Towards the Electronic Nose: Liquid Crystal Chemical Sensors.

The context of the project is to investigate and use the unique properties of liquid crystals to respond to different gases, and act as a sensor. Microfluidics (fluid behaviour on a very small scale) can be used to produce liquid crystal droplets, and their surfaces can have other substances applied to them (be functionalised) to allow a response when a certain gas is passed over them.

The alignment of liquid crystals and their change under different stimuli can be very telling, and this project aims to investigate these changes under different gases, and utilise this knowledge.

Whilst this project could be exclusively either theoretical or experimental, I propose to follow a route that combines both. For example, a more theoretical approach of modelling on equipment such as the high-performance computer ARC4 at Leeds could be used to save money on materials and time in the lab. I have already had experience in this, as well as extensive python experience (with both modelling and data analysis).

This will save time in the project overall, allowing for more rapid progression. My academic competency evidenced through my high first class averages during my degree will allow me to investigate the theoretical side in depth and learn more advance modelling techniques quickly. In addition, the modelling can be used to determine how properties such as the anisotropic elastic constants and surface forces of the liquid crystals can influence the response of the droplets to stimuli.

This will be compared to experimental data to check that the understanding of the alignment properties; a lot of liquid crystal physics can be described mathematically. The success of the project will rely on using the theory to steer the experimental work and investigations into a number of different threads:

How sensor behaviour relates to geometry (e.g. freely suspended droplets, sessile droplets or liquid crystals embedded in porous media), surface alignment and functionalisation.

Droplet sensitivity. Understanding the relationships between alignment changes and liquid crystal phase, or anisotropic properties. To begin to target functionalised surfaces for the Sensor design and fabrication. Computational analysis of the results. Pattern recognition for the electrical and optical responses.

The target is to make a sensitive, working electronic nose, with both optical and electronic responses to gases and to apply the knowledge gained to other sensor systems, such as chemical and bio-sensors.

Understanding the optical and electrical changes the liquid crystal alignment varies when a chemical has run over it can be understood by experiments such as those done with a polarising microscope. For example, a colour change can be looked for, or a voltage change. The latter would be simpler for creating an automated analysis system, which may make it more suitable for uses in the real-world environment, and by the non-expert consumer.

A key aim is to produce sensors that are cheap to make, using the amplification effect from small quantities of liquid crystal materials to provide a sensitive but noticeable effect. Applications range from gas sensing in a working environment to check for different volatile organic contaminants or other gases, for health and safety. However, I'd hope that it may eventually to be able to determine the composition of a mixed gas sample, and be a useful tool more generally, such as in the fight against climate change, where simple sensors help air quality be determined by the consumer.