Optical properties of chitin and chitosan biopolymers with application to structural color analysis

Azofeifa, D. E.; Arguedas, Humberto J.; Vargas, William E.

doi:10.1016/j.optmat.2012.07.024

Cited by 93 publications

(77 citation statements)

References 28 publications

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“…While, unsurprisingly, higher refractive indices result in a stronger average reflectance, up to 84% for n = 2.8 (i.e., close to that of rutile titanium dioxide, a synthetic dielectric material commonly employed in photo nic applications [22] ), the broadband reflectivity rapidly decays for n < 1.6. Given the fact that the refractive index of chitin, varying from 1.6 to 1.55 (blue to red wavelengths, respectively), is among the highest found for purely organic biological materials, [23,24] this simulation illustrates yet another aspect of optical optimization of the network morphology.The careful balance of structural parameters described above begets the question whether the random network morphology exhibits hidden correlations that optimize the scattering of incident light. This question is motivated by the consideration that the optimization of the scattering strength requires an average distance between scatterers just above the wavelength of visible light (to avoid optical crowding) and the absence of periodic order (to avoid a photonic bandgap [25,26] ).…”

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Evolutionary‐Optimized Photonic Network Structure in White Beetle Wing Scales

et al. 2017

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Whiteness arises from the random scattering of incident light from disordered structures. [1] Opaque white materials have to contain a sufficiently large number of scatterers and therefore usually require thicker, material-rich nanostructures than structural color arising from the coherent interference of light. [2,3] In nature, bright white appearance arises from the dense arrays of pterin pigments in pierid butterflies, [4] guanine crystals in spiders, [5] or leucophore cells in the flexible skin of cuttlefish. [6] A striking example of such whiteness is found in the chitinous networks of white beetles, e.g., Lepidiota stigma and Cyphochilus sp. [7][8][9] Previous research investigating these beetle structures has shown that the chitinous network is one of the most strongly scattering materials in nature, and therefore the question arises whether this structure is evolutionary optimized for strong scattering while minimizing the Most studies of structural color in nature concern periodic arrays, which through the interference of light create color. The "color" white however relies on the multiple scattering of light within a randomly structured medium, which randomizes the direction and phase of incident light. Opaque white materials therefore must be much thicker than periodic structures. It is known that flying insects create "white" in extremely thin layers. This raises the question, whether evolution has optimized the wing scale morphology for white reflection at a minimum material use. This hypothesis is difficult to prove, since this requires the detailed knowledge of the scattering morphology combined with a suitable theoretical model. Here, a cryoptychographic X-ray tomography method is employed to obtain a full 3D structural dataset of the network morphology within a white beetle wing scale. By digitally manipulating this 3D representation, this study demonstrates that this morphology indeed provides the highest white retroreflection at the minimum use of material, and hence weight for the organism. Changing any of the network parameters (within the parameter space accessible by biological materials) either increases the weight, increases the thickness, or reduces reflectivity, providing clear evidence for the evolutionary optimization of this morphology. amount of employed material, thus reducing the weight of the organism. The brilliant white reflection from Cyphochilus beetles is assumed to be important for camouflage among white fungi and in a shady environment.In contrast to periodic photonic materials, for which the optical response is straightforward to calculate, the reflection of light from such disordered network morphologies requires a detailed knowledge of local geometry. [2,3,9,10] For these complex cases, the validity of the diffusion approximation is limited, since single scattering elements are difficult to be identified. [7] To fully understand the correlation between the structure and (optical) properties of complex materials, the detailed real-space structure in combination with a s...

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Evolutionary‐Optimized Photonic Network Structure in White Beetle Wing Scales

et al. 2017

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“…Film thickness was obtained after averaging measurements at three different spots per sample, modelling with a simple ambient-layer-substrate model and fixing the refractive index of the polymer coating wavelength-independent to 1.52. 47 Differences in the ellipsometric parameters were analysed with respect to the bare zinc substrate for each sample.…”

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Waterborne chitosan–epoxysilane hybrid pretreatments for corrosion protection of zinc

Fernández-Solis

Erbe

2016

Biointerphases

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Biopolymer-based systems are extensively studied as green alternatives for traditional polymer coatings, e.g. in corrosion protection. Chitosan-epoxysilane hybrid films are presented in this work as a chitosan-based protective system, which could e.g. be applied in a pretreatment step. For the preparation of the chitosan-epoxysilane hybrid systems, a sol-gel procedure was applied. The function of the silane is to ensure adhesion to the substrate. On zinc substrates, homogeneous thin films with thickness of 50 − 70 nm were obtained after thermal curing. The hybrid-coated zinc substrates were characterized by infrared (IR) spectroscopy, ellipsometry and X-ray photoelectron spectroscopy (XPS). As model corrosion experiments, linear polarization resistance was measured, and cathodic delamination of the weak polymer coating poly(vinylbutyral) [PVB] was studied using scanning Kelvin probe. Overall, chitosanepoxysilane hybrid pretreated samples showed lower delamination rates than unmodified chitosan coatings and pure PVB. Electrochemical impedance spectroscopy (EIS) confirmed a reduced ion permeability and water uptake by chitosan-epoxysilane films compared to that of a non-modified chitosan coating. Even though the coatings are hydrophobic and contain water, they slow down cathodic delamination by limiting ion transport.

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“…The Brewster angle ~58° at 633 nm was determined from of chitin [32] and could possibly influence the degree of polarization as mainly s-polarized light will be reflected at that angle.…”

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Scattering and polarization properties of the scarab beetle Cyphochilus insulanus cuticle

et al. 2015

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Received Month X, XXXX; revised Month X, XXXX; accepted Month X, XXXX; posted Month X, XXXX (Doc. ID XXXXX); published Month X, XXXX Optical properties of natural photonic structures can inspire material developments in diversified areas, where spectral design of surfaces for camouflage is one. Here, reflectance, scattering and polarization properties of the cuticle of the scarab beetle Cyphochilus insulanus are studied with Spectral Directional Hemispherical Reflectance (SDHR), Bidirectional Reflection Distribution Function (BRDF) measurements and Mueller-Matrix Spectroscopic Ellipsometry (MMSE). At normal incidence a reflectance (0.6 -0.75) is found in the spectral range 400 -1600 nm and a weaker reflectance < 0.2 in the UV range as well as for wavelengths >1600 nm. A whiteness of W = 42 is observed for mainly the elytra of the beetle. Chitin is a major constituent of the insect cuticle which is verified by the close similarity of the measured IR spectrum to that of -chitin. The BRDF signal shows close to Lambertian properties of the beetle for visible light at small angles of incidence. From the MMSE measurement it is found that the beetles appear as dielectric reflectors reflecting linearly polarized light at oblique incidence with low gloss and low degree of polarization. The measured beetle properties are properties that can be beneficial in a camouflage material.

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Optical properties of chitin and chitosan biopolymers with application to structural color analysis

Cited by 93 publications

References 28 publications

Evolutionary‐Optimized Photonic Network Structure in White Beetle Wing Scales

Evolutionary‐Optimized Photonic Network Structure in White Beetle Wing Scales

Waterborne chitosan–epoxysilane hybrid pretreatments for corrosion protection of zinc

Scattering and polarization properties of the scarab beetle Cyphochilus insulanus cuticle

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