Morphologies et gradients de concentration induits par le séchage dans des solutions polymères et des gels

Cette thèse présente l étude de morphologies de surface induites, à la surface de films polymères et de gels, par le séchage. La première partie porte sur la séparation de phases induite par évaporation du solvant dans des films réalisés à partir d un mélange de deux polymères immiscibles, l un vitreux, l autre cristallin à température ambiante, en solvant commun. La morphologie obtenue dépend des conditions de séchage et des propriétés physicochimiques du système. Nous avons mis en évidence, en fonction de la composition du mélange, une inversion de morphologie. L étude d une composition donnée permet de distinguer, en fonction de la vitesse de séchage, différents régimes. La seconde partie traite de la formation, à la surface de gels chimiques de polyalcool vinylique, d instabilités de plissement dépendant des conditions de séchage et de synthèse. Cette morphologie est attribuée à la formation d une peau vitreuse qui subit, lors de la contraction du gel, une force de compression relaxée par la formation de plis. Nos travaux confirment expérimentalement l existence de cette peau vitreuse (microscopie à force atomique) et estiment son épaisseur par simulation.PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Wrinkling of a nanometric glassy skin/crust induced by drying in poly(vinyl alcohol) gels

International audienceDuring drying of a chemically crosslinked poly(vinyl alcohol) gel, we observed, by atomic force microscopy (AFM) and scanning electronic microscopy, micron-order wrinkling which remains until the end of drying. We show that while at high humidity drying is homogeneous and no surface instability is observed, fast drying at low humidity induces the formation of a glassy skin layer on the soft bulk that wrinkles because the skin is compressed as the bulk contracts. The role of the glass transition is not only to create a mismatch of the elasticity with the bulk but also to remove the in-plane tensile tension which stretches the skin before drying. We proved experimentally the presence of this thin glassy skin on the wet bulk by approach–retract curve measurements in AFM. We also comment on the effect of mechanical restraint and the observation of hierarchical wrinkling over different length scales

Guidelines: Anaesthesia in the context of COVID-19 pandemic

International audienceObjectives: The world is currently facing an unprecedented healthcare crisis caused by the COVID-19 pandemic. The objective of these guidelines is to produce a framework to facilitate the partial and gradual resumption of intervention activity in the context of the COVID-19 pandemic.Methods:The group has endeavoured to produce a minimum number of recommendations to highlight the strengths to be retained in the 7 predefined areas: (1) protection of staff and patients; (2) benefit/risk and patient information; (3) preoperative assessment and decision on intervention; (4) modalities of the preanaesthesia consultation; (5) specificity of anaesthesia and analgesia; (6) dedicated circuits and (7) containment exit type of interventions.Results:The SFAR Guideline panel provides 51 statements on anaesthesia management in the context of COVID-19 pandemic. After one round of discussion and various amendments, a strong agreement was reached for 100% of the recommendations and algorithms.Conclusion:We present suggestions for how the risk of transmission by and to anaesthetists can be minimised and how personal protective equipment policies relate to COVID-19 pandemic context