P 10/02


Modeling of transport of rheological complex multiphase fluids in pores and porous membranes

Emulsions are used for special liquid formulations. For instance, multiple emulsions like w-o-w systems (water in oil in water) are utilized in pharmaceutics, medical and food technology. The inner water phase is encapsulated and can be applied for a controlled release of e.g. drugs. Pickering emulsions are formulated by dispersing colloidal particles at fluidic interphases and thereby encapsulate a fluid that may be released by coalescence of the inner phase or by permeation through the outer membrane. An established method for producing and formulating emulsions and encapsulated liquids is performed by dispersion of liquid/liquid mixtures in micro or meso structured porous membranes. Here especially shear sensitive liquids may be formulated. This premix emulsification process in porous ceramic membranes offers flexibility in droplet size generation, mechanic stabilization of membranes and complex fluid formulations. In the project, micro encapsulation and multiphase transport, mixing and dispersion in porous membrane structures are to be analyzed by means of experiments as well as modeling and simulation. Efficient formulation methods for complex fluid-fluid dispersions and encapsulations of dispersed systems will be derived in this way. In this second phase of the premix-emulsification project, liquid formulations are to be investigated that form complex rheological properties during processing. Liquid surface rheology properties in terms of surface active components (like surfactants, polymers and particles) are mainly responsible for changes in the liquid topology like fragmentation and coalescence. Relevant liquids that are formulated in liquid/liquid dispersions are to be treated by their non-newtonian behavior. Here for instance polymer-solutions either are described as shear-thinning fluids and/or by their viscoelastic behavior. During emulsification processes in pores and channels special focus needs to be done on liquid stretching phenomena. Essential contributions to the dispersion process result from the stretching of liquid filaments. As an example the figure illustrates the stretching of a droplet neck during droplet de-attachment from a porous membrane (left, simulation result) and the formation of secondary droplets (bead on a string) during filament stretching (right, liquid strain experiment in elastic fluid). These properties frequently are found during premix emulsification and need to be adequately addressed. In the project main challenges and tasks are to be addressed as: - Modeling of transport of multiphase fluids in micropores and microporous channel membranes - Derivation of modeling strategies for non-newtonian shear and strain behavior of multiphase liquid/liquid dispersions with sharp or diffusive interface - Modeling of interface rheology (surface convective effects due to concentration gradients) - Modeling of liquid topology changes like filament breakage / liquid coalescence - Experimental analysis of stretching rheology of liquid/liquid dispersions in non-newtonian liquids - Experimental analysis of premix emulsification process of complex liquids in porous membranes - Cooperation in the MIMENIMA frame with fluid transport and mechanical characterization projects and membrane generation and functionalization projects.

Contact: Fritsching , Schulz