Structural Colour in Fruits

Structural colour arises from the constructive interference of light with a material structured on a lengthscale corresponding to optical wavelengths. This phenomenon is responsible for the appearance of many of the brightest colours in nature and recently the existence of structural colouration in plants has been demonstrated across multiple species. This thesis extends our understanding of the effect specifically in fruit epidermal tissues, it uses the physical principles underlying structural colour to understand biological development and it extracts design ideas from biological tissues to enhance the optical response of biomimetic materials. In more detail, this thesis reports the optical characteristics and architecture of structural colour in several fruits of the genera Pollia and Viburnum. Previous work showed that the external cells of Pollia condensata fruits have extremely thick cell walls which act as photonic crystals to reflect circular polarised light. Here, the spectral and morphological characteristics of photonic cell walls in this and three other Pollia species are reported and it is shown that the unusual right handed circular polarisation reflection is apparent in only P. condensata. It is also shown that the occurrence of right circular polarisation is associated with longer wavelength reflection. This thesis extends this analysis by demonstrating the use of structural colour to observe the development of thickened cell walls in Pollia condensata and Pollia japonica using optical microscopy. It is shown that during development, cell wall material is built up gradually and with a fixed structural periodicity in both species, and that significant cell wall growth occurs in the earliest stages of the long fruit maturation period. In the other genus investigated, structural colour analysis is extended to the fruits of Viburnum tinus and Viburnum davidii and found to arise from layers of globular vesicles in the specialised cell wall. Inspired by these studies, a novel templating technique for reflective self-assembled cellulose nanocrystal films is described, which mimics the morphology of Pollia cells by successfully introducing a curvature in the photonic multilayer whilst maintaining its optical response. Enhancement of the angular independence of light reflected from this curved surface is demonstrated.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2019

Author dc:creator

• Middleton, Roxanne

Advisor dc:contributor.advisor

• Vignolini, Silvia

• Pollia
• Pollia condensata
• Pollia japonica
• structural colour
• cellulose
• cell wall
• cell development
• multilayer
• helicoidal
• circular polarisation
• optical microscopy
• biomimetics
• Cellulose Nanocrystals
• CNC
• templating
• coloration
• Viburnum
• V. tinus
• V. davidii
• Fruit coloration

Statement dc:rights

• All figures are clearly labelled with their original source – where citation is given, copyright remains with the original author as labelled and is reproduced under a creative commons license, except in the following cases, in which permission to reproduce the figures was sought and approved from the publisher. This was done in the following cases: Fig 2.3 B p50. Fig 2.3 C p50. Fig 2.3 D p50. Fig 2.3 E p50. Fig 3.1b-e p76 Fig 3.2A p77 Fig 3.2B-C p77 Fig 3.4A-K p79 Fig 3.4L-N p79 Fig 3.4P p79 Fig 6.2e p209

Licence

• https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/db2011ad-50cb-4a02-953c-c2a2f3d46b14/download
• https://creativecommons.org/licenses/by-sa/4.0/

Language dc:language

en

Author Identifier

0000-0002-5309-3517
0000-0003-0664-1418

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/290637