Tuning 3D refractive indices via constrained uniaxial stretch in cellulose triacetate films plasticized with triethyl citrate

Xueqing Han; Xiaoyu Min; Tong Wu; Minfang An; Lingpu Meng; Liangbin Li; Kunpeng Cui

doi:10.1016/j.carbpol.2023.121188

Tuning 3D refractive indices via constrained uniaxial stretch in cellulose triacetate films plasticized with triethyl citrate

Carbohydr Polym. 2023 Nov 15:320:121188. doi: 10.1016/j.carbpol.2023.121188. Epub 2023 Jul 16.

Authors

Xueqing Han¹, Xiaoyu Min¹, Tong Wu¹, Minfang An¹, Lingpu Meng², Liangbin Li¹, Kunpeng Cui³

Affiliations

¹ National Synchrotron Radiation Laboratory, Anhui Provincial Engineering Laboratory of Advanced Functional Polymer Film, CAS Key Laboratory of Soft Matter Chemistry, University of Science and Technology of China, Hefei 230026, China.
² National Synchrotron Radiation Laboratory, Anhui Provincial Engineering Laboratory of Advanced Functional Polymer Film, CAS Key Laboratory of Soft Matter Chemistry, University of Science and Technology of China, Hefei 230026, China. Electronic address: mlp2014@ustc.edu.cn.
³ Key Laboratory of Precision and Intelligent Chemistry, CAS Key Laboratory of Soft Matter Chemistry, Department of Polymer Science and Engineering, University of Science and Technology of China, Hefei 230026, China. Electronic address: kpcui@ustc.edu.cn.

PMID: 37659786
DOI: 10.1016/j.carbpol.2023.121188

Abstract

Tuning 3D refractive indices of polymers is urgently needed for optical films, but it is quite challenging. Here, we proposed a simple constrained uniaxial stretch method that successfully tuned the 3D refractive indices in cellulose triacetate (TAC) films plasticized with triethyl citrate (TEC). Our results suggest that, under constrained uniaxial stretch, the main chains and side groups prefer to orientate in the stretch direction and the constrained direction, respectively. Such a unique chain arrangement differentiates the refractive indices in three directions of the film. The branched small molecule TEC is also crucial for tuning refractive indices, which promotes chain activity and enhances the chain orientation under stretching, leading to a considerable change in refractive indices before samples fracture. The polymer film we fabricated possesses a direction-dependent optical performance, where the refractive index in the film thickness direction is between that of the stretch direction and constrained direction. This work provides a fundamental understanding on the chain structure and optical performance of polymer films. The constrained uniaxial stretch method, in general, should also be applicable to tuning other 3D physical properties through tuning the direction-dependent orientation of polymers.

Keywords: Cellulose triacetate; Constrained uniaxial stretch; Three-dimensional refractive indices; Triethyl citrate.