Homogeneous and homeotropic alignment of bent-core uniaxial and biaxial nematic liquid crystals

The effect of well-established homeotropically and homogeneously aligning polyimides, developed for calamitic liquid crystals, on the alignment of the nematic phases of bent-core mesogens was investigated using polarizing optical microscopy and conoscopy. Two polyimides, the homogeneously aligning SE7792 and the homeotropically aligning S659, were used to align three bent-core mesogens. Two of the mesogens, with an azo group in one of their arms, are found to align in a manner similar to the calamitic mesogens, while a fluorenone core based mesogen counter-intuitively aligns homogeneously on S659 coated surface and homeotropically on SE7792. Attractive interactions between unidirectionally oriented polyimide side-chains and the alkyl chains of mesogens determine the direction of alignment of the nematic director.

[1]  K. A. Suresh,et al.  Nematic biaxiality in a bent-core material. , 2010, Physical review. E, Statistical, nonlinear, and soft matter physics.

[2]  Ehud Y. Isacoff,et al.  Optical Switches for Remote and Noninvasive Control of Cell Signaling , 2008, Science.

[3]  D. W. Berreman,et al.  Solid Surface Shape and the Alignment of an Adjacent Nematic Liquid Crystal , 1972 .

[4]  S. Jewell.  Polarized Light in Liquid Crystals and Polymers , 2009 .

[5]  H. Takezoe,et al.  Electro-optic technique to study biaxiality of liquid crystals with positive dielectric anisotropy: the case of a bent-core material. , 2009, Physical review. E, Statistical, nonlinear, and soft matter physics.

[6]  S. Lee,et al.  Alignment of Liquid Crystals on Polyimide Films Exposed To Ultraviolet Light , 1998 .

[7]  Shin-Tson Wu,et al.  Fundamentals of Liquid Crystal Devices , 2006 .

[8]  Satyendra Kumar,et al.  Biaxial nematic phase in bent-core thermotropic mesogens. , 2004, Physical review letters.

[9]  Birendra Bahadur,et al.  Liquid Crystals — Applications and Uses , 1992 .

[10]  B. Acharya,et al.  Material-independent determination of anchoring properties on rubbed polyimide surfaces. , 1999, Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics.

[11]  U. Kolb,et al.  Shape-Persistent V-Shaped Mesogens-Formation of Nematic Phases with Biaxial Order , 2006 .

[12]  Ingo Dierking,et al.  Alignment Technologies and Applications of Liquid Crystal Devices. Liquid Crystals Book Series, Volume 5. By Kohki Takatoh, Masanori Sakamoto, Ray Hasegawa, Mitsushiro Koden, Nobuyuki Itoh and Masaki Hasegawa. , 2006 .

[13]  Jae-Hoon Kim,et al.  What aligns liquid crystals on solid substrates? The role of surface roughness anisotropy. , 2005, Physical review letters.

[14]  E. Samulski,et al.  Thermotropic biaxial nematic liquid crystals. , 2004, Physical review letters.

[15]  Jing Zhang,et al.  High nematic ordering in a bent-core smectogen showing a biaxial nematic phase: A 13C NMR study , 2007 .

[16]  N. Clark,et al.  Polarized Raman Scattering Studies of Orientational Order in Uniaxial Liquid Crystalline Phases , 1977 .

[17]  K. A. Suresh,et al.  Thermotropic uniaxial and biaxial nematic and smectic phases in bent-core mesogens. , 2005, Journal of the American Chemical Society.

[18]  Jacques Cognard,et al.  Alignment of nematic liquid crystals and their mixtures , 1982 .

[19]  O. Yaroshchuk,et al.  Three-dimensional orientational order in the bulk and on the surface of polymer films and its effect on liquid-crystal alignment. , 2004, Physical review. E, Statistical, nonlinear, and soft matter physics.

[20]  J. Goodby,et al.  Thermotropic biaxial nematic order parameters and phase transitions deduced by Raman scattering , 2008 .

[21]  D. Collard,et al.  Control of the anchoring behavior of polymer-dispersed liquid crystals: effect of branching in the side chains of polyacrylates. , 2002, Journal of the American Chemical Society.

[22]  L. Farrugia,et al.  Experimental X-ray charge density studies on the binary carbonyls Cr(CO)6, Fe(CO)5, and Ni(CO)4. , 2005, The journal of physical chemistry. A.

[23]  Masaki Hasegawa,et al.  Alignment Technology and Applications of Liquid Crystal Devices , 2005 .

[24]  D. W. Berreman,et al.  Alignment of Liquid Crystals by Grooved Surfaces , 1973 .