Applications of Liquid Crystalline Elastomers - Liquid Crystal Elastomers: Materials and Applications - page 68

a b

CLCP

0 s 30 s

Sharp edge

Flat edge

5 s 50

s

UV light

Stationary
point 15 s 65 Extension

s

Visible light

Retraction

Stationary point

Fig. 11 Moving stripe of a composite of polymer film and LCE . [ 103 ]. The photoisomerization of
the incorporated azo dyes controls the bending. The direction of the walk depends on the shape of
the edges. Reproduced by permission of the Royal Society of Chemistry

Using an LCE-coated ribbon, the group of Ikeda has been able to construct a
light-driven motor [ 94 ] . The belt is put around two pulleys with different diameters.
Upon irradiation on one side with UV light and the other side with visible light, the
pulleys is made to rotate due to the consecutive contraction and extension on the
two sides. (Fig. 12 )
The aforementioned examples of bending devices work digitally with two
different states. For other applications it might be necessary to have various
different bending angles. Such a variable bending can be achieved by a gradual
distortion of the director in the LCE with the help of shape-changing molecules
[ 104 ]. Consecutive trans-cis-trans isomerization of azo compounds induced by
polarized light leads to a rotation of the dye out of the polarization direction [ 105 ,
106 ] . In this way, a change of the polarization direction leads to a gradual change of
the LCE's order and thus the flexure [ 104 ].
Cilia are hair-like objects that work as actuators by flexing. Because of their
small size they are used in arrays. They can be prepared easily by inkjet printing
[ 82 ], which offers the possibility to combine polymers with different absorption
wavelengths in one device. If one segment is switched by visible light and the other
by UV light, different shapes can be achieved. These fibers have been attached to a
surface in order to move objects (Fig. 13 ). Cilia could also be attached to devices
that are propelled autonomically.
Recently, a miniaturized gripper that is propelled by an LCE film has been
introduced [ 107 ] . Using lithographic methods, an LCE film and the silicon pincers