Habilitation a diriger des recherches de l’université de savoie

UNIVERSITÉ DE SAVOIE ÉCOLE DOCTORALE DE L'UNIVERSITÉ DE SAVOIE

HABILITATION A DIRIGER DES RECHERCHES DE L’UNIVERSITÉ DE SAVOIE

Nom (1) : Flandin Prénom : Lionel

Date de la soutenance : 27 Octobre 2006 Heure : 14 :00 Salle : Amphi 1 IUT-C
Lieu de la soutenance : IUT de Chambéry

Titre : Multiscale Relationships in Polymer-Based Heterogeneous Systems: Experiments and Simulations

Spécialité : Chimie des matériaux

Résumé 

My research interests are primarily focused on the effect of filler particles, and other heterogeneities on polymers. I have worked on many projects, but there are several things that they all had in common. First, nearly all projects involved searching for the structural parameters that governed the macroscopic properties of the polymers and composite materials. A second common denominator is that even though my work was performed in an “academic context”, the goals were targeted toward industrial needs. Lastly, the methods and procedures were similar; they were all based on experimental results obtained for various scales of measurement.

Hence, multi-scale modeling was very useful and beneficial for these projects. The models developed (mainly numerical and sometimes analytical) were initially derived from experimental evidence and then validated and improved with further experimentation. The refined models provided an efficient means of: (i) optimizing the composites according to specific needs, (ii) better understanding the hierarchical relations between the different scales, (iii) controlling the micro or meso structure and thereby the macroscopic properties. This study of the relations between structure and properties was performed on a wide variety of physical properties and materials. However, the electric and dielectric properties of composites constituted the majority of it and were presented in the report. The remaining property investigations provided supplemental but valuable information. This work often requires altering various conventional experimental techniques or using well-known techniques for new purposes. I also developed, when needed, several unconventional but necessary measurement techniques.
This report contains two major parts which are separated according to the nature of the fillers:

Part I : Conducting fillers. In the first part, the main interest both for application and fundamental point of view, is related to the changes in properties in the vicinity of the sharp percolation transition. After a brief introduction to the percolation theory, this part will be subdivided in three chapters: Chapter 1. presents a numerical method that correlates the mesostructure to the macroscopic electrical properties both in two and three dimensions. Chapter 2. will show that an external variable (the mechanical stress) may largely alter the microstructure of the percolating network within composites as revealed the macroscopic conductivity. The understanding of the mesoscale changes will be based on the chemical structure of the polymer matrix. Chapter 3. is devoted to the description of a unique case in term of percolation behavior, which made possible the control of the phase arrangement within the composite and thereby the control of the macroscopic resistivity.
Part II : Insulating fillers. In the second part, the main interest is to obtain good electrical insulators, i.e. that can withstand large electric fields. This part thus starts with a brief introduction to the common failure mechanisms, associated with the dielectric breakdown and is also divided in three chapters: Chapter 4. is devoted to the description of a numerical simulation of the relationships between mesostructure and dielectric breakdown. Chapter 5. reveals the influence of the processing conditions of a composite utilized in the industry on the microstructure and the quantitative consequences on breakdown properties. Chapter 6. presents the aging of these composites under “real word” conditions which will further be compared to accelerated aging performed in controlled conditions - in the laboratory. A comparison of the two aging situations will furnish a quantitative understanding of the relative influence of the chemical and physical contributions to the aging process.
Mots-clé : Polymer, Composite, Electrical properties, Percolation, Breakdown, Conducting, Insulating
Laboratoire(s) de recherche : LMOPS UMR 5041 – CNRS – Université de Savoie
Directeur(s) de recherche, le cas échéant :

Composition du jury : Prof. N.D. Albérola LMOPS, Université de Savoie Prof. E. Baer CAPRI CWRU, Cleveland, Ohio Prof. Y. Bréchet LTPCM INP de Grenoble [Rapporteur]

Prof. C. Brosseau LETS UBO, Brest Prof. J.-Y. Cavaillé GEMPPM INSA de Lyon [Rapporteur] Prof. A. Hiltner CAPRI CWRU, Cleveland [Rapporteur]