Nature-inspired systems exploiting porous media for multiphase flows

Abstract

This thesis studies multi-phase flows within two different types of porous nature-inspired material systems: multi-layered feathers and synthetic trees. (1) How multilayered feathers enhance underwater superhydrophobicity. Inspired by ducks, here we demonstrate that air pockets can withstand up to five times more hydrostatic pressure when using stacked layers of synthetic feathers instead of a single layer. The mechanism for the multi-layered enhancement is the more tortuous pathway required for water impalement, which serves to pressurize the air pockets enclosed in the pores. We study this air compression effect using a probabilistic model, in which we quantify the tortuous pathway in stacked feather layers in terms of filled volume fraction of the pores. Our findings suggest that multi-layered coatings could enable robust underwater superhydrophobicity. (2) Oil-Water separation using synthetic trees. In the world's tallest trees, water evaporating from leaves generates enough suction to lift water over 100 m high. Transpiration can similarly be attained in synthetic trees by coupling nanoporous leaves" with conduits mimicking xylem capillaries. Here, we demonstrate that by adding filters to the free ends of the xylem conduits, the hydraulic load generated by transpiration can be used for oil-water separation. The working principle is illustrated using the pressure balance equation for the synthetic tree.