1. 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
RESULTS
Bistable electro-optic effect in Smectic A1
A. Pure 10/2 liquid crystal
Bistable
No polarisers
Indefinite storage
High Efficiency!
The electro-optic properties of the host are a consequence of the highly anisotropic conductivity.4 E.g.
B. DGH mixtures
Figure 1. Device Schematic
Scattering:
Frequency, f < critical frequency fC, motion of ionic material generates highly opaque dynamic scattering texture.
Vth ~
Clear:
f > fC. No ionic motion, dielectric reorientation generates haze-free highly clear state:
Vth ~ (d/De)1/2.
All mixtures show comparable or superior behviour even at high concentration
Figure 3. Electro-optic threshold voltages of the write and erase modes for the pure material and DGH mixtures. a)
Materials b)
Figure 4. Electro-optic response times of the a) clear (erase) and b) scattering (write) modes against temperature. Applied voltage = Vth + 50V.
Organosiloxane disperse red 1 dye2.
CONCLUSIONS
Very high solubilities can be achieved
No adverse effect on electro-optic properties
Thinner cells
Microphase separation of constituent moieties into siloxane, alkyl chain and aromatic core regions
Smectic A organosiloxane liquid crystal (“10/2”)3
K – SA 41.1°C SA – I 70.3°C
Mixture preparation – high miscibility
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
Application Areas
Slow update devices
Order parameters:
Dye ~ 0.47
10/2 ~ 0.52
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
Figure 2. Birefringent textures of the 38% w/w mixture showing (left) SA batonnet formation and (right) focal conic texture of the mesophase
References
D. Coates, W. A. Crossland, J. H. Morrissy, and B. Needham, J. Phys. D Appl. Phys. 11, 2025 (1978).
Courtesy of Dow Corning Inc.
J. Newton, H. Coles, P. Hodge, and J. Hannington, J. Mat. Chem. 4, (1994).
D. J. Gardiner and H. J. Coles, J. Appl. Phys. 100, 4903 (2006).
D. J. Gardiner and H. J. Coles, J. Phys. D. Appl. Phys. 39, 4948 (2006).
The authors gratefully acknowledge the financial support of the EPSRC