PhD Opportunities

If you are considering applying for one of the PhD projects below, please feel free to contact the associated supervisor(s) for more information. Applying is relatively straightforward and can be done electronically. Some of the projects below have funding; others will require you to apply for funding from external sources. More information about available scholarships (for UK, EU and international students) can be found here.

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Centre for Doctoral Training in Soft Matter and Functional Interfaces

 

Up to 16 fully funded four-year PhD studentships per year are available for graduates in physical science subjects, food science, mathematics or engineering.
Find out more ›

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Understanding the physics of liquid crystal elastomers and composites

Supervisor: Prof. Helen Gleeson

Liquid crystal elastomers (LCEs) were recently discovered by us to be the first synthetic molecular auxetic materials – they have a negative Poisson’s Ratio and get thicker when stretched rather than thinner. This project will involve experimental studies of LCEs, probing the physics that controls the auxetic response. We will examine how physical properties such as cross-link density, order and glass transition temperature influence the auxetic behaviour of the LCEs using mechanical, scattering and calorimetry approaches. As a PhD student on this project, you will gain skills in experimental methods relating to soft matter, liquid crystal devices and potentially contribute to applications that follow from auxetic behaviour, such as impact resistance, or the acoustic meta material behaviour that is predicted.

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High Speed Materials for Holographic Head-up Displays using Liquid Crystal on Silicon Spatial Light Modulators

Supervisor: Prof. Cliff Jones

The aim of the research project will be to design and optimise polar switching modes of liquid crystals that target Liquid Crystal on Silicon (LCOS) application and the Envisics system. It has previously been shown that flexoelectric switching of the chiral nematic phase provides optical modulation that is much faster than the 5ms switching of conventional nematics. Odd-spaced dimers, of the type that exhibit the Twist-Bend Nematic phase, have been used to induce far higher flexoelectric coefficients than those that occur in calamitic liquid crystals. Furthermore, other novel polar nematic phases based on spontaneous splay have recently been discovered, that have the potential to provide further enhancement that is of yet unexplored. However, obtaining the suitable high-quality alignment of the liquid crystal materials for this mode has proven unsuccessful and unproven for LCOS devices. The Leeds team has developed novel alignment methods based on nano-imprint lithography, embossing and patterned self-adhesion that promise to resolve this issue. Work is currently underway under the supervisor’s EPSRC Manufacturing Fellowship, to move these methods to sub-optical length-scales. These alignment approaches will be refined in this project to suit low-cell gap LCOS spatial light modulators (SLM) and applied to the new flexoelectric materials being developed. Furthermore, the Leeds team has recently developed a novel analogue ferroelectric liquid crystal mode, based on vertically grating alignment. The use of sub-optical gratings for this mode suited to LCOS will be investigate, together with other polar liquid crystal effects, such as the electroclinic effect. Such modes are envisaged to help improve LCOS resolution operation, as well as speed.

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Vitrimers – a new class of materials for sustainable re-processable plastics and novel battery designs

Supervisors: Dr Johan Mattsson and Prof. Andy Wilson (School of Chemistry)

For many materials applications, so-called thermosets i.e. polymers with permanent inter-chain cross-links are the optimum choice due to their long-term mechanical and thermal stability. However, the presence of permanent cross-links makes these materials very difficult to process and almost impossible to effectively re-process and thus recycle. Thus, finding a route to produce polymers that behave like thermosets across their relevant operational temperature range, but which can be readily processed and are malleable above this temperature range, is key for moving towards more sustainable plastics and a more circular economy. This project is focused on a new class of supramolecular polymers, so-called vitrimers [1] which provide a solution to this problem.

Supramolecular materials are based on fundamental molecular units which cross-link to form networks. The cross-links impart physical properties such as mechanical rigidity and by controlling the nature of the cross-links, supramolecular materials can be designed with tuneable and switchable properties, where the trigger could include temperature, a catalyst, or an applied electric or magnetic field. Due to the nature of the chosen type of cross-link interactions, the number of cross-links is always fixed; this gives vitrimers unique properties. Typically, at low temperatures (relevant for a particular application) the cross-links stay intact and the vitrimer mimics a thermoset. At high temperatures, however, cross-link rearrangements allow material shape changes, which makes the vitrimers malleable and processable.

In this project, the link between the nature of the polymeric building-blocks, the cross-link interactions and concentration, and the resulting molecular motions and mechanical response will be systematically characterized for chosen model vitrimer systems. The project aim is to develop a proper understanding of these novel materials and use this understanding to devise design rules, which will help developing materials for practical applications. We are here particularly interested in the design of more sustainable, recyclable, polymers and the incorporation of vitrimers into the design of new types of solid state batteries. The vitrimer systems will be synthesized in Leeds and investigated using a wide range of experimental techniques including dielectric broadband spectroscopy, calorimetry, rheology, scattering (light, x-ray, neutron), and atomic force microscopy.

You will work with Dr. Johan Mattsson in the Soft Matter Physics Group in the School of Physics and Astronomy and Prof. Andrew Wilson in the School of Chemistry in Leeds. You will work in an international dynamic research environment characterised by close collaborations between experimentalists and theorists and an inspiring mix of fundamental and applied research.

[1] D. Montarnal et al., Science 334, 965 (2011)

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Engineering biomaterials through liquid crystal imprinting

Supervisor: Dr Mamatha Nagaraj

Liquid crystals are a fascinating soft materials that elegantly combine characteristics of the conventional solid and isotropic liquid. There are a number of liquid crystal phases and they show unique molecular arrangements and functionalities. The process of transferring of functionalities of liquid crystals into polymer matrices is called as imprinting. In this project you will work on creating and investigating imprinted structures of liquid crystals using biomolecules for applications in medicine and tissue engineering. The student will have the opportunity to learn a number of experimental techniques vital to soft matter physics such as polarizing optical microscopy, X-ray scattering, dielectric spectroscopy, device fabrication techniques and electron microscopies.

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Materials from nature: All Natural Composites

Supervisors: Dr Mike Ries and Dr Peter Hine

Each year we produce 300 million tonnes of plastic waste, with 8 million tonnes entering our oceans and a staggering 100 million tonnes being dumped in landfill. Therefore, we need to develop alternative sustainable processing systems that can generate bio-based products with less environmental impact; all-natural-composites have the potential to replace synthetic plastics in a wide variety of applications. As these materials will be formed entirely from one natural material their recyclability is greatly simplified. This work will incorporate natural biopolymers such as cellulose, silk and keratin, to form a variety of all-natural-composites.

All polymer composites is a growing area of research and development in which the Leeds Soft Matter Physics group has been one of the foremost pioneers. Research to date, on melt processable polymer systems, has led to a number of major patents and via a University spin-off company, to commercial applications. In the view of replacing synthetic polymers by renewable matter, all-natural based composites have great potential. In this project we shall manufacture and study all-natural composites using “green” processing routes. Selective surface solvation of the biopolymer fibres, via environmentally friendly solvents such as ionic liquids, will be used. Preliminary studies (using flax, hemp and cotton fibres) have shown that excellent bonding can be achieved, but composite morphology and mechanical properties are not yet understood. The composition of the solvent (type of solvent and fraction of cosolvent), pre-activation of fibres (distilled water / caustic soda), the fibre type and hence properties (different biopolymer sources), the fibre arrangement (unidirectional, woven) and processing variables (solvation time, temperature and pressure) will be varied. The mechanical properties (tensile, bending, impact) of the composites will be studied and correlated with their structures (WAXS, NMR, SEM).

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Sub-optical and nanoscopic structures in contact with liquid crystals

Supervisor: Prof. Cliff Jones (also Dr Mark Rosamond and Dr Chris Wood from the School of Electrical Engineering)

The next generation of liquid crystal devices will be used in a range of applications including adaptive optics (switchable lenses, beam steerers, phase controllers, switchable holograms) and Virtual / Augmented Reality displays. This project aims to explore additional functionalities to such devices, through the design of sub-optical and nanoscopic features on the contacting surfaces of the liquid crystal. These functionalities include multi-stability, photonic and plasmonic effects. The work is supported by the industrial companies Merck and NVD Ltd.

Initial tests have used electron-beam lithography to fabricate profiled structures on the inner surfaces of liquid crystal devices. The aim is to add functionality to the device, such as producing bistable stable alignment states. The structures need a near sinusoidal shape with controllable blaze, but with an amplitude to pitch ratio of greater than 1. Initial tests succeeded in making 400nm and 300nm pitch gratings (see figure) with the correct shape except but with insufficient amplitudes to produce bistability. However, a number of novel methods for increasing the amplitude have been suggested, and will form the starting point for the successful student working on this project.

Such structures have a real practical purpose, since they would allow higher reflectivity displays to be produced by the company NVD, and importantly allow dual mode LCD / OLED devices for portable applications. However, there is potential for a wealth of longer-term invention using 2D photonic surface structures [1] combined with liquid crystals to allow for full reconfigurable elements with other functionalities, including optical switching, bistable and multistable structures, interactions between lasing structures and topological defects. The area of application that interests industrial partner Merck is in novel Augmented Reality Displays.

The project is best suited to an experimental student that is proficient with some theory. The successful candidate will benefit from interactions with industrial companies including Merck and NVD Ltd, as well has a strong interaction engineering and working in their state-of-the-art cleanroom facility.

[1] Hongbo Huang , Shaoyong Huo and Jiujiu Chen, Reconfigurable Topological Phases in Two-Dimensional Dielectric Photonic Crystals Crystals 2019, 9(4), 221

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The physics of glass – fundamental mechanisms and novel applications

Supervisor: Dr Johan Mattsson

The formation and behavior of glassy disordered non-equilibrium solids is one of the deepest unsolved fundamental questions in physics. Moreover, to better understand the physics of glassy materials is important for a wide range of technologies, for battery and other energy materials, pharmaceuticals, foods, paints and for our understanding of biological matter such as proteins and cells. The fact that neither the microscopic mechanisms involved in glass formation nor the behaviour of the glassy state is well understood makes this a key problem both within the fundamental and applied sciences.

This project will focus on using advanced experimental techniques to investigate the physics of glass-formation, with a particular focus on the effects of molecular topology, the introduction of specific interactions such as hydrogen bonding and the molecular response to high pressures and mechanical deformations. The molecular structure and dynamics will be investigated using techniques including advanced light, x-ray and neutron scattering, dielectric relaxation spectroscopy and calorimetry.

You will work in an international dynamic research environment characterized by close collaborations between experimentalists and theorists and an inspiring mix of fundamental and applied research. The project will also include significant international collaborations with leading international research groups.

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Developing novel mechanical metamaterials

Supervisor: Dr Mamatha Nagaraj

Nature uses unique mechanisms to produce robust architectures such as biological exoskeletons, bones and wood. The internal lattice architectures of these materials are responsible for the structures being simultaneously lightweight and exhibit outstanding mechanical properties. Inspired by nature, the research on lattice miniaturization has developed rapidly over recent years. Artificial nano-lattice materials find numerous applications in biomedical implants, load-bearing structures, fast charging and high capacity batteries, porous membranes and cancer therapy. The focus of this project will be to establish routes to fabricate intricate three dimensional nano-lattices using liquid crystals, polymers and colloidal dispersion and test their applicability as mechanical meta materials.

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Glasses controlled by light

Supervisor: Dr Johan Mattsson and Prof. Cliff Jones

The formation and behaviour of glassy disordered non-equilibrium solids is one of the deepest unsolved fundamental questions in physics. The constituent building blocks of a glass can be either small molecules or polymers and glassy materials are widely used in applications ranging from construction and energy materials, pharmaceuticals, medical technologies, foods and paints.

In this project you will explore different routes to controlling the properties of glass-forming materials by addition of, or functionalisaton with, light-sensitive molecules whose structure can be switched between different conformational states by the application of light. Recent work has demonstrated that inducing local perturbations can have significant effects on the molecular motions of the glass-forming material, for instance driving various relaxation modes and control molecular diffusion. The addition of light-sensitive molecules to glassy materials thus has the potential for design of novel glasses with physical properties controlled by light.

The project will use advanced experimental techniques to characterise the material behaviour, where the molecular structure and dynamics will be investigated using advanced scattering, dielectric relaxation spectroscopy, rheology and calorimetry.

You will work in an international dynamic research environment characterized by close collaborations between experimentalists and theorists and an inspiring mix of fundamental and applied research. The project will also include significant international collaborations with leading international research groups.

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Controlled self assembly of nanoparticles for photonic and plasmonic applications

Supervisor: Dr Mamatha Nagaraj

Self-assembly is a remarkable phenomenon in nature and developing novel self-assembled systems for new technology areas is both exciting and important. Examples of new systems include ones where nanomaterials have been dispersed in liquid crystals to enhance their physical properties and to achieve alignment and self-assembly of nanomaterials into large organized structures in different dimensions. Such systems are potentially important because of their unusual switching properties which could be exploited in devices including, optical switches and diffraction gratings, as well as their novel architectures that will interact with light (photonic structures). The focus of this project will be to develop novel functional materials by combining liquid crystals and nanomaterials. The student will work on uniquely grafted nanoparticles, which allow controlled assembly of nanoparticles into regular lattice structures, hence allow applications in photonics and plasmonics.

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The physics of microgels and other soft colloids

Supervisor: Dr Johan Mattsson

Transitions where a material goes from a fluid state to an arrested but still disordered state arise in a diverse range of systems (colloidal dispersions, molecular or polymeric fluids, granular systems, emulsions, foams, pastes, and biological cells). Colloidal dispersions made from ‘soft’ elastic microgels provide an excellent model system for such behaviour and are also industrially highly important. Microgels are used in applications including biosensing and medical diagnostics, in pharmaceutical delivery systems and switchable materials and are regularly used to control the rheological properties of industrial products such as paints, motor oils, foods, cosmetics and inks. Many applications of microgels are based on highly crowded states, but we presently have little understanding of the rich and fascinating behaviour that takes place in the packing of such soft colloids. This project is aimed at directly addressing key fundamental aspects of the physics of microgel dispersions where important open questions include how the motions of the microgel particles are correlated in time and space, how the motions, arrangements and rheology are affected by the individual microgel particle shape, elasticity (heterogeneity) and by the inter-particle interactions. An important component of the project is the use of the 3D-photon correlation light scattering set-up in Leeds, which will be combined with other light scattering techniques, microscopy and rheology as well as colloidal synthesis techniques to provide a full characterisation and control of these experimental systems

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