Electro-Opto-Mechanical Effects in Swollen Nematic Elastomers - Liquid Crystal Elastomers: Materials and Applications - page 121

deformation mode driven by director rotation. Furthermore, the dynamic aspect of
this phenomenon (i.e., the rate of response to the imposition and removal of electric
fields) is an interesting issue, especially in view of the comparison with the
dynamics of the EO effect in LMM-LCs. The dynamic properties are also important
for exploring the possibility of this effect in novel soft actuators. A primary goal of
this article is to review various aspects of the EOM effects that have been elucidated
by recent studies.
In Sect. 2 , we introduce the details of the materials and the experimental setup.
Static features such as the voltage dependencies of optical birefringence and strain
are described in Sect. 3 . Polarized Fourier transform infrared spectroscopy (FTIR)
studies to characterize the electrically driven mesogen realignment are also dis-
cussed in Sect. 3 . Dynamic features of the optical and mechanical responses are
described in Sect. 4 . A simple model to capture the main characteristics of EOM
effects is introduced in Sect. 5 . Conclusions and directions for future research are
given in Sect. 6 .
2 Materials and Observation Geometry
2.1 Materials
Most of the investigations introduced in this article employed a side-chain-type
nematic elastomer that has the polyacrylate backbone with cyanobiphenyl side
group. This nematic elastomer was obtained by the photopolymerization of the
monoacrylate mesogenic monomer (A-6OCB; Fig. 2 ) and the cross-linker 1,6
hexandiol diacrylate (HDDA; Fig. 2 ) using a miscible nonreactive LMM-LC as a
solvent [ 29 ] . The mixing of the nonreactive nematic solvent with A-6OCB (1:1 by
molar ratio) was required to broaden the temperature range of the nematic state,
since the nematic phase of pure A-6OCB exists in a limited temperature range
because of the high crystallizability.
To obtain monodomain nematic elastomers with a global orientation, the photo-
polymerization was performed in a glass cell whose surfaces were coated with
uniaxially rubbed polyimide layers. In this glass cell, the nematic mixture in the
low-temperature nematic state was allowed to align globally in the rubbing direction.
The photopolymerization was conducted at a temperature in the nematic state by
Fig. 2 Chemical structures
of the mesogenic
monoacrylate monomer
(A-6OCB), cross-linker
(HDDA), and the low
molecular weight nematogen
(5CB)