FPD International CHINA 2013/ Beijing Summit. Study on the Blue Phase Liquid Crystal Materials for next-generation Display.

Transcription

1 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

2 Outline 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

3 FPD Market: nearest future Paul Semenza, A New Chapter for the Display Market, Information Display Magazine, 2010.

4 LCD Development

5 Molecular Arrangement of Liquid Crystals director pitch (a) Smetic (b) Nematic (c) Cholesteric 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.

6 Double Twist Alignment Comparison of simple-twist and double-twist arrangements Ch Phase:simple twists (e) N phase Blue Phase:double twists

7 Structure of BPLC Lattice structure: 1.Bragg reflection 2.Optically isotropic 3.Narrow Temperature range Double twist alignment LC molecule Typical textures of blue phase Double twist cylinder Disclination line

8 Kinds of BPLC BPⅠ BPⅡ BPⅢ Spaghetti - Model Increasing Chirality or Temperature Memmer, R., Computer simulation of chiral liquid crystal phases VIII. Blue phases of the chiral Gay-Berne fluid. Liquid Crystals 2000, 27, (4),

9 Electric field Effects on BPLC As the electric field increases, there will be three distinct transformations: Local reorientation of molecules By Kerr effect, n (E) = λke 2, ~ 0.1ms Lattice distortion In BPI :~10ms Phase transition to a lower symmetry phase 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.

10 Mechanism of the BP-LCD BP-LCD Response speed: < 1 ms TFT-LCD Response speed :~ 5 ms

11 Advantage of the BP-LCD TFT-LCD BP-LCD Response Time millisecond range sub-millisecond range Color Filters Surface Treatment (field sequential displays) (macroscopically isotropic) Compensation Film (tunable viewing angle) Cell-gap Sensitivity sensitive insensitive Productive Facility similar similar Compared with TFT-LCD, BP-LCD would: Enhancing optical efficiency by ~3X, Lowering the power consumption by ~40%, Reducing the manufacturing cost by ~19%.

12 Polymer Stabilized Blue Phases The temperature is more than 60K including room temperature( k). The response time is ~10-4 s. H. Kikuchi, Huai Yang, et al. Nature Materials 1, 64 (2002)

13 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

14 The Fatal Problems on BPLC Four shortcomings must be overcame if applied BPLC in transmission display: 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

15 Outline 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

16 2. Extending the BP temperature range 2-1. Hydrogen-bond stablized BPLCs ~ 20 W. He, Z. Yang, H. Yang*,et al. Adv. Mater., 2009, 21(20):

17 2. Extending the BP temperature range 2-2. BPLCs stablized by 1,3,4-oxadiazoles Liq. Cryst., 2012, 39: Liq. Cryst., 2013, 40, The BP composites with more than 30 o C were prepared by doping the 2,5- disubstituted 1,3,4-oxadiazoles with different rigid cores or different lateral substituents and terminal alkoxy chain length into a BP-exhibiting LC host.

18 2. Extending the BP temperature range 2-3. BPLCs stablized by thiophene-based mesogens L. Wang, H. Yang*, et al., J. Mater. Chem., 2012, 22: Thiophene-based bent-shaped mesogens were firstly applied to extend the BP temperature range of a BP-exhibiting LC host, and the widest BP range has been extended even up to about 25.9 o C.

19 2. Extending the BP temperature range 2-4. BPLCs stablized by rodlike tolane cyano mesogens B. Li, H. Yang*, et al., Soft Matter, 2013, 9, It is found that lateral fluoro substituents are crucial for the rodlike biphenyl tolane cyano compounds to form BP structures.

20 Outline 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

21 3. Reducing the hysteresis of BPLCs 3-1. ZnS Nanoparticles-stabilized BPI Effect of the concentration of ZnS NPs on the BP temperature range L. Wang, H. Yang*, et al., Small, 2012, 8(14), 2189.

22 3. Reducing the hysteresis of BPLCs 3-2. Possible mechanism for the NPs-stabilized BPI The initially freely-moving NPs became trapped once they met a disclination line, and that the volume and the free energy around the disclination were consequently reduced; The volume and the free energy around the disclinations could be continuously suppressed with increasing the concentration of ZnS NPs, but the cubic structures of BPI would be disordered after the critical concentration had been reached.

23 3. Reducing the hysteresis of BPLCs 3-3. Electro-optical performances (1) It is found that the hysteresis of BPLCs can be reduced by dispersing quite a small amount of ZnS NPs. (2) The Kerr constant decreases and driving voltage increases with increasing the concentration of ZnS NPs.

24 3. Reducing the hysteresis of BPLCs 3-4. Comparison with the PSBP Sample No. BPLC/ wt% Monomer/ wt% Initiator/ wt% C6M TMPTA Hysteresis is relatively small and can be considered as hysteresis free in the samples stabilized by more than 9.0 wt% monomers, but the onstate voltage is so high; The reversible switching with hysteresis free can be also achieved by the suspensions of ZnS NPs at a wt% level, and the on-state voltage is much lower than that of PSBP.

25 Outline 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

26 4. Lowing the driving voltage of BPLCs 4-1. Ferroelectric nanoparticles Interaction between the nanoparticles and LC molecules Non-ferroelectric NPs Ferroelectric NPs

27 4. Lowing the driving voltage of BPLCs 4-2. BPLCs stabilized by ferroelectric nanoparticles 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 o CofBPI on cooling at a rate of 0.5 /min. L. Wang, H. Yang*, et al., J. Mater. Chem., 2012, 22:

28 4. Lowing the driving voltage of BPLCs 4-3. Electro-optical performances N*LC/ wt% NPs / wt% BP Range / o C ZnS BaTiO (1) It is found that the hysteresis of BPLCs can be reduced by dispersing quite a small amount of ZnS or BaTiO 3 NPs. (2) The driving voltage of BPLCs stabilized by BaTiO 3 NPs is much lower that of ZnS NPs.

29 4. Lowing the driving voltage of BPLCs 4-4. Possible mechanism The suspension of ferroelectric NPs would not only increase the intrinsic birefringence and dielectric anisotropy of LC materials, but also decrease the device parameter A, which helps to generate a uniform strong electric field in the whole bulk LC layer, consequently enhancing the Kerr effect.

30 Outline 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

31 5. BPLCs toward practical applications 5-1. Polymer stabilized nanoparticle-enriched BPLCs PSBP PSBP + ZnS PSBP + BaTiO 3 No. N*LC/ wt% Monomer / wt% Nanoparticles /wt% Initiato r /wt% Transition temperature / o C C6M TMPTA ZnS BaTiO I-BP BP-N* T A A A A B B B B B B C C C C C C

32 5. BPLCs toward practical applications 5-2. Possible mechanism

33 5. BPLCs toward practical applications 5-3. Electro-optical performances The driving voltage of PSBP doped with BaTiO 3 NPs is much lower that of ZnS NPs. L. Wang, H. Yang*, et al., J. Mater. Chem. C, 2013, DOI: /c3tc31253d.

34 Summary Extending the BP temperature range BPLCs can be stabilized by hydrogen-bond, 1,3,4-oxadiazoles, thiophene-based mesogens or rodlike tolane cyano mesogens. Reducing the hysteresis of BPLCs The hysteresis of BPLCs can be reduced by dispersing quite a small amount of ZnS NPs. Lowing the driving voltage of BPLCs The driving voltage of BPLCs can be reduced by dispersing quite a small amount of BaTiO 3 ferroelectric NPs. BPLCs toward practical applications Polymer-stabilized nanoparticle-enriched methods may be provide an effective and efficient method to stabilize cubic BPs structures and improve the E-O performances.

35 Thanks!