Optical Properties

Full-Atomistic Molecular Dynamics (FAMD) was used to perform uniaxial extension calculations on amorphous structures of polystyrene and polycarbonate to evaluate birefringence arising from molecular orientation. It was confirmed that the orientation direction of benzene rings in polymers can cause both positive and negative birefringence. This can be applied to the design of optical materials such as plastic lenses and optical films.

Use Cases Highlights

Analysis of birefringence caused by molecular orientation
Evaluation of the relationship between benzene ring orientation and refractive index
Utilization for material design such as reducing birefringence by blending

Extension calculation results for polystyrene

Structure of polystyrene with benzene rings oriented perpendicular to elongation direction after uniaxial elongation is shown, explaining negative orientation birefringence.

Elongation calculation results of polystyrene

Uniaxial elongation calculation results for polycarbonate

The structure of polycarbonate (PC) in which benzene ring planes are oriented parallel to the elongation direction is shown. Since the refractive index in the ring plane direction is higher, positive birefringence is expected to occur.

Elongation calculation results for polycarbonate

Comparison of orientation birefringence

Birefringence was evaluated using the scenario function in J-OCTA. From MD calculation results, vectors of all covalent bonds were obtained, and using a bond polarizability database, refractive indices in the X, Y, and Z directions were evaluated for the entire system. The orientation birefringence of PC, PS, PMMA, and PC/PS blends was compared: PC showed positive birefringence, PS negative, PMMA nearly zero, and blends showed reduced birefringence.

Comparison of orientation birefringence

Reference

[1] (in Japanese) Miyazaki, Togawa, Masubuchi, Molding Process '05, IV-312, pp 267-268, (2005)
[2] (in Japanese) Iwashimizu, Okubo, Ozawa, Kimizuka, Molding Process Symposium '06, C-201, pp 107-108, (2006)

Details of analysis

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