Preparation of uniform microcapsules with silicone oil as continuous phase in a micro-dispersion process.
ABSTRACT This paper presents an improved solvent evaporation method with silicone oil (PDMS) as the continuous phase for preparation of microcapsules to make more polymer solvents available. A microchannel device was used to produce emulsions instead of mechanical stirring to prepare the mono-dispersed microcapsules. Under the conditions of lower evaporation temperature and shorter evaporation time, uniform polyacrylonitrile (PAN) microcapsules containing Aliquat 336 (ALQ) have been successfully prepared. N,N-dimethylformamide (DMF) with lower evaporation ability was applied as the polymer solvent. The prepared microcapsules have rough surfaces and homogeneously internal structures. By changing the two-phase flow rate, the mean size of microcapsules can be easily controlled. When more ALQ was added in polymer solution, the loading ratio of microcapsules increased. The mass transfer performance and stability were determined by extraction of Cr (VI) ions from its aqueous solution. The mass transfer rate was fast enough. After three times of repeated extraction and stripping, the microcapsules kept almost the same extraction ability, which indicated that the microcapsules have very good stability.
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ABSTRACT: Immiscible kerosene-water two-phase flows in microchannels connected by a T-junction were numerically studied by a Lattice Boltzmann (LB) method based on field mediators. The two-phase flow lattice Boltzmann model was first validated and improved by several test cases of a still droplet. The five distinct flow regimes of the kerosene-water system, previously identified in the experiments from Zhao et al., were reproduced. The quantitative and qualitative agreement between the simulations and the experimental data show the effectiveness of the numerical method. The roles of the interfacial tension and contact angle on the flow patterns and shapes of droplets were discussed and highlighted according to the numerical results based on the improved two-phase LB model. This work demonstrated that the developed LBM simulator is a viable tool to study immiscible two-phase flows in microchannels, and such a tool could provide tangible guidance for the design of various microfluidic devices that involve immiscible multi-phase flows.Science China-Chemistry 01/2011; 54(1):244-256. · 1.33 Impact Factor
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ABSTRACT: For further understanding the dispersion process in the T-shaped microfluidic device, a double-pore T-shaped microchannel was designed and tested with octane/water system to form monodispersed plugs and droplets in this work. The liquid–liquid two-phase flow patterns were investigated and it was found that only short plugs, relative length L/w<1.4, were produced. Additionally, the droplets flow was realized at phase ratios (F C /F D) just higher than 0.5, which is much smaller than that in the single-pore T-shaped microchannels. A repulsed effect between the initial droplets was observed in the droplet formation process and the periodic fluctuation flow of the dispersed phase was discussed by analyzing the resistances. Besides, the effect of the two-phase flow rates on the plug length and the droplet diameter was investigated. Considering the mutual effect of the initial droplets and the equilibrium between the shearing force with the interfacial tension, phase ratio and Ca number were introduced into the semi-empirical models to present the plug and droplet sizes at different operating conditions.Microfluidics and Nanofluidics 6(4):557-564. · 3.22 Impact Factor
Conference Proceeding: Simulated I-V characteristics of non-uniformly doped microwave GaAs MESFET's[show abstract] [hide abstract]
ABSTRACT: To enhance the performance of a low-noise microwave GaAs MESFET an appropriate doping profile is required. The I-V characteristics of a microwave GaAs MESFETs with graded channel doping have been simulated by using a non-linear model. It has been shown that a device with a graded channel doping may give transconductance, g<sub>m</sub> at least 4 times greater than the uniformly doped device. This shows a significant improvement in the value of g<sub>m</sub> relative to a device having constant channel doping. Furthermore, a low value of Schottky barrier leakage current was also demonstrated by controlling the doping concentration at Schottky barrier interface. This result in improved low noise performance of the device, and a minimum noise figure less than 2 dB at 20 GHz may be attained in these devices. A conservative estimate shows that a 0.25 μm long and 4×25 μm wide GaAs MESFET, with graded channel doping, may exhibit unity gain frequency greater than 200 GHz. Thus, the proposed device structure could give a significant improvement in the exiting MESFET technology.Vacuum Electronics, 2003 4th IEEE International Conference on; 06/2003