1 Measuring Refractive Indices of Nematic LC Elastomers Volodymyr Borshch Research advisor:...
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Transcript of 1 Measuring Refractive Indices of Nematic LC Elastomers Volodymyr Borshch Research advisor:...
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Measuring Refractive Indicesof Nematic LC Elastomers
Volodymyr Borshch
Research advisor:Professor Peter Palffy-Muhoray
25 August 2008
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Outline
• Motivation • Nematic LC elastomer• Methods and previous results• Theory• Materials selection• Experimental setup• Obtained data• Conclusions• Acknowledgments
3
Motivation
• Nematic LC Elastomers have bright future
• Not all physical properties are quite extensively described so far
• E.g. Refractive index
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Nematic LC elastomer
O O
O
O
Mesogen
O
CH3H
CH3
Si O
CH3
SiH
CH3
Si H
85
CH3
Backbone
CH2
O
CH2
O
Crosslinker
From Israel Lazo presentation
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Methods
Israel Lazo presentation
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Yet another approach
• From Fresnel equations:
The main idea of the methodR=0
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High refractive index liquids
• Liquids at or near 20˚CRefractive index Material
1.627 Quinoline
1.660 α-Monobromonaphthalene
1.717 Mercury potassium iodide
1.737 Methylene iodide
1.78 Methylene iodide and sulphur (saturated)
1.793 Barium mercuric iodide aq.
1.82 Potassium iodide and mercuric iodide aq.
1.868 Solutions of 35% by weight CH2I2, 31% SnI4, 16% AsI3, 8% SbI3 and 10% S
1.885 Hydrogen disulphide
1.95 Phosphorus in carbon disulphide
2.06 Yellow phosphorus 8 parts by weight + 1part sulphur + 1 methylene iodide
2.2 Mercuric iodide in aniline or quinolineData from Kaye and Laby, Tables of Physical and Chemical Constants, 1959
Ionic liquids based on 1-alkyl-3-methylimidazolium cations
Most of them were either:
- Highly toxic and poisonous- Not transparent- Not available
A simple, cost-effective and magnificent liquid was used – saturated
solution of NaI
n = 1.496
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Experiment
HeNe
Rotating polarizer
Fish tank with immersed elastomer
Experimental setupMeasuring the reflectance
of the elastomer innormal incidence
λ/4 plate
detector
632.8 nmfilter
Referencebeam
Beam splitter
lens
Lock-inamplifier
detector
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y = -4.95494x + 7.94601
R2 = 0.75418
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
1.410 1.420 1.430 1.440 1.450 1.460 1.470 1.480 1.490 1.500
refractive index, n
Ref
lect
ance
, R
(a.
u.)
perpendicular
Linear (perpendicular)
no measurement
• The polarization is perpendicular to the preferred director orientation n
elastomer with no strainbatch #71 (10% cross linkers)
Fitting and extrapolation gives n=1.60365 ±0.01633
The sample from batch #69 gave similar value n=1.53529
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y = -4.06398x + 6.67013
R2 = 0.61900
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
1.410 1.420 1.430 1.440 1.450 1.460 1.470 1.480 1.490 1.500
refractive index, n
Ref
lect
ance
, R
(a.
u.)
parallel
Linear (parallel)
ne measurement
• The polarization is parallel to the preferred director orientation n
elastomer with no strainbatch #71 (10% cross linkers)
Fitting and extrapolation gives n =1.64128 ±0.03830
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Benefits and drawbacks of the method
• Looks simple
• Inhomogeneity of elastomer
• Scattering
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0 5 10 15 20 25 30 35 40
1.40
1.42
1.44
1.46
1.48
1.50
1.52
1.54
1.56
1.58
1.60
1.62
1.64
1.66
1.68
1.70
1.72
1.74
R
efr
act
ive
Ind
ex
Strain (%)
ne Interferometer
no Interferometer
ne Brewster
no Brewster
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Conclusions
• The sample was different but the results agree with previous measurements
• The refractive indices need to be measured more accurately
• Future work: Generalized Ellipsometry
• Need to measure inhomogeneity
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Acknowledgement
• Prof.Peter Palffy-Muhoray
• Jake Fontana, Israel Lazo
• Paul Luchette, Michele Fontana
• Jeremy Neal, Sabrina Relaix
• Rafael Zola
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Thank you !