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Fractional calculus descriptions of polymer viscoelasticity are becoming increasingly popular, as they allow a concise description of non-Debye relaxation and memory of strain history using a minimal parameter set. Use of fractional calculus to this end is frequently restricted to descriptions of dynamic behaviour, for example in dynamic mechanical thermal analysis (DMTA), where the dependence of the complex modulus on frequency can be expressed algebraically in closed form. However, this approach is only valid in the steady state. The material's approach to the steady state, and the effect of the slowly-decaying transient on DMTA measurements, are addressed here. "Data" are generated by integration of the time-domain fractional integral constitutive equation describing the fractional Zener model, and are analysed by a procedure inspired by a commercial DMTA instrument manual. Results show that the frequency dependence of the decay of the initial transient leads to difficulties in retrieving a single parameter set from the data, demonstrating that a specific procedure is required when evaluating long-memory materials. © 2008 SAGE Publications Los Angeles., SCOPUS: cp.j, info:eu-repo/semantics/published

On a series of examples from the field of viscoelasticity we demonstrate that it is possible to attribute physical meaning to initial conditions expressed in terms of Riemann-Liouville fractional derivatives, and that it is possible to obtain initial values for such initial conditions by appropriate measurements or observations. © Springer-Verlag 2006., SCOPUS: ar.j, info:eu-repo/semantics/published

Les polymères semi-cristallins à chaînes semi-rigides, bien qu’abondamment utilisés dans la vie quotidienne, représentent des systèmes complexes qui ne sont pas encore parfaitement compris. Parmi les nombreux domaines de recherche sur cette famille de polymères, l’étude de la morphologie semi-cristalline et des processus de cristallisation et de fusion de ceux-ci restent des sujets très importants. L’investigation de la morphologie semi-cristalline est rendue difficile car elle présente une structure hiérarchique composée de plusieurs niveaux d’organisation, dont le plus petit est observable à une échelle très réduite de quelques nanomètres. De plus, les aspects liés à la cinétique des processus de cristallisation et de fusion n’ont pas toujours permis de bien les mettre en évidences, les rendant ainsi par très bien compris. Cependant, les nouvelles avancées technologiques dans le domaine de la physique expérimentales ont beaucoup profité à la science des polymères. Dans ce travail, une contribution originale est apportée à cette étude, et cela en combinant diverses techniques expérimentales permettant des mesures calorifiques et structurales en températures et temps réels. L’intérêt c’est porté sur les polymères linéaires aromatiques tels que le polyéthylènes teréphthalate, PET, et le polytriméthylène téréphthalate, PTT, caractérisés par une température de transition vitreuse supérieure à l’ambiante ( Tg > 50°) et une température de fusion élevée (Tm>220°C), offrant ainsi une assez large gamme de température de cristallisation (Tm-Tg). L’étude de la structure semi-cristalline du PET à l’échelle du nanomètre et de la relaxation des phases amorphes présentes dans sa structure est facilitée par l’utilisation d’un diluant amorphe tel que le polyétherimide (PEI), qui forme un mélange miscible avec le PET. L’utilisation de microscopie de force atomique AFM à haute température a permis d’observer la cristallisation isotherme de PET en temps réel et de décrire ainsi, Doctorat en sciences, Spécialisation physique, info:eu-repo/semantics/nonPublished

Depuis une dizaine d'années, les polymères hyperbranchés sont apparus dans la littérature. Ils possèdent un grand nombre de branchements ainsi qu'un grand nombre de groupes terminaux. La structure globulaire des polymères hyperbranchés les empêche de former des enchevêtrements. Il en résulte un avantage décisif pour leur application sous forme de revêtement de surface: les polymères hyperbranchés ont une viscosité plus faible à l'état fondu que les polymères linéaires. Cela permet aisément de les étaler sous forme de films minces sans utiliser de solvant. De plus, les polymères hyperbranchés possèdent un grand nombre de groupes terminaux qui peuvent être fonctionnalisés avec des monomères photoréticulables.Le but du travail de thèse est d'obtenir de nouveaux revêtements de surface, à partir de polymères hyperbranchés ou de polymères fortement branchés, qui trouveront leur application dans l'industrie chimique.La thèse s'articule autour de trois chapitres de synthèse suivis d'un chapitre traitant de la photoréactivité des oligomères linéaires, fortement branchés, et hyperbranchés.La première approche de synthèse envisagée est la copolymérisation alternante radicalaire. Divers maléimides ont été engagés dans des copolymérisations radicalaires avec des allyléthers sans succès. Lorsque ces derniers sont remplacés par des vinyls éthers, une copolymérisation alternante est observée. Néanmoins, une importante irreproductibilité est constatée, certains batchs donnant lieu à une gélification.La seconde voie de synthèse étudiée est l'approche classique de polycondensation de monomères de type AB2 .Le monomère AB2 est obtenu par addition de Michael de la diéthanolamine sur l'acrylate de méthyle. La polycondensation est concomitante avec l'acrylation des fonctions alcools. La compétition entre ces deux réactions limite les masses molaires accessibles bien que les réactions de transestérification soient catalysées par des dérivés du Zr et que la stoechiom, Doctorat en sciences appliquées, info:eu-repo/semantics/nonPublished

Fractional calculus descriptions of polymer viscoelasticity are becoming increasingly popular, because they allow a concise description of non-Debye relaxation and memory of strain history using a small number of parameters. However, use of fractional calculus to this end is frequently restricted to description of dynamic behaviour, such as in dynamic mechanical thermal analysis (DMTA), where the dependence of the complex modulus on frequency can be expressed algebraically in closed form. However, this approach is only valid in the steady state. The problem of the approach to steady state and of the effect of the slowly-decaying transient on DMTA measurements is addressed here. Copyright © 2006 IFAC., SCOPUS: cp.p, info:eu-repo/semantics/published

Liquid crystalline materials forming columnar mesophases are of importance for both the fundamental research and technological applications due to their supramolecular architecture allowing for one-dimensional charge transport. The potential applications of these materials include light emitting diodes, solar cells, field effect transistors and photovoltaic cells. However, to design a LC material suitable for a particular application, a fundamental understanding of the structure-property relationships is needed.In the present thesis, a variety of systems forming columnar mesophases have been explored. They include small molecular weight compounds (triphenylene, phthalocyanine derivatives and star-shaped mesogens) and polymer materials. The research was focused on the study of the influence of the molecular architecture and specific interactions such as hydrogen bonding on the supramolecular organization in the mesophase, as well as on the influence of columnar mesophase on crystal growth. The main results of the thesis are summarized below.The influence of hydrogen bonding on the structure and charge carrier mobility was investigated for a triphenylene derivative, hexaazatriphenylene, having lateral alkyl chains linked to the core via amide groups. These linking groups provide the possibility to form inter- and intra-molecular hydrogen bonds. Acting as “clamps”, the inter-molecular hydrogen bonds are found to enforce the attractive interactions between the molecules in the column. Thus, the columnar mesophase formed by this system is characterized by the smallest inter-disk distance ever found in columnar mesophases (3.18 Å). The improved intra-columnar order brings about a higher charge carrier mobility (0.02 cm2/Vs) as compared to other triphenylene derivatives without hydrogen bonds. Phthalocyanine derivatives, which are liquid crystalline at ambient temperature, could be suitable for opto-electronic applications due to their improved processibility and, Doctorat en sciences, Spécialisation physique, info:eu-repo/semantics/nonPublished

Various experiments involving strain reversal have been described by Kitagawa et al. For example, after initially loading and unloading a polymer sample, stress "relaxation" showed an initial increase in stress. This behaviour was called "Unusual Behaviour after Strain Reversal" or UBASR by Kitagawa et al. and attributed to an effect of non-linear behaviour. This behaviour is however similar in kind to thermal expansion occurring before contraction after an indirect quench as observed some years ago by Kovacs. We show here that this behaviour can also occur in the range of linear viscoelasticity, and it is then simply a result of fading memory. Such fading memory is particularly well described by models containing β elements, or springpots. In this paper, Kitagawa's data is analysed using a viscoelastic model containing springpots, described by a fractional differential constitutive equation. A novel method of integration based on Boltzmann superposition is developed. This method is shown to be applicable to non-linear viscoelasticity. The model affords a good phenomenological description of the changes in so-called "unusual" behaviour induced by non-linearity. © Springer-Verlag 2004., SCOPUS: ar.j, info:eu-repo/semantics/published

In recent decades constitutive equations for polymers involving fractional calculus have been the object of ever increasing interest due to their special suitability for describing self-similarity and memory effects which are typical of viscoelastic behaviour in polymers. Thermodynamic validity of these equations can be ensured by obtaining them from analog models containing spring-pots with positive front factors. Failure of self-similarity in real polymers at short (local) and long (whole chain) scales has been addressed previously. In the past interest in fractional differential descriptions of polymer viscoelasticity has been mainly concerned with linear viscoelasticity despite the fact that in processing and end use conditions are largely in the non-linear range. In this paper extension of fractional calculus models to the non-linear range of viscoelasticity is attempted by accounting for stress activation of deformation and strain acceleration of annealing. Calculated stress-strain curves are compared with experimental results on an amorphous polymer (polycarbonate). The model adequately describes the general trends of yield and post-yield behaviour but does not properly describe the gentle approach to yield observed experimentally. © 2004 Kluwer Academic Publishers., SCOPUS: cp.j, info:eu-repo/semantics/published

Hierarchical viscoelastic elements whose behaviour is intermediate between linear elasticity and Newtonian viscosity (springpots) have been introduced previously into classical analog models describing linear viscoelastic behaviour. This approach allows a concise description of typical polymer behaviour, including non-exponential relaxation, memory effects and hierarchy of viscoelastic transitions. This approach is extended in the present work to describe complex behaviour, including failure of time-temperature superposition in a semi-crystalline polymer, and the terminal transition from self-similar viscoelasticity to pure flow in a thermoplastic elastomer. Tschoegl's formulation of a finite Gross Marvin ladder model is generalized and applied to other models, and this approach is compared with Friedrich's method based on application of an exponential cutoff to the relaxation function. The method is illustrated using dynamic mechanical measurements on a triblock adhesive in isothermal frequency sweeps. This material displays thermorheological complexity precluding application of time-temperature superposition. Tschoegl's formulation affords a better description of this material than Friedrich's approach. The method described here is a useful alternative to time-temperature superposition requiring a limited number of adjustable parameters. © 2003 Elsevier B.V. All rights reserved., SCOPUS: ar.j, info:eu-repo/semantics/published

The present work focuses on the effects of thermomechanical history on the structure and mechanical behaviour of PVDF. In the first part of our investigation differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) are used to follow the evolution of the structure of PVDF after different annealing treatments or deformation. Processing has a significant impact on the quantities of the amorphous and crystalline phases and their interphase. Subsequent annealing affects these phases in a different proportion. This influence depends on the position of the annealing temperature in comparison with the upper glass transition temperature of PVDF. Deformation induces conformational change in the injection moulded samples. Thus, the α conformation is transformed to the β conformation. The β conformation also has a noticeable influence on the mechanical behaviour of the material, which will be discussed in the second part of our study. © 2001 Elsevier Science Ltd., SCOPUS: ar.j, info:eu-repo/semantics/published

Conformational changes are observed during sub-Tg annealing of solution-cast films of BPA-polycarbonate by following changes in the conformationally sensitive IR aromatic breathing band at 1600 cm-1. The rate of conformational relaxation is compared with published data on enthalpy and volume relaxation on the same polymer. The relaxation rates and timescales converge in the immediate vicinity of Tg, but diverge at temperatures below Tg-15 K and conformational energy only accounts for a very small fraction of observed enthalpy relaxation. The results suggest that a single process is active in volume and conformational relaxation and that at least two processes contribute to enthalpy relaxation. © 2001 Elsevier Science Ltd., SCOPUS: ar.j, info:eu-repo/semantics/published

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The following study is the continuation of our previous work, which consisted in analysing the structural evolution of PVDF after different thermomechanical treatments. In this second part, we will discuss the influence of these evolutions on the mechanical behaviour. This has been determined by tensile drawing, creep or dynamic measurements. The observed changes in behaviour are strongly influenced by the different processing routes. Therefore, the beta conformation appears only when stretching injection-moulded samples (IM) and is accompanied by an increase of rupture stress compared to yield stress, which is not the case for compressed samples (CM). The influence of annealing on mechanical behaviour varies with annealing and measurement temperature. Thus, annealing at 80°C after standardisation increases the Young's modulus at 120°C and decreases it during drawing at 23°C compared to other annealing treatments. © 2001 Elsevier Science Ltd., SCOPUS: ar.j, info:eu-repo/semantics/published

The EN 3665 test is used to compare the filiform corrosion of aluminium substrates pretreated with Cr6+ and coated with different powder paints. The influence of the mechanical properties (tensile test and adhesion test), the chemistry (DSC and FTIR analysis) and the physical properties (oxygen and water permeations) of the paints on filiform corrosion is measured. The corrosion promoted filaments are studied morphologically and electrochemically. Their growth seems to be due to a combination between specific mechanical properties of the paints and their adherence on the pre-treated substrates. The influence of the paint thickness is also illustrated. © 2001 Elsevier Science B.V. All rights reserved., SCOPUS: ar.j, info:eu-repo/semantics/published

Several apparently contradictory models predicting critical conditions for chain entanglement in flexible polymers have appeared in recent years. Some model predict entanglement molecular weight to increase, and others to decrease, with chain stiffness. Literature data are used here to compare model predictions. An inverse correlation between characteristic ratio and segmental aspect ratio is found, allowing the contradiction to be resolved. In flexible chains, it is found that the aspect ratio of a Kuhn step length is approximately independent of molecular characteristics and that stiffness depends more strongly on segmental aspect ratio than on characteristic ratio., SCOPUS: ar.j, info:eu-repo/semantics/published

The effect of annealing and ageing on i.r. absorption spectra of polycarbonate are investigated. Annealing is accompanied by conformational rearrangements, visible through changes in trans-trans and trans-cis populations, whereas ageing entails only extremely local rearrangements The connection between these observations and the concept of structural temperature is discussed. © 1997 Elsevier Science Ltd., SCOPUS: ar.j, info:eu-repo/semantics/published

Viscoelastic elements derived from hierarchical models are introduced into classical models. Some of the resulting "modified" models are shown to yield the fractional differential descriptions of viscoelastic behaviour given previously by Friedrich, and to comply automatically with previously formulated thermodynamic constraints. The reasons underlying the previously observed differences between fractional differential and fractional integral formulations are clarified. The "modified" models are shown to be capable of describing experimentally observed dynamic viscoelastic behaviour over a wide frequency range, including multiple transitions, using a limited number of free parameters., SCOPUS: ar.j, info:eu-repo/semantics/published

A differential equation for retarded compliance can be derived from a fractal rheological model. The equation can be generalized to account for aging prior to and during creep, and for non-linearity at high extensions. The generalized equation is shown to give an excellent description of aging in semi-crystalline polymers., SCOPUS: ar.j, info:eu-repo/semantics/published

A constitutive equation for viscoelastic behavior containing time derivatives of stress and strain to fractional order is obtained from a fractal rheological model. Equivalence between tree and ladder fractal models at long times is demonstrated. The fractional differential equation is shown to be equivalent to ordinary differential formulations in the case of a simple power-law response; the adequacy of such formulations to describe non-linearity has been demonstrated previously. The model gives a good description of viscoelastic behavior under all stress modes and will be extended in future to include aging effects. © 1994 Steinkopff-Verlag., SCOPUS: ar.j, info:eu-repo/semantics/published

The experimental dependence of the strain-optical coefficient of hot-stretched polycarbonate on preorientation is investigated and compared with a model based on deformability of orienting elements. The model exhibits an interaction between orientation and distortion, enhancing the contribution of the latter which is never negligible, even at high orientations. The model, which intrinsically requires no free parameters, gives a satisfactory qualitative description of experimental results; with only one free parameter quantitative agreement between theoretical predictions and experimental results is obtained. © 1992 Steinkopff-Verlag., SCOPUS: ar.j, info:eu-repo/semantics/published

A model for the effect of orientation dependence of polarizability anisotropy on birefringence is given and compared with literature data. If this dependence arises through bond angle distortion, the model shows a significant contribution to birefringence but a very small contribution to strain, accounting satisfactorily for differences in birefringence between hot-drawn and cold-drawn samples, for discrepancies between measurements of orientation obtained by different experimental methods and for previous observations on orientational behavior of preoriented polycarbonate at low additional strain., SCOPUS: ar.j, info:eu-repo/semantics/published

The critical draw ratio for initiation of intrinsic crazing in polycarbonate below the glass transition temperature has been determined after preorientation in the melt. Even when referred to the isotropic state, this ratio is found to depend not only on the extent of preorientation but also to be distinctly anisotropic. Under the assumption that intrinsic crazing occurs at the maximum extension of the entanglement network, these results are incompatible with a strain-dependent but homogeneous breakdown of the entanglement network, but can be interpreted in terms of departure from affine transformation of the radius of gyration of an entangled length., SCOPUS: ar.j, info:eu-repo/semantics/published

An expression for the radius of gyration of a deformed chain is derived, assuming affine deformation of end-to-end vectors defining an entangled length, and random chain behaviour on a shorter scale. This expression is compared with small-angle neutron scattering results from the literature on variation with strain of the radius of gyration. The theoretical variation of the radius of gyration with strain is used to derive an expression for the dependence of limiting glassy-state extensibility on rubbery state pre-strain. This expression is found to give an adequate description of experimental observations of limiting extensibility identified with the critical strain for initiation of intrinsic crazing. © 1988 Chapman and Hall Ltd., SCOPUS: ar.j, info:eu-repo/semantics/published

Birefringence has been measured on yielded specimens of polycarbonate in simple tension in creep and stress relaxation. The pseudo-affine and random-chain affine models both fail to describe the experimental relationship between birefringence (or orientation) and strain. A new model assuming affine deformation of chain ends and non-random chains is presented, adequately describing the trends of experimental data. © 1987., SCOPUS: ar.j, info:eu-repo/semantics/published

Mechanical properties of linear polymers are frequently described via identification of the tangle of chains with an equivalent temporary network. An alternative model is presented here assuming diffuse entanglements, in keeping with the tube model. This model allows entanglement molecular weights to be predicted from knowledge of conformational characteristics of the chains. In this paper predictions of the diffuse entanglement model and of the temporary network model are compared with experimental data on critical molecular weight from viscosity and entanglement molecular weight of binary blends, and on crazing properties. Both models exhibit similar trends, although quantitative description is generally better under the assumption of diffuse entanglements. © 1986 Chapman and Hall Ltd., SCOPUS: ar.j, info:eu-repo/semantics/published

Recent investigations into the development of molecular orientation on straining in the glass transition range and above (e.g. refs. 1 and 2) have led to interpretation of results in terms of rubber elasticity theory, discrepancies being accounted for via a strain-dependent entanglement molecular weight. It has been shown recently that experimental orientation functions can also be adequately described by a model involving two components of strain (extensional and orientational)3; nevertheless, it might be wondered whether part of the above-mentioned discrepancy could stem from an inadequacy of the rubber-elasticity theory in the case of short-chain molecules, i.e. chains in which the number of statistical segments is too small for statistical methods to apply. This work was undertaken in order to compare orientation functions obtained using alternative models with those derived from classical theories. © 1986., SCOPUS: ar.j, info:eu-repo/semantics/published

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