Si Bui Quang Tran

Electrospray on superhydrophobic nozzles treated with argon and oxygen plasma

We report on a simple process to fabricate electrohydrodynamic spraying devices with superhydrophobic nozzles. These devices are useful, among other things, in mass spectrometry and printing technology. The superhydrophobic nozzle is created by roughening the surface of the polyfluorotetraethylene (PTFE) by argon and oxygen plasma treatment. We have developed a polymer-based electrospray device with a flat, superhydrophobic nozzle capable of maintaining a high contact angle and stable jetting.

Retreat behavior of a charged droplet for electrohydrodynamic inkjet printing

The charged droplet retreat phenomenon in electrohydrodynamic inkjet printing is experimentally observed and theoretically explained. If the charge concentration of a droplet generated from a nozzle is high enough, Coulomb fission is generated a second time and the main droplet retreats to the meniscus on the nozzle. The retreat phenomenon is due to interactions between the charged droplet, the meniscus, and charges on the substrate. The Rayleigh limit is used to give a theoretical estimate of the amount of charge on the droplet and the meniscus during the retreat.

Semianalytical study of hemispherical meniscus oscillation with an anchored edge on a conductive flat plate under an ac electric field

This paper presents an experimental observation and a semianalytical simulation of the oscillations of an anchored hemispherical liquid meniscus on a conductive flat plate under an ac electric field. For the simulation, the liquid is assumed to be an incompressible, inviscid, and perfectly conductive fluid in a zero-gravity environment. The mutual interaction between the electric field and the hydrodynamics is iteratively solved. As a result, the simulation can follow the oscillating meniscus shapes and contours of the electric field outside the meniscus according to the applied frequency. The velocity profile of the liquid inside the meniscus is also presented. The present theory can be used to predict the oscillation shape of a liquid droplet on a plate with a certain applied frequency. The simulated oscillation shape is in agreement with the experimental result. The effects of the liquid density, the liquid surface tension, and the radius of the hemispherical meniscus on the oscillation are investigate...

Experimental and Numerical Study of Air Entrainment Between Web and Spirally Grooved Roller

This paper presents numerical quasistatic simulation results of the air entrainment phenomenon between a web and a spirally grooved roller. The numerical results show that during one complete rotation of the spirally grooved roller, the traction coefficient between the web and the roller changes with time due to the changing shape of the groove in the contact region, and the average traction coefficient of the circumferentially grooved roller is higher than that of the spirally grooved roller. Using a laser sensor, web deflection is measured and compared with the numerical results at the inlet. Furthermore, a smoke wire experiment shows a clear view of the air entrainment phenomenon at the entrance, between the web and the roller.

Study on super-hydrophobic electro-spray micro thruster and measurement of micro scale thrust

In this article, we fabricated polytetrafluoroethylene(PTFE) nozzle treated by ion beam, in order to fabricate polymer based electrospray micro thruster with super hydrophobic nozzle. To obtain the super hydrophobic surface, PTFE surface is treated by argon and oxygen plasma treatment process. The optimal condition is investigated argon and oxygen flow rate as well as the paalied energy level for the treatment process. Fabricated nozzle was evaluated by measuring contact angle, and the surface morphology was examined by using scanning electron microscope(SEM) and atomic force microscope(AFM). We observe that jetting becomes more stable and repeatable on the treated nozzle. And to evaluate performance of fabricated nozzle, we measure micro scale thrust using a cantilever and a nozzle treated by ion beam laser displacement sensor.

Fabrication and Test of Polymer-Based Electrospray Device

In this paper, interference effect between multi-nozzles has been experimentally investigated for an electrospray device. Array of nozzles is either prepared by electrically conductive stainless steel capillaries and by electrically dielectric nozzle array fabricated using polymer material. The result shows that polymer-based device may reduce or avoid the interference effect when the spacing distance between nozzles is optimized. For a conductive electrospray array, the end effect, which is able to deflect conejets through the outer nozzles of the array due to asymmetric electric field and repulsive forces between adjacent conductive nozzles and the menisi, can be eliminated by using two dry nozzles mounted at the boundary. However, for a polymer-based device, the end effect can be avoided without using extra dry nozzles. In order to eliminate this end effect, a novel ten-nozzle Polymethyl Methacrylate (PMMA)-based electrospray, with inner and outer diameters of 300μm and 500μm, respectively, has been successfully fabricated and evaluated. The performce of the multi-nozzle array device is analysed by measuring the current of the charged droplets through a novel ten nozzles of the polymer-based electrospray device.Copyright