Tough and Variable-Band-Gap Photonic Hydrogel Displaying Programmable Angle-Dependent Colors

Area of Science:

• Materials Science
• Optics
• Polymer Science

Background:

• One-dimensional photonic crystals and multilayer films exhibit angle-dependent colors due to periodic refractive index variations, obeying Bragg's law.
• Recent advancements include multilayered photonic hydrogels with alternating rigid polymeric lamellar bilayers and ductile polyacrylamide (PAAm) matrices.

Purpose of the Study:

• To fabricate composite hydrogels with tunable photonic band gaps by precisely controlling the polyacrylamide (PAAm) layer thickness.
• To investigate the production of programmable angle-dependent and angle-independent structural colors through variations in bulk and internal geometries.

Main Methods:

• Fabrication of composite hydrogels with controlled PAAm layer thickness.
• Investigation of structural color properties in different bulk geometries (sheet and cylindrical).
• Utilizing rocking curves to analyze and justify the angle-dependent optical behavior.

Main Results:

• Photonic gel sheets (lamellae parallel to the surface) display strong angle-dependent colors.
• Photonic gel rods (coaxially aligned lamellae) exhibit angle-independent colors, contrasting with the sheet geometry.
• The tunable photonic gels demonstrate robust mechanical properties and toughness across different geometries.

Conclusions:

• The distinct angle-dependent behaviors achieved by varying geometry highlight the tunability of these photonic hydrogels.
• These tough photonic materials with adjustable band gaps show promise for applications in light modulation for displays and sensor technologies.