Campuses:

Mark Warner and Eugene Terentjev (Remote lecture from Cambridge)

Wednesday, May 25, 2005 - 9:00am - 9:30am
EE/CS 3-180
Douglas Arnold (University of Minnesota, Twin Cities)
Nematic elastomers can elongate or contract by as much as
factors of x4 or x5 in
response to small changes of temperature in response to
illumination. Such
deformations can be rapid and are reversible.

In nematic polymers, changes in liquid crystal ordering gives a
molecular shape
change. When such polymers are crosslinked to form a network,
as in a rubber or
elastomer, then the molecular shape changes induce macroscopic
shape change.
Nematic order is lowered by heating, or by bending rods on the
absorption of a
photon, hence giving rise to the thermal or optical effects
above.

Actuation is a possibility in nematic elastomers. Experiments
show thermo-actuation
where 400+ % strains can lift weights. Artificial muscles have
been speculated upon,
but actuation at the micro and nano-scale, where motors are
relatively less efficient, is
more likely. The photo-analogue seems much richer. We discuss
the photo-bending
of beams and the writing of structures in thin photo-rubber
films stuck to substrates (a
possible route to the control of micro-fluidics). We discuss
the dynamics of lightinduced
strains and in particular the character of the photo-stationary
state.

Polydomain rubbers have been shown to be sensitive to the
polarisation of light.
Their curling follows the polarisation direction which can then
be changed. Problems
for the future include explaining the strange, and seemingly as
yet unremarked,
observation that sheets continue curling after they have
eclipsed the light source and
are in effect illuminated from the reverse side. A
non-equilibrium effect is evidently
at work. Experiments determining the photo-stationary shape of
a sheet or beam are
clearly needed.