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Fundamental and Practical Limits of Achieving Artificial Magnetism and Effective Optical Medium by Using Self-Assembly of Metallic Colloidal Clusters
摘要： The self-assembly of metallic colloidal clusters (so called plasmonic metamolecules) has been viewed as a versatile, but highly effective approach for the materialization of the metamaterials exhibiting artificial magnetism at optical frequencies (including visible and near infrared (NIR) regimes). Indeed, several proofs of concepts of plasmonic metamolecules have been successfully demonstrated in both theoretical and experimental ways. Nevertheless, this self-assembly strategy has barely been used and still remains an underutilized method. For example, the self-assembly and optical utilization of the plasmonic metamolecules have been limited to the discrete unit of the structure; the materialization of effective optical medium made of plasmonic metamolecules is highly challenging. In this work, we theoretically exploited the practical limits of self-assembly technology for the fabrication of optical magnetic metamaterials.
关键词： colloids,magnetism,self-assembly,plasmonic metamolecules
更新于2025-09-23 15:23:52
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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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Facile green synthesis of organosilica nanoparticles by a generic “salt route”
摘要： Colloidal silica has wide applications and the global demand of specialty silica is continually increasing. Therefore, it is significant to develop a synthetic method that is simple, versatile, energy-saving, ecologically benign, and easily scalable. Biomimetic synthesis of colloidal silica represents a promising strategy; however, it often requires the synthesis or extraction of specialized macromolecules. In this paper, we present a novel aqueous, one-pot, and green route for synthesis of organosilica nanoparticles. The reaction systems contain only water, an organosilane precursor, a salt, and a commonly used surfactant or amphiphilic polymer. The reaction was performed at ambient conditions without adding any additional solvent, energy, and harsh chemicals. The key findings include the novel identification of 5 salts (i.e. nitrite, fluoride, dibasic phosphate, acetate, and sulfite) that can catalyze organosilica condensation and the resulting formation of nano-colloids. Moreover, the presence of amphiphilic molecules is essential for salt catalysis at low salt concentrations and at nearly neutral pH. Solid-state NMR and in-situ ATR-FTIR studies confirmed that organosilica condensation is highly efficient under the mild reaction condition. In conclusion, the present study demonstrates that "soft" interaction between salts and surfactants (or polymers) can be utilized to construct an effective platform for synthesis of "hard" organosilica particles. The proposed method is generic and applicable to a wide range of commonly used surfactants (viz. non-ionic, anionic, cationic) and amphiphilic polymers, as well as to organosilanes with various hydrophobic functional groups (e.g. mercaptopropyl, vinyl, and methyl).
关键词： Salts,Microreactors,Surfactants,Organosilica nanoparticles,Biomimetic synthesis,Colloids
更新于2025-09-23 15:22:29
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Structural Coloration with Nonclose-Packed Array of Bidisperse Colloidal Particles
摘要： Colloidal crystals and glasses have their own photonic effects. Colloidal crystals show high reflectivity at narrowband, whereas colloidal glasses show low reflectivity at broadband. To compromise the opposite optical properties, a simple means is suggested to control the colloidal arrangement between crystal and glass by employing two different sizes of silica particles with repulsive interparticle potential. Monodisperse silica particles with repulsive potential spontaneously form crystalline structure at volume fraction far below 0.74. When two different sizes of silica particles coexist, the arrangement of silica particles is significantly influenced by two parameters: size contrast and mixing ratio. When the size contrast is small, a long-range order is partially conserved in the entire mixing ratio, resulting in a pronounced reflectance peak and brilliant structural color. When the size contrast is large, the long-range order is rapidly reduced along with mixing ratio. Nevertheless, a short-range order survives, which causes low reflectivity at a broad wavelength, developing faint structural colors. These findings offer an insight into controlling the colloidal arrangements and provide a simple way to tune the optical property of colloidal arrays for structural coloration.
关键词： colloidal arrays,colloids,mechanochromism,structural colors,repulsive potential
更新于2025-09-23 15:22:29
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Self-assembly of fractal liquid crystal colloids
摘要： Nematic liquid crystals are anisotropic fluids that self-assemble into vector fields, which are governed by geometrical and topological laws. Consequently, particulate or droplet inclusions self-assemble in nematic domains through a balance of topological defects. Here, we use double emulsions of water droplets inside radial nematic liquid crystal droplets to form various structures, ranging from linear chains to three-dimensional fractal structures. The system is modeled as a formation of satellite droplets, distributed around a larger, central core droplet and we extend the problem to explain the formation of fractal structures. We show that a distribution of droplet sizes plays a key role in determining the symmetry properties of the resulting geometric structures. The results are relevant to a variety of inclusions, ranging from colloids suspensions to multi-emulsion systems. Such systems have potential applications for novel switchable photonic structures as well as providing wider insights into the packing of self-assembled structures.
关键词： Self-assembly,Fractal structures,Topological defects,Colloids,Liquid crystals
更新于2025-09-23 15:22:29
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High-throughput laser generation of Si-nanoparticle based surface coatings for antibacterial applications
摘要： High-productivity regime of nanosecond IR-laser ablative generation of silicon colloidal solutions in water for anti-bacterial applications was found in terms of GW/cm2-level laser intensity and scanning velocity by measuring multi-shot ablative mass loss and extinction coefficients of the colloids as sub-linear and third-power intensity functions, respectively. This advantageous regime implies sub-linear mass loss versus laser intensity at the simultaneous third-power yield of nanoparticles, resulting from the subcritical-density, opaque ablative plasma regulating the sample ablation rate and the related plasma-mediated dissociation (dispergation) of the ablation products. In contrast, at higher intensities, there is a drastic increase in mass loss with the corresponding increased yield of (sub) micrometer-sized particles owing to intense plasma-driven expulsion of micro-scale melt droplets and the corresponding saturation of the extinction coefficient of the colloidal solutions because of their dynamic local “self-limiting” effect during the high-rate ablation. The optimal low-intensity regime for Si nanoparticle production demonstrates the monotonous correlated increase of mass loss and extinction coefficient in terms of increasing laser scanning velocity, indicating the diminished cumulative effects. Surface coatings prepared from the generated Si nanoparticles exhibit minor surface oxidation, as acquired as their elemental composition via energy-dispersive X-ray spectroscopy, making their contact angle for water droplets (≈51°) close to that of bare Si wafer (≈58°) with its nanometer-thick native oxide layer. Owing to good wetting, the nanoparticle-based surface coatings show strong antibacterial response regarding Gram-negative Pseudomonas auereginosa bacteria even despite their minor oxidative passivation.
关键词： Silicon nanoparticles,Colloids,Surface oxidation,Extinction coefficient,Wetting,Antibacterial tests,Gram-negative bacteria Pseudomonas auereginosa,Sub-critical ablative plasma,Nanosecond laser ablation,Mass loss
更新于2025-09-23 15:21:21
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Xenobiotic Contamination of Water by Plastics and Pesticides Revealed Through Real-time, Ultrasensitive and Reliable Surface Enhanced Raman Scattering
摘要： Uncontrolled utilization and consequent ubiquitous percolation of carcinogenic and xenobiotic contaminants, such as plasticizers and pesticides, into ecosystem has created an immediate demand for robust analytical detection techniques to identify their presence in water. Addressing this demand, we uncover the presence of xenobiotic contaminants such as Bisphenol A (BPA), Triclosan (TC), and Dimethoate (DM) through a robust, ultrasensitive and reliable Surface Enhanced Raman Scattering (SERS) platform. Thereby, conclusive real-time evidence of degradation of polyethylene terephthalate (PET) leading to release of BPA in water is presented. Worryingly, the release of BPA occurs at ambient temperature (40 0C) and within realistic timescales (12 hours) that are regularly encountered during the handling, transport and storage of PET-based water containers. Complementary mass-spectrometric, surface-specific atomic force microscopy and surface selective X-ray Photoelectron spectroscopy confirms the nanoscale surface degradation of PET through loss of C=O and C-O surface functionalities. Such ultra-sensitive (ppm-level), spectroscopic detection is enabled by the bottom-up assemblies of metal nanoparticles (Soret Colloids, SCs) acting as SERS platform to provide high analytical enhancement factor (108) with high reliability (relative standard deviation, RSD <5%). Effective and rapid detection (30 s) of several other potential xenobiotic contaminants such as Triclosan (TC) and Dimethoate (DM) over a wide range of concentrations (10-5 to 10-1 M) has also been demonstrated. Finally, non-destructive real-time spectroscopic “sniffing” of organophosphorous pesticides from the surface of fruits is achieved, illustrating the multi-phasic versatility of this label-free, non-lithography-based SERS platform.
关键词： plastic degradation,Soret colloids,water and food contamination,real-time detection,nanoparticle assembly,surface enhanced Raman scattering,Xenobiotics
更新于2025-09-23 15:21:01
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Liquid Crystalline Colloidal Mixture of Nanosheets and Rods with Dynamically Variable Length
摘要： Here, we demonstrate the novel double-component liquid crystalline colloids composed of mesogenic inorganic nanosheets and the rods with dynamically variable length controlled by temperature. As the length-controllable rod, stiff biopolymer microtubule is used, which was successfully polymerized/depolymerized from tubulin proteins through a biochemical process even in the presence of the nanosheets. The mesoscopic structure of the liquid crystal phase was reversibly modifiable as caused by the change of the rod length.
关键词： nanosheets,rods,temperature control,liquid crystalline colloids,dynamically variable length
更新于2025-09-23 15:21:01
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Plasmonic Janus Microspheres Created from Pickering Emulsion Drops
摘要： Metal nanostructures have been created in a film format to develop unique plasmonic properties. Here, well-defined metal nanostructures are designed on the surface of microspheres to provide plasmonic microgranules. As conventional techniques are inadequate for nanofabrication on spherical surfaces, photocurable emulsion drops with a regular array of silica particles are employed at the interface to create periodic nanostructures. The silica particles, originating from the dispersed phase, fully cover the interface by forming a non-close-packed hexagonal array after drop generation, and slowly protrude to the continuous phase during aging while their interparticle separation decreases. Therefore, hexagonal arrays of spherical dimples with controlled geometry and separation are created on the surface of microspheres by photocuring the drops and removing the particles. Directional deposition of either aluminum or gold results in a continuous film with a hexagonal array of holes on the outermost surface and isolated curved disks in dimples, which renders the hemisphere of microspheres plasmonically colored. The resonant wavelength is controlled by adjusting the aging time, metal thickness, and size of silica particles, providing various plasmonic colors. This granular format of the plasmonic Janus microspheres will open a new avenue of optical applications including active color pixels, optical barcodes, and microsensors.
关键词： Janus microspheres,self-assembly,colloids,Pickering emulsions,plasmonic colors
更新于2025-09-23 15:21:01
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Solution-processed p-type nanocrystalline CoO films for inverted mixed perovskite solar cells
摘要： Inorganic p-type materials show great potential as the hole transport layer in perovskite solar cells with the merits of low costs and enhanced chemical stability. As a p-type material, cobalt oxide (CoO) has received so far not that level of attention despite its high hole mobility. Herein, solution-processed p-type CoO nanocrystalline films are developed for inverted mixed perovskite solar cells. The ultrafine CoO nanocrystals are synthesized via an oil phase method, which are subsequently treated by a ligand exchange process using pyridine solvent to remove the long alkyl chains covering the nanocrystals. From this homogeneous colloidal solution CoO films are obtained, which exhibit a smooth and pin-hole free surface morphology with high transparency and good conductivity. The ultraviolet photoelectron spectrum also indicates that the energy levels of the CoO film match well with the mixed perovskite Cs0.05(FA0.83MA0.17)0.95(I0.83Br0.17)3. Inverted solar cells based on crystalline CoO films with ligand exchange show a reasonable energy conversion efficiency, whereas devices based on CoO films without ligand exchange suffer from a strong S-shape JV-characteristic. Thus, the crystalline CoO films are foreseen to pave a new way of inorganic hole transport materials in the fields of perovskite solar cells.
关键词： Perovskite solar cells,p-type,Cobalt oxide,Colloids,Hole transport layers
更新于2025-09-23 15:21:01