On-demand emulsions from oscillatory two-phase shear flows
Lead Research Organisation:
University of Manchester
Department Name: Physics and Astronomy
Abstract
Solvent extraction across a liquid-liquid interface is a diffusion-limited process that relies on the dispersion of one phase in the other to maximise the surface area between the phases, e.g., the purification of nuclear fuel in the PUREX process. Similarly, chemical reaction kinetics in liquid liquid systems, e.g., nitration of aromatics, are controlled by the rate of generation interfacial area. Surfactant-stabilized emulsification of the two phases is routinely used to disperse them. However, this creates industrial design challenges because of the added requirement of rapid phase separation following the process. The project aims to propose a purely hydrodynamic method to generate on-demand stabilizer-free emulsions through external forcing, which rapidly return to separated phases upon interruption of the forcing.
The specific objectives are threefold: a) characterize the fundamental interface breakup mechanism which relies on competition between inertial, viscous, and surface tension forces; b) tailor emulsion properties depending on the fluid properties and vibrational parameters; c) use the fluid mechanical device to optimize on-demand solvent extraction. We will use a combined approach of quantitative experiments and Lattice-Boltzmann (LB) simulations to gain insights into interface breakup with a focus on deriving simple models for interface breakup in two-layer oscillatory shear flows (objective (a) & (b)). Herein we will additionally characterize interface breakup in two-phase systems where one fluid exhibits non-Newtonian properties. We then turn to the development of a laboratory model of solvent extraction and provide a proof-of-concept of our system and evaluate its efficiency depending on the vibrational regime (objective (c)). The proposed project will not only advance fundamental understanding of interface breakup in both Newtonian and complex fluids but also potentially offer new design solutions for industrial diffusion-limited processes.
The specific objectives are threefold: a) characterize the fundamental interface breakup mechanism which relies on competition between inertial, viscous, and surface tension forces; b) tailor emulsion properties depending on the fluid properties and vibrational parameters; c) use the fluid mechanical device to optimize on-demand solvent extraction. We will use a combined approach of quantitative experiments and Lattice-Boltzmann (LB) simulations to gain insights into interface breakup with a focus on deriving simple models for interface breakup in two-layer oscillatory shear flows (objective (a) & (b)). Herein we will additionally characterize interface breakup in two-phase systems where one fluid exhibits non-Newtonian properties. We then turn to the development of a laboratory model of solvent extraction and provide a proof-of-concept of our system and evaluate its efficiency depending on the vibrational regime (objective (c)). The proposed project will not only advance fundamental understanding of interface breakup in both Newtonian and complex fluids but also potentially offer new design solutions for industrial diffusion-limited processes.
| Description | We have demonstrated a novel method for producing tunable monodisperse emulsions from the fragmentation of an interface between two stably stratified layers of immiscible liquids in a horizontally vibrated container. The horizontal oscillation, which drives an oscillatory shear flow between the fluid layers, is redirected into vertical forcing near the vibrating end-walls by harmonic sloshing. The sloshing front is in turn destabilized into subharmonic surface waves (SWs) through a Faraday instability. A further increase in forcing acceleration leads to the pinch-off of droplets from the tips of the SWs. The external forcing (EF), mediated by shear forces in the more viscous upper layer, acts to elongate droplet-forming liquid ligaments. Using scaling arguments, we show that irregular droplet formation observed for modest upper-layer viscosities results from a balance between the EF and surface tension forces, while for larger upper layer viscosities, EF balances extensional viscous forces within the liquid ligaments to generate monodisperse droplets. We show how our emulsions can be tuned by varying frequency and amplitude of forcing. |
| Exploitation Route | We have demonstrated a novel "top-down" method for producing bespoke monodisperse emulsions with a similar accuracy to microfluidic generation methods but with the potential for upscaling. Our emulsification method enables large-scale production of monodisperse emulsions through simple manipulation of vibrational forcing and offers the advantage of surfactant-free emulsions which rapidly phase-separate when the forcing is interrupted.. |
| Sectors | Agriculture Food and Drink Environment Manufacturing including Industrial Biotechology |