The reinforcement of polymer nanocomposites can be achieved through alignment or percolation of cellulose nanocrystals (CNCs). Here, we compare the efficacy of these reinforcement mechanisms in thermoplastic polyurethane (PU) elastomer nanocomposites containing thermally stable cotton CNCs. CNC alignment was achieved by melt spinning nanocomposite fibers, while a percolating CNC network was generated by solvent casting nanocomposite films with CNC contents up to 20 wt %. While in films both the CNCs and the PU matrix were entirely isotropic at all concentrations as confirmed by wide-angle X-ray scattering and birefringence analysis, the CNCs in the fibers exhibited a preferential orientation, which improved with increasing CNC concentration. Increasing the CNC concentration in the fibers reduces, however, the alignment of the PU chains, resulting in an entirely isotropic PU matrix at high CNC contents. The mechanical properties of films and fibers were evaluated using stress− strain measurements. Nanocomposite fibers with low CNC content exhibited superior stiffness, extensibility, and strength compared to the films, while the films displayed superior mechanical properties at high CNC concentrations. These findings are rationalized using common semiempirical models describing the reinforcing effects of CNC alignment in fibers (Halpin−Tsai) and CNC percolation in films (percolation model). The formation of a percolating CNC network leads to a stronger reinforcement than CNC alignment, as the reinforcing effect of the latter is limited by the comparably low aspect ratio of CNCs extracted from cotton. As a consequence, above the percolation threshold for cotton CNCs, isotropic nanocomposite PU films show a higher stiffness than aligned nanocomposite PU fibers.

The bright colors of Pachyrhynchus weevils originate from complex dielectric nanostructures within their elytral scales. In contrast to previous work exhibiting highly ordered single‐network diamond‐type photonic crystals, here, it is shown by combining optical microscopy and spectroscopy measurements with 3D focused ion beam (FIB) tomography that the blue scales of P. congestus mirabilis differ from that of an ordered diamond structure. Through the use of FIB tomography on elytral scales filled with platinum (Pt) by electron beam‐assisted deposition, it is revealed that the red scales of this weevil possess a periodic diamond structure, while the network morphology of the blue scales exhibit diamond morphology only on the single scattering unit level with disorder on longer length scales. Full wave simulations performed on the reconstructed volumes indicate that this local order is sufficient to open a partial photonic bandgap even at low dielectric constant contrast between chitin and air in the absence of long‐range or translational order. The observation of disordered and ordered photonic crystals within a single organism opens up interesting questions on the cellular origin of coloration and studies on bio‐inspired replication of angle‐independent colors.

Approaches that enable the preparation of robust polymeric photonic particles are of interest for the development of nonfading and highly reflective pigments for applications such as paints and display technologies. Here, the preparation of photonic particles that display structural color in both, aqueous suspension and the dry solid state is reported. This is achieved by exploiting the confined self-assembly of a supramolecular comb-like block copolymer (BCP) that microphase separates into a well-ordered lamellar morphology with dimensions that promote a photonic bandgap in the visible range. The comb-like BCP is formed by robust ionic interactions between poly(styrene-b-4-vinyl-pyridine) (PS-b-P4VP) BCP and dodecylbenzene sulfonic acid (DBSA), which selectively interacts with P4VP blocks. The components are combined in chloroform, and an aqueous emulsion is prepared. Evaporation of the organic solvent leads to the formation of solid microparticles with an onion-like 3D morphology. These photonic pigments display brilliant colors with reflectance spectra featuring pronounced optical bandgaps across the entire visible wavelength range with a peak reflectivity of 80-90%.