The knowledge of solid-state second phase heterogeneous nucleation process is limited due to the experimental difficulty, such as tiny length scale, short time period, and high temperature condition. In recent years, some significant breakthroughs in nucleation studies have been achieved by aid of computational techniques. In this study, we apply molecular dynamics (MD) simulations to perform with heterogeneous nucleation occurring at grain boundaries (GB) during the austenite (FCC) phase to ferrite (BCC) phase transformation in a pure Fe polycrystalline system. A neighbor vector analysis (NVA) method has been introduced and it is shown how the NVA can be used to determine the misorientation of grain or interphase boundaries, which allow a further investigation of the boundary structure correlated to interfacial energy and mobility during the nucleation and early grain growth stage. Meanwhile, benefited from the MD technique, the bulk energy, grain boundary energy, and interfacial energy can be individually captured during the simulations, which allow a detail analyze of the shape, critical size and nucleation energy of specific nuclei, through the classical nucleation theory (CNT) and according to a faceted-spherical cap geometric model (FSC). In addition, we also compared the results from the classical approach with a new algorithm that combination of the multi-phase field model (MPFM) and the nudged elastic band (NEB) method to demonstrate the CNT in the solid-state conduction. Finally, we extend our simulation method to a more complex triple GB junction nucleation event, and investigate the non-classical barrier-free nucleation behaviors. The results support the critical informations to clarify the initial state of austenite to ferrite transition, and improve our knowledge of the heterogeneous nucleation process, which help to bridge the gap between the experimental measurements and the theoretical calculations. The simulation method also provided a new approach for studying the complicate heterogeneous nucleation phenomenon in solid-state for a wide variety of polycrystalline material systems. / Thesis / Doctor of Philosophy (PhD)

Les biopuces connaissent un grand essor depuis quelques années avec des applications possibles pour l’ADN, les protéines et les oligosaccharides. Une puce à oligosaccharides présente des difficultés par rapport à une puce à ADN notamment par les contraintes en température et il existe moins de travaux dans ce domaine. Ce travail est donc consacré à l’étude d’une puce à oligosaccharide, par synthèse supportée et par masquage avec un film de polymère. Le procédé de fabrications est particulièrement détaillé.Nous étudions tout d’abord expérimentalement la formation d’un film de polymère obtenu par évaporation d’une goutte de solution polymérique sur une surface structurée chimiquement(zone de mouillabilité différente) en suivant son évolution transitoire. Nous montrons que ce type de surface hétérogène est particulièrement adapté pour la fabrication de biopuces.D’autre part, nous réalisons un modèle numérique de l’évaporation d’une goutte de solution polymérique sur une surface chauffée à partir de la méthode de la lubrification et d’un modèle de « hauteur de résine ». Les résultats expérimentaux et de simulation numérique sont comparés et montrent un bon accord qualitatif sur la forme des films de polymères résultant de l’évaporation.Dans ce travail, la synthèse supportée de biopuces à oligosaccharide est menée à bien en utilisant des polymères et des surfaces judicieusement choisies. En particulier, la technique de masquage par film de polymère se révèle être très bien adaptée pour protéger les oligomères à la fois à hautes et à très basses températures. / Biochips are experiencing recently a great success with possible applications for DNA,proteins and oligosaccharides. An oligosaccharide chip presents difficulties compared to aDNA chip because of the many temperature constraints and less work has been performed inthis area. This work is devoted to the study of a oligosaccharide chip fabricated par supportedsynthesis and protected with a polymer film. The manufacturing process is particularlydetailed.We first examine experimentally the formation of a polymer film obtained by evaporation of adrop of polymer solution on a chemically structured surface (zone of different wettability) byfollowing its transient evolution. We show that this type of heterogeneous surface isparticularly suitable for manufacturing biochips. On the other hand, we propose a numericalmodel of the evaporation of a drop of polymer solution on a heated surface using thelubrication method and a “height of resin”. The experimental results and numericalsimulations are compared and show good qualitative agreement on the shape of the polymerfilms obtained after evaporation.In this work, the supported synthesis of oligosaccharide microarrays was carried out usingpolymers and surfaces which have been carefully chosen in preliminary testing. In particular,the masking technique using polymer film turns out to be highly suitable for protectingoligomers at both high and very low temperatures.