Drops and jets: fundamental science and applications

Lead Research Organisation: University of Oxford
Department Name: Engineering Science

Abstract

The broad objective of this project is to study the generation of droplets by external and self-stimulation of liquid jets. A fundamental understanding of splashing and drop breakup has a wide range of industrial applications, from rainfall, crop spraying and spray coating to inkjet printing. One particular application of interest is inkjet printing - a mature technology for document printing that offers promising expansions into the deposition of active matter and LCs (Liquid Crystals).

In-house LC inkjet systems have successfully been built in the Fluid Dynamics Laboratory in Oxford and used to deposit tunable microlenses. However, this provides little insight into the underlying dynamics of the drop formation and impact processes, in particular the relaxation of the director during the microseconds after impact. Preliminary investigations suggest that the timescale over which this occurs is similar to that of the droplet formation. It may therefore be possible to 'freeze' the director field in the microseconds after impact, allowing for the creation of novel LC structures. High-speed imaging rigs in the lab will be combined with computer simulations (Lattice-Boltzmann) to provide a more comprehensive understanding of this process.
To make observations of the director, a time-resolved transmission- and reflection-based polarization imaging system will be built with a high-speed colour camera, enabled by an angled dropping path. These observations will be made concurrently with shadowgraphy measurements of the droplet's shape. CFD simulations will be used to support the development of new jetting and breakup simulation techniques, to verify experimental results and prompt wider explorations within the topic of jet breakup.
In the long term, the range of possible deposition materials and substrates will be expanded to include active nematics and soft matter. Primary challenges include the suppression of undesirable 'satellite' drops, and the development of alternative drop generation mechanisms (the current methods in use all being piezoelectric) - if overcome these may open avenues to the expansion of the range of length and time-scales over which dropping is practicable.

This falls within the EPSRC Continuum Mechanics and Complex Fluids and Rheology research area. The project is a collaboration between the Fluid Dynamics Laboratory in Oxford Engineering Science and the Soft and Biological Matter group in the Department of Theoretical Physics, University of Oxford.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509711/1 01/10/2016 30/09/2021
2290926 Studentship EP/N509711/1 01/10/2019 31/03/2023 Andrew Clifford Orr