Control of Three-Dimensional Refractive Indices of Uniaxially-Stretched Cellulose Triacetate with Low-Molecular-Weight Compounds

A method to control the 3D refractive indices and wavelength dispersion of birefringence of polymer films by uniaxial stretching with addition of various low-molecular-weight compounds (LMCs) with strong polarizability anisotropy is developed. Biomass-derived cellulose triacetate (CTA) films containing a small amount of crystallites at the stretching temperature are found to show planar deformation to some degree only by uniaxial stretching. Although molecular orientation evaluated from the in-plane and out-of-plane birefringences of pure CTA seems consistent with uniaxial deformation, LMC addition pronounces the deviation of the refractive index from uniaxial symmetry. Rod-shaped molecules are found to greatly enhance both in-plane and out-of-plane birefringences because of their marked orientation in the stretching direction. Conversely, the out-of-plane birefringence increases more than the in-plane one upon addition of disk-shaped molecules, because the LMC molecules tend to be embedded in the film plane. Consequently, 3D refractive indices of CTA can be controlled only by uniaxial stretching, not biaxial one, with an aid of an anisotropic LMC.
identifier:https://dspace.jaist.ac.jp/dspace/handle/10119/13704