Rainbow colours from lignin

Digital microscope image of a cross-section of a photonic crystal.

Researchers in Sustainable Materials Chemistry (SUSMATCHEM) research group at Department of Materials and Environmental Chemistry, Stockholm University are thrilled to announce a groundbreaking advancement in the field of functional lignin materials.

Lignin

Lignin is the component that gives trees the ability to grow strong and resistant woody structures. When isolated from wood, lignin powders display different shades of brown color. This long-standing paradigm has discouraged exploration of lignin in applications where visual appearance is appreciated.

Photonic crystals

Photonic crystals, optical materials with periodic arrangements of particles, have shown tremendous potential in various applications. However, the assembly of lignin particles into close-packed structures has been limited due to the lack of suitable methods and a comprehensive understanding of packing mechanisms.

The research conducted by Jinrong Liu and co-workers introduces a centrifugation-assisted fabrication technique that classifies spherical lignin particles based on their physical size. This straightforward method enables the assembly of lignin particle crystals with mesmerizing rainbow colors.

New approach to size distribution

This new approach overcomes the challenge of broad size distributions typically associated with lignin particles and produces monodispersed particle layers through centrifugal forces. The resulting layers exhibit gradient colors ranging from red to violet, in accordance with their size distribution and reflectance spectra. Importantly, each assembled layer of LNPs demonstrates semi-closed packing structures, which enables coherent scattering and give rise to well-defined structural colors. In situ optical microscopy along with electron microscopy further confirmed the dynamic rearrangement of LNPs during their assembly into semi-closed packed structures, providing valuable insights into the assembly process.

Findings pave the way to new discoveries

In addition to their beautiful color these new lignin materials represent a significant milestone in the development of sustainable photonic crystals. The findings have broad implications for numerous fields, including optics, materials science, and sustainable technologies.

"We are thrilled to see publication of this groundbreaking research, which has the potential to revolutionize the fabrication of photonic crystals using lignin nanoparticles," says Mika Sipponen, Assistant Professor and leader of the research group. "Our centrifugation-assisted method allows for the controlled arrangement of LNPs, resulting in mesmerizing structural colors. This breakthrough opens up new avenues for sustainable and customizable optical materials based on abundantly available lignin resources."

The research article titled "Centrifugation-Assisted Fabrication of Photonic Crystals with Lignin Nanoparticles" has been published in Nature Communications.

DOI : 10.1038/s41467-023-38819-5.
Title : Photonic crystals with rainbow colors by centrifugation-assisted assembly of colloidal lignin nanoparticles.

For more information or media inquiries regarding this research, please contact:

Mika Sipponen
Assistant Professor
+46 (0) 8 16 12 58
mika.sipponen@mmk.su.se