Research

 

Free surface flows of complex liquids in microscale occur in many different situations, such as continuous coating process of a substrate, fluid displacement flows inside small passages and porous materials, flow of emulsions and complex dispersions and two-phase flows in microfluidics devices. That is the focus of our research.

 

Research on these aspects are challenging. The complex structure of the liquid may lead to non-linear behavior of the fluid when sheared or extended. Indeed, they can depart substantially from Newtonian behavior at the strain rates they suffer in these small scale flows. The presence of the free boundaries (liquid/air and liquid/deformable solid interfaces) leads to strong non-linearities on the flow.

The geometry of the flows is only a fraction of a milimeter (microscale) and capillary effects are usually very important in all the situations. We study these flows by both theory and experiments. The theoretical analysis consists of solving the conservation equations for steady and transient free surface flows coupled with appropriate constitutive models that describe the mechanical behavior of different complex liquids. The stability of the flows are analyzed by linear stability theory and its response to ongoing periodic oscillation is studied by transient and frequency response analysis. The system of differential equations are solved by Galerkin and Petrov-Galerkin / Finite Element Method. The experimental analysis consists of preparation and characterization of complex liquids, flow visualization and measurements in benchtop physical models of the real situation and porous media flow experiments (core flooding tests).

The applications of the different research projects are focused on coating processes, flow of complex liquids through porous materials, microfluidics and microencapsulation, and emulsion formation and stability. The activities have been developed with collaboration and financial support from different industries in Brazil (Petrobras, 3M, Repsol-Sinopec Brasil, Chevron Brasil, Statoil Brasil, Shell), USA (3M, Dow Chemicals) and Japan (Fuji Photo Film); and from Brazilian government research funding agencies (CNPq, FINEP and FAPERJ).