Anisotropic Liquid Dielectrophoresis and Interfacial Forces

There is a growing technology-driven interest in using external influences to move or shape small quantities of liquids, a process that is referred to as "microfluidic actuation". Using electrical, rather than mechanical, forces to achieve this actuation is convenient because this involves relatively simple device architectures that contain no moving parts. Existing non-mechanical microfluidic actuation techniques that are driven by the application of a voltage include electrowetting, which only works with conducting liquids, and dielectrophoresis, which works with both conducting and non-conducting liquids. We have previously shown how dielectrophoresis forces in non-conducting isotropic liquids can be used to create not only forced wetting and liquid spreading, but also liquid film wrinkling in which an engineered electric field distribution imprints a replica of itself as a distortion pattern at the liquid-air interface of the film. In this proposal the possibility that liquid dielectrophoresis can lead to added functionality and greater control within a pure anisotropic liquid, i.e. a nematic liquid crystal rather than a simple isotropic liquid, will be investigated. Liquid dielectrophoresis in pure anisotropic liquids has not been studied before, either experimentally or theoretically. Our proposed integrated collaborative experimental and theoretical research approach aims to understand and exploit the forces that can be created within, and at the surface of, free and confined anisotropic liquids when they are subject to electric fields. The proposed research will investigate an exciting new possibility of using anisotropic liquids along with particular confinement geometries which allow voltage controlled actuated microfluidic pumping to be produced even with simplified electrode architectures. Our industrial supporters include Merck Chemicals Ltd, the world-leading researcher, developer and manufacturer of liquid crystals and reactive mesogens, together with Hewlett-Packard and ADT, who are developing the next generation of information displays based on liquid crystal and microfluidic effects.

Potential beneficiaries from the research include the follow sectors:

(1) UK and European companies in the commercial private sector. Potential exploitation areas already identified with our Industrial Supporters (see letters of support from Merck, ADT Displays, and Hewlett-Packard) include 3d displays, microfluidics (lab-on-a-chip), liquid based optics, and novel multi/bi-stable colour reflective displays. These supporters identify reduction in power requirements (e.g. multistability or where stronger coupling to voltages is produced) and easier fabrication (due to simpler structures and voltage driving techniques) as key potential outcomes for electronic devices based on these technologies. This would reduce the environmental impact of the manufacturing processes (less steps and materials), the in-life use (less power), and the disposal/recycling (less component parts) of the devices. The timescale for these impacts is 5-10 years after the start of the project. Other potential industrial beneficiaries will be engaged with, for example, through Science Parks, Industry Associations and KTNs.

(2) Professional organisations (e.g. Institute of Physics) and the primary and secondary education sector (e.g. individual schools, Learning Teaching Scotland, Glow Science, SEP) would benefit during the project from the development of bespoke teaching resources (Kit-in-a-Kase) and the delivery of an "LCD Displays" masterclass. For teachers the masterclass would be run in conjunction with a Teacher Continuous Professional Development event. The materials developed would be available to the resource libraries of these professional and outreach organisations.

(3) Museums (Glasgow Science Centre) and the public (at events such as Nottingham "Gamecity") would benefit during the project from the planned additions to and use of the liquid crystal outreach exhibit and resource "Liquid crystals: living cells and flat screen TVs" (originally developed for the Royal Society 2011 exhibition).

(4) The UK and EU skills base would benefit from the availability of trained researchers at the end of the project. The staff will have gained both specific and generic knowledge and expertise in (i) microstructure fabrication, thin film processing, surface profiling, electro-optical device analysis and electrical addressing, and dielectric spectroscopy or (ii) thin-film theory, asymptotic analysis, investigating solutions of differential equations, and predictive simulation of optoelectronic devices. In addition they will acquire transferable skills in public engagement and communication. Evidence of the demand for staff with such skills is provided by the wide range of organisations that have recruited or now work with the investigators' previous RCUK funded researchers who gained related skill sets, for example in the Scientific Sector: Visteon, Hewlett-Packard, AWE, PlasmaQuest, Philips, Subsea7, Cancer Research UK, Unilever; in the Financial Sector: Arthur Anderson, Bank of Scotland, KPMG; in Teaching; and in Universities such as Imperial, Oxford, Toronto, and Kyoto.

(5) The academic community beyond the immediate professional circle of the applicants have the potential to benefit from increased experimental and theoretical knowledge in the areas of liquid actuation, applications of liquid crystals beyond displays, and non-Newtonian fluid flow.