Ce travail porte sur la description et la compréhension de l’inversion de phase catastrophique utilisée pour l’émulsification de produits visqueux, à travers l’analyse des effets de formulation et de procédé sur la fraction de phase dispersée à laquelle le processus se produit et sur les mécanismes mis en jeu. Les suivis rhéologique et conductimétrique simultanés in situ de l’émulsification ont permis, du point de vue procédé, de mettre en avant l’influence du débit d’addition de la phase aqueuse sur la formation d’émulsions multiples du type e/H/E lesquelles, en augmentant notablement la fraction de phase dispersée apparente, sont responsables de l’inversion dès de faibles fractions de phase dispersée ajoutée. Au niveau formulation, l’augmentation de la viscosité de l’huile induit de manière remarquable la tendance de cette phase à devenir le milieu dispersé, conduisant à une inversion pour de très faibles fractions de phase aqueuse et donc à des émulsions finales très concentrées (de 80 à 95% en volume). Le suivi au microscope du phénomène d’inversion de phase par l’intermédiaire d’un écoulement de type « squeezing flow », a permis d’établir les conditions et les mécanismes conduisant à une inversion complète ou seulement partielle. La viscosité relative des phases aqueuse et huileuse est responsable d’une inversion catastrophique suivant un mécanisme de type agglomération – coalescence plutôt que de type inclusion/fuite tel que généralement admis. L’établissement d’un modèle mathématique basé sur les bilans de population et le caractère fractal du phénomène a permis de décrire l’évolution de la taille des gouttes multiples ainsi que la fraction de phase dispersée ajoutée à laquelle l’inversion se produit / This study deals with the description and understanding of catastrophic phase inversion during high viscous oil emulsification, through the analysis of the effects of formulation and process variables on the dispersed phase fraction at which the inversion is triggered and on the involved mechanisms. The simultaneous follow – up in situ of viscosity and conductivity measurements allowed, from a process point of view, to emphasize on the effect that the aqueous phase addition rate has on the formation of multiple w/O/W emulsions. Due to the formation of w/o/W emulsions, the volume of the effective dispersed phase greatly increases while at the same time, if the aqueous phase is added by very small fractions inversion of the w/o/W system can occur. In relation with formulation, an increase in oil viscosity greatly increased the tendency of the oily phase to become the dispersed phase. At the same time, it promoted the formation of highly concentrated emulsions (about 80 to 95 % in volume) after the inversion had occurred. The microscopical follow-up of emulsion morphology by means of squeezing flow, allowed us to establish the conditions and mechanisms that lead to partial or complete inversion. Even though literature sources lead us believe that inversion will occur through the “inclusion/escape” mechanism, experimental results showed that the relative viscosity between the phases promoted inversion through the mechanism of “agglomeration – coalescence” rather than “inclusion/escape”. A mathematical model based on population balances and on the fractal nature of multiple emulsions allowed us to describe the multiples drop size and effective dispersed phase evolution until inversion phenomena

[pt] Esta pesquisa focou-se no estudo da reologia de emulsões A O preparadas com diferentes óleos crus, dando atenção especial ao seu comportamento quando sujeitas a forças brownianas e hidrodinâmicas. Em uma microescala, as interações partícula-partícula e partícula-meio, ambas envolvidas no fenômeno de agregação, definem o comportamento reológico da emulsão devido às complexas estruturas criadas pelas gotículas quando sua concentração aumenta. Um estudo experimental foi realizado para visualizar as características da emulsão de acordo com sua concentração de fase dispersa e a taxa de cisalhamento aplicada, verificando-se a existência de tanto o fenômeno de coalescência quanto o de floculação durante o cisalhamento. A modelagem das interações entre as gotículas permitiu a previsão do comportamento da emulsão a partir da termodinâmica de coloides. Com isso, uma metodologia que ajustasse os dados experimentais incluindo parâmetros da taxa de cisalhamento e da concentração da fase dispersa foi proposto. Essa metodologia foi então aplicada a algumas equações reológicas comuns, encontradas na literatura. Este trabalho enfatiza a importância do estudo de emulsões em escala micro a fim de obter uma melhor compreensão dos processos de formação e quebra das complexas estruturas randômicas de agregados. Isso permite prever seu comportamento reológico e propor um modelo fenomenológico que o descreva. / [en] This research focused on studying the rheology of W O emulsions formed by different crude oils, with special attention to their behavior when subjected to Brownian and hydrodynamic forces. At a microscale level, particle-particle and particle-medium interactions, both of which are involved in the phenomenon of aggregation, define the emulsion s rheological behavior due to the complex structures created by the droplets as their concentration rises. An experimental study was performed in order to visualize the emulsions characteristics according to its disperse phase concentration and the shear rate applied, verifying the existence of both coalescence and flocculation phenomena during shearing. The modeling of interactions between droplets allowed the prediction of the emulsion s behavior by colloidal thermodynamics. With it, a methodology to fit the experimental data that included both the shear rate and disperse phase concentration parameters was proposed. This work emphasizes the importance of studying emulsion systems at a micro-scale level in order to obtain a better comprehension of the formation and breakage processes of complex and random aggregate structures. This allows the prediction of the emulsion s rheological behavior, and the proposition of a phenomenological model to best describe it.