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

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DOI：https://doi.org/10.1021/acsapm.1c01300

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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 (ω5CB) 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 ω5CB 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 ω5CB ≥ 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-ω5CB) 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 (Δnin), such as quarter-wave film and half-wave films.