13 research outputs found
Tack energy and switchable adhesion of liquid crystal elastomers
The mechanical properties of liquid crystal elastomers (LCEs) make them
suitable candidates for pressure-sensitive adhesives (PSAs). Using the nematic
dumbbell constitutive model, and the block model of PSAs, we study their tack
energy and the debonding process as could be measured experimentally in the
probe-tack test. To investigate their performance as switchable PSAs we compare
the tack energy for the director aligned parallel, and perpendicular to the
substrate normal, and for the isotropic state. We find that the tack energy is
larger in the parallel alignment than the isotropic case by over a factor of
two. The tack energy for the perpendicular alignment can be 50% less than the
isotropic case. We propose a mechanism for reversibly switchable adhesion based
on the reversibility of the isotropic to nematic transition. Finally we
consider the influence of several material parameters that could be used to
tune the stress-strain response
Effect of the network on the director fluctuations in a nematic side-group elastomer analysed by static and dynamic light scattering
Static and dynamic light scattering experiments
were performed on monodomains of a crosslinked nematic side-group polysiloxane.
The depolarized scattering caused by fluctuations of the nematic director was
analysed. Due to a superposed strong static scattering produced by heterogeneities
the fluctuating part of the scattering intensity was found to be rather small.
In contrast to low molar mass nematics, the relaxation rates and strength did
not show a significant dependence on the scattering vector. The results can
be explained by restoring torques on the director originating from the coupling
to the network elasticity which dominate those originating from the Frank elasticity.
Quantities describing the coupling as well as effective viscosities for the
director reorientation were obtained