Study On Surface Tention Driving And Self-motion Behaviors Of A Liquid Droplet

In recent years, the preparation of microfluidic driving technology has attract more and more attention, and controllable surface wettability plays a key role in its realization. In this thesis, we fabricated surfaces with gradient surface energy by VUV irradiation, which can make liquid droplets move on it. Then the movement of different liquid on gradient surfaces was studied in detail. Finally, it was studied that the characteristics of reversible change between superhydrophilic and superhydrophobic on ZnO film. The result revealed that:(1) Along with the illumination time increasing, the etching strengthened gradually, which resulted in the decreasing of contact angle and the increasing of surface energy. Base on this effect, surfaces with gradient surface energy were prepared on FAS-SAM.(2) The droplet could move from low surface energy regions to the high ones. The motion of the droplet on the gradient surface was divided into the accelerating stage and the decelerating stage. The change of contact angle was about 39°in the range of 4.23mm, which is from 55.82°to 16.74°. The maxium velocity of the water droplet (2μl) is about 23.28mm/s.(3) The velocity of droplet was proportional to the size of the liquid droplet and was inversely proportional to the velocity of the baffle. That is to say, the larger of the drop size was and the slower of the baffle moved, the quicker of the droplet moved. In addition, the velocity of droplet on the horizontal surface was larger than that on the inclined surface, the velocity of water was larger than the velocity of the form amide droplet and the diglycol droplet on the same horizontal surface.(4) The gradient surface also could be fabricated by changing the illumination distance. The movement station was similar to that fabricated by changing the illumination time.(5) The gradient surface also could be fabricated on ODS-SAM surface and FAS-SAM surface, but the droplet could not move spontaneously.(6) The ZnO film was hydrophilic in the beginning. After stored in the dark for many days or heated by low temperature, the film could turn to hydrophobic state ; then treated by vacuum ultraviolet (VUV) or high temperature, the ZnO film would be superhydrophilic with the contact angle of 0°. That is to say, this film could be reversed between hydrophilic and hydrophobic state. It has been demonstrate that the critical temperature of wetting transition was 165℃. This ZnO film can fabricate gradient energy surface.Surface tension-driven has many potential applications in MEMS. The research about Surface tension change controllably and droplet motion will be significant for our study of MEMS.