Jianyi Zheng

The effect of surfactants on the diameter and morphology of electrospun ultrafine nanofiber

Different surfactants are introduced to study the diameter and morphology transformation characteristics of electrospun nanofiber. Surfactants increase the net charge density and instability motion of charged jet. The instability motion provides a good way to stretch the charged jets into finer ones, by which the beaded structures are also prevented. Ultrafine nanofiber with average diameter less than 65nm can be fabricated. The nanofiber diameter decreases with the increase of surfactant concentration in polymer solution. The nanofibers with anionic surfactant sodium dodecyl sulfate (SDS) have the smallest diameter. The cationic surfactant hexadecyl trimethyl ammonium bromide (HTAB) plays the best role to prevent the formation of beaded structures in nanofibers, and helps to increase the uniformity of electrospun nanofiber. The effects of surfactants on the nanofiber diameter and morphology have been studied, which would promote the industrial application of ultrafine polymeric nanofibers.

Electrospun nickel oxide nanofibers for gas sensor application

Oxide gas sensor based on electrospun nanofibers were fabricated and studied in this paper. Polyvinyl pyrrolidone (PVP)/Nickel acetate precursor nanofibers were electrospun, which were sintered into Nickel oxide (NiO) nanofibers with diameter in the range of 100 to 400 nm. The morphology and structure of NiO nanofiber were characterized by scanning electron microscopy and X-ray diffraction. The Gas sensing properties (C₃H₆O, C₂H₅OH and NH3) of NiO nanofibers were also investigated. The NiO nanofibers exhibited rapid response/recovery sensitivity with all the three target gases at room temperature. The response/recovery time of electrospun NiO nanofiber gas sensor for C₃H₆O, C₂H₅OH and NH₃ were 4/5.5s, 2.5/2s and 16/5s; and the sensitivity were 11.0, 15.9 and 72.3, respectively. These results suggest that the electrospun NiO nanofibers are promising for gas sensor applications.

Improving the performance of IPMCs with a gradient in thickness

Natural Science Foundation of Fujian Province of China [2011J05140]; Fundamental Research Funds for Central Universities of Xiamen University [2011121045]

Electrohydrodynamic direct-writing orderly pattern with sheath gas focusing

Laminar sheath gas is introduced to increase the stability of Electrohydrodynamic Direct-Writing (EDW). The external stretching force from sheath gas promotes the ejection threshold, the diameter of jet and printed fibers as well. The critical voltage decreases with the increase of sheath gas pressure. The stretching force from sheath gas decreases the diameter of printed fiber as well as that of charged jet. As sheath gas pressure increases from 0 to 25 kPa, the average diameter of micro/nano structure reduces from 4.46μm to 845.25 nm. The laminar field flow of sheath gas shelters the charged jet free from the surrounding interferences, and helps charged jet to move in a straight line. With the help of sheath gas, the stability of charged jet can be improved to direct-write precise complex micro-pattern. The position precision of direct-written pattern is less than 5μm. As a novel method, EDW with laminar sheath gas would promote the deposition precision of printed micro/nano structure and its application.

Electrospun zinc oxide nanofibrous gas sensors for alcohol and acetone

The application of electrospinning fabrication technology in micro/nano sensor production was investigated.Mixed solutions of praecursor bodies PVP(Polyvinyl Pyrrlidone)/Zn(Ac)2and PEO(Polyoxyethylene)/Zn(Ac)2were used as the electrospinning materials to make a precursor nanofiber.The precursor nanofiber was calcined at 500°C in the air to remove polymers and the Zn(Ac)2was thermally decomposed and oxidized into ZnO.X-ray diffraction(XRD)was used to charaterize the components of a ZnO nanofiber.The sensing response of a ZnO nanofibrous gas sensor on the ethanol and acetone vapors were tested.The test results indicate that the average diameters of ZnO nanofiber made from PVP/Zn(Ac)2,PEO/Zn(Ac)2precursor are 308nm and 184nm,respectively.XRD spectrograms show that the ZnO nanofiber with high purity can be obtained from a blended precursornanofiber through thermal oxidation.The response time of the ZnO nanofibrous sensor on the objective gas is less than 1sat room temperature and its sensitivity increases with the increment of gas concentration.Furthermore,the ZnO nanofiber made from PEO/Zn(Ac)2 precursor shows a roughness surface,a larger specific surface area and higher sensing sensitivity,and the maximal sensitivity of ZnO nanofibrous gas sensor on ethanol and acetone vapor have been up to 215.69and 118.13,respectively.This work presents a novel method for the integration fabrication of semiconductor micro/nano gas sensors.

Micro/nano structure written via sheath gas assisted EHD jet

Laminar sheath gas is introduced into the Electrohydrodynamic Direct-Write (EDW) to promote the stability of charged jet and deposition precision of printed micro/nano structure. A novel EDW spinneret with sheath gas is designed to fabricate fine 1D micro/nano structure under lower applied voltage. The laminar sheath gas restricts the whipping motion of charged jet as well as decreases the required voltage. With the help of stretch force stems from sheath gas, the initiation voltage and sustaining voltage of EDW can be decreased obviously; the average diameter of micro/nano structure can be decreased from 21.58μm to 505.58nm. Different patterns can be also obtained by adjusting the moving speed of the collector in a sheath gas cases. Therefore, it can be concluded that provides a unique way for the precision deposition and integration of EDW micro/nano structure with in the micro/nanosystems.

Research on Glass Frit Deposition Based on the Electrospray Process

In this paper, the electrospray technology is used to easily deposit the glass frit into patterns at a micro-scale level. First, far-field electrospray process was carried out with a mixture of glass frit in the presence of ethanol. A uniform, smooth, and dense glass frit film was obtained, verifying that the electrospray technology was feasible. Then, the distance between the nozzle and the substrate was reduced to 2 mm to carry out near-field electrospray. The experimental process was improved by setting the range of the feed rate of the substrate to match both the concentration and the flow rate of the solution. Spray diameter could be less at the voltage of 2 kV, in which the glass frit film was expected to reach the minimum line width. A uniform glass frit film with a line width within the range of 400–500 μm was prepared when the speed of the substrate was 25 mm/s. It indicates that electrospray is an efficient technique for the patterned deposition of glass frit in wafer-level hermetic encapsulation.

Printing of highly conductive solution by alternating current electrohydrodynamic direct-write

Electrohydrodynamic Direct-Write (EDW) is a novel technology for the printing of micro/nano structures. In this paper, Alternating Current (AC) electrical field was introduced to improve the ejection stability of jet with highly conductive solution. By alternating the electrical field, the polarity of free charges on the surface of jet was changed and the average density of charge, as well as the repulsive force, was reduced to stabilize the jet. When the frequency of AC electrical field increased, the EDW process became more stable and the shape of deposited droplets became more regular. The diameter of printed droplets decreased and the deposition frequency increased with the increase of voltage frequency. The phenomenon of corona discharge was overcome effectively as well. To further evaluate the performance of AC EDW for highly conductive solution, more NaCl was added to the solution and the conductivity was increased to 2810μs/cm. With such high conductivity, the problem of serious corona discharge could still be prevented by AC EDW, and the diameter of printed droplets decreased significantly. This work provides an effective way to accelerate industrial applications of EDW.

Jet behaviors and ejection mode recognition of electrohydrodynamic direct-write

By introducing image recognition and micro-current testing, jet behavior research was conducted, in which the real-time recognition of ejection mode was realized. To study the factors influencing ejection modes and the current variation trends under different modes, an Electrohydrodynamic Direct-Write (EDW) system with functions of current detection and ejection mode recognition was firstly built. Then a program was developed to recognize the jet modes. As the voltage applied to the metal tip increased, four jet ejection modes in EDW occurred: droplet ejection mode, Taylor cone ejection mode, retractive ejection mode and forked ejection mode. In this work, the corresponding relationship between the ejection modes and the effect on fiber deposition as well as current was studied. The real-time identification of ejection mode and detection of electrospinning current was realized. The results in this paper are contributed to enhancing the ejection stability, providing a good technical basis to produce contin...

Electrosprayed membrane with heat treatment

In this paper, electrospray technology was utilized to fabricate micro membrane. The stable cone-jet injection mode was the key role to atomize uniformity particle and smooth membrane. As applied voltage ranged from 2.5kV to 7.5kV, the stable cone-jet model was built up. When the applied voltage increased from 2.5kV to 7.5kV, the average linear jet length increased from 3.699mm to 4.653mm under the stable cone-jet mode. Under the smaller distance between the nozzle and collector of 3~5cm, electrospray particles with higher solvent content was syncretized into membrane. Larger applied voltage led to higher surface charge density and multiple jets injection mode, in which electrospray particles can be syncretized into membrane structure. The uniformity and compactness of the membranes can be improved through the heat treatment. Smooth and uniform membrane can be fabricated with the heat treatment temperature of 100°C. With the help of heat treatment, the thickness of electrospray membrane was decreased from 9.06 μm to 6.41 μm. Electrospray technology provides an excellent way to fabricate polymer micro membrane and had great application potential.