Polyimide precursor pattern induced by banded liquid crystal matrix: Effect of dianhydride moieties flexibility

Blends of hydroxypropyl cellulose (HPC) in lyotropic phase with two types of polymide precursors have been prepared in different ratios and their characteristics as alignment layers have been evaluated. The poly(amidic acids) (PAA) were prepared from a fluorinated diamine in combination with two types of alicyclic dianhydrides: (1) a flexible, planar, and non-symmetric structure 5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic acid anhydride (DOCDA) and (2) a rigid, non-planar, and symmetric structure, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (BOCA). FTIR data showed that the blend components interact through hydrogen bonding, which is useful in stabilizing the morphology. The surface orientation after shearing is analyzed through infrared dichroism analysis indicating that there is a pronounced anisotropy on the some bands absorbance. The detailed surface topography of the PAA/HPC films is examined by atomic force microscopy, revealing that the band texture of sheared HPC can be transferred to the obtained blends whatever the PAA content. The surface texture of the blends depends on both the mixing ratio and the PAA conformation and its dimensions can be tuned through these parameters. The alignment properties of the prepared blends are tested with a nematic liquid crystal. Dark and bright states are obtained under crossed polarizers when the blend samples are rotated with 360A degrees. The contrast of these states is higher for the PAA(DOCDA)/HPC system because it develops a finer bands structure comparatively with PAA(BOCA)/HPC. The obtained results recommend the DOCDA-based samples as mixed alignment layers for nematics or structured biocompatible layer for guided cell growth.