FPD International CHINA 2013/ Beijing Summit

Study on the Blue Phase Liquid Crystal Materials for next-generation Display

Huai Yang

Peking University

09/10/2013

1. Research background

2. Extending the BP temperature range

3. Reducing the hysteresis of BPLCs

4. Lowing the driving voltage of BPLCs

5. BPLCs toward practical applications

6. Summary

Outline

FPD Market: nearest future

Paul Semenza, A New Chapter for the Display Market, Information Display Magazine, 2010.

LCD Development

Molecular Arrangement of Liquid Crystals

Liquid crystals (LCs) are matter in a state that has properties between those

of conventional liquid and those of solid crystal, and an LC may flow like a

liquid, but its molecules may be orientated in a crystal-like way.

(a) Smetic (b) Nematic (c) Cholesteric

pitch

director

Double Twist Alignment

(e)N phase

Ch Phase：simple twists

Blue Phase：double twists

Comparison of simple-twist and double-twist arrangements

Structure of BPLCLattice structure:

1.Bragg reflection

2.Optically isotropic

3.Narrow Temperature range

LC molecule

Double twist cylinder Disclination line

Double twist alignment

Typical textures of blue phase

Kinds of BPLCBPⅠ BPⅡ BPⅢ

Memmer, R., Computer simulation of chiral liquid crystal phases VIII. Blue phases of the chiral Gay-Berne fluid. Liquid Crystals 2000, 27, (4), 533-546.

Spaghetti - Model

Increasing Chirality or Temperature

Electric field Effects on BPLC

Local reorientation of molecules

Lattice distortion

Phase transition to a lower symmetry phase

As the electric field increases, there will be three distinct transformations:

By Kerr effect, △n (E) = λKE2 , ~ 0.1ms

In BPI ：~10ms

Switching from BPI to BPII : ~few seconds

Kitzerow, H. S. Blue phases come of age: a review, Proceedings of SPIE,2009, 7232(05):1-14.

Mechanism of the BP-LCD

Response speed：﹤1 ms

Response speed：~ 5 ms

BP-LCD

TFT-LCD

Advantage of the BP-LCD

Response Time millisecond range sub-millisecond rangeColor Filters √ ×（field sequential displays）

Surface Treatment √ ×（macroscopically isotropic）

Compensation Film √ × （tunable viewing angle）

Cell-gap Sensitivity sensitive insensitiveProductive Facility similar similar

TFT-LCD BP-LCD

Compared with TFT-LCD, BP-LCD would:Enhancing optical efficiency by ~3X, Lowering the power consumption by ~40％,Reducing the manufacturing cost by ~19%.

Polymer Stabilized Blue Phases

H. Kikuchi, Huai Yang, et al. Nature Materials 1, 64 (2002)

The temperature is more than 60K including room temperature(260-326K).

The response time is ~10-4s.

The world’s first BP LCD prototype

SID 08’ Exhibition SID 09’ Exhibition

Key Features

1) Ultra-Fast Switching Time

2) No Alignment Layers

3) No Color Filters

4) High CR

5) Cell Gap Insensitivity

6) Wide Viewing Angle

The Fatal Problems on BPLC

High operating voltage and Low transmittance

Optimizing the electrode structure

Developing materials with larger K

Easy fragile character under external electrical field

polymer & polymer %

Narrow temperature range and heavy hysteresis

Device Physics & Materials

Four shortcomings must be overcame if applied BPLC in transmission display:

1. Research background

2. Extending the BP temperature range

3. Reducing the hysteresis of BPLCs

4. Lowing the driving voltage of BPLCs

5. BPLCs toward practical applications

6. Summary

Outline

2-1. Hydrogen-bond stablized BPLCs

2. Extending the BP temperature range

16

W. He, Z. Yang, H. Yang*，et al. Adv. Mater., 2009, 21(20): 2050.

~ 20℃

2-2. BPLCs stablized by 1,3,4-oxadiazoles

2. Extending the BP temperature range

17

Liq. Cryst., 2012, 39: 629–638. Liq. Cryst., 2013, 40, 354.

The BP composites with more than 30 oC were prepared by doping the 2,5-disubstituted 1,3,4-oxadiazoles with different rigid cores or different lateralsubstituents and terminal alkoxy chain length into a BP-exhibiting LC host.

2-3. BPLCs stablized by thiophene-based mesogens

2. Extending the BP temperature range

18

L. Wang, H. Yang*, et al., J. Mater. Chem., 2012, 22: 2383.

Thiophene-based bent-shaped mesogens were firstly applied to extend theBP temperature range of a BP-exhibiting LC host, and the widest BP rangehas been extended even up to about 25.9 oC.

2-4. BPLCs stablized by rodlike tolane cyano mesogens

2. Extending the BP temperature range

B. Li, H. Yang*, et al., Soft Matter, 2013, 9, 1172.

It is found that lateral fluoro substituents are crucial for the rodlikebiphenyl tolane cyano compounds to form BP structures.

1. Research background

2. Extending the BP temperature range

3. Reducing the hysteresis of BPLCs

4. Lowing the driving voltage of BPLCs

5. BPLCs toward practical applications

6. Summary

Outline

3-1. ZnS Nanoparticles-stabilized BPI

3. Reducing the hysteresis of BPLCs

L. Wang, H. Yang*, et al., Small, 2012, 8(14), 2189.

Effect of the concentration of ZnS NPs on the BP temperature range

3-2. Possible mechanism for the NPs-stabilized BPI

3. Reducing the hysteresis of BPLCs

The initially freely-moving NPs became trapped once they met adisclination line, and that the volume and the free energy around thedisclination were consequently reduced;The volume and the free energy around the disclinations could becontinuously suppressed with increasing the concentration of ZnS NPs, butthe cubic structures of BPI would be disordered after the criticalconcentration had been reached.

3-3. Electro-optical performances

3. Reducing the hysteresis of BPLCs

(1) It is found that the hysteresis of BPLCs can be reduced bydispersing quite a small amount of ZnS NPs.

(2) The Kerr constant decreases and driving voltage increaseswith increasing the concentration of ZnS NPs.

3-4. Comparison with the PSBP

3. Reducing the hysteresis of BPLCs

Sample No. BPLC/ wt%Monomer/ wt% Initiator/ wt%

C6M TMPTA 651

1 96.5 1.7 1.3 0.5

2 94.5 2.8 2.2 0.5

3 92.5 3.9 3.1 0.5

4 90.5 5.0 4.0 0.5

5 84.5 8.3 6.7 0.5

Hysteresis is relatively small andcan be considered as hysteresis freein the samples stabilized by morethan 9.0 wt% monomers, but the on-state voltage is so high;

The reversible switching withhysteresis free can be also achievedby the suspensions of ZnS NPs at a0.5-0.7 wt% level, and the on-statevoltage is much lower than that ofPSBP.

1. Research background

2. Extending the BP temperature range

3. Reducing the hysteresis of BPLCs

4. Lowing the driving voltage of BPLCs

5. BPLCs toward practical applications

6. Summary

Outline

4-1. Ferroelectric nanoparticles

4. Lowing the driving voltage of BPLCs

Non-ferroelectric NPs Ferroelectric NPs

Interaction between the nanoparticles and LC molecules

4-2. BPLCs stabilized by ferroelectric nanoparticles

4. Lowing the driving voltage of BPLCs

Effect of the concentration of ZnS NPs on the BP temperature range

Host BPLCs：82.0 wt% SLC-4, 10.0 wt%

R811 and 8.0 wt% Iso-(6OBA)2,

which shows about 10 oC of BP I

on cooling at a rate of 0.5℃/min.

L. Wang, H. Yang*, et al., J. Mater. Chem., 2012, 22: 19629.

4-3. Electro-optical performances

4. Lowing the driving voltage of BPLCs

N*LC/ wt%

NPs / wt%

BP Range / oC

ZnS BaTiO3

100.0 0.0 55.0-45.0 55.0-45.0

99.9 0.1 56.4-44.4 55.8-44.5

99.7 0.3 57.2-43.0 57.0-43.2

99.5 0.5 56.8-41.2 59.3-42.6

99.3 0.7 56.6-42.4 60.5-44.0

99.0 1.0 56.0-44.2 62.0-48.2

98.5 1.5 55.4-46.7 63.4-53.9

(1) It is found that the hysteresis of BPLCs can be reduced bydispersing quite a small amount of ZnS or BaTiO3 NPs.

(2) The driving voltage of BPLCs stabilized by BaTiO3 NPs is muchlower that of ZnS NPs.

4-4. Possible mechanism

4. Lowing the driving voltage of BPLCs

The suspension offerroelectric NPs would notonly increase the intrinsicbirefringence and dielectricanisotropy of LC materials,but also decrease the deviceparameter A, which helps togenerate a uniform strongelectric field in the whole bulkLC layer, consequentlyenhancing the Kerr effect.

1. Research background

2. Extending the BP temperature range

3. Reducing the hysteresis of BPLCs

4. Lowing the driving voltage of BPLCs

5. BPLCs toward practical applications

6. Summary

Outline

5-1. Polymer stabilized nanoparticle-enriched BPLCs

5. BPLCs toward practical applications

No.N*LC/wt%

Monomer/ wt%

Nanoparticles/ wt%

Initiator

/ wt%

Transition temperature/ oC

C6M TMPTA ZnS BaTiO3 651 I-BP BP-N* ∆T

A0 100.0 - - - - - 53.1 42.5 10.6

A1 96.5 1.7 1.3 - - 0.5 48.0 29.1 18.9

A2 94.5 2.8 2.2 - - 0.5 48.1 24.3 23.8

A3 92.5 3.9 3.1 - - 0.5 47.9 18.6 29.3

B1 94.4 2.8 2.2 0.1 - 0.5 48.3 17.8 30.5

B2 94.2 2.8 2.2 0.3 - 0.5 48.1 13.6 34.5

B3 94.0 2.8 2.2 0.5 - 0.5 48.7 7.5 41.2

B4 93.8 2.8 2.2 0.7 - 0.5 48.5 12.7 35.8

B5 93.5 2.8 2.2 1.0 - 0.5 48.9 16.5 32.4

B6 93.0 2.8 2.2 1.5 - 0.5 48.3 23.9 24.4

C1 94.4 2.8 2.2 - 0.1 0.5 49.7 18.3 31.4

C2 94.2 2.8 2.2 - 0.3 0.5 49.9 11.6 38.3

C3 94.0 2.8 2.2 - 0.5 0.5 52.2 6.3 45.9

C4 93.8 2.8 2.2 - 0.7 0.5 53.4 12.4 41.0

C5 93.5 2.8 2.2 - 1.0 0.5 54.9 19.9 35.0

C6 93.0 2.8 2.2 - 1.5 0.5 56.3 23.7 32.6

PSBP

PSBP+

ZnS

PSBP+

BaTiO3

5-2. Possible mechanism

5. BPLCs toward practical applications

5-3. Electro-optical performances

5. BPLCs toward practical applications

The driving voltage of PSBP doped with BaTiO3 NPs is muchlower that of ZnS NPs.

L. Wang, H. Yang*, et al., J. Mater. Chem. C, 2013, DOI:10.1039/c3tc31253d.

Summary

Extending the BP temperature range

Lowing the driving voltage of BPLCs

BPLCs toward practical applications

BPLCs can be stabilized by hydrogen-bond, 1,3,4-oxadiazoles,thiophene-based mesogens or rodlike tolane cyano mesogens.

Reducing the hysteresis of BPLCsThe hysteresis of BPLCs can be reduced by dispersing quite asmall amount of ZnS NPs.

The driving voltage of BPLCs can be reduced by dispersingquite a small amount of BaTiO3 ferroelectric NPs.

Polymer-stabilized nanoparticle-enriched methods may be provide aneffective and efficient method to stabilize cubic BPs structures andimprove the E-O performances.

Thanks！