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: gardiner.damian@gmail.com, hjc37@cam.ac.uk

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)