Research On The Bubble Dynamic Characteristics And The Wettability Control Technology In Microchannels

With the development of micro/nano meter technology, bubble technology is playing a remarkable role in biomedical science, chemical engineering, national defense and military and many other fields. As the key point of realizing the bubble technology is how to control the bubble dynamic characteristics. In this dissertation, the effects of the microchannel configuration on bubble dynamics and the controlling technology of wall wettability were systematically studied, which can provide technique support for the design of microfluidic system. The main works are as follows.The processes of bubble generation in the micro T-junction were recorded by the high speed camera system, and the influences of the flow velocity, the gas-liquid flow radio and the channel size on bubble dynamics were emphatically investigated. The results show that, there are four generation patterns for bubble generation, and the corresponding mechanisms of bubble generation are squeezing, shear, compound of squeezing and shear, and wall resistance. Moreover, with the increase of the flow velocity, the gas-liquid flow radio and the channel size, bubble's size increases.With the use of the high speed record technology and the computational fluid dynamics, bubble dynamics in micro T-junction, Y-junction and venturi were researched, respectively. After research, we can reveal the following principles. The two main mechanisms of the bubble breakup in micro T-junction and Y-junction are the channel structure and the flow field. While, when bubbles move in the venturi, their breakup mechanism is the flow field. The intensity of the bubble breakup or deformation increases with the increase of the flow velocity, and decreases with the increase of the bubble size and the channel size.By using the technology of laser manufacture and self-assemble, micro channels with different wall wettabilities were obtained. In addition, the moving processes of bubbles in the microchannel were recorded by the high speed camera system. The effects of the flow velocity and the wall wettability on bubble dynamics were emphatically studied, and the following results can be obtained. With the increase of the flow velocity, the dynamic contact angle and its ratio between channel's two sides decrease. There is a one to one relationship between the dynamic contact angle ratio and the wettability of the left wall, and the relationship can be used as a method to evaluate the wettability of microchannel's walls.Hydrophobic/superhydrophobic surfaces whose wettability can be controlled, were designed and produced by the assembled slice technique and the self-assembled mono-layer technique. The wettabilities of the controllable surface with different micro-rib heights were measured by the contact angle meter. After measurement, the main characteristics of the controllable surfaces are brought to light. With the precise control of the micro-rib's height, the wettability of the controllable surface can be easily changed between weak hydrophobic and strong hydrophobic or even superhydrophobic, and the effect of the wettability control is continuous.After being improved, the controllable surfaces were applied into the microchannels. Then, the effects of the flow velocity and the wall wettability on dynamic contact angle of bubble were studied in detail. The following results are contained. By changing the structure of micro-rib, the contact state of the gas-liquid-solid phase changed, and then the wettability also changed. The wettability of the controllable surface can be reversibly changed between strong hydrophobic and hydrophilic. Moreover, there is an effect of the flow velocity and the walls'thickness on wettability control and bubble's dynamic contact angle.