This thesis describes new Liquid Crystal Elastomers (LCEs) and the study of their mechanical behaviours with the aim of designing a concept "Accommodating Intra-Ocular Lens" (AIOL) - a device which could be used to treat conditions affecting the ageing eye. In this process we discover new physics of LCEs.
Five acrylate-based LCEs with glass transition temperatures <15 degrees Celsius are developed from commercially available materials.
We detail the opto-mechanical properties of one of these materials - LCE A. When monodomains of LCE A are stressed perpendicular to the liquid crystal (LC) "director", we observe a new deformation mode whereby the polymer conformation deforms through a state of negative backbone order parameter, measured as Q_B=-0.41±0.01. This implies a negative LC order parameter. Moreover, this state coincides with the emergence of a negative Poisson's ratio of maximum magnitude -0.8. We deduce LCE A is the first example of a synthetic "molecular auxetic".
Our characterisation LCE A's mechanical anisotropy shows the initial elastic moduli varies between 4.1±0.6 and 20±2 MPa depending on the angle between the director and stress axis. Unexpectedly, the maximum and minimum of the elastic modulus does not correspond to stresses applied parallel and perpendicular to the director respectively. We develop an empirical model describing generalised uniaxial deformations of LCE A which we use to predict the stress distribution within a director-patterned film of LCE A when strained.
In studying uniaxial deformations of LCE B, which becomes nematic under stress, we record a stress-optic coefficient of (1.3±0.1)x10^5 Brewsters - ~50x greater than that of typical polymeric materials. Upon radial deformation of LCE B we deduce a state of negative ordering for which we calculate Q_B=-0.14±0.03.
The promise of the AIOL concept developed as a consequence of our results and the new physics discovered is testament to LCEs currently being one of the most exciting soft materials.
