Prediction of birefringence for polymer optical products based on a novel molecular chain orientation model

Abstract Optical polymer materials are widely used in aerospace, electronics, and other engineering fields, which have strict requirements on optical properties such as the birefringence of products. The present birefringence calculation method is based on the stress-birefringence law and is still difficult in accurate prediction, owing to extremely difficulty in predict residual stress. Actually, the birefringence of polymer optical products is essentially caused by the molecular chain orientation. Thus, a quantitative mathematical model between molecular orientation and birefringence is proposed in this study. The coupling simulation of the macroscopic flow field and microscopic orientation is realized through internal stress. The accuracy of the proposed model is verified by the polarized Raman and birefringence distribution experimental results. Compared with the stress-birefringence method, the proposed model and numerical method can more accurately simulate molecular orientation and birefringence. Meanwhile, the simulated average orientation degree in the thickness direction under different melt and mold temperatures are compared with the measured results, which verifies the effectiveness of the proposed model and simulation method at different process conditions.