Pretilt study of double‐layer alignment film (DLAF)

Abstract

A novel double‐layer alignment film (DLAF) was developed to obtain greater control of the alignment characteristics of the liquid crystal director. The DLAF consists of a thin fluorinated polymer layer on the top of a rubbed non‐fluorinated, non‐branched polyimide layer (PI 2555). Two types of fluorinated polymer with different chemical structures and wetting behaviour on PI 2555 were chosen, to provide either continuous or discontinuous top layers. The continuous top layer DLAF (DLAF‐1) exhibits an abrupt pretilt transition from planar to homeotropic as the top layer thickness increases. The discontinuous top layer DLAF (DLAF‐2) exhibits a gradual transition where the pretilt correlates with the coverage of fluorinated top layer. These two types of transitions fit with de Gennes' local Frederick's transition and Kwok's inhomogeneous alignment theories, respectively. The abrupt pretilt transition system may be promising for chemical/biosensor applications, whereas the gradual transition system is suitable for pretilt control in LCD devices.

Keywords:

• alignment
• liquid crystal display
• pretilt
• double‐layer alignment film
• sensor

Acknowledgements

This work was supported by DuPont. The authors would like to thank Fenghua Li at the Liquid Crystal Institute for characterisation of the properties of fluorinated polyimide materials; Liou Qiu, Sergij Shiyanoviskii, and Rui Guo at the Liquid Crystal Institute for AFM analysis; Wayne Jennings at Case Western Reserve University for the XPS study; and David Stiff at 3M company for providing FC samples.