Chong Liu

Dalian University of Technology, Lü-ta-shih, Liaoning, China

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Publications (68)125.97 Total impact

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    ABSTRACT: Silicon insert is a promising tool for microinjection moulding (MIM). However, its fracture problem induced by impact in MIM creates a bottleneck for application. The purpose of this paper is to investigate the impact behaviour in MIM and the effect on the fracture of silicon inserts. The finite element method is utilised to calculate the crack propagation of silicon inserts with pressure load and thermal load in the MIM process. The simulation result shows that the crack propagation is more easily induced by the increase of pressure load, while the temperature change has little effect on the crack propagation. An experimental platform, including a novel rotatable insert mould, is developed to investigate the dynamic pressure in the MIM process. The result shows that both the maximum pressure and the maximum loading rate occur in the initial period of MIM process. It indicates that the silicon insert is more prone to fracture at the beginning of the MIM process, and spatial pressure peaks are observed in the cavity as well. The nearly consistent distribution between the peak positions and the insert fracture zones shows that the pressure distribution is quite relevant to the fracture of the silicon insert. The result is helpful because it reveals the fracture phenomenon of silicon inserts.
    AIP Advances 04/2015; 5(4):041317. DOI:10.1063/1.4905950 · 1.59 Impact Factor
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    ABSTRACT: An external-integrated biomimetic micropump for a microfluidic system is demonstrated. An "artificial leaf" is constituted, which mimics the stomatal transpiration process in plants and utilizes the negative pressure generated to drive the fluid flow. The biomimetic micropump integrated an SU-8 film with a micropore array, agarose gel, a flow rate control unit, and additional necessary operating auxiliaries. SU-8 film with micropores and agarose gel is used to mimic the stomata and the mesophyll cells in a leaf, respectively. The flow rate control unit can change the flow rate of the micropump by adjusting the number of micropores that participate in transpiration. Additional necessary operating auxiliaries can fix a microchip, provide a continuous fluid supply, and speed up the fluid flow rate. Experiments on a microchip are conducted to evaluate the performance of the micropump platform. Results have shown that the flow rate of the micropump can be increased by accelerating the wind speed or raising the temperature. (C) 2014 Society of Photo-Optical Instrumentation Engineers (SPIE)
    Journal of Micro/ Nanolithography, MEMS, and MOEMS 07/2014; 13(3):033008. DOI:10.1117/1.JMM.13.3.033008 · 1.21 Impact Factor
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    ABSTRACT: A novel method for fabricating a three-layer SU-8 mould with inverted T-shaped cavities is presented. The first two SU-8 layers were spin coated and exposed separately, and simultaneously developed to fabricate the bottom and the horizontal part of the inverted T-shaped cavity. Then, a positive photoresist was filled into the cavity, and a wet lapping process was performed to remove the excess photoresist and make a temporary substrate. The third SU-8 layer was spin coated on the temporary substrate to make the vertical part of the inverted T-shaped cavity. The sacrificial photoresist layer can prevent the first two SU-8 layers from being secondly exposed, and make a temporary substrate for the third SU-8 layer at the same time. Moreover, the photoresist can be easily removed with the development of the third SU-8 layer. A polydimethylsiloxane (PDMS) microchip with arrays of T-shaped cantilevers for studying the mechanics of cells was fabricated by using the SU-8 mould.
    Biomedical Microdevices 05/2014; 16(5). DOI:10.1007/s10544-014-9868-y · 2.72 Impact Factor
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    ABSTRACT: Temperature drift error usually exists in the strain-temperature measurement of continuous welded rail (CWR) temperature force. A piece of invar with low (close to zero) coefficient of thermal expansion is used to simulate the actual CWR. Then the temperature drift of the strain sensor node is measured by using a programmable temperature chamber. The temperature drift error is compensated during the monitoring of the temperature force in actual CWR. Results show that the measured temperature force vibration of the CWR is-681kN~149kN and the stress-free temperature vibration is-2.4~1.0°Cwithin a month after temperature drift error compensation. The temperature force and stress-free temperature after compensation meets the stability condition of the CWR.
    03/2014; 541-542:1370-1375. DOI:10.4028/www.scientific.net/AMM.541-542.1370
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    ABSTRACT: A method for fabricating SU-8 moulds on glass substrates is presented. A common thin negative photoresist was coated on the glass slide as an adhesive layer, and then SU-8 was patterned on the adhesive layer. The presence of the adhesive layer improved the lifetime of a SU-8 mould from a few cycles to over 50 cycles. Moreover, the fabrication of the adhesive layer is quite simple and no additional equipment is required. The effects of the adhesion behavior of the negative photoresist and SU-8 on substrates on the durability of the SU-8 mould were investigated. The work of adhesion of the common thin negative photoresist on glass was 51.2 mJ m−2, which is 22.5% higher than that of SU-8 on silicon and 32.3% higher than that of SU-8 on glass. The abilities of the method for replicating high-aspect-ratio microstructures were also tested. One SU-8 mould with 60 × 60 array micropillars with aspect ratios lower than 3 could be used to cast at least 20 polydimethylsiloxane devices.
    Journal of Micromechanics and Microengineering 02/2014; 24(3):035009. DOI:10.1088/0960-1317/24/3/035009 · 1.73 Impact Factor
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    ABSTRACT: A new method for fabrication of micro-nanofluidic devices through photopolymerization was developed and related experimental research on trace enrichment was undertaken. COMSOL software was utilized to calculate and analyze the gel photopolymerization process on microscale. Moreover, a mathematical model of photopolymerization including photoinitiator decomposition, radical consumption, polymerization, etc., was established and the influence of the exposure time and the light intensity on gel nanosieve width was obtained. With an inverted fluorescence microscope, the micro-nanofluidic chip was prepared by integrating pore density-tunable gel nanosieves into specific areas of the microchannels through focusing, beam splitting and other control means. Based on the Poisson-Nernst-Planck model, the process of nanofluid-based electrokinetic enrichment process was simulated numerically, and the relationship between nanopore density and concentration ratio was investigated. By utilizing the prepared chips, the experiments of nanofluid-based electrokinetic enrichment were performed and the enrichment ratio of fluorescein isothiocyanate (FITC) could reach 600-fold when the mass ratio of the monomer acrylamide to the crosslinker N,N'-methylenebisacrylamide is 9:1.
    Chinese Journal of Analytical Chemistry 02/2014; 42(2):166–172. DOI:10.1016/S1872-2040(13)60707-0 · 0.79 Impact Factor
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    ABSTRACT: In this paper, we present a new approach for ion-enrichment and ion-depletion effect (IEID) in micro-nanofluidic chips without external power source. The method utilizes different reducibility of various electrodes in the weak oxidizing solution to generate the electrochemical potential and then induce IEID at a micro-nano junction. The results show that the average gray values of the micro-nano junction based on Al–Pt, Fe–Pt, and Cu–Pt electrodes increase from 14.7 to 40.2, 27.1, 15.0 after 20 s, and electric currents for Al–Pt, Fe–Pt, and Cu–Pt electrodes are 5.0, 2.9 and 0 nA respectively. Metal cations generating from oxidation–reduction reaction and electroosmotic convection flow are evaluated and their influences to IEID can be neglected in this case. The IEID method based on the electrochemical potential is power-free and weak flow convective that will be beneficial to the integrity of micro-nanofluidic chips and stability of IEID.
    Microsystem Technologies 01/2014; 20(1). DOI:10.1007/s00542-013-1887-8 · 0.95 Impact Factor
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    ABSTRACT: A modified biomimetic micropump based on the stomatal transpiration principle is presented. The micropump is designed to have a layer of SU-8 microporous membrane and a layer of hydrophilic microporous ceramics, which reflects the natural plant stomata and mesophyll cells. The evaporation characteristics of the different stomata are analysed qualitatively by an established model. There is a positive connection between the stomata evaporation flux and the micropump flow rate. Corresponding experiments on micropump flow rate are conducted. The presented micropump has favourable assembly and reuse properties. The results indicate that the water vapour distribution in the stomata has a trend of edge effect. It also shows that the fluid flow rate in the micropump changes regularly with the stomata size and spacing.
    Micro & Nano Letters 01/2014; 9(1):41-45. DOI:10.1049/mnl.2013.0554 · 0.80 Impact Factor
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    ABSTRACT: Nanocrystalline nickel was produced by pulse reverse microelectroforming. The pulse microelectroforming was also performed for the comparative purposes. The surface morphology and microstructure of electroformed nickel layers were investigated by scanning electron microscopy and X-ray diffractometry. The microhardness of nickel layers was measured with a Vickers microhardness tester. The friction and wear experiments for nickel layers were performed on a friction and wear tester. The results indicate that the nickel layers prepared by pulse reverse microelectroforming exhibit higher density and their grain sizes in the nanometer range. The nickel layers with fine grains, high microhardness and better wear resistance are obtained at positive current density of 20 A/dm2 and negative current density of 2 A/dm2. The microhardness and wear resistance of nickel layers are improved as the positive and negative current densities are increased.
    Journal of Experimental Nanoscience 01/2014; 9(3). DOI:10.1080/17458080.2012.660547 · 1.04 Impact Factor
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    ABSTRACT: A novel equivalent circuit model of capacitively coupled contactless conductivity detection (C4D) on microfluidic chips is presented. The impedance of the solution in microchannels facing the two electrodes for C4D was first introduced in the model of C4D on microfluidic chips. The electrodes and the solution facing electrodes were divided into individual segments in the model, and the effect of the length of divided segments on the model was studied. A back-calculating method was put forward to calculate the stray capacitance between the electrodes, and the variation between the calculated value and the simulated value was only 6 %. To evaluate the accuracy of the model, a hybrid poly (methyl methacrylate) (PMMA)/polydimethylsiloxane (PDMS) microchip was fabricated and a simple model was built. Compared with the outputs of the simple model, the data predicted by the novel model show a much closer fit to experimental results, and the variations were within 8 % over a wide concentration range of 1–500 μm for potassium chloride.
    Microsystem Technologies 12/2013; DOI:10.1007/s00542-013-1736-9 · 0.95 Impact Factor
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    ABSTRACT: We present a new method to fabricate one-dimensional (1D) nanochannels on a thermoplastic substrate. This method has two main steps. First, a mold with microscale features is used to replicate microchannels on a thermoplastic substrate. Second, the fabricated microchannel is compressed to a 1D nanochannel at a temperature above the glass transition temperature (Tg) of the themoplastics. The effects of compression temperature, compression pressure, retaining time and loading rate on microchannel compression have been studied. Results have shown that a 1D nanochannel of 1–30 μm wide and 200–300 nm deep can be readily fabricated by using this method.
    Microsystem Technologies 11/2013; 19(11). DOI:10.1007/s00542-012-1733-4 · 0.95 Impact Factor
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    ABSTRACT: In this paper, the nanopore density effect on ion enrichment is quantitatively described with the ratio between electrophoresis flux and electroosmotic flow flux based on the Poisson-Nernst-Planck equations. A polyacrylamide gel plug is integrated into a microchannel to form a micro-nanofluidic chip. With the chip, electrokinetic ion enrichment is relatively stable and enrichment ratio of fluorescein isothiocyanate can increase to 600-fold within 120 s at the electric voltage of 300 V. Both theoretical research and experiments show that enrichment ratio can be improved through increasing nanopore density. The result will be beneficial to the design of micro-nanofluidic chips.
    Applied Physics Letters 07/2013; 103(4). DOI:10.1063/1.4816342 · 3.52 Impact Factor
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    ABSTRACT: A method based on OEMD (Orthogonal Empirical Mode Decomposition) and the theory of time-frequency entropy was applied to detect different rail fastener conditions. The original vertical vibration acceleration response of rail under different fastening conditions was obtained from outdoor experiment. The OEMD method was used to get orthogonal IMFs (Intrinsic Mode Functions) of the original vibration signal. The Hilbert time-frequency spectrum was then obtained based on the orthogonal IMFs and corresponding entropy was calculated and compared. The results show that the method is available to detect different rail fastener conditions.
    07/2013; 333-335:1708-1712. DOI:10.4028/www.scientific.net/AMM.333-335.1708
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    ABSTRACT: Monolithic integration of three-material microelectrodes for electrochemical detection on poly (methyl methacrylate) (PMMA) substrates is presented. Au–Ag–Pt three-material electrodes were all fabricated based on polymer compatible photolithography processes, and the fabrication sequence of the electrodes was optimized. The C–Ag–Pt three-electrode system was also demonstrated. To reduce the electrical resistance, the carbon electrode was made on a silver intermediate layer which was simultaneously fabricated with Ag electrodes. A PMMA/poly(dimethylsiloxane) electrochemical sensing microchip with the Au–Ag–Pt three-electrode systems was constructed. The reproducibility of the three-electrode system from single and different microchips was characterized. The performance of the microchip was evaluated by two kinds of electrochemical probes (Ru(bpy)3Cl2 and dopamine).
    Electrochemistry Communications 06/2013; 31:20–23. DOI:10.1016/j.elecom.2013.02.024 · 4.29 Impact Factor
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    ABSTRACT: In this work, an integrated catalyst-coated membrane (CCM) is prepared by successively spray deposit Pt/C nano-suspension, Nafion solution and Pt–Ru/C nano-suspension on a cathode gas diffusion layer using electrohydrodynamic atomization (EHDA) Layer-by-Layer (LbL) deposition. Porous cathode and anode catalyst layers and dense Nafion membrane are deposited using the EHDA LbL deposition technique. It is also found that the EHDA LbL deposited CCM presents close packed structure. An 85 h life test shows that the EHDA LbL deposited cathode electrode side of the integrated CCM still presents well compact feature. Whereas, the delamination of the anode electrode side formed by direct pressing method is evident. The performance of the cell with different methanol concentrations is also examined. It is found that the 3 M methanol concentration gives the highest cell performance. Moreover, the polarization behaviour, methanol crossover and impedance response of the cell at different working temperatures are analysed. The cell performance demonstrates faster increase between 20 °C and 50 °C than between 50 °C and 70 °C. The methanol crossover test shows that the cell presents higher increase level of methanol crossover between 40 °C and 50 °C than other 10 °C temperature increase steps.
    Journal of Power Sources 02/2013; 224:202–210. DOI:10.1016/j.jpowsour.2012.09.092 · 5.21 Impact Factor
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    ABSTRACT: “Reservoir unsealed” and “boundary layer separation” are two main issues in the fabrication of a multilayer poly(methyl methacrylate) (PMMA) microfluidic chip. In this paper, embedded sacrificial layer bonding (ESLB) and laser edge welding (LEW) are presented to avoid them. ESLB is performed by inserting a sacrificial-layer into a reservoir to enhance the transfer of bonding pressure among different layers. LEW is performed by using CO2 laser to weld the edge of a bonded multilayer chip. By using these two methods, a three-layer microchip and a five layer micro-mixer are fabricated. Our results demonstrated that ESLB and LEW can be implemented readily in the fabrication of a multilayer thermoplastic microfluidic chip which may facilitate the development of sophisticated microfluidic systems.
    Journal of Materials Processing Technology 11/2012; 212(11):2315–2320. DOI:10.1016/j.jmatprotec.2012.06.022 · 2.04 Impact Factor
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    ABSTRACT: A polydimethylsiloxane (PDMS) electrophoresis microchip with a thickness-controllable insulating layer for capacitatively coupled contactless conductivity detection is presented. A PDMS film is spin-coated on a glass slide with Pt microelectrodes to be the insulating layer, and then permanently bonded with a PDMS channel plate to make the whole microchip. The thickness of PDMS films can be precisely controlled down to submicrometers. With a microchip with a 0.6 μm-thick PDMS insulating layer, a superior limit of detection (LOD) of 0.07 μM for Na+ was obtained. For comparison, another two microchips with the same design but different insulating layer thicknesses (15 μm and 50 μm) were tested, and LODs were 1 μM and 3 μM respectively, which are almost two orders of magnitude higher. Moreover, the microchip detector also exhibited excellent linearity, reproducibilities and separation efficiencies.
    Electrochemistry Communications 11/2012; 25:147–150. DOI:10.1016/j.elecom.2012.10.012 · 4.29 Impact Factor
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    ABSTRACT: The only way is up! "Bottom-up" construction of a robust chiral porous polymer (JH-CPP) embedded with the Jørgensen-Hayashi catalyst (JH) has been successfully achieved for highly efficient heterogeneous organocatalysis. The high BET surface area, wide openings and interconnected nanopores of JH-CPP increase the accessibility of catalytic sites and as such the catalyst shows excellent activity in catalyzing the asymmetric Michael addition reaction.
    Chemistry - A European Journal 10/2012; 18(22):6718-23. DOI:10.1002/chem.201200753 · 5.93 Impact Factor
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    ABSTRACT: One method of fabricating micro/nanofluidic chips is to form microchannels and nanochannels in different plates and then assemble them together. In this paper, two practicable methods for the assembly of the micro/nanofluidic chips were built up. One was the rotating-then-pushing method (RP) and the other was the picking-up-then-placing-down method (PP). Only an inverted microscope and a few mechanical parts were needed. With the well-assembled chips, the experiments of enrichment and micro/nano-flow were conducted. Relevant devices, processes, and characteristics were presented in detail. These flexible assembly methods present the advantages such as low-cost, flexibility, and interchangeability.
    Microelectronic Engineering 09/2012; 97:1–7. DOI:10.1016/j.mee.2012.02.040 · 1.34 Impact Factor
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    ABSTRACT: In this paper, we present a new approach that is capable of fabricating nanochannels in a poly(methyl methacrylate) (PMMA) substrate. This method, which we call microchannel refill (MR), utilizes the refilling of glassy thermoplastics under thermal compression to reduce a microscopic channel to a nanochannel. It only has two main steps. First, a microchannel is fabricated in a PMMA substrate using normal hot embossing. Second, the microchannel is compressed under a certain temperature and pressure to obtain a nanochannel. We show that a nanochannel with a width as small as 132 nm (with a depth of 85 nm) can be easily produced by choosing the appropriate compression temperature, compression pressure, original microchannel width and original microchannel aspect ratio. Compared with most current nanochannel fabrication methods, MR is a quick, simple and cost-effective way to produce nanochannels in polymer substrates.
    Lab on a Chip 08/2012; 12(20):4059-62. DOI:10.1039/c2lc40078b · 5.70 Impact Factor