Key Engineering Materials Vols. 609-610

Abstract: In this paper, we fabricated a novel multilayer microfluidic device with vertical embedded electrodes. The device was composed of printed circuit board (PCB) substrate with vertical embedded electrodes, the polyimide insulating layer and the polymethyl methacrylate (PMMA) with micro structures. The vertical electrodes were made by metal wire and integrated on the PCB substrate, they can be replaced when fail or broken. In addition, we investigated the relationship between electrodes height and the electro-osmotic flow by using numerical simulation. The results show that, with the increase electrodes height inside the microchannel, the speed of electro-osmotic flow increased and concentration field distribution improved significantly.

Abstract: We research removable electrodes based on microfluidic chip in this paper. The electrodes can be assembled and fixed quickly and easily. We could change toxic electrodes conveniently during experiment. In addition the design of removable electrodes fits different size of channels, because the detection electrodes could be set its position close to outlet of microchannel under the microscope. We provide numerical simulations of COMSOL and hotomicrographs to proving our design in this article.

Abstract: We discuss the effect of joule heat which comes from eletroosmosis flow on the microfluidic chip. Our microfluidic chips are fabricated from polymethyl methacrylate (PMMA). As everyone knows, PMMA is a poor conductor of heat, and its transfer coefficient is only 0.19W/m·K in room temperature. So, the heat is generated by eletroosmosis canʼt conduct outside the microchannels of microfluidic chip easily. We research the effect joule heat on walls of microchannels which are made of PMMA. During our study, interior surface of microchannelsʼ hydrophobicity is changed by effect of joule heat.

Abstract: Dynamic characteristics of micro bubble are the key for its applications. A thermal bubble is produced on the wall of microchannel with flowing fluid. Generation of bubble, including nucleation and growth, is observed and measured with different volume flow rates. The results show that nucleation becomes more difficult and instable with volume flow rate increasing. Bubble growth could be divided into three stages, while the second stage becomes shorter and even disappears as volume flow rate increasing. When volume flow rate increases suddenly, bubble shrinks, and it is more remarkable for larger volume flow rate. Furthermore it needs more time for bubble to reach and keep the minimum volume.

Abstract: Effect of wall slip on melt filling flow behaviors in micro injection molding are investigated based on analysis of wall slip mechanism for polymer melt flowing at filling stage. By means of comparisons, slip coefficients in different microchannels are confirmed. With finite element method, the relationship between slip velocity and inlet flow rate or length-diameter ratio is analyzed. The results indicate that the wall slip happen for polymeric melt in microchannels, and slip coefficients are related with the size characteristics of microchannels. Moreover, wall slip velocity has the size effect and increase with the decrease of the section size of microchannels, which cause melt velocity distribution to smooth. At the same time, slip velocity is proportional to length-diameter ratio of microchannel, namely when wall shear stress is uniform, the slip velocity rises with increasing length-diameter ratio of microchannel.

Abstract: The nonlinear characteristic is the one of essential characteristics about the magnetic fluid. The orthogonal stationary magnetic field is caused by the mutual orthogonal DC. According to the grads of magnetic field in the area filled with magnetic fluid, the magnetic density of magnetic fluid changes with the grads of magnetic field. With the increasing magnitude of DC, the magnetic density of magnetic fluid can be increased. Error of the measured voltage wll be increased as the volume of the changing rate of DC increasing.

Abstract: In this paper, jetting behavior of two immiscible liquids, water as the outer liquid and silicone oil as the inner liquid in typical flow focusing microchannels were numerically studied using VOF method. At low capillary number, uniform microdroplets were obtained by the absolute instability. With the increasing of fluid flow ratio, the jet is thinner and tends to break up further away the cross junction. The results showed that the flow rate ratio is the main factor that influences the microdroplet sizes, while the frequency of microdroplets formation can be controlled mainly by the surface tension when it is in the jetting regime.

Abstract: The bubbles in the microfluidic based electro-spray ionizing chips seriously affect the performance of the system. This paper presents a bubble capture method to stabilize the current of the microfluidic based electro-spray ionizing sources. A bubble capture structure was introduced to collect the bubbles. A normal close clamp valve assured a suitable pressure in the bubble capture structure that no liquid in the microfluidic channel can enter; when the bubble capture structure was filled with gas bubbles, the clamp valve was opened to release the bubble and balance the pressure. The results indicated that the current fluctuation, which reflects the stability of the electro-spray ionizing devices, was below 1.8% during the stable cone-jet electro-spray stage (2000V~4500V) for the proposed system, which was a notable improvement comparing with normal microfluidic-based electro-spray ionizing chip without the bubble capture structure.

Abstract: Trapping and positioning of single cells has played a major role in various fields of bioengineering, such as cell screening, analysis, induction and pathologic diagnosis, etc. In this work, we report a new non-contact microfluidic-based method for single cells trapping and positioning. A pair of microtubes of same specification is symmetrically placed on opposite sides of the cell. When fluid flowing through microtubes squirts in the same velocity toward the cell, the cell will be immobilized and clamped due to symmetrical fluid pressure generated around it. Feasibility of the reported method is validated by experiments. This method is also capable of trapping and positioning micro particles.

Abstract: We present a tunable wavelength filter in plasmonic metaldielectricmetal (MIM) side-coupled-cavity waveguide with optofluidics pump system proposed to realize tunable mechanism. The peak wavelength can shift by manipulating the length of liquid column and the effective refractive index. The finite difference time domain method is used in the numerically simulated experiment and the resonant wavelengths from 1000 to around 1800nm had been analyzed. The results reveal that the resonant wavelengths are proportional to the liquid volume length and refractive index of liquid in the cavity. This waveguide filter can be used in integrated optical circuits.