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Winton Programme for the Physics of Sustainability

Department of Physics

Prof Mark Warner (Theory of Condensed Matter)

Two projects will be enabled at the Cavendish through this funding, which will bring Professor Čopič to Cambridge.  Professor Čopič has made seminal contributions to the understanding of nematic elastomers through light scattering.  He is uniquely placed to carry out the proposed study on polydomain deformations by light scattering.  Professor Čopič brings not only great expertise in the field, but also invaluable other collaborators.

(i) To investigate the mechanisms of mechanical response of polydomain nematic liquid crystals by light scattering.  Difficult problems in multiple scattering in anisotropic media will have to be overcome.  The photo-responsive versions of these unusual, polydomain solids will be used as the working materials of solar to mechanical energy converters that are the second part of the theoretical PhD of Milos Knezevic (a Winton Scholar).

(ii) To understand the fundamental processes in photo-tuneable ferroelectric smectic C* liquid crystals, including the effect of non-linear light absorption and non-uniform polarisation.  Applications to solar energy harvesting will be pursued after the fundamentals have been clarified.

Project Completed end of October 2013

The visit of Professor Martin Čopič focussed on two areas underpinning prospective methods for solar to mechanical or electrical conversion.

  1. The dynamics of photo-contraction of nematic photo-elastomers was modelled and accurately matched to experiment without any fitting parameters.  The propagation of optical saturation fronts through photo-elastic strips determine the build up of force when they are used in photomechanical motors that we have proposed under Winton and which are being further worked up as mechanical turbines.
  2. The dynamics and the variation with depth of photo-conversion in ferro-electric SmC* liquids with dye hosts was investigated experimentally.  These liquids are ferro-electric to an extent determined by the liquid crystal (LC) order and so there is a strong ferro-electric response when light decreases the LC order.  Experiments were carried out to resolve confusion about the spatial and temporal extent of conversion from trans to cis (ground state to excited state) states in the dye guest population, and what the role of non-linear effects are.  Sample stability under illumination, and the presence of stray charges, complicated experiments that are now showing exciting results as the programme continues in Ljubljana, Slovenia in Professor Čopič’s Lab.

Winton Annual Report 2019

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