Biomimicry of structural color applied totextile
2 LITERATURE REVIEW
2.1 NATURAL STRUCTURAL COLOR
2.1.1 THIN FILM INTERFERENCE
2.1.2 MULTILAYER INTERFERENCE
2.1.3 DIFFRACTION GRATRING
2.1.4 LIGHT SCATTERING
2.1.5 PHONTONIC CRYSTAL
2.2 THE COLOR IN NATURE
2.3 METHODOLOGY OF BIOMIMICRY
2.4 CHOLESTERIC LIQUID CRYSTAL
2.4.1 LIQUID CRYSTAL
2.4.2 THERMOTROPIC LIQUID CRYSTAL
2.4.3 OPTICAL PROPERTIES OF CLC
2.4.4 COAXIAL ELECTROSPINNING
3 METHOD AND EXPERIMENT DETAIL
3.1 MATERIAL PREPARATION
4 EXPECTED RESULT
5 PROJECT PLAN
APPENDIX 1 RESEARCH FLOW CHART
APPENDIX 2 GANTT CHART
In nature, creatures have evolved for million years. Each of the creatures has their certain color. Due to the scanning electron microscope (SEM) has been introduced in the 1940s, some of the creatures’ color can be explained. These color has been called as structural color because it is a series photon interact with object’s surface in Nano-scale. These optical processes derive several phenomena as thin film interference, multilayer interference, diffraction grating, light scattering and photonic crystal. A typical case is Morpho butterfly’s wings. The shinny blue is created by the lamellar structure in the wings surface.
Applying this concept in the textile industry, the clothes manufacturing requires like dyes, pigments, chemicals and water, would be reduced.
The aim of this MSc project is to produce and apply a structural color fiber to textile goods. Precisely, to create a non-pigment, non-dye, non-faded and anti-bleach with high tensile strength structural color fiber.
The project will be divided into four parts (A, B, C and D). By fundamental concept to practical experiment progressively.
Part A includes exploring natural structural color; to understand the coloration mechanism of creatures and identify phenomena of the optical process in classic examples as Morpho butterfly’s wings, Chrysina Gloriosa Beetle, the skin of Pollia fruit, Anna’s Hummingbird color changing feather and natural opals iridescent colors.
Part B covers investigating methodology of biomimicry. To attribute the success of microfabrication technologies, replicating structural color is taking a step forward. There are two main strategies to build biomimicry structure, “top-down” and “bottom-up.” Both of strategies will be introduced in a further section.
Part C involves representing one of a past successful method to produce structural color fiber. In this MSc experiment, the author attempt to replicate core-sheath fiber with CLC through the coaxial electrospinning method.
Part D contains comparing the performance of structural color fiber with different material. In another word, the author tends to use a different material to fabricate structural color fiber and compares with Part C experiment result.
2 Literature review
In this chapter, it presents several essential background knowledge which helps a better understanding of the project.
2.1 Natural Structural Color
Color from nature has been studied for centuries. Along with technology thrives,
these color can be redefined and explained as reflection, refraction and
polarization characteristics of light in a tiny-scale pattern.
Due to human observes this color is derived by structures on the submicron scale interact with light, it is so-called structural color.
S. Kinoshita and S. Yoshioka state that structural color is a combination of several optical processes as thin film interference, multilayer interference, diffraction grating, Light scattering and photonic crystal.
2.1.1 Thin film interference
Thin film interference is an elementary example of structural color. A single layer thickness is defined as a wavelength of visible light (380-780nm)[2,3] Due to the refractive index differences of the light source and thin film, the amplitude of wavelength reflect as the sum of multiple beams as color retardation. To illustrate this, Figure 1 can be seen d is the thickness of the layer and its refractive index is n2. The light source impinges on a thin layer with the angle θ1 and the surrounding refractive index is n1. (Where n1≠n2) Then refraction angleθ2 can be calculated. An example of a soap bubble is explained with Newton’s color retardation, which can be seen as Figure 2.
Figure 1: Thin film module 
Figure 2: Newton’s color scale for bubble example 
2.1.2 Multilayer interference
Following the previous section, multilayers obey the same physical optics principle. Multilayers are often catagorized into narrow-band and broadband multilayers. The narrow-band multilayers are designated with pairs of thin layer piles periodically. To demonstrate this, Figure 3 shows material A and B with their thickness dA and dB, follows by their refractive index nA and nB respectively. It can be manipulated the value of the lowest layer in dark or lighter. When the lowest layer is dark, it absorbs all the light which will not be reflected, thus making the color rich. If the base layer is set in lighter color, it reflects more light, which the light transmits to the upper layers, then gaining in a white and vague color. On the other hand, Broadband multilayers have varied wavelength and they reflect most of light. Then it will not be effected by base layer absorption and present a bright, shiny color. It can be compared with narrow-band multilayer in Figure 3.[2,3]
Figure 3: Multilayer module 
2.1.3 Diffraction grating
A diffraction grating is a normal existence in our lives. For instance, a compact disc displays a non-separation color. The physical optics principle behide is a single reflection material with the surface is designed in the repeated sub-wavelength pattern. Due to the incident light satisfys the angle of amplitude while interacting with the periodical pattern, enhance the exhibit peaks which located at a certain set wavelength.
Figure 4: Diffraction grating module 
2.1.4 Light scattering
Light scattering can be divided into two regimes on particles. The particles are much smaller than the wavelength of incident light is Rayleigh scattering. On the other hand, the particles are larger than the wavelength is called Mie scattering.
Rayleigh scattering is used to explain the color of the sky. The color of the sky is a result of series Sun’s emission spectrum (UV and voilet light) is absorbed by ozone in the atmosphere. When the incident light impinges the atmorsphere with wave vector, the particles of the atmosphere will be dipolized. Then derive the radiation which the light wave is induced.
Mie scattering desribes all or almost of white color. Because of the large size of particles, less and less light is scattered backwards and to the side concluded by Hana Majaron (2013)
Figure 5: Light Scattering module 
2.1.5 Photonic crystal
There is a periodic refractive index in Photonic crystal materials. And it can be classified as1-dimensional photonic crystals, 2-dimensional and 3-dimensional photonic crystals as Figure 6.
Figure 6: Photonic Crystal module 
Due to the dielectricity exitists periodically in the material, it occurs refractive index difference and shows the photonic band-gap. In that optical modes, the frequency ranges in which the propagation of light is prohibited. A. G. Dumanli and T. Savin (2016) point out that “Band-gap depend on the orientation of the propagation in the crystal, often quantified in the lattice reciprocal space and correspond to iridescent reflectance peaks.”[2,3]
2.2 The Color in Nature
After we have a concept of the science behind the structural color, we will discover some color in nature creatures. They are above Morpho butterfly, Chrysina Gloriosa Beetle, Pollia fruit, Anna’s Hummingbird and natural opals iridescent colors. Most of the structural color can not be explained in one phenomenon in the previous section. The natural structural color is a combination of this phemona.
In Morpho butterfly’s wings, there are plenlty of rods with branches and those rods align in a certain pattern closely. The rod branches are laminlar and they are similar to multilayer structure. Also the gap of branches could work as a light diffraction grating. To bracklet all, we can assume there is a photonic crystal system too.
Chrysina Gloriosa Beetle
The exoskeleton of Chrysina Gloriosa Beetle displays shiny green or flat color in a particular angle. The exoskeleton has been discovered there is a matter like cholesteric liquid crystal in its chitin layers. Due to the characteristic of CLC, the exoskeleton is able to reflect the polarized light from incident white light.
In Pollia fruit outer epicarp appears vibrant blue/purple color. The epicarp not only obtains multilayer photonic crystal but also hexagonal shape cell in its cellulose microfiber. There is a phenomenon like Chrysina Gloriosa Beetle, changing unpolarised light into polarized.[2,5]
Some feathers of bird perform iridescent color. The secret of these color is the detail of feathers structure. There is air-filled platelet on the barblues. It is the same concept as Morpho butterfly’s wings acting a light scattering and diffraction.[6,7]
A. G. Dumanli and T. Savin (2016) review that natural opals exhibit lustrous colors because of the crystal arrangement of silica spheres. It can be described like photonic crystal and Rayleigh scattering; when the incident light impinges the particle smaller than the wavelength.
Figure 7: Morpho Butterfly’s wing 
Figure 8: Chrysina Gloriosa Beetle(Left) and Pollia fruit(Right) 
Figure 9: Hummingbird colorful feather(Left) and ari-filled platelet(Right) 
Figure 10: Opal iridescent color (Left) and Silica sphere surface (Right) 
2.3 Methodology of biomimicry
In this section, it shows the methodology of biomimicry. According to the material and instrument decided by the author, only Anisotropic Particle Self-Assenbly method will be discussed.
Figure 11: Category of biomimicry methodology 
Normally, thin film interference, multilayer interference, diffraction grating, Light scattering and photonic crystal could be produced by a specific pattern in nano-micro scale. With modern technology, there is mainly two categories as Top-Down and Bottom-up to present these phenomena. There are numerous advantages of fabricating nanostructures with Top-Down Strategy. However, most of them cost a lot of money, because of manufacturing processes are alike semiconductor process. In the A. G. Dumanli and T. Savin (2016) investigation, bottom-up method use physico-chemical interaction for the hieratchical organisation of nanostructure, which are mosr cost- and time -effective, and widen application. According to the shapes and sizes of particle, and alignment of material, it develops a phenomena to display structural color. For example, some of the liquid crystals are rod-like and plate-like. In the high volume fraction and closet packing, incident light will be reflected as a certain wavelength. In the next section will discuss a specific liquid crystal, Cholesteric Liquid Crystal.
2.4 Cholesteric Liquid Crystal
2.4.1 Liquid Crystal
In generally, by increasing the temperature, the solid state turns into a liquid state. However in some material, there is an intermediate state between solid and liquid. It is also referred to as mesophases. Within this phase, at a certain range of temperature exhibiting orientation sequence like crystalline and fluid-like isotropic liquid at the same time. A compound that has the ability transform between mesophase is called mesogen. [2,4] According to the formation process of the Liquid Crystal, it can be divided into two types as Figure 8 demonstrate.
Figure 13: Thermotropic Liquid Crystal 
Figure 12: Category of Liquid Crystal 
2.4.2 Thermotropic Liquid Crystal
Thermotropic LC describes the changing of temperature occurs LC phases. The shape of mesogen molecular can be calamitic, disotic or sanidic. And it has an excellent optical characteristic. According to the arrangement of molecules, thermotropic LC can be categorized into nematic, smectic and cholesteric.
Nematic Liquid Crystal
Figure 13 illustrates Nematic mesophase is a random arrangement of molecules. This means Nematic Liquid Crystal can flow as high viscosity isotropic liquid.
Smectic Liquid Crystal
The molecules of Smectic Liquid Crystal maintain as parallel or certain angle orientation as layers. When the molecules are arranged perpendicular as the layer is called Smectic A. And Smectic C is referred as molecules tilt angle from the director.
Cholesteric Liquid Crystal
Cholesteric Liquid Crystal is a chiral type of NLC. It is normally made by adding chiral dopant with nematic mesogen. The dopant produces intermolecular forces which tune a slight angle between molecules. This results in the formation of a twisting helical structure.
2.4.3 Optical Properties of CLC
Cholesteric Liquid Crystal has a number of properties interested by a scientist. First, it has a significant optical rotation of light. In the other word, when unpolarized white incident light passes through CLC, the light reflects as right/left circularly polarized light. Second, due to the size of the pitch (p, As it is shown in Figure 13) in the chiral helix and refraction index of CLC molecules, the white incident light reflects certain wavelength.[2,4]
It is precisely explained in Figure 14, how the polarized light be reflected and transmit. Figure 14 also demonstrates the concept of structural color in CLC.
Figure 14: The mechanism of polarized light be reflected (Left) and Structural color of CLC (Right) 
2.5 Coaxial Electrospinning
Coaxial Electrospinning is an additional nozzle aligned into eletrospinning nozzle symmetrically and concentrically. It means the end of two nozzles is well centered in the Taylor cone. When a high voltage is applied to the Taylor cone, the solution in the outer nozzle will be ejected out. Meanwhile, the inner solution will be dragged out simultaneously. Because of high voltage occurs negative charges, and such positive charges accumulated at the surface to drop the solution. With this method, it is useful to create a core-sheath structure or hollow fibers. Thus, the author attempt to encapsulate CLC in the core and fabricates structural color fiber by Coaxial Electrospinning method.
Figure 15: Coaxial Electrospinning module 
3 Method and experiment detail
In this experiment, the author tries to produce structural color applied to fiber and test its performance. Research by Che-Pei Chen et al.,(2016) suggested using coaxial electrospinning to create a hollow fiber as the sheath and encapsulate CLC inside as core. In other words, this structural color and fiber are made simultaneously. Outer sheath provides tensile properties and inner core, CLC, displays the selected color by CLC molecules alignment. By controling spinning speed and accurate concertraction of CLC, this structural color fiber can be produced continuously and color homogeneously. In the end, this fiber will be examine color and tensile strength.
3.1 Material preparation
The materials used in this project includes Paliocolor LC756 (chiral dopant), LC242 (Nematic Liquid Crystal), Irgacure 127® (photoinitiator)and Polyvinylpyrrolidone (PVP). Research by Jones (2016) notes, Paliocolor LC756, LC242 and Irgacure 127® (BASF) can be dissolved with solvent MEK (methyl ethyl ketone). And also de-ion water, salt and ethanol is required to operate with coaxial electrospinning suggested by Che-Pei Chen(2016)
Figure 16: Paliocolor LC756 
Figure 17: Paliocolor LC242 
Figure 18: Irgacure 127®  Figure 19: Polyvinylpyrrolidone (PVP) 
A solution of the core part and sheath part are prepared separately. According to Jones’ research (2016), a solution of the core is set in the specific ratio as Table 1.
Table 1: Core Solution Materials 
Following Che-Pei Chen’s study (2016), a solution of the sheath is prepared in the certain ratio as Table 2.
Table 2: Sheath Solution Material 
Both of prepared solution will be injected into two syringes and those syringes also are setup on syringes pumps for the coaxial electrospinning.
Figure 20: Coaxial Electrospinning System with UV Source 
As Figure 20 presents, applying High-voltage power, coaxial nozzle ejects sheath fiber and core fiber synchronously. At the same time, UV light actives photoinitiator to proceed the polymerization of CLC.
After sample harvesting, the author will examine the color of fiber through a spectrometer and test tensile strength by a universal testing machine (UTM).
4 Expected result
Based on several literatures review the following results can be expected. The structural color fiber should be made successfully. Due to the different condition of coaxial electrospinning, there are three type of fiber can be observed. For example, a beading fiber, quasi-continuous fiber and smearing-out type fiber. The quasi-continuous fiber indicates that the CLC in the core along the fiber is uniform and present the highest reflective pitch in selected wavelength amoung 530nm-580nm. To predict PVP/CLC fiber tensile strength, compare with commercial fiber applied on textile.
Figure 21: Three condition of spinning fiber 
Figure 22: Prediction of Spectrometer data 
Figure 23: Prediction of Tensile Strength data 
5 Project plan
Table 3 shows the numbers of tasks and the intended project plan for the MSc dissertation. The corresponding Gantt chart can be seen in the appendix. All Start/ Finish date and duration could be fixed if needed.
Table 3: Research Plan
 Shuichi Kinoshita. “Structural Colors in the Realm of Nature.” ChemPhysChem, 6, 1442-1459 (2005)
 Ahu, G.D and Thierry, S. ”Recent advances in the biomimicry of structural colors.” Chem. Soc. Rev. 45, 6698-6724 (2016)
 Hana, M. (2013). Structural coloration. Thesis University of Ljubljana Faculty of Mathematics and Physics.
 Celina, J. (2016). Textile Materials Inspired by Structural Color in Nature. PhD Manchester School of Material.
 Silvia V, Paula J. R., Alice V. R., Alison R., Edwige M., Robert B. F.,
Jeremy J. B., Beverley J. G., and Ullrich S.” Pointillist structural color in Pollia fruit” PNAS, Vol. 109, No. 39, 5712-5715 (2012)
 Jerry’s (2017) Exploring Iridescence in Ruby-throated Hummingbirds. January 30 2017. Available at: http://jerryjourdan.blogspot.com/2017/01/exploring-iridescence-in-ruby-throated.html (Accessed: 9 Dec. 2018)
 TheCornellLab of Ornithology(2017) “All About Birds-Anna’s Hummingbird” Available at: https://www.allaboutbirds.org/guide/Annas_Hummingbird/id (Accessed: 9 Dec. 2018)
 Che-Pei, C., Jia-De, L., Lin-Jer, C., Yu-Chou, C., Shuan-Yu, H., & Chia-Rong, L. (2016) “Morphological appearances and photocontrollable coloration of dye-doped cholesteric liquid crystal/polymer coaxial microfibers fabricated by coaxial electrospinning technique.” Opt. Express 24(3), 3112–3126 (2016).
 Paliocolor LC756, Wilshire Technologies Main website. http://www.
5D-d-glucitol,%20CAS%20223572-88-1.pdf, July 2015. (Accessed: 9 Dec. 2018)
 Paliocolor LC242 from Wilshire Technologies, Main website. www.wilshiretechnologies.com/master_pdf/4-[[[4-[(1-Oxo-2-propen-1-yl)oxy]butoxy]carbonyl]oxy]benzoic%20Acid-1,1′-(2-methyl-1,4-phenylene)%20Ester,%20CAS%20187585-64-4.pdf, July 2015. (Accessed: 9 Dec. 2018)
 Irgacure 127 Manual. http://product-finder.basf.com/group/corporate/product-finder/en/literature-documen.pdf, June 2015. (Accessed: 9 Dec. 2018)
 Md, S.R.S.(2015) Tensile stress-stain behavior of some fiber. February 4 2015. Available at: https://textilestudycenter.com/tensile-properties-of-textile-fibers/ (Accessed: 30 Nov. 2018)
Research Flow Chart
Red: Submitting Orange: Meeting
Green: Lecture review Purple: Vacation + Exam
Blue: Daily Work