• Journal of ILASS-Korea
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• v.9 no.2
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• pp.41-49
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• 2004

Liquid breakup under the variation of AC frequency has been studied experimentally in the electrohydrodynamic atomization. The effect of parameters such as charging voltage, flow rate, nozzle tip inner diameter and power frequency have been considered. This work was performed to investigate the experimental analysis for the effect of AC frequency on breakup process, the mapping of occurrence of disintegration region, and the relationship between the applied power and the droplet radius. The experimental results show that the increase of applied voltage in a certain frequency band leads to a reduction in the droplet size within the limits from 50Hz to 400Hz. The transition phenomena from dripping mode to spindle mode were observed under the band of sudden fall of droplet radius changing ratio, and the synchronous region were produced within the range of applied voltage from 5kV to 6kV.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.1.2-1.2
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• 2011

Electrohydrodynamics is a good approach to produce uniform-sized colloids and fibers in a continuous process. The dimension can be controlled from tens of nanometers to a few micrometers. The structure of the colloids and nanofibers from electrohydrodynamics has been diversified according to the uses. Especially, core-shell structure and hybridization with functional nanomaterials are fascinating due to their possible uses in drug-delivery systems, multifunctional scaffolds, organic/inorganic hybrids with new functions, and highly sensitive gas- or bio-sensors. This talk will present the structural variations in the colloids and fibers by simply employing phase separation during electrohydrodynamic process and demonstrate their possible applications.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.10
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• pp.1841-1846
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• 2008

In this paper, we present the fabrication of microlens by electrohydrodynamic atomization(EHDA) of PDMS prepolymer. The diameter and contact angle of PDMS microlens can be altered by changing the applied voltage and substrate temperature at the experimental setup. It is considered that PDMS microlens can be integrated into the Lab-on-a-chip directly without any photolithographic process by EHDA. The property of PDMS microlens is confirmed by transmitting and measuring the Gaussian beam through microlens.

• Applied Chemistry for Engineering
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• v.27 no.2
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• pp.205-209
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• 2016

The influence of titania nanorods with an average diameter of 10 nm and an average length of 30 nm on the electrohydrodynamic instability of block copolymer (polystyrene-b-poly(2-vinylpyridine)) thin film was investigated in this article. The presence of titania nanorods increased the dielectric constant of the film, which resulted in a systematic reduction in the wavelength of the surface instability. Cross-sectional transmission electron microscopy analysis indicated that the migration/aggregation of titania nanorods did not occur as a result of the applied electric field. This work can provide a simple route to the pattern formation using electrohydrodynamic instability with an aid of nanoparticles.

• Polymer(Korea)
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• v.38 no.1
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• pp.98-102
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• 2014

Nowadays, silk fibroin receives a lot of attention as novel natural biomaterials due to its excellent biocompatibility and biodegradability. Electrohydrodynamic spraying (EHDS) is one of the method for the preparation of micro or nanoparticles by applying high voltage to the polymer solution. In this research, we fabricated silk fibroin porous microparticles by electrohydrodynamic spraying. Poly(ethylene glycol) (PEG) was added to the fibroin solution to give pores to silk fibroin microparticles. By the addition of PEG, the microparticle size was decreased despite of the decrease in conductivity and the increase of viscosity of the spraying solution. It seems that the immiscibility of silk fibroin and PEG affected much more to the microparticle size than the conductivity and viscosity. Immersing the as-sprayed microparticles into the water removed the phase-separated PEG, and finally, porous silk fibroin microparticles were prepared. The porous silk fibroin microparticles are expected to be applied as drug carriers in drug delivery or cell carriers in tissue engineering.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.7
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• pp.923-932
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• 2001

A series of experiments were conducted to generate fine liquid(water) drops through the electrohydrodynamic atomization process. The atomization mode depended on flow rate and DC voltage input. For water, having electric conductivity larger than 10(sup)-7S/m, the spindle mode turned out to be the only mode to generate uniform-size drops within the range of 30-450 microns that have wide applications. Within this mode, both the uniformity and the fineness of drops were improved at an optimum voltage input for a given flow rate. This optimum voltage increased with increasing of the liquid flow rate. Another important parameter considered was the nozzle material with different electric conductivity and liquid wettability. A stainless-steel nozzle (the material with high electric conductivity and high liquid wettability) and a silica nozzle (the electrically non-conducting material with low liquid wettability) were tested and compared; and more uniform drops could be obtained with the silica nozzle.

• Journal of the Korean Society of Visualization
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• v.11 no.1
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• pp.48-52
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• 2013

This paper presents experimental observation of asymmetric electrohydrodynamic flow generated around a pair of symmetric coplanar electrodes. Electrodes are attached on the bottom of the cavity containing a dielectric liquid, i.e., a mixture of dodecane and 0.5% wt Span80. In the first experiment, an AC voltage of 1500 V is applied with the frequency varying in the range 10~500 hz and the left electrode being grounded. The flow patterns show that the center line of vortices is unexpectedly tilted to the left side. If the right side electrode is grounded, the center line is tilted to the right side. The magnitude of the fluid velocity shows an irregular variation with the frequency in the range 10 Hz~100 Hz, beyond which it simply decays. In the second experiment, we applied fixed AC with 1000 V and 60 Hz superposed by DC voltage varying in the range -1000 V ~ +1000 V. The center line of the flow pattern is tilted to the right side with positive DC voltage and to the left side with negative DC. We have managed to show that the flow pattern can be symmetric with a suitable combination of DC and AC, e.g., DC 850 V plus AC 1000 V with the frequency 10 Hz.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.9
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• pp.593-597
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• 2015

Ni ink for electrohydrodynamic (EHD) continuous jet printing has been developed by using Ni nanoparticles mixed with conhesiveness provider. EHD continuous jet printing was used in order to realize $20{\mu}m$ pattern width. Ink stability was investigated by using Turbi-scan which monitors agglomeration and precipitation of nanoparticles in the ink for three days. The Turbi-scan results showed that the formulated Ni ink had been stable for 3 days without any indication of precipitation across the entire ink. Antireflection coating (ARC) layer in crystalline solar cell wafers was removed by laser ablation technique leading to the formation of 84 grooves where the Ni ink was printed by EHD continuous jet printing. The printability and microstructure of EHD-jet-printed Ni lines were investigated by using optical and electron microscopes. 84 Ni lines with the width less than $20{\mu}m$ were successfully printed by one-time printing without any misalignment and fill the laser-ablated ARC grooves.

• 한국전산유체공학회:학술대회논문집
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• 2008.08a
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• pp.30.4-30.4
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• 2008

• Proceedings of the Korean Vacuum Society Conference
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• 1994.02a
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• pp.19-21
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• 1994