Silica Nanowires Research Articles

Stable and Tunable Quantum Conductance in Spider-Silk-like Synaptic Device for Neurocomputing.

The quantum conductance (QC) behaviors in synaptic devices with stable and tunable conductance states are essential for high-density storage and brain-like neurocomputing (NC). In this work, inspired by the discontinuous transport of fluid in spider silk, a synaptic device composed of a silicon oxide nanowire network embedded with silicon quantum dots (Si-QDs@SiOx) is designed. The tunable QC behaviors are achieved in both the SET and RESET processes, and the QC states exhibit stable retention time exceeding 104 s in the synaptic device and show stable reproducibility after an interval of two months. The synaptic plasticity, including long-term potentiation/depression and Pavlovian conditioning function, is simulated based on the tunable conductance. The mechanism of stable and tunable QC behaviors is analyzed and clarified by beading effect of spider silk in Si-QDs@SiOx nanowires structure. The digit recognition capability of the device is evaluated by simulation using an artificial neural network consisting of the Si-QDs@SiOx-based synaptic device. These results provide insights into the development of neurocomputing systems with high classification accuracy.

PNA-Functionalized, Silica Nanowires-Filled Glass Microtube for Ultrasensitive and Label-Free Detection of miRNA-21.

MicroRNAs (miRNAs) are endogenous and noncoding single-stranded RNA molecules with a length of approximately 18-25 nucleotides, which play an undeniable role in early cancer screening. Therefore, it is very important to develop an ultrasensitive and highly specific method for detecting miRNAs. Here, we present a bottom-up assembly approach for modifying glass microtubes with silica nanowires (SiNWs) and develop a label-free sensing platform for miRNA-21 detection. The three-dimensional (3D) networks formed by SiNWs make them abundant and highly accessible sites for binding with peptide nucleic acid (PNA). As a receptor, PNA has no phosphate groups and exhibits an overall electrically neutral state, resulting in a relatively small repulsion between PNA and RNA, which can improve the hybridization efficiency. The SiNWs-filled glass microtube (SiNWs@GMT) sensor enables ultrasensitive, label-free detection of miRNA-21 with a detection limit as low as 1 aM at a detection range of 1 aM-100 nM. Noteworthy, the sensor can still detect miRNA-21 in the range of 102-108 fM in complex solutions containing 1000-fold homologous interference of miRNAs. The high anti-interference performance of the sensor enables it to specifically recognize target miRNA-21 in the presence of other miRNAs and distinguish 1-, 3-mismatch nucleotide sequences. Significantly, the sensor platform is able to detect miRNA-21 in the lysate of breast cancer cell lines (e.g., MCF-7 cells and MDA-MB-231 cells), indicating that it has good potential in the screening of early breast cancers.

Robust and renewable hierarchical silica nanowires grown on a stainless steel mesh for oil/water separation

Porous filters with selective wetting properties offer a more effective route for separating oil and water than traditional industrial processes. However, developing durable structures for emulsion purification remains a challenge. Herein, we present a filter comprising a stainless steel mesh decorated with silica nanowires, which is highly resistant to fouling (almost 0° water contact angle and 166° underwater oil contact angle) and demonstrates excellent separation efficiency and reusability. The nanowire filter is particularly suited for separating n-hexane/water emulsions, where the oil phase could be completely separated by the filter. In addition, it demonstrates remarkable resistance to acid (pH 2 for 10 days), salt solution (37 days), butane flame, and abrasion, indicating its applicability in harsh environmental conditions. By combining the advantages of low-cost production, excellent separation, and enhanced durability, this nanowire filter holds significant potential for oil/water separation applications.

Graphene-Based Hybrid Fillers for Rubber Composites.

Graphene and its derivatives have been confirmed to be among the best fillers for rubber due to their excellent properties, such as high mechanical strength, improved interface interaction, and strain-induced crystallization capabilities. Graphene rubber materials can be widely used in tires, shoes, high-barrier conductive seals, electromagnetic shielding seals, shock absorbers, etc. In order to reduce the graphene loading and endow more desirable functions to rubber materials, graphene-based hybrid fillers are extensively employed, which can effectively enhance the performance of rubber composites. This review briefly summarizes the recent research on rubber composites with graphene-based hybrid fillers consisting of carbon black, silica, carbon nanotubes, metal oxide, and one-dimensional nanowires. The preparation methods, performance improvements, and applications of different graphene-based hybrid fillers/rubber composites have been investigated. This study also focuses on methods that can ensure the effectiveness of graphene hybrid fillers in reinforcing rubber composites. Furthermore, the enhanced mechanism of graphene- and graphene derivative-based hybrid fillers in rubber composites is investigated to provide a foundation for future studies.

Silica nanowires-reinforced silica aerogels with outstanding thermal insulation, thermal stability and mechanical properties

Silica aerogels possess extremely low thermal conductivity, low density and high porosity, which can be regarded as candidates for new thermal insulation materials. However, silica aerogels suffer from low strength, brittleness, modeling difficulties and high moisture absorption. In this work, compatible inorganic silica nanowires are introduced as one-dimensional reinforcing materials, and silica nanowires-reinforced silica aerogels (SiO2NWs-MSAs) are synthesized using a two-step acid-base catalytic in-situ sol-gel method combined with atmospheric pressure drying, aiming to improve the comprehensive performances of the composite aerogels. The composite aerogels exhibit good mechanical properties, and the composite aerogel has a compressive strength of 1.379 MPa at a strain of 60 % when the doping amount of silica nanowires is 11 %. The volumetric shrinkage of the composite aerogels varies between 11.58 and 12.81 % and the density ranges from 0.11 to 0.13 g cm−3. SiO2NWs-MSA2 has a low thermal conductivity and good high-temperature insulation properties with thermal conductivity of 0.039 W m−1 K−1 at 25 °C and 0.046 W m−1 K−1 at 150 °C. The thermal stability of the composite aerogels is improved, and the thermal decomposition temperature reaches 500 °C. Meanwhile, the water contact angles of the composite aerogels all exceed 140°. In addition, the composite aerogels can maintain the amorphous state at 1200 °C, and the microstructure remains basically unchanged at 1000 °C, showing excellent high-temperature resistance.

Significantly improved interfacial properties of silicon dioxide nanowire functionalized poly(p-phenylene-2,6-benzobisoxazole) (PBO) fibers/polytetrafluoroethylene (PTFE) wave-transparent laminated composites

Poly(p-phenylene-2,6-benzobisoxazole) (PBO) fiber and polytetrafluoroethylene (PTFE) resin have been widely acknowledged as excellent wave-transparent materials for future high-frequency applications due to their exceptional dielectric properties. However, the weak interfacial bonding between these two materials hampers their full potential. In this study, we successfully addressed this limitation by enhancing the surface roughness of PBO fibers and introducing active sites through the in-situ grafting of silica nanowires. The added silica acted as an interfacial anchor on the PBO fiber surface, significantly improving the bonding force between PBO and PTFE. PBO/PTFE wave-transparent laminated composites were fabricated using hot compression molding. The results demonstrate that the PBO (treated with in-situ grown silica)/PTFE laminated composites exhibit superior interlaminar shear strength (ILSS), flexural strength, flexural modulus, and tensile modulus compared to the pristine PBO/PTFE laminated composites. Specifically, these properties are found to be 58.6%, 32.9%, 138.1%, and 25.35% higher, respectively. Additionally, these composites demonstrate low dielectric constant and dielectric loss. Most notably, they achieve a wave transmittance of 91.45% at 10 GHz, indicating significant potential for wide-range applications in next-generation advanced military weapons, such as “lightweight/high-strength/wave-transparent” electromagnetic window materials, as well as civilian communication base stations.

Dual-Silica Template-Mediated Synthesis of Nitrogen-Doped Mesoporous Carbon Nanotubes for Supercapacitor Applications.

1D carbon nanotubes have been widely applied in many fields, such as catalysis, sensing and energy storage. However, the long tunnel-like pores and relatively low specific surface area of carbon nanotubes often restrict their performance in certain applications. Herein, a dual-silica template-mediated method to prepare nitrogen-doped mesoporous carbon nanotubes (NMCTs) through co-depositing polydopamine (both carbon and nitrogen precursors) and silica nanoparticles (the porogen for mesopore formation) on a silica nanowire template is proposed. The obtained NMCTs have a hierarchical pore structure of large open mesopores and tubular macropores, a high specific surface area (1037 m2 g-1 ), and homogeneous nitrogen doping. The NMCT-45 (prepared at an interval time of 45min) shows excellent performance in supercapacitor applications with a high capacitance (373.6 F g-1 at 1.0 A g-1 ), excellent rate capability, high energy density (11.6W h kg-1 at a power density of 313W kg-1 ), and outstanding cycling stability (98.2% capacity retention after 10000 cycles at 10 A g-1 ). Owing to the unique tubular morphology, hierarchical porosity and homogeneous N-doping, the NMCT also has tremendous potential in electrochemical catalysis and sensing applications.

Biocompatibility and Connectivity of Semiconductor Nanostructures for Cardiac Tissue Engineering Applications.

Nano- or microdevices, enabling simultaneous, long-term, multisite, cellular recording and stimulation from many excitable cells, are expected to make a strategic turn in basic and applied cardiology (particularly tissue engineering) and neuroscience. We propose an innovative approach aiming to elicit bioelectrical information from the cell membrane using an integrated circuit (IC) bearing a coating of nanowires on the chip surface. Nanowires grow directly on the backend of the ICs, thus allowing on-site amplification of bioelectric signals with uniform and controlled morphology and growth of the NWs on templates. To implement this technology, we evaluated the biocompatibility of silicon and zinc oxide nanowires (NWs), used as a seeding substrate for cells in culture, on two different primary cell lines. Human cardiac stromal cells were used to evaluate the effects of ZnO NWs of different lengths on cell behavior, morphology and growth, while BV-2 microglial-like cells and GH4-C1 neuroendocrine-like cell lines were used to evaluate cell membrane-NW interaction and contact when cultured on Si NWs. As the optimization of the contact between integrated microelectronics circuits and cellular membranes represents a long-standing issue, our technological approach may lay the basis for a new era of devices exploiting the microelectronics' sensitivity and "smartness" to both improve investigation of biological systems and to develop suitable NW-based systems available for tissue engineering and regenerative medicine.

A Facile Method for the Fabrication of Luminescent Eu3+-Doped SiO2 Nanowires.

Europium trivalent ion (Eu3+)-doped silica nanowires were prepared, and the positioning of Eu3+ in the silicon dioxide nanowire matrix was researched. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction analysis (XRD) and energy-dispersive X-ray spectroscope analysis (EDX) were used to characterize the product’s morphology and structure. The representation of Fourier transform infrared spectra (FT-IR) and X-ray photoelectron spectroscopy (XPS) were indicative of the presence of a covalent Eu-O-Si bond. The results suggest that Eu3+ was successfully doped into amorphous silica. Furthermore, a sol-gel inorganic−organic co-assembly mechanism model was proposed to illuminate the formation of the rare-earth ion-doped nanowires. In addition, photoluminescent emission of europium ions in a silica matrix was further discussed. It was demonstrated that a 10% content of Eu3+ resulted in a quenching effect and after annealing at 650 °C, the europium ions in the nanowires had a high luminescence intensity due to the silica network structure.

High-Resolution 3D Fabrication of Glass Fiber-Reinforced Polymer Nanocomposite (FRPN) Objects by Two-Photon Direct Laser Writing.

This paper reports on the nanofabrication of a fiber-reinforced polymer nanocomposite (FRPN) by two-photon direct laser writing (TP-DLW) using silica nanowires (SiO2 NWs) as nanofillers, since they feature a refractive index very close to that of the photoresist used as a polymeric matrix. This allows for the best resolution offered by the TP-DLW technique, even with high loads of SiO2 NWs, up to 70 wt %. The FRPN presented an increase of approximately 4 times in Young’s modulus (8.23 GPa) and nanohardness (120 MPa) when compared to those of the bare photoresist, indicating how the proposed technique is well-suited for applications with higher structural requirements. Moreover, three different printing configurations can be implemented thanks to the use of silicon chips, on which the SiO2 NWs are grown, as fabrication substrates. First, they can be effectively used as an adhesive layer when the laser beam is focused at the interface with the silicon substrate. Second, they can be used as a sacrificial layer, when the laser beam is focused in a plane inside the SiO2 NW layer. Third, only the outer shell of the object is printed so that the SiO2 NW tangle acts as the internal skeleton for the structure being fabricated in the so-called shell and scaffold printing strategy.

Alkyl Silica Hybrid Nanowire Assembly in Improved Superhydrophobic Membranes for RO Filtration.

Alkyl silica membranes and wires were synthesized by a sol–gel method, which has the capacity to control the size of the particles or membranes by controlling the reactions. Trimethoxyoctylsilane (C8TMOS) was used as a chemical surfactant; poly(vinylpyrrolidone) (PVP) as an emulsifier, dissolved in butanol for emulsion; and tetraethylorthosilicate (TEOS) as a precursor and a source of silica. An assembly of silica wires was fabricated on glass and cotton substrates by the dip-coating technique. Porous membranes and silica wires were observed using scanning electron microscopy (SEM) images. The contact angles of all of the samples were in the range of 140–154° as measured by ImageJ software, which confirmed the hydrophobic nature of the samples. The contact angle was increased by increasing the amount of the surfactant. Phase changes of silica wires and membranes were investigated by thermogravimetric analysis. Chemical bonds of the sample were studied using Fourier transform infrared (FTIR) spectroscopy. The band gap of silica nanowires was measured to be 3.8–3.4 eV using the UV–visible spectrum and decreased as compared to that of bulk silica. These silica-based porous membranes with enhanced transport properties can be used in filtration and separation techniques. This fabricated hybrid silica membrane showed ∼96% salt rejection within a permeation flux of 3.04 L/m2 h.

Silica Nanowires Reinforced with Poly(vinylidene fluoride‐co‐hexafluoropropylene): Separator for High‐Performance Lithium Batteries

AbstractSeparators are key components that physically separate and chemically connect the anode and cathode to guarantee the safety and cycle stability of batteries. Herein, based on the building concept of a bird's nest, we have developed separators comprising SiO2 nanowires reinforced with poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP). In particular, the hybrid separators with 39% of PVDF‐HFP exhibit much enhanced tensile strength, Young's moduli, flexibility, and elongation as a result of a strong crosslink effect, compared to bare SiO2 nanowire separator, while yet maintaining excellent electrolyte wettability, high ionic conductivity, and wide electrochemical window. Moreover, the hybrid separators also demonstrate excellent thermal stability and dendrite suppression capability. Lithium metal batteries assembled using the hybrid separators with LiFePO4 as the cathode achieve excellent rate performance and cyclic stability. The discharge capacities attained at a current density equivalent to 0.2 C and 2 C rate are 157 and 126 mAh g−1, respectively. A capacity of 99 mAh g−1 is still maintained at 2 C rate after 500 cycles. This study illuminates SiO2 nanowires reinforced with PVDF‐HFP as promising separators for high‐energy, high‐power and safe lithium batteries.

Effect of fluoropolymer spots on pool boiling heat transfer

In this paper, the investigation of pool boiling heat transfer on biphilic micro/nanostructured surfaces is presented. An array of micrococoons from silicon oxide nanowires was synthesized on the surface of a copper heater using the gas-jet electron beam plasma chemical vapor deposition method. The biphilic properties of the surface were achieved by applying fluoropolymer spots by hot wire chemical vapor deposition. Technology of creating biphilic surfaces was developed and boiling curves were obtained for used samples. The advantages of using a biphilic surface to enhance heat transfer were demonstrated in comparison with a smooth surface and a micro-nanostructured surface without local hydrophobic fluoropolymer regions. This technology can be applied to enhance boiling heat transfer.

Effect of the distance between the micro/nanostructures on pool boiling heat transfer with water on a copper heater

Copper heaters were made. On the surface of these heaters the arrays of micrococoons were synthesized from silicon oxide (SiOx) nanowires with different concentrations of micro/nanostructures and hence different average distances between them. Boiling curves were obtained for these samples and it was found that heat transfer enhancement during boiling occurs on them in comparison with a smooth copper surface. It was shown that the effect increases with decreasing concentration of micro/nanostructures and reaches a maximum for microrelief with an approximate concentration of microstructures equal to unity per square micron. It was found that surfaces with micrococoons are sufficiently stable and suitable for enhancing heat transfer during boiling.

Experimental Study of Pool Boiling on Heaters with Nanomodified Surfaces under Saturation

A technology has been developed for the synthesis of arrays of oriented microropes and cocoon-like microstructures consisting of silicon oxide nanowires on a copper substrate with barrier layers of silicon dioxide, molybdenum, and tungsten. In experiments, a copper surface coated with a tungsten layer showed the best stability and technological applicability. Experiments were performed to study pool boiling heat transfer on copper heaters with nanomodified surfaces under saturation conditions. A comparison of the data on heat transfer enhancement on smooth and nanomodified hydrophilic and hydrophobic copper surfaces was made. Relatively high heat transfer coefficients were observed on copper surfaces with a tungsten barrier layer initially coated with microropes and micrococoons. The experiments showed that microropes from nanowires were not resistant to boiling; micrococoons from nanowires were more stable. Superhydrophobic surfaces were produced by hot-wire chemical vapor deposition (HWCVD) of fluoropolymer coatings on micrococoons. In the boiling experiments, the greatest heat transfer enhancement was obtained on such surfaces. The fluoropolymer coating was shown to lose its continuity. As a result, a random biphilic coating was formed and intense bubble boiling occurred in local hydrophobic areas of the fluoropolymer, resulting in heat transfer enhancement.

Room Temperature Growth of Silica Nanowires on Top of Ultrathin Si Nanowires Synthesized with Sn‐Cu Bimetallic Seeds

Si nanowires (NWs) are grown by the vapor–liquid–solid method using Cu–Sn bimetallic catalysts in a plasma‐enhanced chemical vapor deposition (PECVD) reactor. The microstructure of the NWs is analyzed by transmission electron microscopy and energy‐dispersive X‐ray spectroscopy. An amorphous SiO2 region, much larger than the native oxide, is present on top of each crystalline SiNW: in SiNWs with diameter below 10 nm, it takes the form of a silica NW of up to 50 nm in length. The new NW separates the initial catalyst particle into one that stays in contact with the SiNW and one or more that lies at the top of the new NW. The former is made of Cu and Cu3Si and contains no Sn, whereas the latter keeps amounts of both elements. The observed microstructure appears to be the result of a mechanism of Si oxidation catalyzed by Cu3Si. The deposit after SiNW growth, in the PECVD reactor, of a protecting 2 nm thick layer of hydrogenated amorphous Si, completely suppresses this mechanism. Reference for future applications based on Cu–Sn‐catalyzed quantum‐sized SiNWs is provided.

A Hard Templating Approach to Functional Mesoporous Poly(norborn‐2‐ene)‐Based Monolithic Supports

AbstractA hard‐templating method is presented for the synthesis of functional ring‐opening metathesis polymerization (ROMP) derived, poly(norborn‐2‐ene)‐based monolithic supports prepared under solvent‐induced phase separation conditions using the first‐generation Grubbs initiator RuCl2(PCy3)2(CHPh) (1, Cy = cyclohexyl). Norborn‐2‐ene (NBE), 1,4,4a,5,8,8a‐hexahydro‐1,4,5,8‐exo,endo‐dimethanonaphthalene (DMN‐H6) and trimethylolpropane‐tris‐(5‐norbornene‐2‐yl‐carboxylate (TMPTNC) are used as monomers and crosslinkers, respectively. 2‐Propanol and toluene are used as macro‐ and microporogen. Silica (SiO2) nanowires (SNWs) surface‐modified with NBE are used as hard templates. exo,endo‐Norborn‐5‐ene‐2‐ylmethanol (NBE‐CH2OH) is used as functional comonomer. The tailored porogenic system together with the surface‐functionalized SNWs allows for a full dispersion of the SNWs in the polymerization mixture and their incorporation into the monolithic structure during the phase separation process. This way, ROMP‐derived monoliths with pore dimensions of 10–15 nm, specific surface areas up to 3.7 m2 g−1, and pore porosities up to 33% are obtained after removal of the SNWs by chemical etching at room temperature.

Deep UV to NIR frequency combs via cascaded harmonic generation in a silica nanowire using nanojoule pulse energies

Compact, turnkey frequency combs in the deep ultraviolet (UV) to near-infrared (NIR) wavelength region are important for applications ranging from ultralow power spectroscopy and quantum memory to light–atom interactions. Translation of an IR (1550 nm) comb from a compact mode-locked laser (MLL) to visible wavelength region, using cascading of optical nonlinearities, provides the simplest way to realize an on-demand deep UV to NIR comb. However, the translation of an IR comb to the visible region extending from deep UV to NIR has been difficult to achieve in a single device. We exploit chirped pulsed compression and dispersion engineering to report the simultaneous generation of second- (780 nm), third- (520 nm) and sixth-order (260 nm) harmonics of a 1560 nm MLL in a 10 mm long silica nanowire using nanojoule pulse energies. RF spectrum measurements of the 520 nm signal show that the 82 MHz frequency comb at 1560 nm is translated to visible. The use of a single-mode fiber nanotaper and turnkey mode-locked IR laser creates a hybrid platform that provides deep UV to NIR comb and enables applications in quantum optics through trapping and probing of atoms using the evanescent field of nanotaper.

Simulated synthesis of silica nanowires by lyotropic liquid crystal template method

ABSTRACT Dissipative particle dynamics simulations were adopted to study the mechanism of lyotropic liquid crystal (LLC) formation and the synthesis process of silica nanowires by LLC template method. Simulation results show that the one-dimensional (1D) LLC channel can be formed at the Pluronic F127 concentration range of 61 ∼ 67%. With the increase of Pluronic F127 concentration, the diameter of LLC channel decreases and the deformation degree increases. The effect of PEO: PPO ratio on the diameter of LLC channel is slight. The appropriate PEO: PPO ratio of Pluronic is 40:70 for the formation of 1D LLC channel, as the deformation degree of channel is the smallest in this case. The effect of polymerisation degree on the diameter and deformation degree of LLC channel is both little. With the increase of TEOS concentration, the nanowire diameter increases rapidly at first, and then increases quite slowly. This work can provide guidance for silica nanowires synthesis by LLC template method.

The extraction and process optimization of Cu (II) and Cd (II) using Pickering emulsion liquid membrane.

In the present study, the extraction of divalent heavy metals like copper [Cu (II)] and cadmium [Cd (II)] using a Pickering Emulsion Liquid Membrane (PELM) has been investigated by using three different surfactants such as Amphiphilic silica nanowires (ASNWs), Aluminum oxide nanoparticles (Alumina) and Sorbitan monooleate (SPAN 80). The influence of the process parameters such as pH, the stripping phase concentration, the agitation speed, and the carrier concentration on the extraction efficiency have been examined to find the optimum conditions at which the maximum recovery of Cu (II) and Cd (II) could take place. At optimum conditions, the extraction efficiency of 89.77% and 91.19% for Cu (II) and Cd (II) ions were achieved. Non-edible oils were used as diluent in this present study to reduce the need for toxic organic solvents in preparing PELM. The impact of each process factor on the extraction efficiency of Cu (II) and Cd (II) ions has been verified using analysis of variance (ANOVA). The higher values of F and lower values of P (less than 0.05) indicate pH is the most significant parameter on the percentage extraction of Cu (II) and Cd (II) using the Taguchi design approach.