Computational modelling explains why blues and greens are brightest
colors in nature

Date:
September 11, 2020
Source:
University of Cambridge
Summary:
Researchers have shown why intense, pure red colors in nature are
mainly produced by pigments, instead of the structural color that
produces bright blue and green hues.



FULL STORY ========================================================================== Researchers have shown why intense, pure red colours in nature are mainly produced by pigments, instead of the structural colour that produces
bright blue and green hues.


==========================================================================
The researchers, from the University of Cambridge, used a numerical
experiment to determine the limits of matt structural colour -- a
phenomenon which is responsible for some of the most intense colours in
nature -- and found that it extends only as far as blue and green in
the visible spectrum. The results, published in PNAS, could be useful
in the development of non-toxic paints or coatings with intense colour
that never fades.

Structural colour, which is seen in some bird feathers, butterfly wings
or insects, is not caused by pigments or dyes, but internal structure
alone. The appearance of the colour, whether matt or iridescent, will
depending on how the structures are arranged at the nanoscale.

Ordered, or crystalline, structures result in iridescent colours, which
change when viewed from different angles. Disordered, or correlated,
structures result in angle-independent matt colours, which look the same
from any viewing angle.

Since structural colour does not fade, these angle-independent matt
colours would be highly useful for applications such as paints or
coatings, where metallic effects are not wanted.

"In addition to their intensity and resistance to fading, a
matt paint which uses structural colour would also be far more environmentally-friendly, as toxic dyes and pigments would not be
needed," said first author Gianni Jacucci from Cambridge's Department of Chemistry. "However, we first need to understand what the limitations are
for recreating these types of colours before any commercial applications
are possible." "Most of the examples of structural colour in nature are iridescent -- so far, examples of naturally-occurring matt structural
colour only exist in blue or green hues," said co-author Lukas
Schertel. "When we've tried to artificially recreate matt structural
colour for reds or oranges, we end up with a poor- quality result, both in terms of saturation and colour purity." The researchers, who are based in
the lab of Dr Silvia Vignolini, used numerical modelling to determine the limitations of creating saturated, pure and matt red structural colour.

The researchers modelled the optical response and colour appearance of nanostructures, as found in the natural world. They found that saturated,
matt structural colours cannot be recreated in the red region of the
visible spectrum, which might explain the absence of these hues in
natural systems.

"Because of the complex interplay between single scattering and multiple scattering, and contributions from correlated scattering, we found
that in addition to red, yellow and orange can also hardly be reached,"
said Vignolini.

Despite the apparent limitations of structural colour, the researchers
say these can be overcome by using other kind of nanostructures, such
as network structures or multi-layered hierarchical structures, although
these systems are not fully understood yet.


========================================================================== Story Source: Materials provided by University_of_Cambridge. The original
story is licensed under a Creative_Commons_License. Note: Content may
be edited for style and length.


========================================================================== Journal Reference:
1. Gianni Jacucci, Silvia Vignolini, Lukas Schertel. The limitations of
extending nature's color palette in correlated, disordered systems.

Proceedings of the National Academy of Sciences, 2020; 202010486
DOI: 10.1073/pnas.2010486117 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200911141656.htm

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