Electro-Opto-Mechanical Effects in Swollen Nematic Elastomers - Liquid Crystal Elastomers: Materials and Applications - page 143

response times are about an order of magnitude larger than the optical times.
Importantly, the recovery rate of the director (estimated from the optical decay
time) in nematic gels is about three orders of magnitude higher than that in LMM-
LCs confined in the cell with the same gap as the gel thickness. This indicates that
the memory effect of the initial director, which is imprinted at cross-linking, is
much stronger than the Frank elasticity. The memory effect of the initial director in
nematic gels is a bulk matrix effect. This is also recognized by the fact that the
threshold for the onset of EOM effects is determined by the field strength, in
contrast to the Fredericks transition of LMM-LCs whose threshold is determined
by voltage.
So far, EOM effects have been reported for only a limited number of nematic
gels. There is great potential for enhancing the performance of the electric-field
response. The molecular characteristics of nematic elastomers and solvents have
not yet been optimized for high performance. Possible options might include: (1)
employment of main-chain-type nematic elastomers; (2) optimization of the cross-
linker geometry; and (3) an increase in the dielectric anisotropy of mesogens. The
first and second options are aimed at increasing the electrical strain, i.e., enhancing
the coupling between mesogen orientation and macroscopic deformation. Many
investigations of thermally induced deformation have indicated that these options
are effective for this purpose. The third option contributes to reducing the actuation
voltage [see ( 23 ) ] and to shortening the field-on response time. This is based on an
analogy with the effect of dielectric anisotropy on EO effects in LMM-LCs.
The EM effects of nematic elastomers have great potential for practical applica-
tions such as soft actuators. For practical purposes, actuation must be fast and low-
voltage with a large strain (generating a large stress). Establishing the fundamentals
of the molecular design of nematic elastomers with high EM performance will also
meet these industrial demands.
Acknowledgments The author thanks Y. O. Arai, H. Kondo, S. Honda, A. Fukunaga, S. Kohjiya,
and T. Takigawa for their great contributions to the experiments. The author appreciates
P. Koelsch for his crucial comment in polarized FT-IR. The author also thanks A. DeSimone
and L. Teresi for their principal contribution to the modeling. The author is grateful for a Grant-in-
Aid in the Priority Area “Soft Matter Physics” (No. 21015014) and a Grant-in-Aid for Scientific
Research (B) (No. 21350123). Valuable support was also received from the Global COE Program
“International Center for Integrated Research and Advanced Education in Materials Science” (No.
B-09) from the Ministry of Education, Culture, Sports, Science and Technology of Japan.
References
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