1. Department of Photonics, Chiao Tung University
Improving Liquid Crystal (LC) Orientational Order on Photo-Alignment Surface with a LC Polymeric Layer
Jung Y. Huang 黃中垚
Department of Photonics, Chiao Tung University
Hsinchu, Taiwan
September 13, 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 LC control are needed to realize such applications.

3. But how to analyze LC alignment?
Other technologies that may benefit from the method of improving LC alignment, such as:
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.
But how to analyze LC alignment?

4. Vibrational Spectroscopy
Unique finger-printing capability of vibrational spectroscopy :
highly localized
well characterized by theory
Vibrational Spectroscopy

5. Apparatus of sum-frequency vibrational spectroscopy (SFVS)---the Laser System

6. Apparatus of sum-frequency vibrational spectroscopy (SFVS)---the Experimental Geometry
Visible

7. Sum-frequency vibrational spectroscopy of a LPUV-defined layer for liquid crystal alignment

8. UVA RN1349
LCP/UVA RN1349

9. Improving LCP Alignment on a LPUV-defined Surface
f=0o
f=90o

11. Dynamic Light Scattering
Scattered photons
Analyzer
Polarizer
Incident light

12. Twist Anchoring Strength Revealed by Dynamic Light Scattering
Rubbed RN1349: t=0.54 ms, s=0.93
PhotoAlign RN1349: t=3.51 ms, s=0.88
LCP/PhotoAlign RN1349: t=3.56 ms, s=0.93
The intensity correlation functions showed a relaxation component of LC director, which can be described by

13. Twist Anchoring Strength Revealed by Dynamic Light Scattering
Rubbed RN1349: Af=6.0x10-4 J/m2
PhotoAlign RN1349: Af=8.1x10-6 J/m2
LCP/PhotoAlign RN1349: Af=7.9x10-6 J/m2
DLS shows that the deposition of LCP does not change the twist anchoring strength of LC molecules.

14. Like an expitaxial growth, the LCP does not change the anchoring properties of the underlying alignment layer, but improves the orientational order of phenyl groups, which results in a narrower azimuthal distribution of LC.

15. Conclusions Rubbed RN1349: Af=6.0x10-4 J/m2
Photo-align RN1349: Af=8.1x10-6 J/m2
LCP/PhotoAlign RN1349: Af=7.9x10-6 J/m2
LCP coupling layer does not change the anchoring properties, but can improve the orientational order of phenyl groups, which results in narrower azimuthal distribution of LC lying on the LCP coupling layer.