Orientation Birefringence Regulation for the Binary Blend Film of Cellulose Triacetate and Rigid-Rod-Like 5CB Molecules

Abstract

By physical blending of the rigid-rod-like 4-cyano-4′-pentylbiphenyl (5CB) molecule with the cellulose triacetate (CTA), we have prepared the CTA/5CB blend films with different weight fractions of 5CB molecules (ω 5CB ) ranging from 0 to 15%. Even if only a small amount of 5CB molecules are added to the CTA matrix, the orientation birefringence of the stretched blend films becomes positive. With the increasing ω 5CB and the strain ε, the orientation birefringence gets significantly increased. The orientation degrees of CTA chains and 5CB molecules in the stretched blend films are acquired from the infrared dichroism measurements. Then, the nematic interaction strength between CTA chains and 5CB molecules is evaluated to be about 0.43. As ω 5CB ≥ 10%, aggregation of 5CB molecules occurs in the stretched blend films, while it does not affect the transmittance of films. We further show that the aggregation can improve the orientation birefringence of blend films significantly because of the strong nematic interaction between 5CB molecules. A physical picture at the molecular level is proposed to explain why the orientation birefringence of the stretched blend films gets increased. Finally, the orientation birefringence diagrams of the pure CTA films and the CTA/5CB blend films stretched at two different temperatures (170 and 200 °C) in the strain weight fraction of 5CB molecule (ε-ω 5CB ) space are established. We expect that these diagrams would provide a great potential guiding significance for the fabrication of CTA retardation films with specific values of orientation birefringence (Δn in ), such as quarter-wave film and half-wave films.

Preparation and Characterization of Cellulose Nanocrystal‐Doped Cellulose Triacetate Optical Films by Sol‐Gel Process

“…[3] To address this problem, researchers have enhanced and optimized the optical properties of TAC films through graft copolymerization, doping birefringent crystals or polar rod-like molecules. [4][5][6][7] In recent years, nanomaterials have performed prominently as blend fillers in the preparation of optical films, and composite films blended with nanomaterials exhibit excellent flexibility, strength and light transmittance. [8,9] Due to their low density and abundance in nature, as well as high mechanical properties and excellent thermal stability, biobased and biodegradable cellulose nanocrystals (CNCs) have attracted attention for the fabrication of green bio-nanocomposites.…”

“…This hinders the polarization state of light and leads to degradation of optical device performance [3] . To address this problem, researchers have enhanced and optimized the optical properties of TAC films through graft copolymerization, doping birefringent crystals or polar rod‐like molecules [4–7] . In recent years, nanomaterials have performed prominently as blend fillers in the preparation of optical films, and composite films blended with nanomaterials exhibit excellent flexibility, strength and light transmittance [8,9] .…”

Zero–Zero Birefringence Cellulose Acetate-Based Optical Films by Benzoylation

“…The intrinsic birefringence (Δ n 0 ) of optical material and the chain orientation are the primary factors to control Δ n and the consequent retardation R of the optical films . Various common approaches are proposed to regulate the birefringence of optical films, such as blending with other components, − copolymerization, , and multilayer lamination. , Nevertheless, many efforts are still required for the production of cellulose acetate-based zero–zero birefringence films. The available temperature range is limited by the thermal expansion mismatch between the polymer sheets when laminating multilayers, ,, and the complicated processing and a thick display lead to poor cost performance .…”

“…Copolymerization can be used to synthesize new polymer materials, but there are some limitations, such as reducing thermo-resistance . Physically blending low-mass molecules is a simple and effective approach, , but may suffer compatibility and migration issues . As cellulose acetate possesses the acetyl group with a negative contribution to birefringence and reactive hydroxyl groups, chemical modification is a good strategy for the design and preparation of optical compensation films.…”