is a continuous water phase and a microscopic particle phase. The microscopic particles in this work are amphiphilic block copolymers that change their solubility in water with temperature and also have functionalities that should allow for the binding of metals from water-based systems.

La perméabilité aux gaz et aux liquides des matériaux polymères est une propriété qui est mise à profit dans de nombreux domaines industriels. Cette thèse est effectuée dans l'optique de mieux appréhender la problématique de l'étanchéité des conduites flexibles par les polymères. Ainsi, les perméabilités de H2S, CO2 et CH4 dans le polyéthylène (PE) ont fait l'objet d'une étude effectuée dans le contexte de cette thèse. La perméabilité est une propriété qui résulte de la solubilisation des gaz dans le polymère puis de la diffusion de ces produits à travers la matière. La solubilité, qui caractérise l’aptitude d’un gaz à pouvoir s’absorber dans le polymère, est une propriété d’équilibre, qui pourra être étudiée par les techniques de Monte Carlo. La diffusion, qui caractérise l’aptitude d’un gaz à se mouvoir plus ou moins rapidement dans le réseau polymère, sera quant à elle, étudiée par dynamique moléculaire. Au dessous de la température de fusion, le polyéthylène est à l'état semi-cristallin. Cet état est composé de régions contenant des chaînes orientées aléatoirement (régions amorphes) et des régions contenant des chaînes orientées sur un réseau (régions cristallines). La morphologie complexe des polymères semi-cristallins présente des hétérogénéités de dimensions nanométriques, ce qui est difficilement accessible par la simulation moléculaire. A fin d'étudier la solubilité et la diffusion de gaz dans le polyéthylène semi-cristallin, nous modéliserons uniquement la phase amorphe au cours de ce travail. Par contre, l’effet des régions cristallines sur la phase amorphe sera pris en compte dans la simulation par une contrainte ad-hoc. / The gas permeability through the polymers is a property that is exploited in many industrial fields. The objective of this thesis is to better understand the problem of sealing of flexible pipes with polymers. Thus, the permeability of H2S, CO2 and CH4 in polyethylene (PE) was studied during this work. Permeability is a property resulting from the dissolution of gases in the polymer and then diffusion of these products through the material. Solubility, which characterizes the ability of a gas to be absorbed in the polymer, is a property of equilibrium, which can be studied by Monte Carlo techniques. Diffusion coefficient, which characterizes the ability of a gas to move more or less rapidly into the polymer network, will in turn studied by molecular dynamics.Below the melting temperature, polyethylene is in semi-crystalline state. This state is composed of regions containing randomly oriented chains (amorphous regions) and regions containing chains oriented regularly on a network (crystalline regions). The complex morphology of semi-crystalline polymers has nanometric heterogeneities, which is not easily accessible by molecular simulation. In order to study the solubility and diffusion coefficient of gases in semi-crystalline polyethylene, we model only the amorphous phase in this work. However, the effect of crystalline regions on the amorphous phase will be taken into account in the simulation by an ad-hoc constraint.