ORCID Profile
0000-0003-4181-1291
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Publisher: Elsevier BV
Date: 09-2018
Publisher: IOP Publishing
Date: 18-08-2020
Publisher: Elsevier BV
Date: 09-2022
Publisher: IOP Publishing
Date: 29-07-2020
Publisher: IOP Publishing
Date: 26-02-2019
Publisher: IOP Publishing
Date: 05-05-2020
Publisher: Elsevier BV
Date: 11-2011
DOI: 10.1016/J.JCIS.2011.07.019
Abstract: Low cost pliable electronics portend the advancement of novel inexpensive microfluidic electrochemical devices. In the direct printing approach, the manner of deposition of conductive material from a liquid suspension to ensure electrical continuity is crucial. We describe here an approach in which V-groove networks that make up the path of circuitry are first scribed on non-porous inexpensive surfaces. Liquid drops of carbon nanotube ink are then placed on the surface adjacent to the V-grooves to enable wicking to produce the electrical circuit. This method essentially bypasses the need for inkjet printing. We investigate the basic efficacy of the conductive networks developed using this approach and demonstrate its use in generating electrically driven liquid flow of particles in a simple open capillary channel.
Publisher: Elsevier BV
Date: 05-2021
Publisher: Elsevier BV
Date: 11-2021
Publisher: American Chemical Society (ACS)
Date: 05-10-2010
DOI: 10.1021/LA1028959
Abstract: The transport of liquid droplets on surfaces carrying reactants offers advantages in the creation of fluidic devices crucial for life science applications. In a majority of situations, a selection of these droplets on a surface, rather than all of them, will need to be moved at any one time. It is a formidable challenge to deliver the motive energy source only to specific droplets while leaving the others unmoved. Here, we describe an alternative novel solution of momentarily pinning specific droplets to the surface while allowing the rest to be moved. We demonstrate this concept via the injection of a sizable bubble that is attached to a PTFE surface within a droplet. This then affects the contact line of the droplet, pinning it despite the introduction of an incline that will normally result in sliding. The use of bubbles offers easy release of pinning at will by simple rupture using mechanical means.
Publisher: IOP Publishing
Date: 07-2013
Publisher: AIP Publishing
Date: 08-2020
DOI: 10.1063/5.0002936
Abstract: Pulsed plasma thrusters (PPTs) are attractive micro-thrusters for their advantages such as compactness and lightweight compared to other electric propulsion systems. Accordingly, PPTs have been used in station-keeping, drag makeup, and attitude control for small satellites. Instead of the most common PPT propellant PTFE (polytetrafluoroethylene), hydroxyl-terminated polybutadiene (HTPB) propellant was used and some interesting experimental results were obtained however, the ablation and ionization characteristics of such propellant have never been investigated. In this research, performance experiments using rectangular breech-fed PPT were conducted with HTPB propellant. Mass shot, electrical parameters, and plasma properties were obtained. The ablation process was further analyzed from three perspectives: electrical thermal energy, chemical energy, and ablation energy. The experimental result shows that all mass shots of different HTPB propellants are less than that of PTFE propellant, and the mass shot of HTPB propellant increases with increasing oxidant content. The difference in ablation between HTPB propellant and PTFE propellant could be explained by ablation energy while the difference between HTPB propellants with different proportional compositions could be elucidated by chemical energy. It was observed that the electron densities of these two kinds of propellants were not significantly different. This could be explained by the fact that HTPB propellant produced about three times more electrons than PTFE did even though less mass shot was produced by HTPB propellant.
Publisher: Elsevier BV
Date: 05-2020
Publisher: IOP Publishing
Date: 21-08-2018
Publisher: Springer Science and Business Media LLC
Date: 23-05-2019
Publisher: American Chemical Society (ACS)
Date: 26-10-2011
DOI: 10.1021/LA203247Q
Abstract: The commonly used sessile drop method for measuring contact angles and surface tension suffers from errors on superhydrophobic surfaces. This occurs from unavoidable experimental error in determining the vertical location of the liquid-solid-vapor interface due to a camera's finite pixel resolution, thereby necessitating the development and application of subpixel algorithms. We demonstrate here the advantage of a pendant bubble in decreasing the resulting error prior to the application of additional algorithms. For sessile drops to attain an equivalent accuracy, the pixel count would have to be increased by 2 orders of magnitude.
Publisher: The Optical Society
Date: 10-01-2011
DOI: 10.1364/OL.36.000175
Publisher: IOP Publishing
Date: 24-12-2018
Publisher: American Chemical Society (ACS)
Date: 03-2011
DOI: 10.1021/LA104982P
Abstract: Computational and theoretical models of millimeter-sized bubbles placed on upright hydrophobic and superhydrophobic surfaces are compared with experimental data here. Although the experimental data for a hydrophobic surface corroborated the computational and theoretical data, the case of a superhydrophobic surface showed the bubbles to be able to contain significantly larger volumes than predicted. This is attributed to the greater ability of the bubble contact line to advance compared with its tendency to detach from the surface because of buoyancy. We surmise that a static model therefore describes only an unstable equilibrium for these bubbles, which unless heavily isolated from external influences are more likely to assume a larger stable size.
Publisher: American Chemical Society (ACS)
Date: 10-12-2012
DOI: 10.1021/LA303375V
Abstract: Droplet-based microfluidics is inherently based on the ability to control the motion of liquid drops. In most situations, drops are required to be controlled in idually. Here, we examine how the rupture of an encapsulated bubble causes the detachment of a drop previously pinned on an incline. When the drop is located on a horizontal surface with a low liquid-solid adhesion energy (such as water on a superhydrophobic surface), the entire drop is propelled vertically off the surface without the input of an external energy source. From an energy balance, we determined that the majority of the stored surface energy is consumed by the formation of a large jet. When a surfactant is introduced into the system, the adhesion energy is then too large to overcome, resulting in a pinned oscillating drop. We also show that the process can be used to selectively cause drops to slide (at usually stable inclines) on a hydrophobic surface. The required sliding angle was decreased by almost 20° for a 48 μL water drop and a 10 μL bubble. This process enables the selective pinning and depinning of drops, a method that may prove useful for future droplet control techniques.
Publisher: Elsevier BV
Date: 02-2011
DOI: 10.1016/J.JCIS.2010.11.027
Abstract: The ability of a liquid droplet to move on an incline has important ramifications in discrete volume fluidic devices. By taking advantage of the spontaneous and copious formation of visible air bubbles within water droplets on a polytetrafluoroethylene (PTFE) surface, we uncovered a direct correlation between their presence and the ability of droplets to slide down an incline. We forward two possible mechanisms to account for this behavior. The first is attributed to the air bubbles creating regions where additional solid-liquid-vapor phase interfaces are present wherein due to the buoyancy force acting upwards, the orientation of the contact angles of each bubble (which should also be in hysteresis but in the opposite direction of the hysteresis at the droplet rim contact lines) dictate that the net force of the bubbles in the droplet act down an incline. We show here that this mechanism cannot fully account for the bubble enhanced sliding behavior. The second mechanism is based on the occurrence of the droplet front advancing first, causing the droplet to elongate and thus allowing the receding contact line to partially sweep inwards over the bubbles. This causes a series of point-wise disruptions on the contact line that permits the droplet to slide down more readily. The relatively short time of ∼180s during which these micron sized bubbles decrease in size indicates a possibility of this mechanism contributing to a transient means to reduce the retention force of droplets that reside on hydrophobic surfaces.
Publisher: Elsevier BV
Date: 08-2022
Publisher: Elsevier BV
Date: 12-2020
Publisher: IOP Publishing
Date: 26-08-2020
Publisher: IOP Publishing
Date: 05-08-2020
Publisher: IOP Publishing
Date: 26-03-2020
Publisher: Elsevier BV
Date: 08-2020
Publisher: IOP Publishing
Date: 15-10-2018
Publisher: IOP Publishing
Date: 12-2021
Abstract: Electric propulsion offers the advantage of a high specific impulse through a large exhaust velocity and has seen significant progress in space flight applications. Recently, we observed a transient plasma shockwave during pulsed plasma thruster operation when the plasma beam impacted a probe surface. However, details regarding the plasma shockwave formation are still unknown. This work is an experimental investigation of the compression-induced plasma shockwave in the presence of a planar obstruction. To study the complete shockwave buildup and dissipation process, an ultra-high-speed imaging system was set up to visualize the time-resolved shockwave morphology at a sub-microsecond level. In addition, the local magnetic field and plasma density were measured using 2D magnetic coils and a triple Langmuir probe, respectively. The successive images of the shockwave give us a comprehensive understanding of the shockwave buildup process. During the 12 μ s operational period of the thruster, two shockwaves were formed during the first cycle of the discharge. It is also interesting to note that there is a 1 μ s dissipation period between the two shockwaves with the same cloud of plasma compressing against the probe surface. A shockwave model is also developed to predict the appearance of the two shockwaves. The implication is that the local magnetic field strength can be a key indicator for the plasma shockwave buildup and dissipation process.
Publisher: AIP Publishing
Date: 15-02-2017
DOI: 10.1063/1.4975349
Abstract: In the past several decades, the use of electric propulsion in spacecraft has experienced tremendous growth. With the increasing adoption of small satellites in the kilogram range, suitable propulsion systems will be necessary in the near future. Pulsed plasma thrusters (PPTs) were the first form of electric propulsion to be deployed in orbit, and are highly suitable for small satellites due to their inherent simplicity. However, their lifetime is limited by disadvantages such as carbon deposition leading to thruster failure, and complicated feeding systems required due to the conventional use of solid propellants (usually polytetrafluoroethylene (PTFE)). A promising alternative to solid propellants has recently emerged in the form of non-volatile liquids that are stable in vacuum. This study presents a broad comparison of the non-volatile liquid perfluoropolyether (PFPE) and solid PTFE as propellants on a PPT with a common design base. We show that liquid PFPE can be successfully used as a propellant, and exhibits similar plasma discharge properties to conventional solid PTFE, but with a mass bit that is an order of magnitude higher for an identical ablation area. We also demonstrate that the liquid PFPE propellant has exceptional resistance to carbon deposition, completely negating one of the major causes of thruster failure, while solid PTFE exhibited considerable carbon build-up. Energy dispersive X-ray spectroscopy was used to examine the elemental compositions of the surface deposition on the electrodes and the ablation area of the propellant (or PFPE encapsulator). The results show that based on its physical characteristics and behavior, non-volatile liquid PFPE is an extremely promising propellant for use in PPTs, with an extensive scope available for future research and development.
Publisher: AIP Publishing
Date: 03-07-2017
DOI: 10.1063/1.4991713
Abstract: Pulsed plasma thrusters (PPTs) are a form of electric spacecraft propulsion. They have an extremely simple structure and are highly suitable for nano/micro-spacecraft with weights in the kilogram range. Such small spacecraft have recently experienced increased growth but still lack suitable efficient propulsion systems. PPTs operate in a pulsed mode (one discharge = one shot) and typically use solid polytetrafluoroethylene (PTFE) as a propellant. However, new non-volatile liquids in the perfluoropolyether (PFPE) family have recently been found to be promising alternatives. A recent study presented results on the physical characteristics of PFPE vs. PTFE, showing that PFPE is superior in terms of physical characteristics such as its resistance to carbon deposition. This letter will examine the electrical discharge characteristics of PFPE vs. PTFE. The results demonstrate that PFPE has excellent shot-to-shot repeatability and a lower discharge resistance when compared with PTFE. Taken together with its physical characteristics, PFPE appears to be a strong contender to PTFE as a PPT propellant.
Publisher: Elsevier BV
Date: 03-2021
Publisher: AIP Publishing
Date: 15-11-2011
DOI: 10.1063/1.3662191
Abstract: Discrete microfluidics offers distinct advantages over continuous microfluidics since the need for flow presents significant problems. Here, we demonstrate a method of achieving the gentle transfer of liquid s les between two capillaries with the use of air actuation which limits flow and is amenable to automation. Since the stability of liquid bridges is in operation, there is a relationship established between the gap distance and the liquid volume, thereby resulting in three physical response types that were identified. Only one of these allows for efficient liquid transfer. We advance a model for the optimal gap distance and show that it is in good agreement with the experimental data. During the process of liquid transfer, favorable mixing is also achieved.
Publisher: IOP Publishing
Date: 15-12-2017
Location: Australia
No related grants have been discovered for William Ling.