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Adaptive Shape Ripening and Interparticle Bridging of L-Arginine-Stabilized Silica Nanoparticles During Evaporative Colloidal Crystal Assembly
摘要： During evaporative self-assembly of colloidal crystal films, spherical L-arginine-stabilized silica colloids adapt to different close-packed geometries by faceting and forming bridge connections with their nearest neighbors. We systematically studied the morphological changes of 37 and 138 nm diameter colloids during evaporative assembly and compared them to 65 nm St?ber silica colloids prepared without L-arginine. Colloidal crystal films were grown from particles that had been dialyzed against water or L-arginine, and tetraethylorthosilicate (TEOS) and/or L-arginine were added to solutions during colloidal film growth. Solid-state 29Si NMR spectra showed the presence of L-arginine and incompletely condensed silica in colloids grown from silica seeds in L-arginine solutions. These colloids were especially susceptible to chemical ripening during the colloidal assembly process, adopting faceted shapes that reflected the packing symmetry of the colloidal crystal films. The addition of L-arginine and TEOS accelerated these shape changes by catalyzing the hydrolysis and olation of silica, and by adding a source of silica to the solution, respectively. This chemistry provides a route to single-component and binary colloidal crystals composed of non-spherical silica building blocks.
关键词： evaporative self-assembly,colloids,silica nanoparticles,colloidal crystal,L-arginine
更新于2025-09-23 15:23:52
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Optical Characterization of the Photonic Ball as a Structurally Colored Pigment
摘要： A photonic ball is a spherical colloidal crystal. Because it can exhibit vivid structural colors, many attempts have been made to apply it as a structurally colored pigment. However, the optical properties of the photonic ball are complicated because di?erent crystal planes can be involved in the coloration mechanism, depending on the size of the constituent colloidal particles. In this paper, we report a comparative study of photonic balls consisting of silica particles with sizes ranging from 220 to 500 nm. We ?rst analyze the re?ectance spectra acquired in a nearly backscattering geometry and con?rm that Bragg di?raction from di?erent crystal planes causes several spectral peaks. Second, the angular dependence of re?ection is experimentally characterized and theoretically analyzed with appropriate models. These analyses and a comparison with a planar colloidal crystal reveal that the spherical shape plays an essential role in the minor iridescence of photonic balls. We ?nally discuss a method to enhance color saturation by incorporating small light-absorbing particles. We also discuss the iridescence of the photonic ball under directional and ambient illumination conditions.
关键词： structural coloration,photonic ball,iridescence,colloidal crystal,Bragg diffraction
更新于2025-09-23 15:21:01
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Position Dependence of Emission Wavelength of a SiO2 Colloidal Photonic-Crystal Laser
摘要： In this paper, a wavelength tunable colloidal-crystal laser with monodispersed silica particles was demonstrated. Silica particles were synthesized through the modified St?ber process and self-assembled into the colloidal photonic-crystal structure, which was then used to form the optic cavity of a wavelength tunable laser device. Due to Bragg’s diffraction of the colloidal photonic-crystal and the coffee ring effect, the forbidden energy gap of light varied with different lattice sizes at different positions of the colloidal photonic-crystal. When the pumping pulsed laser irradiated on the gain medium of the sample, the fluorescence was restricted and enhanced by the colloidal photonic-crystal. Lasing emission with a single peak occurred when the energy of the pumping laser exceeded the threshold energy. The threshold energy and the full-width at half-maximum (FWHM) of the proposed laser were 7.63 μJ/pulse and 2.88 nm, respectively. Moreover, the lasing wavelength of the colloidal photonic-crystal laser could be tuned from 604 nm to 594 nm, corresponding to the various positions in the sample due to the coffee ring effect.
关键词： St?ber process,colloidal-crystal laser,wavelength tunable,self-assemble,silica particles
更新于2025-09-19 17:13:59
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Phase diagram of colloidal crystals of poly(methyl methacrylate) spheres in the exhaustively deionized dispersion
摘要： Phase diagram of colloidal crystals of poly(methyl methacrylate) (PMMA) spheres (100 to 300 nm in diameter) was measured precisely for the exhaustively deionized aqueous dispersion. Strong iridescent colors changed from bluish to reddish and metallic as sphere size increased at high sphere concentrations around 0.1 in volume fraction. Large single crystals, on the other hand, were recognized with the naked eyes at low sphere concentrations around 0.0005 to 0.001 especially for PMMA spheres smaller than 200 nm. The critical concentrations of melting (or crystallization), ?c of all the PMMA spheres examined were quite low between 0.00025 and 0.00060 in volume fraction. The ?c values were insensitive to kind (polystyrene, silica, and fluorine-containing spheres) and also to size (90~300 nm) of colloidal spheres. The ?c value of the deionized dispersion with the coexistence of the ion-exchange resins was lowest, and that without resins was tenfold large. Addition of sodium chloride increased the ?c values sharply. Extension of the electrical double layers forming around the colloidal spheres is most important to determine the ?c values.
关键词： Critical concentration of melting,Phase diagram,Colloidal crystal,Deionized dispersion,Poly(methyl methacrylate) spheres
更新于2025-09-10 09:29:36
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Preparation of monolayer hollow spherical tungsten oxide films with enhanced near infrared electrochromic performances
摘要： In this study, monolayer hollow spherical tungsten oxide (WO3) films have been prepared for the first time by magnetron sputtering combined with the colloidal crystal template method. Due to the large specific surface area, short ion diffusion distances, and weak scattering of the monolayer hollow structure, the hollow spherical WO3 film exhibits excellent electrochromic performance. This includes high transmittance modulation in the near-infrared spectral range (78.8% at l ? 1000 nm), fast switching (cid:2)1) response time (2.41 s for coloration and 1.28 s for bleaching), and high coloring efficiency (102.9 cm2 C at 1000 nm. The results show that the hollow spherical WO3 film can effectively regulate incident light, especially in the near infrared band, which is not visible but has significant thermal effects.
关键词： Electrochromics,Hollow spherical tungsten oxide,Colloidal crystal template,Magnetron sputtering
更新于2025-09-04 15:30:14