Browsing by Author "Cao, Yuanzhi"

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    A 3D microfluidic device fabrication method using thermopress bonding with multiple layers of polystyrene film
    (IOP, 2015-05) Cao, Yuanzhi; Bontrager-Singer, Jacob; Zhu, Likun; Department of Mechanical Engineering, School of Engineering
    In this article, we present a fabrication method that is capable of making (3D) microfluidic devices with multiple layers of homogeneous polystyrene (PS) film. PS film was chosen as the primary device material because of its advantageous features for microfluidics applications. Thermopress is used as a bonding method because it provides sufficient bonding strength while requiring no heterogeneous bonding materials. By aligning and sequentially stacking multiple layers (3 to 20) of patterned PS film that were achieved by a craft cutter, complicated 3D structured microfluidic devices can be fabricated by multiple steps of thermopress bonding. The smallest feature that can be achieved with this method is approximately 100 μm, which is limited by the resolution of the cutter (25 μm) as well as the thickness of the PS films. Bonding characteristics of PS films are provided in this article, including a PS film bonding strength test, bonding precision assessment, and PS surface wettability manipulation. To demonstrate the capability of this method, the design, fabrication, and testing results of a 3D interacting L-shaped passive mixer are presented.
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    DEVELOPMENT OF A MICROFLUIDIC GAS GENERATOR FROM AN EFFICIENT FILM-BASED MICROFABRICATION METHOD
    (Office of the Vice Chancellor for Research, 2015-04-17) Cao, Yuanzhi; Bontrager-Singer, Jacob; Zamani Farahani, Mahmoud R.; Meng, Dennis D.; Yu, Whitney H.; Zhu, Likun
    Recently, tape&film based microfabrication method has been studied for rapid prototyping of microfluidic devices due to its low cost and ease of fabrication [1]. But most of the reported film-based microfluidic devices are simple single-layer patterned 2-dimentional (2D) designs, whose potential applications are limited. In this paper, we present the design, fabrication and testing results of a 3-dimentional (3D) structured microfluidic gas generator prototype. This gas generator is used as an example to introduce our new approach of film-based fabrication method towards lab-use microfluidic research, which usually requires constant change of design and prefers low fabrication cost and short fabrication period. The prototype is a film-based comprehensive microfluidic gas generator which integrates self-circulation, self-regulation, catalytic reaction, and gas/liquid separation. Time and economy efficiency are the biggest merit of this method. The only required facility during the whole process is a digital craft-cutter. The working principle of the device is illustrated in Fig.1 [2]. The film-based prototype is an alternate version of the silicon-based self-circulating self-regulating gas generator developed by Meng [2]. Fig.2 shows the schematic of the filmbased prototype. It consists of 15 layers of films, tapes, glass slide, tubing connectors, and cube supporting. As shown in Fig.3, the prototype device was obtained by sequentially aligning and stacking multiple layers of patterned films and double-sided Kapton tape. The patterns were obtained by a digital craft-cutter from CAD drawings. The 3D structure was made from both the pattern and the thickness of the layer material, as shown in Fig.4. Besides, functional features can be easily added into the device. For instance, Pt-black was partially sprayed on the tape layer for catalytic reaction using a shadow mask, and nanoporous membrane was cut in the desired shape and stack-placed in position as the gas/liquid separator. The self-circulating and self-regulating functions were achieved by capillary force difference in different channels as shown in Fig.4, which can be achieved by fabricating different channel depths and treating the surface of certain channel into hydrophilic and leave others hydrophobic. The treatment for polystyrene (PS) film was achieved by spraying Lotus Leaf® hydrophilic coating or using oxygen plasma machine [3]. The fabricated device was tested with H2O2 solutions (for O2) and NH3BH3 solutions (for H2) at different concentrations (Fig.5). A pressure difference (1 psi) was applied across the gas/liquid separation membrane to provide better venting. The gas generation profiles are shown in Fig.6 and the summarized characteristics is given in Table 1. The generated gas flow rate is measured by a gas flow meter, and liquid pumping rate measured by monitoring the movement of a liquid/gas meniscus. Fig. 6 shows that higher reactant concentration causes higher gas generation rate. The fluctuation of gas generation rate is due to the pulsatile pumping of this self-pumping mechanism. It is expected that designs with multiple parallel channels can make the gas generation profile smooth due to the interactions among the channels. Detailed characterization results and discussion on reaction kinetics and pumping dynamics in the microfluidic reactor will be reported.
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    Development of a microfluidic gas generator from QQQAN efficient film-based microfabrication method
    (MicroTAS, 2014-10) Cao, Yuanzhi; Bontrager-Singer, Jacob; Zamani Farahani, Mahmoud R.; Meng, Dennis D.; Yu, Whitney H.; Zhu, Likun; Department of Engineering Technology, School of Engineering and Technology
    We report the development of a microfluidic gas generator using polymer film-based microfabrication method. The method is time and cost efficient and capable of fabricating microfluidic devices with feature resolution lower than 100 μm. Complicated 3-dimentional devices can be fabricated by aligning and stacking multiple layers of patterned polymer (polystyrene, polycarbonate) films and double-sided tapes which are obtained from a digital craft-cutter. Integrated with functional features like Pt catalyst, the device can generate a variety of gas (O2, H2, etc) through controllable catalytic reaction.
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    Study on coalescence dynamics of unequal-sized microbubbles captive on solid substrate
    (Elsevier, 2018-11) Zhou, Shuyi; Cao, Yuanzhi; Chen, Rou; Sun, Tao; Fezzaa, Kamel; Yu, Huidan; Zhu, Likun; Mechanical Engineering, School of Engineering and Technology
    The dynamics of bubble coalescence are of importance for a number of industrial processes, in which the size inequality of the parent bubbles plays a significant role in mass transport, topological change and overall motion. In this study, coalescence of unequal-sized microbubbles captive on a solid substrate was observed from cross-section view using synchrotron high-speed imaging technique and a microfluidic gas generation device. The bridging neck growth and surface wave propagation at the early stage of coalescence were investigated by experimental and numerical methods. The results show that theoretical half-power-law of neck growth rate is still valid when viscous effect is neglected. However, the inertial-capillary time scale is associated with the initial radius of the smaller parent microbubble. The surface wave propagation rate on the larger parent microbubble is proportional to the inertial-capillary time scale.
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    Understanding Microbubble Coalescence Using High-Speed Imaging and Lattice Boltzmann Method Simulation
    (Office of the Vice Chancellor for Research, 2016-04-08) Zhou, Shuyi; Cao, Yuanzhi; Chen, Rou; Chen, Chuanyi; Yu, Huidan (Whitney); Zhu, Likun; Sun, Tao
    Microbubble coalescence is one of the important research areas of bubble dynamics. The purpose of this research is to seek deeper understanding and relative mathematical relation on microbubble coalescence. To fulfill that, we conducted both experiments and simulations. For the part of experiment, we fabricated a microfluidic gas generator with better performance leading corresponding fluidic chemical reaction. After that we utilized ultrafast synchrotron X-ray imaging facility at the Advanced Photon Source of Argonne National Laboratory to capture the gas generating and microbubble merging phenomena using high speed imaging. These experiments show how the microbubbles with the same ratio contact and merge in the reaction channel and different concentration of reactants. As for the part of simulation, we lead the simulation basing on lattice Boltzmann method to simulate microbubble coalescence in water with unequal diameter ratio. Focuses are on the effects of size inequality of parent bubbles on the coalescence geometry and time. The “coalescence preference” of coalesced bubble closer to the larger parent bubble is well captured. A power-law relation between the preferential relative distance and size inequality is consistent to the recent experimental observations. Meanwhile, the coalescence time also exhibits power-law scaling, indicating that unequal bubbles coalesce faster than equal bubbles.