. Devenir, La dynamique de disparition est aisément visible sur un diagramme spatio-temporel (cf fig. 4.2)Des expériences préliminaires montrent que le temps de disparition peut varier d'un facteur 10 d'une expériencè a l'autre. Nous allonsétudierallonsétudier l'influence de quelques paramètres afin d'indiquer des pistes de réflexion pour la compréhension du comportement d'une goutte d'eau sur un gel d' agar. Si deséchellesdeséchelles de temps différentes semblent exister, le processus de disparition présente des caractéristiques communes dans tous les cas de figure : lors du dépôt une déformation est visible de part et d'autre de la ligne de contact (cf fig. 4.1 et fig. 4.2) ; et avec le temps la goutte s'affaisse, puis lorsque la ligne triple atteint l'angle limite de rétraction, elle recule jusqu'` a disparitioncompì ete du liquide. Si le phénomène physiquè a l'origine de la disparition de la goutte est la diffusion, il n'est pasévidentpasévident, expérimentalement de savoir s'il s'agit de diffusion dans le gel ou bien de diffusion du liquide dans l'air ambiant, c'est-` a-dire d'´ evaporation. Les deux phénomènes sont envisageables : la situation d'une goutte de liquide en mouillage partiel sur un substrat poreux est en partie analoguè a celle d'une goutte d'encre sur du papier qui a ´ eté largementétudiéelargementétudiée pour les besoins de l'industrie de l'´ editionimprégnation se fait par capillarité : il s'agit d'unécoulementunécoulement dans un poreux dont l'efficacité dépend

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