How To Do SHEATH GAS-ASSISTED ELECTROHYDRODYNAMIC DIRECT WRITING

To further improve the deposition behavior, a core-shell-shaped spinneret has been designed and in this design a sheath gas goes out from the peripheral channel to travel around the jet. The sheath gas provides an additional stretching and focusing force on the ejecting jet, which is beneficial to overcoming interference from the surrounding environment and gaining precise micropatterns. He et al. utilized sheath gas to fabricate micro/nanostructures under a lower applied voltage. With the help of the stretching force stemming from the sheath gas, the initiation voltage and sustaining voltage decrease obviously. Low applied voltage is helpful to restrain the instability of the printing process and promote the integration fabrication of micro/nanodevices. The average diameter of the micro/nanostructure decreases from 21.58 mm to 505.58 nm when the assisted gas pressure increases to 50 kPa. In addition, based on the same setup, Zheng et al. investigated the patterned deposition behavior of a charged jet. With the help of a sheath gas, the surrounding interference can be weakened and the charged jet can be free from the influence of the microstructures. Fig. 9.16 shows that precise complex micropatterns such as parallel lines and grids can be direct written with position precision to less than 5 mm.

Maghemite (γ-Fe2O3) Fiber-in-tube And Tube-in-tube Nanostructures

Inspired by the nanowire-in-microtube structure, Jian-guo Guan and colleagues proposed a facile and effective nonequilibrium heat-treatment approach combined with electrospinning for fabrication of maghemite (γ-Fe2O3) fiber-in-tube and tube-in-tube nanostructures. The pre cursor was composed of PVP and iron citrate. Fig. 5.21 shows SEM images and corresponding TEM images of as-obtained γ-Fe2O3 fiber-in-tube and tube-in-tube fibers. The figure reveals that the tips of the inner structures are totally separated from the outer tube, and the inner and outer tubes have a closed end. The resultant γ-Fe2O3 fiber-in-tube and tube-in-tube nanostructures may have important applications in a number of fields, such as magnetic separable catalysts or catalyst-supporting mate rials, sensors, absorbents, microreactors, and so forth, because of their structural characteristics and good magnetic properties. This method can intentionally control the contraction direction of the precursor nanofibers during the heat-treatment process by adjusting only heating rate (R) of the calcination, as R can be easily utilized to tune the temperature gradient established in