Prof Helen Gleeson - research
I have worked in liquid crystals throughout my career and have a particular interest in structure and order in systems with reduced symmetry (e.g. chiral and biaxial liquid crystals). One of my major projects over the past few years has been the study antiferroelectric, ferrielectric and ferroelectric liquid crystals, formed from chiral materials (usually provided by my collaborators, Goodby (York) and Hird (Hull)).
Particular research interests and experiments include:?
Biaxial nematic phases. We made the first direct measurements of a uniaxial to biaxial nematic phase transition, and deduced methods of measuring biaxial order using Raman scattering. Investigations currently include examination of the electrical properties of biaxial nematic materials, including distinguishing phase regimes via electrohydrodynamic patterns.
Blue Phases. We have studied the symmetry, lattice distortions and order parameters in blue phases providing the first investigations of the phase of the blue phase structures and the first quantitative measurements of order parameters in blue phases. While the blue phases were originally only of scientific interest, they are increasingly being considered for devices; we carried out some of the earliest work on field effects and factors affecting stability of blue phases.
Resonant and time-resolved x-ray scattering. We carried out the first resonant x-ray scattering experiments on antiferroelectric, ferrielectric and ferroelectric liquid crystal devices. Resonant x-ray scattering techniques allow us to deduce the exact structures of the liquid crystal intermediate phases in novel materials. Our measurements deduced the biaxial nature of the 3-layer structures and details of the biaxial structure of the 4-layer phase. We have also very recently used this methodology in the discovery of a new ferrielectric liquid crystal phase. This work, alongside small angle x-ray scattering, can also be carried out with superb time resolution, giving new insight into switching mechanisms.
Liquid crystals on surfaces. We pioneered the use ferroelectric ceramic substrates decorated with liquid crystals and identified the interaction of the liquid crystal with the substrate as a local Freedericksz transition. More recently, our work has developed to study liquid crystal amplification of surface properties to develop new sensors.
Biological systems. The study self-organising materials is of great importance in biological systems. Our work includes the study of liquid crystal based systems for use in controlled drug release applications, as well as the application of our understanding of self-assembled chiral systems to understanding mechanisms of polarized light vision in animals (with Nick Roberts, now at Bristol University).
Laser manipulation and tweezing. We have studied particles in achiral and chiral liquid crystal media, and the transfer of optical angular momentum from circularly polarized light to liquid crystalline droplets. We deduced a completely new method of causing liquid crystal droplets to rotate, uniquely, following illumination with linearly polarized light.