Color Evaluation of Structurally Colored Films by Angle of Incidence

Importance of Topic

Structural coloration—color produced by microscopic film or scale structures rather than pigments—provides durable, angle‐dependent optical effects that resist fading. Understanding and quantifying these effects is crucial in biomimetic research, coatings development, security printing, and advanced display technologies.

Objectives and Overview

This study investigates the angle‐dependent color appearance of three multilayer polymer films (MLF-13.0, MLF-16.5, MLF-19.0). It aims to correlate spectral transmission changes with perceived color shifts using spectrophotometric and colorimetric analysis.

Methodology

Films were measured over a 300–800 nm wavelength range at incidence angles of 0°, 15°, 30°, 45°, and 60°. Transmission spectra were recorded with a medium scanning speed and 1 nm pitch. Polarization was set at 45° to simulate unpolarized light.

Instrumentation Used

• SolidSpec-3700DUV spectrophotometer
• Variable angle absolute reflectance attachment
• Large polarizer assembly
• Integrating sphere with photodetector

Main Results and Discussion

MLF-13.0: At 0° incidence, blue light (400–500 nm) is absorbed, yielding a yellow appearance. Increasing angle shifts absorption to shorter wavelengths, reducing visible absorption and rendering the film nearly transparent.

MLF-16.5: Initially absorbs green light (500–600 nm), appearing violet. With higher angles, absorption moves toward shorter wavelengths; by 60°, blue light is absorbed and the film appears yellow.

MLF-19.0: At normal incidence, red light (600–700 nm) is absorbed, producing a pale blue hue. At 60°, absorption shifts to green (500–600 nm), resulting in a violet appearance.

Colorimetric mapping in L*a*b* space confirmed the complementary‐color transitions and increase in lightness (L*) at higher angles.

Benefits and Practical Applications

• Non‐fading, pigment‐free color for long‐lasting optical coatings.
• Angle‐tunable coloration for anti‐counterfeiting and security labeling.
• Potential use in smart sensors and responsive displays.

Future Trends and Possibilities

Advancements may include dynamic multilayer films with electrically or thermally tunable refractive indices, integration into wearable photonic devices, and scalable manufacturing of structurally colored materials for consumer products.

Conclusion

Angle‐resolved spectrophotometry combined with colorimetric analysis effectively characterizes structural color in multilayer films. This approach supports the design and quality control of next‐generation biomimetic optical materials.

References

1) Teijin Laboratories, “Morphotex” structurally colored fibers created with advanced nanotechnology.
2) Hirose H.; Polymers 60(5), 298–301 (2011).
3) Teijin DuPont Films Japan Limited, PET Film MLF Product Overview.
4) Konica Minolta, IROIROZATSUGAKU.