Journal of Nano Research Vol. 27

Abstract: Fe²⁺ doped silica sol was prepared using tetraethoxysilane (TEOS) as precursor, ethanol as solvent, hydrochloric acid as catalyst and aqueous solution of ferrous iron by sol-gel method under the follow condition: [TEO:n [EtO:n [H₂=1:6:11, reacted at 70°C for 120 min with stirring. Through characterization of the prepared silica sol using particle size analyzer, X-ray diffraction (XRD) and UV-visible spectrum, it could be concluded that even and stable silica sol with nanosize and color was prepared. The prepared Fe²⁺ doped silica sol was applied in silk modification to endow silk with multifunctional properties and color. X-ray Photoelectron Spectroscopy (XPS) and atomic force microscopy (AFM) indicated that Fe²⁺-doped silica sol was treated onto the surface of silk fabric. The results showed that the Fe²⁺ doped silica sol treated silk had good flame retardance, water repellence and antistatic property. At the same time, silk fabric treated by the Fe²⁺-doped silica sol was also endowed with color.

Abstract: Chinese drug-loaded nanoporous materials were prepared from electrospinning Poly (butylenes succinate) (PBS) solutions with an additive of Chinese drug and a mixed solvent of chloroform and iso-propylalcohol in a single processing step. Characterizations of the samples, such as morphology, wettability and permeability, were studied by means of scanning electron microscope, full automatic micro droplet wettability measurement instrument and fabric air permeability performance tester. The results showed these characterizations could be controlled by adjusting electrospinning parameters such as flow rate and drug concentration. And the electrospun nanoporous materials might offer the potential for direct fabrication of biologically based and high-surface-area porous materials.

Abstract: Lightning is a natural phenomenon caused by an atmospheric electrical discharge, and lightning strikes are of hierarchical structure. Similar phenomenon is first observed in a charged jet in the presence of a high electrostatic field, the process is widely adopted for fabrication of superfine fibers, and its mechanism of lightning-like charged jet is still unknown. Our observation reveals that a daughter jet can be ejected from the surface of a micro/nanoscale charged jet to form an initial two-stage cascade, whereby the daughter charged jet can reduce size over three orders of magnitude, while at the ultimate stage, the jets have almost same size from several nanometers to dozens of nanometers. The origin of this phenomenon might be central to nanotechnology. Here we demonstrate that an electrostatic field can accelerate a charged jet, and the surface charge repels each other. When the repelling force reaches a threshold to overcome its surface tension, one or more daughter charged jets are ejected from the surface. The daughter jets behave similarly to the initial jet, the process is iterative, creating a lightning-like multi-stage cascade. This observation opens the door to mimicking the lightning to produce two dimensional superfine fiber web with hierarchical structure.

Abstract: Ionizing radiation directly causes serious damage to human health, and a protective system capable of absorbing or reflecting ionizing radiation is required urgently. In this work, electrospun poly (vinyl alcohol) (PVA) and Poly (vinyl Alcohol)/Erbium Oxide (PVA/Er₂O₃) nanocomposite fibrous mats were fabricated. These PVA or PVA/Er₂O₃ composite nanofibers were completely characterized using scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, Thermogravimetric Analysis (TGA) and X-ray photoelectron spectroscopy (XPS). Furthemore, air permeability and ionizing radiation protection properties of these mats were also measured. Under a certain constant electropinning condition, the PVA or PVA/Er₂O₃ composite nanofibers showed an excellent morphology. The ionizing radiation protection capability of nanofibrous mats is considerably improved when incorporated with Er₂O₃ nanoparticles.

Abstract: Fabricated nanowebs are successfully coated with polypropylene spun bonded non-woven fabric with various coating density ranges from 0.25-1.2 gsm. This study describes an electrospinning coating process of pure Chitosan dissolved in TFA and DCM and its detailed characterizations. The optimal solution condition for electrospinning was studied and, thereby, the process was successfully established. The best optimal condition: 11 % Chitosan was successfully electrospun (superlative web structure) in the electric field of 75 KV, distance between spinning electrodes 135 mm and rotation of spinning electrode 5 rpm (throughput). Once it was determined the ideal condition for fabricating web thereafter under identical conditions electro coating process was done by varying collector speed. The resultant nanofibrous web was found to be uniformly coated having mean fiber diameter ranges from 1210-1221 nm. AFM microphotographs indicated the interconnected porous structure of the prepared Chitosan web. Fibrous break down at a solution concentration (2 & 5 %) was revealed by AFM and FESEM images. At higher concentration (14%) web spinability was poor in the form of lumps deposition. Morphology of spun web was greatly influenced by coating density. Thus, these nanofibrous coated membranes have great potential for using as a layer for developing futuristic antimicrobial, biomedical and filtration clothing. Moreover, the developed coated web has a significantly higher production rate (approx 0.25 g/m²min) is potential for commercial viability and could be translated into bulk production.

Abstract: Si-based consolidants, most widely used in the restoration of porous stones exposed to the environmental decay mechanisms, present some serious limitations, such as the tendency to crack and shrink during drying. This deficiency has been the focus of several studies with the objective of modifying and improving the above mentioned materials. The addition of nanoparticle dispersions into silica matrix has been found to enhance their effectiveness in several respects. Objective of the current research was to study the preparation of particle modified consolidants (PMC), consisting of an ethyl silicate matrix loaded with colloidal oxide titania (TiO₂) particles and silica (SiO₂) nanoparticles and the evaluation of their consolidation effect, applied to different porous limestones. Two compositions were prepared and then evaluated based on their stability in the liquid phase, the particle size, the% solids content and their morphological characteristics during the drying process. The characterization of the particles is made through dynamic light scattering (DLS). Penetration depth of the material is examined by scanning electron microscopy (SEM-EDAX). The color changes of the treated surfaces were measured by a portable spectrophotometer before and after treatment. Changes in the porosity and characteristics of the microstructure were determined by applying mercury porosimetry in untreated and treated samples. Based on the techniques applied, PMCs appear to be promising materials in stone consolidation, as they show a reduction of silicate network shrinkage and cracking during drying compared with the silicon-based consolidant. Treatment causes some changes in the properties of the substrate such as a reduction of the % water uptake (up to 15%) as well as an increase in the elastic modulus (up to 10%).

Abstract: Crater-like Taylor cone electrospinning is a novel, simple, and powerful approach to mass produce nanofibers. The Taylor cone, crater-like liquid bump on the free liquid surface, in this electrospinning process plays a key role to produce multiple fluid jets which finally solidifies nanofibers. A multi-physics coupled FEM method was employed to simulate the dynamic formation process of crater-like Taylor Cone in crater-like electrospinning. A blended k−ω /k−ε model for turbulence and dynamic overset grids to resolve large amplitude motions were used to simulate two-dimensional uncompressed flow, which was described in axisymmetrical coordinates. The numerical calculation results were obtained by a computational fluid dynamics (CFD) method. The effect of gas flow on the formation of crater-like Taylor cone and the production of nanofibers were also discussed. The experiments were carried out to validate the numerical results. The Polyvinyl Alcohol (PVA)/ distilled water solution with 18wt% and the air pressures ranged varied from 4 to 50kPa were used in our experiments. The results showed that the numerical results were in good agreement with the experimental results. This work provides a deep understanding of the mechanisms of micro fluid jets production in electrospinning processes and two-phase flow in specific type of industrial equipment.

Abstract: In the traditional PECVD method for growing carbon nanotubes (CNTs), the electric field is an important parameter. Its role is to orient CNT growth and dissociate the H-C bond from hydrocarbon gases. Therefore, high energy ions, molecules, and radicals as plasma elements can affect the verticality of CNTs. In this paper, a new configuration for an electric field for the growth of field-oriented and long CNTs on a glass substrate at temperatures below 400°C is reported. Simulation and experimental data show that CNTs are grown at a considerably lower voltage than traditional methods. Using this method, growing vertical CNT on such low-cost substrate glass is more possible for CNT-based devices and bio-applications where price is important.