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Bio-Inspired Melanin-Based Structural Colors Through Self

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Bio-Inspired Melanin-Based Structural Colors Through Self BIO-INSPIRED MELANIN-BASED STRUCTURAL COLORS THROUGH SELF- ASSEMBLY A Dissertation Presented to The Graduate School of the University of Akron In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy Ming Xiao August, 2017 BIO-INSPIRED MELANIN-BASED STRUCTURAL COLORS THROUGH SELF-ASSEMBLY Ming Xiao Dissertation Approved: Accepted: _____________________________ _____________________________ Advisor Department Chair Dr. Ali Dhinojwala Dr. Coleen Pugh _____________________________ _____________________________ Co-advisor Dean of the College Dr. Matthew D. Shawkey Dr. Eric J. Amis _____________________________ _____________________________ Committee Member Dean of the Graduate School Dr. Mesfin Tsige Dr. Chand Midha _____________________________ _____________________________ Committee Member Date Dr. Toshikazu Miyoshi ______________________________ Committee Member Dr. Hunter King ______________________________ Committee Member Dr. Thein Kyu ii ABSTRACT Structural colors enable creation of a spectrum of non-fading visible colors without using pigments, potentially reducing the use of toxic metal oxides and conjugated organic pigments. Although many top-down and bottom-up methods have been used to produce structurally colored materials, significant challenges remain to achieve the contrast needed for producing a complete gamut of colors and a scalable process for industrial applications. Nature provides some intriguing palettes of structural colors in avian feathers using three main ingredients, melanin, keratin, and air. Recently, we have demonstrated that the rainbow-like iridescent colors in a single feather of Australia pigeon (common bronzewing) are caused by a slight variation of the layer thickness of multilayered melanosome (organelles filled with melanin) nanostructures. Learning from these color production mechanisms, we have synthesized melanin nanoparticle (SMNPs) ranging from 100-200 nm in diameter. Using an evaporation-based process we have assembled these nanoparticles to produce a wide spectrum of visible colors. We have shown the high absorption of SMNPs leads to more saturated colors than those produced using polystyrene or glass nanospheres. In addition, SMNP films show rapid, large, reversible color changes responsive to variation in ambient humidity, due to swelling/shrinking of SMNPs. iii To produce brighter colors in a scalable process, we have designed core-shell nanoparticles with melanin core (RI ~1.74) and silica shell (RI ~ 1.45). A one-pot reverse emulsion process has been used to assemble these core-shell nanoparticles to produce a full-spectrum of colorful supraballs. Similar to mixing pigmentary colors, we can also blend these core-shell SMNPs with different shell thicknesses to control the spacing and continuously tune colors. The new bio-inspired melanin-based structurally materials pave the way for producing novel photonic inks, suitable for applications like painting, textiles, and displays. iv DEDICATION This dissertation is dedicated to my family. A deep gratitude to my father Renping Xiao, my mother Zixia Wang, my wife Hong Chen, and my sister Xian Xiao. Their constant love and support encourage me all the time. v ACKNOWLEDGEMENTS My PhD has been a really fruitful journal filled with struggle with what to start, curiosity for new knowledge, excitement of examining on new hypothesis, and personal mental maturity. During this process, I own my gratitude to lots of people. First and foremost, I would like to acknowledge my advisors, Prof. Ali Dhinojwala and Prof. Matthew Shawkey for insightful mentorships and continuous supports. They are both best supervisors and are so nice, tolerant to allow me to try all types of new things. Ali has taught me a lot on the way of thinking and solving problems. I have also learnt a lot from Matt, ranging from TEM imaging, scientific writing, to keeping broad curiosities. I really feel lucky that Ali started the collaboration with Matt for my project and then Matt provided the chance to collaborate with Prof. Nathan Gianneschi group. Secondly, I want to thank all my collaborators: Dr. Yiwen Li, Ziying Hu, Zhao Wang, and Prof. Gianneschi at UCSD for continuously providing different types of melanin samples; Dr. Wei Chen, Dr. Youlee Hong and Prof. Toshikazu Miyoshi for the help with solid-state NMR experiments; Alejandro Diaz Tormo, Prof. Nicolas Thomas for teaching me how to use finite-difference time-domain simulations; Dr. Min Gao for the help with environmental SEM experiment; and Boxiang Wang for performing the scattering calculation. I should also extend my thanks to three master students, Jiuzhou Zhao, Weiyao Li, and Xiaozhou Yang, I worked and have been working with for their hardworking and vi great help on several of my projects. I also want to thank Dr. He Zhu, Dr. Yu Zhang, Mena Klittich, Michael Wilson, Siddhesh Dalvi and all other Dhinojwala lab members for lots of discussion and different types of help. I am grateful to Dr. Chad Eliason, Dr. Rafael Maia, Dr. Liliana D’Alba, Dr. Branislav Igic, Asritha Nallapaneni and other Shawkey lab members for their instrument tutoring and helpful discussions on all my manuscripts. Finally, I want to thank my family and friends for their love and support. vii TABLE OF CONTENTS Page TABLE OF CONTENTS ................................................................................................. viii LIST OF TABLES ........................................................................................................... xiii LIST OF FIGURES ......................................................................................................... xiv CHAPTER I RESEARCH OVERVIEW ............................................................................................................................................. 1 1.1 Introduction ............................................................................................................... 1 1.2 Melanin structure and functions ................................................................................ 4 1.3. Melanin-based colors in nature ................................................................................ 8 1.3.1 An absorbing layer.............................................................................................. 9 1.3.2 Arrays of solid melanosomes ........................................................................... 11 1.3.3 Hollow melanosomes ....................................................................................... 14 1.4. Optical benefits of melanins for structural colors .................................................. 15 1.5 Melanin in synthetic structural colors ..................................................................... 17 1.5.1 Absorber to increase saturation ........................................................................ 18 viii 1.5.2 Solid thin film ................................................................................................... 19 1.5.3 Solid melanin nanoparticles.............................................................................. 20 1.5.4 Core-shell melanin nanoparticles ..................................................................... 22 1.5.6 Conclusions .......................................................................................................... 23 CHAPTER II NANOSTRUCTURAL BASIS OF RAINBOW-LIKE IRIDESCENCE IN COMMON BRONZEWING PHAPS CHALCOPTERA FEATHERS ............................. 24 2.1 Introduction ............................................................................................................. 24 2.2 Materials and Methods ............................................................................................ 25 2.2.1 Barbule macrostructure ..................................................................................... 25 2.2.2 Reflectance measurement ................................................................................. 25 2.3 Barbule nanostructure .......................................................................................... 28 2.3 Results and Discussion ............................................................................................ 29 2.3.1 Rainbow-like iridescent reflectance ................................................................. 29 2.3.2 Nanostructure of iridescent barbules ................................................................ 31 2.3.3 Multilayer interference modeling ..................................................................... 33 2.4. Conclusions ............................................................................................................ 42 ix CHAPTER III BIO-INSPIRED STRUCTURAL COLORS PRODUCED VIA SELF- ASSEMBLY OF SYNTHETIC MELANIN NANOPARTICLES................................... 45 3.1 Introduction ............................................................................................................. 45 3.2 Materials and Methods ............................................................................................ 47 3.2.1 Synthesis and characterization of SMNPs ........................................................ 47 3.2.2 Evaporation-based assembly ............................................................................ 48 3.2.3 Characterization of the SMNP film .................................................................. 48 3.2.4 Measurements of the complex RI of SMNPs ................................................... 50 3.2.5 Optical Modeling .............................................................................................
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