Enhancing Liquid Crystal Applications through Advanced Alignment Methods

1. Improving the Alignment and Application Properties of Liquid Crystals改進軟物質-液晶材料-配向與應用性能的新方法 Jung Y. Huang 黃中垚 Department of Photonics, Chiao Tung University Hsinchu, Taiwan http://www.jyhuang.idv.tw March 16, 2007

2. Multi-billion dollar LCD industry is based on only ONE such coupling! Many more possibilities can be explored further. However, techniques with better control are needed to realize such applications.

3. Methods to be Used to Improve the Alignment and Application Properties of Liquid Crystals 1. Method that improves molecular alignment order on surface; 2. Method that can be used to accurately control pretilt angle of organic molecules on surface; 3. Method that yields orientational coupling amplification in an ferroelectric liquid crystal film.

4. Technologies that may Benefit from Our Achievements • Enhanced carrier mobility in organic thin film transistors: Field-effect mobility (m=v/E) as much as 8 cm2/V.sec had been reported in literature by improving molecular ordering; • Accurately Control High Pretilt Angle for Bistable LC Displays, with the Advantage of Energy Savings: Many new types of liquid crystal displays including bistable displays can be realized only if high pretilt angles are available. Fast response liquid crystal displays can also be better made with large pretilt angles.

5. Technologies that may Benefit from Our Achievements • Doping FLC with nc-ZnO results in a more ordered structure of alkyl chains and more organized field-induced reorientation of sub molecular segments: Material evaluation for SSFLC panel application is under joint development with Forth Dimension Displays Limited, UK, http: www.forthdd.com.

6. 1. Method that improves molecular alignment order on surface Liquid Crystal Polymer (LCP): 1,4-phenylene bis(4-(6-(acryloyloxy) hexyloxy benzoate)

7. Sum-Frequency Vibrational Spectroscopy probes the molecular alignment order on surface Resonance can be employed to yield sensitivity to molecular species. • SFG: (2)eff = (2)eff(bulk) + (2)s(surface) • In a medium with an inversion symmetry: • (2)eff(bulk) = 0, (2)s(surface)  0

8. LCP/UVA RN1349 UVA RN1349

10. Similar to expitaxial growth, the LCP preserves the anchoring properties of the underlying alignment layer, and improves the orientational order of phenyl groups, which results in a narrower azimuthal distribution of LC.

11. Twist Anchoring Strength Revealed by Dynamic Light Scattering • The intensity correlation functions showed a relaxation component of LC director, which can be described by • The fluctuation power spectra of DLS indicate that the deposition of LCP does not significantly change the twist anchoring strength of LC molecules.

12. 2. Method that can control pretilt angle of organic molecules on surface • Rubbed PVA surface can be modified by reacting with alkyl carboxilic acid to produce side chains with varying alkyl chain length.

13. Method that can control pretilt angle of organic molecules on surface • SFG spectroscopy verifies the dehydration reaction of methyl carboxilic acid group with a rubbed PVA surface

14. Method that can control pretilt angle of organic molecules on surface • Further increase in the LC pretilt may be obtained by using longer alkyl chain length or perfluoro species.

15. 3. Method that results in orientational coupling amplification in an ferroelectric liquid crystal film • The diluted ferroelectric liquid crystal suspensions are stable, because the small concentration of nanoparticles does not significantly perturb the director field in the LC. • At the same time, the nanoparticles share their intrinsic ferroelectric properties with the LC matrix due to the anchoring with the LC. The distorted molecular orientation distribution propagates on a scale much larger than the size of molecules.

16. Method that results in orientational coupling amplification in an ferroelectric liquid crystal film nc-ZnO:SSFLC Polarized IR spectra taken on a SSFLC cell at 35 ˚C and zero field with an IR polarizer orientation varying from -90˚ to 90˚. Pure SSFLC

17. Uniform Dispersion of nc-ZnO in SSFLC:The homogeneous dispersion of nanocrystals leads to stronger correlation among the IR active modes of the FLC cores and among alkyl chains of SSFLC film. Synchronous IR Correlation Plot: reveal uniaxial alignment FLC nc-ZnO doped FLC

18. Asynchronous IR Correlation Plot: Revelation of angular deviation Long alkyl chains at the two ends of the FLC molecules favor the formation of layers. nc-ZnO doped FLC FLC

19. 2D IR shows that doping of SSFLC with ZnO quantum dots results in more organized field-induced reorientation of sub molecular segments in the SSFLC cell

20. Right after the rising edge of an external field, the C=O stretching modes at 1759 cm-1 reacts faster than that that of core group at 1608 cm-1, indicating that the field-induced reorientation leads by the chiral C=O, and the molecular core part follows. Response Times

21. ZnO nano dots function as a molecular binder by tying together electric-dipole species, which results in an enhanced dynamic alignment and response speed of the SSFLC cell. Interaction between induced LC dipoles due to the presence of ferroelectric nano particle can be estimated to be

22. Conclusions • Deposition of LCP on an alignment layer can improve LC alignment order. • Modified PVA alignment layer by reaction with methyl carboxilic acid yields high LC pretilt with precise angle control. • Doping LCs with ferroelectric nanoparticles is to be a perspective technology for tailoring novel LC materials.