Understanding the Physics of Liquid Crystalline Elastomers

This thesis presents the ability to select an optimal material design for a specific
function, such as laminates for impact resistant glass. This has been achieved by the
full comprehension of the impact of templating and composition on the optical,
physical, thermal, and mechanical properties of a series of acrylate-based Liquid
Crystalline Elastomers (LCEs).
The elastomeric materials were examined for three different templates, which
display distinctive behaviour: the monodomain nematic, the polydomain nematic,
and the isotropic. The transparent monodomain nematic template will be of
particular interest since this exhibits an auxetic response to an applied strain and
lends this material as a unique candidate for impact resistance. The composition
was altered for this series of LCEs via the control of the mesogenic content within
the network and was investigated between 51 - 84 mol% mesogenic content for the
polymerized LCEs.
We demonstrate that a 10 mol% increase in the mesogenic content of an LCE (from
62 mol% to 72 mol%) subsequently provides a ~ 7°C higher glass transition
temperature, an 11% increase in ordering, an enhanced energy dissipation, a 3%
increase in density, and an 18% greater birefringence of the material. However, we
also show that there is an upper limit of the mesogenic content that can be used to
produce these monodomain nematic LCEs; at 72 mol% mesogenic content, we
observe more smectic characteristics of the materials and a failure to display an
auxetic response.
This work provides the formulation limitations and design rules for LCE materials
and also offers an opportunity to select the ideal composition and template for a
particular application. Following careful contemplation of all the materials, we will
propose that the monodomain nematic material of 66 mol% mesogenic content is
the optimal composition from this family of materials, as a laminate for impact
resistant glass.