The alignment of liquid crystals on the film surfaces of soluble aromatic polyimides bearingt-butylphenyl and trimethylsilylphenyl side groups

Abstract

With the study goal of firstly elucidating the anisotropic interactions between oriented polymer chain segments and liquid crystal (LC) molecules, and secondly of determining the contributions of the chemical components of the polymer segments to the film surface topography, LC alignment, pretilt, and anchoring energy, we synthesized three dianhydrides, 1,4-bis(4'-t-butylphenyl)pyromellitic dianhydride (BBPD), 1,4-bis(4'-trimethylsilylphenyl)pyromellitic dianhydride (BTPD), and 2,2'-bis(4''-tert-butylphenyl)-4,4',5,5'-biphenyltetracarboxylic dianhydride (BBBPAn), and a series of their organosoluble polyimides, BBPD-ODA, BBPD-MDA, BBPD-FDA, BTPD-FDA, and BBBPAn-FDA, which contain the diamines 4,4'-oxydianiline (ODA), 4,4'-methylenediamine (MDA), and 4,4'-(hexafluoroisopropylidene)dianiline (FDA). All the polyimides were determined to be positive birefringent polymers, regardless of the chemical components. Although all the rubbed polyimide films exhibited microgrooves which were created by rubbing process, the film surface topography varied depending on the polyimides. In all the rubbed films, the polymer chains were unidirectionally oriented along the rubbing direction. However, the degree of in-plane birefringence in the rubbed film varied depending on the polyimides. The rubbing-aligned polymer chains in the polyimide films effectively induced the alignment of nematic LCs along their orientation directors by anisotropic interactions between the preferentially oriented polymer chain segments and the LCs. The azimuthal and polar anchoring energies of the LCs ranged from 0.45×10 -4 -1.37×10 -4 J/m 2 and from 0.86×10 -5 -4.26×10 -5 J/m 2 , respectively, depending on the polyimides. The pretilt angles of the LCs were in the range 0.10-0.62 o .In summary, the soluble aromatic polyimides reported here are promising LC alignment layer candidates for the production of advanced LC display devices.

Synthesis and characterization of low-CTE polyimide films containing trifluoromethyl groups with water-repellant characteristics

“…In general, API films used for flexible copper clad laminates (FCCLs) should have a great combination of mechanical, thermal, and dielectric properties, including high modulus and toughness, high glass transition temperature (T g ), low coefficient of thermal expansion (CTE), low coefficient of humidity expansion, low dielectric constant, and dissipation factor, because the films must contact and support the copper circuits and resist the harsh thermal shocks during production of electric circuits. [1][2][3][4][5][6][7][8][9][10] It has been known that the common API films usually have CTE values in the film plane direction of 40-60 ppm/ K, much higher than that of copper foil (17.8 ppm/K).…”

Preparation and characterization of polyimide/modified layered double hydroxide nanocomposites

“…Aromatic polyimides (PIs) are well known as high‐performance polymeric materials because of their excellent thermal stability and balanced mechanical and electrical properties 6–8. In addition, these high‐performance materials have also attracted interest in the photonics or optics industries for applications in optics coatings and thin photonic devices.…”