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<p>The substitution of acetyl groups significantly affects the birefringence properties of cellulose acetate (CA) and is a crucial factor in the design and fabrication of high-performance CA optical films. In this paper, the contribution of CA monomers, their conformations and acetyl substitutions at different sites to the intrinsic birefringence (Δn<sup>0</sup>) was studied by molecular modeling and density functional theory (DFT) calculations. Combined with <sup>13</sup>C nuclear magnetic resonance (NMR) analysis, the relationship between the monomer composition and birefringence (Δn) of commercial CA was evaluated. The results show that in CA monomers containing C6 acetyl groups (6OAc), the conformational type and proportion of 6OAc will lead to changes in both the sign and magnitude of Δn<sup>0</sup>. Additionally, the contribution of acetyl groups to Δn<sup>0</sup> at different sites is in the following order: 6OAc &gt; 3OAc &gt; 2OAc, and 6OAc plays a greater role in regulating the Δn<sup>0</sup> of CA. The measured Δn value of commercial CA is consistent with the theoretical value in terms of the change trend and relative size. This study illustrates the feasibility of calculating and evaluating CA birefringence and its wavelength dispersion by analyzing the substitution situation and combining the theoretical Δn<sup>0</sup> contribution of the substituent.</p>

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The effect of substitution in cellulose acetate on birefringence and its wavelength dispersion studied by DFT calculations and NMR analysis

  • 期刊论文

  • 发表日期：

    2025年11月17日

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  • Yuan Zhou,
  • Xiaoyu Bai,
  • Mengyu Wan,
  • Cuihong Hou,
  • Guixin Wang,
  • Yong Zhang

摘要

The substitution of acetyl groups significantly affects the birefringence properties of cellulose acetate (CA) and is a crucial factor in the design and fabrication of high-performance CA optical films. In this paper, the contribution of CA monomers, their conformations and acetyl substitutions at different sites to the intrinsic birefringence (Δn0) was studied by molecular modeling and density functional theory (DFT) calculations. Combined with 13C nuclear magnetic resonance (NMR) analysis, the relationship between the monomer composition and birefringence (Δn) of commercial CA was evaluated. The results show that in CA monomers containing C6 acetyl groups (6OAc), the conformational type and proportion of 6OAc will lead to changes in both the sign and magnitude of Δn0. Additionally, the contribution of acetyl groups to Δn0 at different sites is in the following order: 6OAc > 3OAc > 2OAc, and 6OAc plays a greater role in regulating the Δn0 of CA. The measured Δn value of commercial CA is consistent with the theoretical value in terms of the change trend and relative size. This study illustrates the feasibility of calculating and evaluating CA birefringence and its wavelength dispersion by analyzing the substitution situation and combining the theoretical Δn0 contribution of the substituent.