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Cyphochilus beetle scales are amongst the brightest structural whites in nature, being highly opacifying whilst extremely thin. However, the formation mechanism for the voided intra-scale structure is unknown. Here we report 3D x-ray nanotomography data for the voided chitin networks of intact white scales of Cyphochilus and Lepidiota stigma. Chitin-filling fractions are found to be 31 ± 2% for Cyphochilus and 34 ± 1% for Lepidiota stigma, indicating previous measurements overestimated their density. Optical simulations using finite-difference time domain for the chitin morphologies and simulated Cahn-Hilliard spinodal structures show excellent agreement. Reflectance curves spanning filling fraction of 5-95% for simulated spinodal structures, pinpoint optimal whiteness for 25% chitin filling. We make a simulacrum from a polymer undergoing a strong solvent quench, resulting in highly reflective (~94%) white films. In-situ X-ray scattering confirms the nanostructure is formed through spinodal decomposition phase separation. We conclude that the ultra-white beetle scale nanostructure is made via liquid–liquid phase separation. White beetle scales strongly scatter white light, whilst being very thin. Here, the authors measured the internal scale nanostructure for the beetles, Cyphochilus and L. stigma, and demonstrate that the optical structure can be simulated using liquid–liquid phase separation nanostructures, pointing to this as the formation mechanism.

High resolution X-ray nano-tomography experiments are often limited to a few tens of micrometer size volumes due to detector size. It is possible, through the use of multiple overlapping tomography scans, to produce a large area scan which can encompass a sample in its entirety. Mounting and positioning regions to be scanned is highly challenging and normally requires focused ion beam approaches. In this work we have imaged intact beetle scale cells mounted on the tip of a needle using a micromanipulator stage. Here we show X-ray holotomography data for single ultra-white scales from the beetles Lepidiota stigma (L. stigma) and Cyphochilus which exhibit the most effective scattering of white light in the literature. The final thresholded matrices represent a scan area of 25 × 70 × 362.5 µm and 25 × 67.5 × 235µm while maintaining a pixel resolution of 25 nm. This tomographic approach allowed the internal structure of the scales to be captured completely intact and undistorted by the sectioning required for traditional microscopy techniques., Measurement(s)chitin • scaleTechnology Type(s)computed tomography • x-ray holotomographySample Characteristic - OrganismLepidiota • Cyphochilus Machine-accessible metadata file describing the reported data: 10.6084/m9.figshare.12251450

We study the color fading of paints films composed of mixtures of white rutile titanium dioxide and yellow arylide pigments dispersed in two polymer binders at different volume concentrations. The samples were exposed to ultraviolet radiations in an accelerated weathering tester during three weeks. The measured patterns in color variations appeared to be independent of the chemistry of the binders. We then developed a theoretical framework, based on the Radiative transfer Equation of light and the One Particle T-Matrix formalism to simulate the color fading process. The loss of color is correlated to the progressive decrease of the original colored pigment volume-filling fraction as the destructive UV radiations penetrate deeper into the films. The calculated patterns of color variations of paints film composed by mixtures of white pigments with yellow Cadmium Sulfate (CdS) and red Cerium Sulfide (Ce2S3) pigments showed the same trend as that seen experimentally.

We present an extensive theoretical study of the optical properties of hollow polymer particles (HPP) dispersed into a polymer resin as functions of their structure and volume-filling fraction. We show that a dependent light scattering model predicts the occurrence of three different light propagation regimes, the existence of which is consistent with experimental data gathered in the literature. We then analyze the effect of the polymer shell thickness on the magnitude of the near-field and far-field dependent light scattering phenomena. We also discuss and compare the variation of the scattering efficiency of Ropaque™, measured in our laboratory, as a function of the pigment volume-filling fraction, with dependent light scattering model. In particular, we show that in the case of HPP, quasi-linear variation of the scattering efficiency as a function of the particle volume-filling fraction is not an undeniable indication of the absence of electromagnetic couplings in the system. Finally, we used a solution of the radiative transfer equation to compare the prediction of the opacity of several simple paint films when a dependent light scattering model is used instead of the independent scattering approximation to calculate the optical properties of the films at a local scale.

We have studied aggregate formation between dodecyltrimethylammonium bromide (DTAB) and monodisperse short fragments of DNA (50 nm length). DTAB is a cationic surfactant, able to bind to polyelectrolyte chains bearing electrical charges of opposite sign such as DNA, and to precipitate them out above a certain concentration. Light scattering was used to determine the size, shape and composition of the surfactant-polymer aggregates. The aggregates have a low polydispersity, contain several polymer chains and grow in a nonlinear manner with increasing binding ratio (as obtained with surfactant selective electrodes), when surfactant concentration increases. In addition, small DNA secondary structural changes upon surfactant binding were found (by using several spectroscopic methods). As surfactant concentration is increased further, phase separation is observed and X-ray scattering data for the DNA-rich phase shows that it has a liquid crystalline structure.

We have evidenced bundle formation in DNA solutions, induced by the addition of a monovalent cationic surfactant to a solution of short DNA rods. The bundles are rod-like, with a large axial ratio ( ~ 10). Their formation is very likely controlled not only by electrostatic interactions, but also by hydrophobic interactions between surfactant chains, once bound to the DNA. The bundles have diameters and lengths both remarkably well defined and possess internal organisation. The value of the diameter is close to that predicted by a model in which interactions are mediated by condensed counterions; the length might be limited by steric hindrance due to bundle overlapping or by intrinsic chain flexibility.

We have investigated the interactions between anionic polyelectrolytes and a cationic surfactant at the air/water interface and in bulk, for increasing surfactant concentrations. Mixed aggregates are formed at the air/water surface at extremely low surfactant concentrations. Above a critical aggregation concentration, a viscosity drop indicates that polymer chains undergo a rapid collapse. At higher surfactant concentrations, light scattering shows the existence of larger structures, which are surprisingly monodisperse. Their size increases with surfactant concentration. During this bulk evolution, surface tension remains constant, suggesting that the surface aggregates remain unchanged.