an artificial light driven goldfish
DESCRIPTION
An Artificial Light Driven Goldfish. Liquid Crystal Institute Kent State University Kent, OH Institute fur Macromoleculare Chemie, Albert-Ludwigs Universitat, Freiburg, Germany Courant Institute of Mathematical Sciences, New York University, NY. Jeremy Neal Peter Palffy-Muhoray - PowerPoint PPT PresentationTRANSCRIPT
March 21, 2005March Meeting of the APS
Los Angeles, CA
An Artificial Light Driven Goldfish
Jeremy Neal Peter Palffy-MuhorayTibor Toth-Katona
Heino Finkelmann
Michael Shelley
Liquid Crystal InstituteKent State UniversityKent, OH
Institute fur Macromoleculare Chemie, Albert-Ludwigs Universitat, Freiburg, Germany
Courant Institute of Mathematical Sciences, New York University, NY
Work supported by NSF-EC DMR 0132611
March 21, 2005March Meeting of the APS
Los Angeles, CA
Project Aims:
• to better understand of the interaction between light and liquid crystal elastomer (LCE) materials
• folding & motion of leaves in wind
• fish swimming in water
• peristaltic pumps
• to understand how soft active materials interact with a fluid environment as in:
March 21, 2005March Meeting of the APS
Los Angeles, CA
Liquid Crystal Elastomers
• strong coupling between nematic order and mechanical strain
• order parameter changes induce shape changes
• light can change the order parameter, resulting in shape changes
mesogenic unit
backbone
cross-linker
• LCE: liquid crystal rubber
March 21, 2005March Meeting of the APS
Los Angeles, CA
Elastomer Free Energy
2 21 1 11 ....
2 2 2c
TQ E E Q
TC Q
F =
Liquid Crystals: Order Parameter Tensor Qαβ
Elastomers: Strain Tensor εαβ
Nematic Free Energy
Coupling Term
Elastomer Free Energy
η – Young’s modulus – external stress tensor
C – constant
E-field Term
March 21, 2005March Meeting of the APS
Los Angeles, CA
Light Induced Order Parameter Changes
Light can change the order parameter via:
• direct heating of the sample
• disruption of nematic order due to photoisomerization
• direct optical torque due to direct angular momentum transfer from the light
• indirect optical torque
All these mechanisms could be contributing.
March 21, 2005March Meeting of the APS
Los Angeles, CA
LCE Composition
Si O
CH3
H
O C
O
O OCH3
O
O
O
O C
O
O
CH3
CH3
CH3
CH3
CH3
n
9
9
9
1
2
3
4
100 mol.%
72 mol.%
18 mol.%
10 mol.%
Si O
CH3
H
O C
O
O OCH3
O
O
O
O C
O
O
CH3
CH3
CH3
CH3
CH3
n
9
9
9
1
2
3
4
100 mol.%
72 mol.%
18 mol.%
10 mol.%
Si O
CH3
H
O C
O
O OCH3
O
O
O
O C
O
O
CH3
CH3
CH3
CH3
CH3
n
9
9
9
1
2
3
4
100 mol.%
72 mol.%
18 mol.%
10 mol.%
Si O
CH3
H
O C
O
O OCH3
O
O
O
O C
O
O
CH3
CH3
CH3
CH3
CH3
n
9
9
9
1
2
3
4
100 mol.%
72 mol.%
18 mol.%
10 mol.%
• methylsiloxane monomer (main chain)
• mesogenic biphenyl
(side group)
• trifunctional crosslinker
Si O
CH3
H
O C
O
O OCH3
O
O
O
O C
O
O
CH3
CH3
CH3
CH3
CH3
n
9
9
9
1
2
3
4
100 mol.%
72 mol.%
18 mol.%
10 mol.%
Si O
CH3
H
O C
O
O OCH3
O
O
O
O C
O
O
CH3
CH3
CH3
CH3
CH3
n
9
9
9
1
2
3
4
100 mol.%
72 mol.%
18 mol.%
10 mol.%
March 21, 2005March Meeting of the APS
Los Angeles, CA
Our LCE Materialssamples have the following properties:
Typical LCE sample size.
• nematic monodomain
• 8 – 12% cross-linking
• 0.1% dissolved azo-dye
6mm
300 m3mm
March 21, 2005March Meeting of the APS
Los Angeles, CA
Azo-Dyes
trans-
h
kT , h’
• contain a N = N double bond connecting aromatic benzene rings
• undergo photoisomerization, from the trans- to cis- configuration on absorption of a photon
• align with the nematic director
• are dissolved in our LCEs to aid in light absorption
cis-
March 21, 2005March Meeting of the APS
Los Angeles, CA
Light Induced Bending of LCEs
• laser illumination causes the elastomer to bend towards the beam, as shown
Sample
ArLaser
1.5mm
March 21, 2005March Meeting of the APS
Los Angeles, CA
Experiment
LabVIEW
• switchable mirror allows alternate illumination of each side of LCE sample
Switchable Mirror Elastomer
Fish(3 x 6 mm)
MirrorArgon Laser
shutter
March 21, 2005March Meeting of the APS
Los Angeles, CA
Experiment• sample immersed in rheoscopic fluid, which allows for flow visualization
• sample is illuminated alternately on both sides by light at 514nm from Ar laser
March 21, 2005March Meeting of the APS
Los Angeles, CA
Experimental Results
• highest pumping rates are achieved with the shortest delay time between laser pulses
• all curves peak near the same exposure time of 700 ms
0.065
0.075
0.0850.095
0.105
0.115
0.125
0.1350.145
0.155
0.165
0 200 400 600 800 1000 1200
Laser Exposure Time (ms)
Flu
id F
low
Vel
oci
ty (
cm/s
) 100 ms Delay
200 ms Delay
300 ms Delay
Fluid velocities for various elastomer driving excitations
March 21, 2005March Meeting of the APS
Los Angeles, CA
Momentum Transfer
• laser light provides energy to the LCE, but not momentum
• energy transfer induces a stress in the LCE sample, causing it to bend.
• bending of the elastomer sample transfers momentum to the surrounding fluid
• fluid transfers momentum to the LCE sample• This is similar to a conventional motor, where energy is
used to cause momentum transfer.
March 21, 2005March Meeting of the APS
Los Angeles, CA
Drag ReductionGrey’s Paradox*: actively swimming fish experience a
significant drag reduction through the swimming process• possibly due to
• viscous damping by fluid cells under the skin• swimming motion
• we would like to determine if soft active materials can lead to a drag reduction
• could lead to new applications such as• soft active materials to coat boats for reduced
energy consumption
* Gray, J. Studies in animal locomotion, J. Exp. Biol. 13, pp. 192-199 (1936).
March 21, 2005March Meeting of the APS
Los Angeles, CA
Conclusions
• laser supplies energy to the system which results in momentum transfer between fish & surrounding fluid
• fluid is pumped backwards• results of this experiment will be compared with
modeling• expect new insight into soft active materials
Future work• design experiment to determine if drag reduction is
present in our system