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International audience; Fischer-Tropsch synthesis (FTS) is an essential approach to convert coal, biomass, and shale gas into fuels and chemicals, such as lower olefins, gasoline, diesel, and so on. In recent years, there has been increasing motivation to deploy FTS at commercial scales which has been boosting the discovery of high performance catalysts. In particular, the importance of support in modulating the activity of metals has been recognized and carbonaceous materials have attracted attention as supports for FTS. In this review, we summarised the substantial progress in the preparation of carbon-based catalysts for FTS by applying activated carbon (AC), carbon nanotubes (CNTs), carbon nanofibers (CNFs), carbon spheres (CSs), and metal-organic frameworks (MOFs) derived carbonaceous materials as supports. A general assessment of carbon-based catalysts for FTS, concerning the support and metal properties, activity and products selectivity, and their interactions is systematically discussed. Finally, current challenges and future trends in the development of carbon-based catalysts for commercial utilization in FTS are proposed.

Artificial photosynthesis, the biomimetic approach to converting sunlight's energy directly into chemical fuels, offers an attractive way to address the need for a clean, renewable source of energy. In plants, chloroplasts store the sun's energy using a system of integrated photosynthetic nanostructures including light-absorbing pigments, electron-transport chains, and chemical catalysts. However, neither such integration of nanostructures nor energy conversion efficiency suitable for practical applications has been achieved in artificial photosynthesis. In this context, the subject of my graduate research is to develop an integrated system using nanowire-based nanostructures to imitate natural photosynthesis. This centers on two themes: (1) constructing novel integrated nanostructures for solar-to-fuel conversion, and (2) developing next-generation materials and catalysts for improved photoelectrochemical (PEC) performance.Although natural photosynthesis organizes its active components at the nanometer scale to better control the process of energy conversion, this level of integration had not been realized until recently for artificial photosynthesis. Here the construction of a nanowire-based integrated system to realize such a nanoscopic control is demonstrated. Since all of the processes in PEC relate to the interfaces among semiconductor light-absorbers, electrocatalysts, and the electrolyte, the first to realize an integrated nanosystem was to under how photo-excited carriers would transfer within these interfaces. By using kelvin probe force microscopy (KPFM), the local electrostatic potential of an asymmetric nanowire composed of Si and a TiO2 shell, which was covered in a layer of water. Different local potentials were observed in dark and under illumination, which provides the knowledge that the heterojunction of Si and TiO2 could function as a Z-scheme system for solar water splitting.After obtaining this piece of information, we moved forward to develop an integrated nanosystem for artificial photosynthesis. Taking the concept of Z-scheme, we used Si and TiO2 nanowires as building blocks to construct a tree-shaped heterostructure. In this structure, the positions of the reduction and oxidation components were pre-defined to mimic the spatial control found in chloroplasts. The integrated standalone device splits H2O into H2 and O2 under simulated sunlight, with an efficiency of solar-to-fuel conversion comparable to that of natural photosynthesis. This first demonstration paves the way for using nano-sized building blocks to achieve efficient solar-to-fuel conversion. The nanowire-based integration allows individual building blocks to be replaced with newly developed ones. In this dissertation advanced building blocks for artificial photosynthesis is also demonstrated.We have explored new materials and methods to improve the energy conversion efficiency of semiconductor light-absorbers. Solution-phase synthesis of III-V semiconductor nanowires was successfully demonstrated for photocatalytic reactions, and the nanowires' electronic properties could be fine-tuned to fit the needs of device integration. Also we demonstrated enhancement of the photoanodic activity of hematite (Fe2O3) using the surface plasmon resonance of exquisitely controlled Au nanostructures. Additionally, new electrocatalysts suitable for practical applications are developed. We first looked into the lower limit of platinum (Pt) loading as a catalyst for the H2 evolution reaction (HER). Using the atomic layer deposition (ALD) technique, it is possible to quantitatively controlled the Pt loading down to about 0.2% of a monolayer (~10 ng/cm2), which is sufficient for some PEC applications. Cobalt sulfide, an earth-abundant catalyst, was also synthesized by electrodeposition. It acted as a HER catalyst in water at neutral pH and could be coupled with a Si photocathode for solar H2 production. Moreover we are developing an effective CO2 reduction catalyst of near unity selectivity for acetate production, which could be added into the integrated nanostructure.¬¬¬In conclusion, my graduate research focuses on the integration of nanowire-based structures to achieve more efficient artificial photosynthesis. This is demonstrated in this dissertation not only at system level for an intergrated nanostructure, but also at component level for advanced building blocks. This research can serve as a foundation for the efforts of other researches in the field of artificial photosynthesis.

Geometrical patterns of textured fixed-abrasive pads (T-FAPs) play a key role during the lapping or polishing process, which not only affect the fluid liquidity but also affect the global distribution of fixed abrasives located at the pad surface. However, the T-FAP performance caused by the changed abrasive distribution was seldom revealed and evaluated. As the trajectory distribution on the workpiece surface is mainly determined by the abrasive distribution and machining parameters, the present work intended to evaluate trajectories induced by the different geometrical patterns of T-FAPs and their influences on the lapping process. For this purpose, a test method consisting of T-FAP digital modelling and kinematic analysis was demonstrated. A digital modelling method of T-FAPs was proposed to build T-FAPs containing information of testing abrasives distributed on the pad geometrical surface, and the kinematic analysis was used to obtain trajectories on the workpiece surface. Based on the method, the trajectory profiles and their non-uniformity induced by the specific T-FAP and the non-textured fixed-abrasive pad (NT-TAP) were studied. Validation experiments were carried out in lapping of sapphire slices, using 90 min of lapping time and the distilled water as lubricant. The surface profile, total thickness variation, surface roughness and material removal due to the lapping were measured. The results show that better lapping performance can be reflected by the lower non-uniformity of trajectory (NUT) induced by the geometrical patterns of T-FAPs. The values of NUT influenced by the different T-FAPs were found to be either minimized or maximized according to the specific geometrical patterns on the T-FAP surface, and the maximum value could be up to 0.3 while the minimum value is less than 0.1.

To investigate the characteristic of carbon nanotube (CNT) arrays with high resistance to the hazardous conditions of atomic oxygen in space environment, the erosion effects of atomic oxygen on CNT arrays with different density have been studied by atomic oxygen simulation equipment. To characterizing the change of the surface morphologies of CNT arrays before and after atomic oxygen exposition, A scanning electron microscope (SEM) analysis method have been used. The SEM images shows that the morphologies of the surface of CNT arrays after atomic oxygen experiment are quite different from those before atomic oxygen experiment. The higher density CNT arrays are etched away more uniformly. The erosion yield of the CNT arrays with higher density is much less than that with lower density, which means that the CNT materials have different atomic oxygen erosion yield. The resistance ability of CNT materials to atomic oxygen is depending on their density.

In order to improve the data processing accuracy of multi-spectral thermometry and reduce the error of temperature calculation caused by the increase of temperature measurement range when using BP neural network for data processing, a data processing model based on emissivity ratio for multispectral thermometry is proposed. In this method, the ratio of voltage measurements by adjacent channels is used to replace the ratio of reference temperature, so that the emissivity type can be more accurately distinguished by BP neural network in data processing. The simulation experiment proves that the maximum error of temperature calculation is less than 10K in the range of 1000K ~ 2500K, which greatly improves the accuracy of BP neural network in multispectral thermometry data processing.

High-pressure hydraulic fractures are often reported in real engineering applications, which occur due to the existence of discontinuities such as cracks, faults, or shear bands. In this paper, a hybrid finite volume and extended finite element method (FVM-XFEM) is developed for simulating hydro-fracture propagation in quasi-brittle materials, in which the coupling between fluids and deformation is considered. Flow within the fracture is modelled using lubrication theory for a one-dimensional laminar flow that obeys the cubic law. The solid deformation is governed by the linear momentum balance equation under quasi-static conditions. The cohesive crack model is used to analyze the non-linear fracture process zone ahead of the crack tip. The discretization of the pressure field is implemented by employing the FVM, while the discretization of the displacement field is accomplished through the use of the XFEM. The final governing equations of a fully coupled hydro-mechanical problem is solved using the Picard iteration method. Finally, the validity of the proposed method is demonstrated through three examples. Moreover, the fluid pressure distribution along the fracture, the fracture mouth width, and the pattern of the fracture are investigated. It is shown that the numerical results correlated well with the theoretical solutions and experimental results.

A fabrication method of micro-injection mold cavity for a cell culture device was explored in this paper.Based on the structural characteristics of the micro-injection mold cavity and overlay UV-LIGA technology,a microstructure using appropriate alloy steel as the substrate was fabricated through SU-8 photoresist optical lithography and micro-electroforming technology respectively twice.Then,a micro exhaust duct was etched on an electroforming deposit through mask etching technology.Meanwhile,the swelling problem of SU-8 thick photoresist,poor surface evenness through spin-coating and SU-8 photoresist removal in the experiment process were analyzed,and a method of designing and fabricating a 20 μm wide closed isolation strip around the mask graphics was presented to reduce the volume of SU-8 thick photoresist around the graphics and to improve the swelling deformation of plating mold.By which,the dimension error of the electroforming deposit is from 35 μm down to 10 μm and 300 μm high micro-square-cylinder side wall is steep.The introduction of closed isolation strip improves the dimensional and shape precisions of nickel electroforming deposit effectively and the uses of scraping photoresist and oleum techniques eliminates the edge bead effect and removes SU-8 photoresist completely.As a result,the micro-injection mold cavity with good quality and the high bonding strength between substrate and nickel electroforming deposit is obtained successfully.

The properties of novel supramolecular complex fracturing fluid are discussed in this paper. Based on the supramolecular polymer thickener (SMPT), the thickening system forms a gel with viscoelastic surfactant (VES) wormlike micelles through experimental design. The resultant gel contains very efficient cross-links between the wormlike micelles and polymer chains that can be advantages in elastic and viscous properties of the fluid. The fracturing fluid contains nearly twentieth of conventional surfactant fracturing fluid. Both VES and SMPT synergistically enhance the shear-tolerant property in high-temperature much more than the single. The electron microscopy photos of the solution microstructure and rheological results reveal the suitable ratio of SMPT and VES forms a supramolecular network honeycomb structure, which is built by strong hyper-branched compound structures through noncovalent interactions. Meanwhile, the physical model can legitimately expound the gelation mechanism of the supramolecular viscoelastic gel. Moreover, proppant suspension behavior, gel breaking test and the permeability damage rate of core matrix were studied. Laboratory data showed that the viscosity of new fluid could be maintained above 50 cp with the formation of 0.8%SMPT and 0.5%VES. The steady shear viscosity test has been conducted for 2 hours at 150 °C and 170s−1. Shear restoration experiment proved the new supramolecular viscoelastic fluid was in high viscosity at low shear rate and a strong reversible shear thinning behavior. The dynamic rheological properties showed high viscoelasticity, while elastic modulus was higher than loss moduli at an oscillation frequency 0.01Hz. The result of sand sedimentation experiment with 20% sand ratio was well. The supramolecular viscoelastic fluid was completely broken and gel breaking liquid was transparent with no water insoluble residue. The permeability damage rate of core matrix caused by this fracturing fluid was 20% less than guar fluid. The supramolecular viscoelastic fluid presents in this paper could be a total or partial alternative to VES and guar for hydraulic fracturing whose price is subjected to harvest areas. Results show that the new supramolecular viscoelastic fluid is an effective fracturing fluid satisfies high temperature tight gas reservoir.

To improve the bonding efficiency of microfluidic chips,an in-mold bonding method is researched by taking a Polymethyl Methacrylate(PMMA) microfluidic chip as an research object and a micro injection machine as a working platform.Clamping forces and bonding temperatures are provided by the micro injection machine and a mold temperature machine.Isopropanol is selected as assistant solvent to reduce the bonding temperature and bonding pressure with its solubility.At 30 ℃ to 70 ℃,a microscope and a step profiler are used to analyze the influence of assistant solvent on surface morphologies and micro channel structures of chips at different temperatures.An in-mold bonding experiment is operated with the assistant solvent,then the electric universal testing machine is utilized to measure the bonding strength and to optimize the process parameters.Experimental results illustrate that the influence of isopropanol on bonding quality is related with the bonding temperature and bonding period.The surfaces of chips chap and the micro grooves become deformed or block at higher temperatures.The surface quality and morphologies of micro grooves are correspondingly improved when the bonding temperature is 35 ℃,the bonding time is 5 min,and the bonding strength is no less than 2.64 MPa.

In order to improve the production efficiency,surface quality and reduce the grinding margins of Polycrystalline Diamond(PCD) compact cutting tools,a series of experiments of Low-speed Wire Cutting Electric Discharge Machining(LS-WEDM) for a PCD compact were taken.The PCD compact was cut by the WEDM for five times,then the surface roughness of cutting section,the machining quality of cobalt-rich interface layer and the edge of PCD layer were measured and discussed.The results indicate that the PCD compact shows better surface quality in its cutting section after multiple processing by LS-WEDM,and the machining quality is affected by diamond particle sizes greatly.For two kinds of PCD compacts,CTH025 and CTB010,the surface roughness are Ra=0.85 μm and Ra=0.57 μm,and the depths of the grooves of cobalt-rich interface layer are 16.3 μm and 5.7 μm,respectively.The size of the defect in the edge of PCD compact is matched with that of the diamond particle.The minimum grinding margins of PCD cutting tools can be controlled in 4-15 μm after LS-WEDM.

By utilizing the numerical solution and Finite Element Analysis(FEA) approach,the effect of the air gap beneath a heating membrane on the performemce of a micro heater was calculated and simulated.The thermal convection coefficient was acquired from a heating experiment.Then,a 1D Fourier heat transfer equation was derived.By using the Biot number calculated and the lumped-capacity solution,the model was simplified into a multi-layer thin slab one.Furthermore,the transient temperature response and stable thermal distribution of the air gap in thickness of 0(pure Si substrate),100,200,300,400 μm and completely through(heating membrane) were compared under the conditions of heat convection and heat transfer.Calculation results show the climax temperature has increased approximately 17% by utilizing the heating membrane structure.The results of steady state and transient thermal-electrical coupled field FEA reveal that 200 μm air gap structure indeed enhances the climax temperature to 390 K and reduces the power consumption to 134 mW,which is coherent with the numerical calculation results and experiences.

We report on the observation of a superconducting gap of about 14-15 meV, significantly enlarged compared with the value of 2.2 meV for bulk FeSe, in monolayer FeSe film interfaced with MgO epitaxial on SrTiO3(001) substrate by using the scanning tunneling microscopy. While the MgO exhibits the same work function as SrTiO3 substrate, the gap magnitude is in coincidence with that of surface K-doped two-unit-cell FeSe film on SrTiO3(001), suggesting that the interface enhanced superconductivity might be attributed to cooperation of interface charge transfer driven by band bending with interface electron-phonon coupling as discovered at FeSe/TiO2 interfaces. On the other hand, the observation of such an enlarged superconducting gap, complementary to our previous transport observation of an onset superconducting transition temperature of 18 K in monolayer FeSe film on a bulk MgO substrate, implies that FeSe/MgO interface is likely to be a new interface high-temperature superconducting system, providing a new platform for investigating the mechanism of interface hightemperature superconductivity.

Spherical aberrations of the thermal lens of the active media are severe when solid state lasers are strongly pumped. The fundamental mode proflle deteriorates due to the aberrations. Self-consistent modes of a resonator with aberrations are calculated by using the Fox{Li difiraction iterative algorithm. Calculation results show that the aberration induced fundamental mode beam quality deterioration depends greatly on the resonator design. The tolerance of a ∞at{∞at resonator to the aberration coe‐cient is about 30‚ in the middle of stability, where ‚ is the wavelength of laser beam. But for a dynamically stable resonator, 2‚ of spherical aberration will create difiraction loss of more than 40%, if inappropriate design criteria are used. A birefringence compensated laser resonator with two Nd:YAG rods is experimentally studied. The experimental data are in quite good agreement with simulation results.

Cellular force sensing is an important part of microrobotic cell manipulation systems. In this paper, a micro force sensor capable of providing real-time cell force feedback is proposed. A novel fixed-simply supported force sensing beam structure is first designed. The PVDF (polyvinylidene fluoride) is chose as the sensing element. The mechanical and electrical transformation models are then derived. The performance of the sensor is test with repeatability, linearity and frequency response. Finally, a real-time zebrafish embryo microinjection experiments were conducted. The experimental results showed that the effeteness of the designed sensor in real-time cell microinjection force measure.

UV-LIGA technique is used to fabricate hot embossing mold of PMMA microfluidic chip. Pre-polished Ni plate serves as electroforming substrate and the micro channel is the only structure to be electroformed in the fabricated mold. The precision of the micro channel strongly depends on the process parameters. Experiments show that the width of micro channel varies with the electroforming time. With the electroforming time of 108, 140 and 160 min, the width of micro channel reduces to 89, 86 and 82% of patterned SU-8 mold respectively, which is caused by swelling of SU-8 in acidic, high temperature electroforming solution. This swelling is the key answer to the slope of the sidewalls of the electroformed structure. This study is beneficial to optimizing microfluidic chip mold design.

During the measurement and analysis of micro-total analysis system (μ-TAS), the bulk of the sample injected is about nano-liter, so that the study of microfluidic sensor has been becoming an important aspect of the analytical instrument. According to the principle of the thermal distribution pattern, a microfluidic sensor based on silicon is fabricated with the microelectronic technique and micromechanical process in this paper, including a micro-heater and two temperature sensors. Under the operational mode of the constant heating power, the characteristics of the microfluidic sensor are analyzed. The experimental results indicate that the measurement range of the microfluidic sensor is from 10 to 700 μl/min.

Two compounds have been studied by means of powder diffraction and their unit cell parameters are reported. The monoclinic cell parameters for dimethylgermanyl-bridged bis cyclopentadienyl tetracarbonyl diruthenium are a=11.03(2) Å, b=13.65(2) Å, c=11.609(2) Å, β=105.81(1)°, Z=4, space group P21/n (No. 14), Dx=2.135 mg/m3. The monoclinic cell parameters for λ-dimethylsilyl-dicyclopentadienyl-π, π′-tetracarbonyl diruthenium, are a=11.113(3) Å, b=13.60(1) Å, c=11.674(7) Å, and β=106.00(3)°, Z=4, space group P21/n (No. 14), and Dx=1.946 mg/m3. The cells found for the two compounds are in good agreement with those obtained from single crystal X-ray diffractometry.

The traversal rate for the liquid medium near a point-of-care testing (POCT) device microfluidic channel edge is faster than that through the body of the channel, which makes the fluid front meniscus becomes concave rather than convex or flat. The concave front is unwished due to its influences on quantitative analysis accuracy and the possibility to generate air bubbles. Here, a unique method, named hydrophobic marking line, is demonstrated. This method used a soft pen with hydrophobic ink to draw two lines along the edges of the channel of a POCT device. Results have shown that the marking lines will eliminate the edge effects and generate convex liquid front. The curvature of the liquid front can be changed by adjusting the marking line width or ink solutions.

Power IGBT module is widely used in high power conversion applications in various fields because of the advantages of high voltage and high current applications. In order to avoid the influence of temperature rise to the device measurement, pulse test method is widely used to test its static and dynamic parameters, So there are single high pulse voltage source and single pulse high current source in power IGBT modules test instruments. For now in the metrology field, how to calibrate its Single High Pulse Voltage source is a difficult problem. Now the amplitude of single high pulse voltage source is above 7kV with the pulse width as 50 microseconds. Based on detailed research on the test principles of the power IGBT modules test instruments, the pulse high voltage divider and the data acquisition unit are used to setup a calibration device for Single High Pulse Voltage source to calibrate the amplitude of Single High Pulse Voltage source. Resistors are usedto develop the pulse high voltage divider, and did carefully research on the pulse response time, voltage dispersion, voltage regulation of the pulse high voltage divider. Also the data acquisition unit with 20MHz bandwidth and 100MS/s acquisition rate is evaluated through tests including vertical accuracy test, bandwidth test, rise time test, comparison test and etc.. Through above relevant test results, with the comprehensive consideration of the influence of each measurement uncertainty component, It have finished that the evaluation of the uncertainties of the amplitude measurement for Single High Pulse Voltage source. The uncertainty of measurement is better than 2% with the coverage factor as 2.

Asymmetric property of wedge lens in 3 omega optical path which is used as frequency separation, and focusing element is considered to be an unfavourable factor for target alignment in inertial confinement fusion (ICF). Furthermore, the thickness of wedge lens in 3 omega optical path will lead to laser induced damage inevitably. For the purpose of scheme improvement of final optical assembly, types I and II noncollinear sum frequency generation in KDP crystal at room temperature are discussed based on nonlinear coupled wave theory. As illustrated by simulated result, in addition to type II collinear SFG used in ICF recently, 351 nm (3 omega) waves can be generated by type I or II noncollinear SFG process. This method can realize color separations of omega, 2 omega, 3 omega in far field without asymmetric element such as wedge lens and posses adequate tolerance of matching angle corresponding to the high efficiency conversion. As calculated, for type I SFG, when the noncollinear angle alpha is in the interval from 0 degrees to 19.99 degrees, phase matching condition can be satisfied in KDP crystal. The noncritical phase matching angle theta(3) is 90 degrees and the corresponding noncollinear angle alpha is about 19.99 degrees. The tolerance of mismatching angle is about +/- 20 mrad. For type II SFG, the noncollinear angle interval that can satisfy phase matching process is about 0 degrees-13.55 degrees. Like type I SFG, there is also an noncritical solution in type II process whose matching angle is about theta(3 omega) = 86.53 degrees. Because of the smaller effective nonlinear coefficient in this case, high efficiency conversion needs about 5 cm thick SFG crystal under 1 GW/cm(2). Correspondingly, tolerance of mismatching angle is about +/- 20 mrad. Because of the harsh tolerance of noncollinear angle between omega and 2 omega and for the purpose of compactness of final optical assembly, another method of noncollinear SFG is proposed: a piece of silica wedge with 12 degrees wedged angle is mounted behind the SHG crystal in order to produce a 3.5 mrad intersection angle between ! and 2 omega, and after type II noncollinear SFG process, omega, 2 omega, 3 omega will be frequency separated in far field automatically by using thin lens. The tolerance of incident angle corresponding to high efficient conversion is about +/- 1.0 mrad. This scheme can improve the the final optical assembly used recently.

A novel solid adsorption refrigerator driven by solar energy, which adopted activated carbon fiber and ethanol as its adsorption pair, has been designed. The constant refrigerating process, different components of the machine and the theoretical feasibility analysis of the refrigeration system are discussed in detail. As the adsorbent bed, the rotary ripple board is designed and it is the key part of this rotary solid adsorption refrigerator. In order to increase the utilization efficiency of the low-temperature heat resource such as solar heat and waste heat, structure of the adsorbent bed was optimized to enhance the heat and mass transfer performance of the refrigerant in the adsorbent bed. The mass transfer process during the course of adsorption and desorption is improved due to an increase in the adsorption rate. Results indicate that the solar solid adsorption refrigerating or air conditioning for tropical locations as residential applications is feasible and can replace conventional vapor compression systems, thus reducing the need of energy systems based on fossil fuel for cooling purposes.

The application of plastic microfluidic chips can be extended with quartz capillaries connected at the end of their microchannels, e.g. UV absorption detection method can be carried out, which responds to almost 80% chemical compounds in detection. Experiment system for automatic microassembly was developed to carry out the task of joining capillaries to plastic microfluidic chips. Experiments were done with different viscosity of UV curing adhesives, dispensing time, dispensing pressure and curing time. Suitable process parameters were determined. Visual feedback is employed in the microassembly system. The automatic positioning of capillary with visual information is described. The problems met during assembly are discussed and solved

An automatic fabrication system for batch production of plastic microfluidic chips was developed. The fabricated chips can be used for capillary electrophoresis analysis. The processing technique of chip fabrication mainly includes three steps: microchannel fabrication using hot-embossing technique, precise alignment of the chip's substrate and cover, thermal bonding of the substrate and the cover. Hot-embossing machine, automatic aligning equipment for transparent substrates and thermal bonding machine were developed according to the processing technique. The automatic fabrication system and its constitutional equipments, the embedded processing techniques and auxiliary functions are described and explained in the paper. The auxiliary functions, such as automatic de-embossing and pre-joining of the plastic substrate and cover, are realized for fully automatic fabrication.

Electroosmotic flow is widely used as a primary method of species transport in microfluidic devices. In this work, the characteristics of electroosmotic flow in rectangular microchannels with the hydraulic diameter of 20 /spl mu/m/spl sim/30 /spl mu/m were investigated. Exact solutions for the velocity distribution and electroosmotic flow field are obtained by solving the complete Poisson-Boltzmann equation, describing the net charge field distribution induced by electric double layer next to a charged solid surface, and the Navier-Stokes equation, describing the hydromechanical momentum, under analytical approximation for rectangular microchannel. The simulation results of flows driven by mixed electroosmotic and pressure gradient are given. A method to extract the velocity profile from time sequence images was presented. The experiments consist of accurate observation and the behavior measurement of flow mean velocity by the digital particle images velocity (DPIV) systems. The experimental images of the electroosmotic flows profile under various value of the pressure gradient are consistent with the normalized velocity distribution. The microfluidic velocity were measured and studied as a function of hydraulic diameter ranging from 20 /spl mu/m to 30 /spl mu/m. The flow rate are linearly dependent on applied electric field strength. The linearity errors with standard deviation are (0.0050-0.0202) cm/s. No significant departures from continuum fluid theory have been observed ignoring the temperature changes. Thus, the behaviors of the microfluidic flow, at least down to 30 /spl mu/m diameter, can be predicted by the traditional fluid theory and EDL theory. At the same time, the Joule heating gradient effect caused by the high electric strength must be considered when the channel's dimensional size increase.

Design and fabrication of microfluidic chip on polymethylmethacrylate (PMMA) substrates for analytical chemistry and biomedical-related application using novel microfabrication methods based on automatic fabrication system are described. The image of microchannels is transferred from nickel mold possessing the inverse image of the microfluidic chip to plastic plates by using hot embossing methods. The microstructure on nickel mold is formed based on UV-LIGA technology. In this study, the nickel mold has been made from nickel micro electroforming based on the epoxy-based negative ultra-thick SU-8 photoresist. The micro nickel mold can be used repeatedly to replicate cheap and disposable microfluidic chip. The reproducibility of the hot embossing method is evaluated using 6 channels on different PMMA plastics. The relative standard deviation of the channel profile (depth and width direction) on the plastic chips is less than 2%. In this study, the PMMA microfluidic chips have been demonstrated as a microcapillary electrophoresis device for pharmaceutical separation and detection.