The self‐assembly of films that mimic color‐producing nanostructures in bird feathers is described. These structures are isotropic and have a characteristic length‐scale comparable to the wavelength of visible light. Structural colors are produced when wavelength‐independent scattering is suppressed by limiting the optical path length through geometry or absorption.

Multi‐walled carbon nanotube (MWNT)‐sheet‐reinforced bismaleimide (BMI) resin nanocomposites with high concentrations (∼60 wt%) of aligned MWNTs are successfully fabricated. Applying simple mechanical stretching and prepregging (pre‐resin impregnation) processes on initially randomly dispersed, commercially available sheets of millimeter‐long MWNTs leads to substantial alignment enhancement, good dispersion, and high packing density of nanotubes in the resultant nanocomposites. The tensile strength and Young's modulus of the nanocomposites reaches 2 088 MPa and 169 GPa, respectively, which are very high experimental results and comparable to the state‐of‐the‐art unidirectional IM7 carbon‐fiber‐reinforced composites for high‐performance structural applications. The nanocomposites demonstrate unprecedentedly high electrical conductivity of 5 500 S cm−1 along the alignment direction. Such unique integration of high mechanical properties and electrical conductance opens the door for developing polymeric composite conductors and eventually structural composites with multifunctionalities. New fracture morphology and failure modes due to self‐assembly and spreading of MWNT bundles are also observed.

We describe a method for producing highly monodisperse dumbbell-shaped polymer nanoparticles with dimensions on the order of a few hundred nanometers in extremely high yields. Our technique is based on seeded polymerization, where suspended core-shell particles (linear polystyrene core with polystyrene-co-trimethoxysilylpropylacrylate shell) are used as seeds. When an aqueous suspension of seed particles is mixed with monomer solution, the core-shell particles display dramatic changes in their morphology. Subsequent heating drives the polymerization of monomer, resulting in the formation of dumbbell-shaped particles. The relative sizes of the two lobes can be controlled by varying the relative volume of the monomer with respect to the seed particle. These particles are well-suited for future studies of the assembly of photonic crystals of anisotropic particles.

Structurally colored materials could potentially replace dyes and pigments in many applications, but it is challenging to fabricate structural colors that mimic the appearance of absorbing pigments. We demonstrate the microfluidic fabrication of “photonic pigments” consisting of microcapsules containing dense amorphous packings of core–shell colloidal particles. These microcapsules show non‐iridescent structural colors that are independent of viewing angle, a critical requirement for applications such as displays or coatings. We show that the design of the microcapsules facilitates the suppression of incoherent and multiple scattering, enabling the fabrication of photonic pigments with colors spanning the visible spectrum. Our findings should provide new insights into the design and synthesis of materials with structural colors.

Colloidal glasses, bird feathers, and beetle scales can all show structural colors arising from short-ranged spatial correlations between scattering centers. Unlike the structural colors arising from Bragg diffraction in ordered materials like opals, the colors of these photonic glasses are independent of orientation, owing to their disordered, isotropic microstructures. However, there are few examples of photonic glasses with angle-independent red colors in nature, and colloidal glasses with particle sizes chosen to yield structural colors in the red show weak color saturation. Using scattering theory, we show that the absence of angle-independent red color can be explained by the tendency of individual particles to backscatter light more strongly in the blue. We discuss how the backscattering resonances of individual particles arise from cavity-like modes and how they interact with the structural resonances to prevent red. Finally, we use the model to develop design rules for colloidal glasses with red, angle-independent structural colors.

w, d(CH)], 1349 [vw, n(CN)], 1322 [vw, d(CH)], 1298 [vw, d(C±O±CH 2 ) [b]], 1196 [w, d(CO)], 1119 [m, n(C±C=O) [b]], 1053 [w, n(SiO)], 962 [w, n(WO)], 926 [w, n(WO)], 902 [w, n(WO)], 866 [w, n(WO)], 820 [w, n(WO)], 749 [w, n(WO)], 627 [vs, n(FeO)], 561 [vs, n(FeO)]. The BA ferrogels were prepared under the same conditions as the POM ferrogels but replacing POM by N,N¢-methylenebis(acrylamide) (BA) (0.017, 0.042, and 0.084 mol/L). The infrared data of a BA ferrogel with 0.017 M of BA and 5.5 % (volume fraction) of maghemite g-Fe 2 O 3 : IR (KBr): n = 1665 [s, n(CO) [a]], 1615 [s, d(NH)], 1448 [m, d(CH 2 )], 1414 [m, d(CH)], 1349 [m, n(CN)], 1322 [w, d(CH)], 1119 [vw, n(C±C=O) [b]], 627 [vs, n(FeO)], 561 [vs, n(FeO)]. Physical Measurements: The compound g-K 8 [SiW 10 O 36 ]×12H 2 O was prepared according to the literature [16]. Other reagents, [RSi(OMe) 3 ], and solvents were purchased from Aldrich and used as received. Elemental analyses were performed by the ªService central de microanalyses du CNRSº, Vernaison, France. The IR spectra (4000±250 cm ±1 ) were recorded on a Bio-Rad FTS 165 FTIR spectrometer with compounds and dried hydroferrogels sampled in KBr pellets. The volume fraction of magnetic particles in the different hydroferrogels and the particle sizes are deduced from magnetic measurements using a classical Foner device [17]. The rotational diffusion coefficient of particles is determined by the relaxation of birefringence. This method has already been described in the literature [15]. Transmission electron microscopy (TEM) (microscope JEOL 100 CX2) was performed on a microcoat of hydroferrogel deposited on a grid after microtomy. The gels are filmed with a charge coupled device (CCD) color camera (Vista, VPC 4130, UK). The degree of swelling of the hydroferrogel samples was characterized by the ratio m/m 0 , where m is the mass of the hydroferrogel sample swollen in aqueous solution and m 0 is the mass of the dry hydroferrogel.

Colloidal crystals are promising structures for photonic applications requiring dynamic control over optical properties. However, for ease of processing and reconfigurability, the crystals should be encapsulated to form 'ink' capsules rather than confined in a thin film. Here we demonstrate a class of encapsulated colloidal photonic structures whose optical properties can be controlled through osmotic pressure. The ordering and separation of the particles within the microfluidically created capsules can be tuned by changing the colloidal concentration through osmotic pressure-induced control of the size of the individual capsules, modulating photonic stop band. The rubber capsules exhibit a reversible change in the diffracted colour, depending on osmotic pressure, a property we call osmochromaticity. The high encapsulation efficiency and capsule uniformity of this microfluidic approach, combined with the highly reconfigurable shapes and the broad control over photonic properties, make this class of structures particularly suitable for photonic applications such as electronic inks and reflective displays.

We describe the self-assembly of nonspherical particles into crystals with novel structure and optical properties combining a partial photonic band gap with birefringence that can be modulated by an external field or quenched by solvent evaporation. Specifically, we study symmetric optical-scale polymer dumbbells with an aspect ratio of 1.58. Hard particles with this geometry have been predicted to crystallize in equilibrium at high concentrations. However, unlike spherical particles, which readily crystallize in the bulk, previous experiments have shown that these dumbbells crystallize only under strong confinement. Here, we demonstrate the use of an external electric field to align and assemble the dumbbells to make a birefringent suspension with structural color. When the electric field is turned off, the dumbbells rapidly lose their orientational order and the color and birefringence quickly go away. In this way, dumbbells combine the structural color of photonic crystals with the field addressability of liquid crystals. In addition, we find that if the solvent is removed in the presence of an electric field, the particles self-assemble into a novel, dense crystalline packing hundreds of particles thick. Analysis of the crystal structure indicates that the dumbbells have a packing fraction of 0.7862, higher than the densest known packings of spheres and ellipsoids. We perform numerical experiments to more generally demonstrate the importance of controlling the orientation of anisotropic particles during a concentration quench to achieve long-range order.