Novel polypyromellitimides and their liquid crystal aligning properties

High performance polyimides for applications in microelectronics and flat panel displays

“…[155][156][157][158][159] PIs are widely used as LC alignment layers because of their advantageous properties, such as excellent optical transparency, adhesion, heat resistance, dimensional stability and insulation. [65][66][67][68][69][70][71][72][73]95,124,125,155,156,[160][161][162][163][164][165][166][167] Such PI film surfaces need to be treated if they are to produce a uniform alignment of LC molecules with a defined range of pretilt angle values. [37][38][39][40][41][42]55,83,84,[108][109][110][111][112][113][114][115][116][117][118][119]…”

“…This process has become the method of choice because of its simplicity and the controllability with this method of both the LC anchoring energy and the pretilt angle. [65][66][67][68][69][70][71][72][73]95,124,125,[155][156][157][158][159][160][161][162][163][164][165][166][167][168][169][170][171] Much effort has been exerted to understand the mechanism behind the alignment of LC molecules on the rubbed polymer surface. A variety of factors have been proposed to explain the surface anchoring and alignment mechanism of the LC molecules: (i) microgrooves in connection with anisotropic LC orientational elasticity via steric interaction, [172][173][174][175][176][177][178] (ii) polymer molecules from the velvet fabric deposited and oriented on the alignment layer surface during the rubbing process, 179,180 (iii) surface electric fields, 181 (iv) anisotropically oriented polymer chains, [65][66][67][68]…”

“…A variety of factors have been proposed to explain the surface anchoring and alignment mechanism of the LC molecules: (i) microgrooves in connection with anisotropic LC orientational elasticity via steric interaction, [172][173][174][175][176][177][178] (ii) polymer molecules from the velvet fabric deposited and oriented on the alignment layer surface during the rubbing process, 179,180 (iii) surface electric fields, 181 (iv) anisotropically oriented polymer chains, [65][66][67][68][69][70][71][72][73]95,124,125,[155][156][157][158][159][160][161][162][163][164][165][166][167][168][169][170][171] (v) a near-surface order parameter different from the bulk LC molecules, 182,183 and (vi) coupling of a bending mode of the LC director to the surface electric fields (i.e., flexoelectricity). 184 Of these suggestions, the two models for the alignment process that have received the most attention are the microgroove mechanism …”

“…Some investigators have proposed that the outof-plane LC tilt angle is governed by van der Waals interactions between the LC molecules and the alkyl side chains of the polyimide. [65][66][67][68][69][70][71][72][73]95,124,125,[155][156][157][158][159][160][161][162][163][164][165][166][167][168][169][170][171]185 In contrast, other investigators have suggested that LC pretilt is determined by the polymer backbone structure but is independent of the length of the side chains. [186][187][188][189] The exact mechanism controlling the LC pretilt angle on rubbed surfaces has not yet been unambiguously elucidated.…”

Rubbed films of isomeric poly(4-vinylpyridine) and poly(2-vinylpyridine): surface morphology, molecular orientation, and liquid crystal alignability

“…Of the polymers used as alignment layers, polyimides (PIs) are widely used as LC alignment layers because of their advantageous properties . Most rubbed PIs have been reported to align LCs parallel to the rubbing direction [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Recently two other PIs have, however, been discovered to align LCs in a direction perpendicular to the rubbing direction [19][20][21][22].…”