A New Order of Liquids: Polar and ferroelectric orientationally modulated soft materials

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Liquid crystals (LC) combine liquid-like fluidity with some of the optical properties of crystalline materials (such as birefringence). Nematic liquid crystals are those in which the constituent molecules (or particles) have orientational order, (i.e. they align roughly parallel or antiparallel) but lack positional order. It is nematic LCs that underpin modern liquid crystal display (LCD) technology which is now ubiquitous to the point of being invisible in our daily lives, and via which you are perhaps reading this document. Other types of nematic liquid crystal had been the subject of intense speculation but eluded experimental discovery: notably, ferroelectric nematics were predicted independently by Peter Debye and Max Born, both Nobel laureates, in the early 20th century. Ferroelectricity, in which a material exhibits a permanent electric polarization (PS) which varies in strength under an applied electric field, is typically weak in organic and/or fluid materials and only approaches application-ready levels in ceramics, which can be brittle, difficult to fabricate, and costly.The discovery of new nematic ground states is rare; the discovery of the twist-bend nematic phase (NTB) in 2011 was the first new nematic state in over a century. The NTB phase features nematic molecular ordering which oscillates periodically, hence, it is known as a modulated nematic. Recently I discovered the second known modulated nematic phases, the splay-nematic (NS); this phase is formed when wedge shaped molecules organise themselves into a structure reminiscent of an array of Japanese fans arranged head-to-tail. This head-tail ordering makes the NS phase is the first - and to date only - bona fide example of a ferroelectric nematic. The values of PS of NS materials rival those of solid materials but retain the fluidity of a liquid, conferring two principal advantages; materials processing is simplified, and there is much increased tolerance to mechanical force (self-healing) due to the fluidity of the active medium. The remarkable electric-field response of the NS phase has the potential to remake nematic based technology anew, enabling transformative applications utilising these soft materials: potential areas of benefit include temperature regulation via the electrocaloric effect, and computing via ferroelectric random-access memory and field effect transistors. One key advantage of NS materials is that they can use existing processing/alignment technologies developed for existing LCD technology, significantly lowering the barrier to future applications. The NS phase is such a recent discovery that new research is required to engineer the properties of materials that exhibit this phase in order to realise their unrivalled potential by: reducing their high operating temperatures, increasing their short working temperature ranges, and improving their stability (chemical and thermal). The design of new materials to satisfy these requirements is non-trivial, and complicated by a need to develop our understanding of the relationship between the incidence of these phases of matter and molecular structure. This Fellowship will deliver a paradigm shift in our understanding of the chemistry and physics that underpins modulated nematics. The growth in knowledge required will arise from linking molecular design (chemistry) with molecular modelling (chemistry/physics), and material characterisation (physics). As the discoverer of the NS phase with a background in both sciences I am uniquely placed to lead this research from scientific curiosity towards real-world application. I will develop materials with superior properties and growing our understanding of the molecular features that drive the incidence of this phase. My research will deliver materials for real world applications while also adding entirely new chapters to the rulebook on liquid crystals, and will set the research agenda in liquid crystals and soft matter in the decades to come