Cellulose Films as Alignment Layers for Liquid Crystals: Application of Flow-Induced Molecular Orientation

Abstract

An important feature of liquid crystal displays is surface alignment of the LCs. While mechanical rubbing has been used extensively to induce such alignment, this process also produces dust and static electricity. However, surface alignment in films of hydroxypropylcellulose has recently been achieved in situ during high‐speed thin film production, which utilizes the long relaxation time of flow‐induced orientation (see Figure). Results are summarized in this report.

Mechanically activated cholesteric polymer dispersed liquid crystals

“…The surface anisotropy of the mechanical and optical properties of the polymeric films [11] makes these systems very interesting from the applicative point of view for liquid-crystal displays. Films prepared from anisotropic solutions of cellulose derivatives used as alignment layers of liquid crystals have been described in the literature [12][13][14]. The surface topography and structure of these films could be finely tuned by modifying the experimental parameters [13].…”

“…Likewise for other cellulose derivative lyotropic solutions, the bands and stripes can be frozen in and their size controlled to some extent by varying the casting shearing conditions [7,9,10]. We have used a constant shear rate and the solvent was allowed to evaporate at room temperature.…”

“…Studies were also performed on the effects of the polymer orientation surrounding droplets of low molecular weight liquid crystal in a cellulose polymer surface [9] and a strong influence over the liquid-crystal orientation within the droplet was found [9,10].…”

Liquid crystalline cellulosic elastomers: free standing anisotropic films under stretching

“…After the cast the molecular chains have a collective relaxation that results in the formation of that pattern. This morphology has been observed in other cellulose derivative films and was found to be influenced by the precursor solution composition, solvent evaporation rate, film thickness, and rate and duration of shear Wang and Labes 1992;Mori et al 1999). The application of successive stretches in the direction of the casting (i.e., in our experimental configuration, parallel to the analyzer direction) showed that the texture of the film becomes increasingly dark.…”

“…These stripes appear perpendicular to the shear direction, and represent a periodic variation of the director around the direction of the shear. The precursor solution composition, solvent evaporation time, film thickness, rate and shear duration strongly influences the morphology of the striped texture Wang and Labes 1992;Mori et al 1999).…”