high solubility liquid crystal dye guest-host device · the authors gratefully acknowledge the...
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The authors gratefully acknowledge the financial support of the EPSRC
High solubility liquid crystal dye guest-host device
D.J. Gardiner and H. J. Coles
Centre of Molecular Materials for Photonics and Electronics,
Electrical Engineering Division,
Cambridge University Engineering Department,
9 JJ Thomson Avenue,
CB3 0FA, UK
Bistable electro-optic effect in Smectic A1
1) Scattering:
• Frequency, f < critical frequency fC, motion of ionic material
generates highly opaque dynamic scattering texture.
• Vth ~
2) Clear:
• f > fC. No ionic motion, dielectric reorientation generates haze-
free highly clear state:
• Vth ~ (d/∆ε)1/2.
Figure 1. Device Schematic
A. Pure 10/2 liquid crystal
Bistable
"o polarisers
Indefinite storage
High Efficiency!
RESULTS
CO"CLUSIO"S•Very high solubilities can be achieved
•"o adverse effect on electro-optic properties
•Thinner cells
•Microphase separation of constituent moieties into
siloxane, alkyl chain and aromatic core regions
CLEAR (> 1 kHz) SCATTERING (< 100 Hz)
Materials
− ⊥σσ ||1(d
Si
CH3
CH3
O Si
CH3
CH3
CH3
NO2
N
CH3
N N
• Organosiloxane disperse red 1 dye2.
Si
CH3
CH3
O Si
CH3
CH3
CH3 CNO
• Smectic A organosiloxane liquid crystal (“10/2”)3
• K – SA 41.1°C SA – I 70.3°C
Mixture preparation – high miscibility
Figure 2. Birefringent textures of the 38% w/w mixture
showing (left) SA batonnet formation and (right) focal conic
texture of the mesophase
• Three mixtures prepared: 4%, 22% and 38% w/w DR
dye in 10/2 host
• All mixtures showed complete miscibility, even at
the highest concentration
DGH Mixture
SA to Isotropic transition
10/2 72°C
4% w/w DR 72°C
22% w/w DR 67°C
38% w/w DR 56°C
Application Areas•Slow update devices
0
50
100
150
200
250
300
-35 -30 -25 -20 -15 -10 -5
Th
resh
old
Vo
lta
ge
(V, R
MS
)
10/2 write
10/2 erase
TS (°C)
0
50
100
150
200
250
300
0 10 20 30 40
Concentration of dye (% w/w)
Th
resh
old
Vo
lta
ge (
V,
rms)
Ts = - 30
Ts = - 10
Ts = - 30
Ts = - 10
°CWrite
°C
Erase °C
°C
FUTURE WORK•Increase order parameter of dye and host
•Other dyes, for example anthraquinone and fluorescent dyes.
•Reduce operating voltages by using thinner cells and optimizing material parameters:
dielectric anisotropy and conductivity ratio.5
• Order parameters:
• Dye ~ 0.47
• 10/2 ~ 0.52
1) D. Coates, W. A. Crossland, J. H. Morrissy, and B. Needham, J. Phys. D Appl. Phys. 11, 2025 (1978).
2) Courtesy of Dow Corning Inc.
3) J. Newton, H. Coles, P. Hodge, and J. Hannington, J. Mat. Chem. 4, 869-874 (1994).
4) D. J. Gardiner and H. J. Coles, J. Appl. Phys. 100, 4903 (2006).
5) D. J. Gardiner and H. J. Coles, J. Phys. D. Appl. Phys. 39, 4948 (2006).
Email: [email protected], [email protected]
Absorbance against wavelength
0
0.2
0.4
0.6
0.8
1
400 450 500 550 600 650 700
Wavelength (nm)
Ab
sorb
an
ce
References
All mixtures show comparable
or superior behviour even at
high concentration
B. DGH mixtures
Figure 3. Electro-optic threshold voltages
of the write and erase modes for the pure
material and DGH mixtures.
0
20
40
60
80
100
120
140
160
180
200
-35 -30 -25 -20 -15 -10 -5 0
Resp
on
se t
ime (
ms)
Pure 10/2
+ 4% w/w DR
+22% w/w DR
+ 38% w/w DR
TS (°C)
0
5
10
15
20
25
30
35
40
45
50
-35 -30 -25 -20 -15 -10 -5 0
Res
pon
se t
ime
(ms)
Pure 10/2
+ 4% w/w DR
+22% w/w DR
+ 38% w/w DR
TS (°C)
Figure 4. Electro-optic response times of
the a) clear (erase) and b) scattering
(write) modes against temperature.
Applied voltage = Vth + 50V.
The electro-optic properties of the host
are a consequence of the highly
anisotropic conductivity.4 E.g.
0.8 to0.5 ~ 8CBfor ,005.0~|| ⊥σσ
a)
b)