A common strategy to optimize whiteness in living organisms consists in using 3D random networks with dense and polydisperse scattering elements constituted by relatively low refractive index materials. Inspired by these natural architectures, a fast and scalable method to produce highly scattering porous polymer films via phase separation is developed. By varying the molecular weight of the polymer, the morphology of the porous films is modified, and therefore their scattering properties are tuned. The achieved transport mean free paths are in the micrometer range, improving the scattering strength of analogous low refractive index systems, e.g., standard white paper, by an order of magnitude. The produced porous films show a broadband reflectivity of ≈75% while only 4 µm thick. In addition, the films are flexible and can be readily index-matched with water (i.e., they become transparent when wet), allowing for various applications such as coatings with tunable transmittance and responsive paints. elements must be randomly arranged, typically decreasing the packing efficiency. [5][6][7] To compensate for the non-ideal packing, materials that are very highly scattering strength are generally chosen for industrial applications (i.e., materials with high refractive indexes). DOIA great example of multiple scattering optimization in a low refractive index medium is observed in the scales of Cyphochilus beetles (Figure 1a,c). Here, the anisotropic chitin network inside the scales which cover the insect's body outperforms all man-made low refractive index materials known to date. [3,[8][9][10][11] The key to such optimization lies in the tuning of the filling fraction and in the anisotropic nature of the fibrillar structure in the scales. [3,10] Inspired by these natural design principles, we fabricated highly scattering white networks solely constituted by poly methyl methacrylate (PMMA) (Figure 1b,d). The resulting porous films are flexible and show the shortest transport mean free path reported in the literature for low refractive index materials. We demonstrated that the scattering strength of the network can be enhanced by varying the molecular weight of PMMA to achieve transport mean free paths (l t ) as low as 1 µm for an incident wavelength around 500 nm. Having such a short transport mean free path yields a reflectance of 75% for a 4 µm thick film. Due to their low refractive index (close to 1.5 over the whole visible range) and porosity, the produced free-standing films can be easily index-matched with water and other conventional solvents, providing a tunable response, which transitions from white to transparent upon wetting (Figure 1b; Figure S1 and Movie S1, Supporting Information). This property, in addition with the high flexibility of the films ( Figure S2 and Movie S2, Supporting Information), allows for various coating applications. We demonstrated that the scattering properties are maintained when the porous films are grinded into powders, opening their exploitation as white enhancers in paints, pa...

Inspired by the white beetle of the genus Cyphochilus, we fabricate ultra-thin, porous PMMA films by foaming with CO2 saturation. Optimising pore diameter and fraction in terms of broad-band reflectance results in very thin films with exceptional whiteness. Already films with 60 µm-thick scattering layer feature a whiteness with a reflectance of 90%. Even 9 µm thin scattering layers appear white with a reflectance above 57%. The transport mean free path in the artificial films is between 3.5 µm and 4 µm being close to the evolutionary optimised natural prototype. The bio-inspired white films do not lose their whiteness during further shaping, allowing for various applications.

The locally defined growth of carbon nanofibers with lambda shape in an open flame process is demonstrated. Via the growth time, the geometry of the structures can be tailored to a Λor λ-type shape. Microchannel cantilever spotting and dip-pen nanolithography are utilized for the deposition of catalytic salt NiCl 2 · 6H 2 O for locally controlled growth of lambda-shaped carbon nanofibers. Rigorous downscaling reveals a critical catalytic salt volume of 0.033 µm³, resulting in exactly one lambda-shaped carbon nanofiber at a highly predefined position. An empirical model explains the observed growth process. Carbon Nanofibers www.advancedsciencenews.com

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Based on magnetic-field-assisted growth of carbon nanofibers in an open ethanol flame we fabricated arrays of carbon nanofibers with different degrees of orientation. Inspired by the dry adhesive system of geckos we investigated the adhesive properties of such carbon nanofiber arrays with ordered and random orientation. AFM-based force spectroscopy revealed that adhesion force and energy rise linear with preload force. Carbon nanofibers oriented by a magnetic field show a 68% higher adhesion (0.66 N/cm2) than the randomly oriented fibers. Endurance tests revealed that the carbon nanofiber arrays withstand 50.000 attachment/detachment cycles without observable wear.

Background: Inspired by structural hierarchies and the related excellent mechanical properties of biological materials, we created a smoothly graded micro-to nanoporous structure from a thermoplastic polymer.

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