In uniaxially stretched films, the refractive indices perpendicular to the stretching direction have the same value, and so, the out-of-plane birefringence is half that of the in-plane birefringence. This means that these values cannot be controlled independently in uniaxially stretched films. The same relationship was previously observed when needle-shaped nanoparticles were added to uniaxially stretched films. This paper presents a method to achieve the three-dimensional birefringence control of uniaxially stretched films. When we added plate-shaped smectite nanoparticles to uniaxially stretched films, different relationships were observed for the in- and out-of-plane birefringence. The magnitude of the out-of-plane birefringence increased more than would be expected according to the usual relationship. According to our results, uniaxially stretched films with no out-of-plane birefringence and negative in-plane birefringence can be formed by adding smectite nanoparticles to polymer films with negative in-plane birefringence. Using our method, the three-dimensional birefringence of uniaxial polymers can be controlled, and the possibility of the uniaxial films could be drastically extended.
Three dimensional birefringence control using nanoparticles for uniaxially oriented films
Kohki Takatoh, Kazuya Goda, Mitsuhiro Akimoto, Tomohiro Abo; Three dimensional birefringence control using nanoparticles for uniaxially oriented films. J. Appl. Phys. 7 July 2017; 122 (1): 013106. https://doi.org/10.1063/1.4992804
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