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Recently, microfluidic devices have been actively studied in varieties of fields such as chemical, biological, and analytical industries [1-3]. The micro channel and tube application are recognized important key technologies. In functional microchannel fabrication, it is required to design some corrugated surfaces or some pillars at an intersection among microchannels. In this regard, environmental scanning electron microscope (ESEM) is an effective system in order to evaluate wetting phenomena in a microstructure. In this paper, we discuss the effects of a pillar type sub-pattern for guiding liquid propagation at the junction of the microchannel by the ESEM observation. On the points of Young-Laplace equation and pinning effect, we focus on the effectiveness of a sub-pattern of controlling the liquid flow in the microchannel network. In this experiment, Vand T-shaped junctions of microchannel were formed by photolithography. In the V-shaped microchannel fabrication, a glass substrate was cleaned up with organic solvents prior to photolithography. As a channel material, negative type dry film resist (DFR) (NCP250, the Nippon Synthetic Chemical Industry Co., Ltd.) of 50μm thickness was employed. Then, the DFR film was laminated on the glass substrate. Pattern development was carried out by dipping into a sodium hydroxide aqueous solution for 40s. The width and height of the micro channel becomes 10 and 50 μm, respectively. The corner angle of V-shape channel was 40 degree. In the case of T-shaped microchannel, a Si substrate was cleaned up with organic solvents. The microchannel was formed with SU-8 photoresist (3050, Kayaku Chemical Corp.) by the typical photolithography process. The details of fabrication processes are described in our previous report [3]. The width and height of the channel became 100 and 50 μm, respectively. At the channel junction, a pillar shape sub-pattern was designed at the left side position in the junction. The diameter and height of the pillar were 60 and 50 μm, respectively. The in-situ observations of water condensation and propagation in the Vand T-shaped microchannels were carried out using a ESEM (XL30: Royal Philips). A peltier cooling stage is equipped in order to control the sample temperature around water dew point. The microchannels were cooled at around 0 °C, then relative humidity on the surface of the samples reached to a saturation condition. The vaporized distilled water progressively condense on the whole area of the sample surface. Figure 1 shows the time-lapse ESEM images of the water propagation in the V-shaped channel. In Fig. 1a, a slight amount of water condensed in the V-shaped corner at which the channel area is relatively wide. Then, the water meniscus forms in the channel and propagates from each side toward the corner as shown in Fig. 1b. In this case, the condensed water at the channel corner was disappeared. Finally, as shown in Fig. 1c, the

Effect of Sub-Pattern on Guiding Liquid Propagation at Microchannel Junction