Colloidal inks from bumpy colloidal nanoparticles for the assembly of ultrasmooth and uniform structural colors

Area of Science:

• Materials Science
• Nanotechnology
• Optics

Background:

• Angle-independent structural colors from colloidal nanoparticles (NPs) are desirable for displays, printing, and direct writing.
• Challenges include preparing uniform structural colors from colloidal inks with suppressed coffee-ring effects and ultrasmooth film thickness for layer-by-layer stacking.

Purpose of the Study:

• To synthesize polypyrrole (PPy) black coated silica NPs for uniform, angle-independent structural colors.
• To overcome coffee-ring effects and achieve ultrasmooth films for direct writing and layer-by-layer applications.

Main Methods:

• Synthesis of polypyrrole (PPy) black coated silica NPs with a low coverage of bumpy PPy nanogranules.
• Drop-casting the PPy@silica NPs to form films and evaluating their structural color properties.
• Demonstrating direct writing of colored lines and stacked color drops.

Main Results:

• The surface roughness of PPy@silica NPs effectively suppressed coffee-ring effects and center aggregation during drying.
• Ultrasmooth surfaces with sub-micron thickness and uniform structural colors with wide viewing angles were achieved.
• PPy black enhanced color contrast by suppressing light scattering, and the ink showed versatility with different solvents and substrates.

Conclusions:

• PPy@silica NPs enable the preparation of uniform structural colors with suppressed coffee-ring effects and ultrasmooth films.
• The developed colloidal ink is versatile and suitable for direct writing and layer-by-layer stacking applications.
• This method offers a promising route for advanced color generation and patterning technologies.