| Summary: | 碩士 === 國立臺灣大學 === 化學工程學研究所 === 101 === There are two topics discussed in this study: water evaporation on soft patterned surfaces and the observation of the Cassie impregnating wetting state.
First, we demonstrate the evaporation mechanism of water sessile drop on different softness of fixed patterned PDMS (polydimethylsiloxane) substrate and also compare the results from the viewing angle of 0° with that from the viewing angle of 45°. The evaporation mechanism generally starts from the constant contact radius mode and turns into constant contact angle mode when the receding contact angle is reached. The softer the substrate is, the smaller the receding contact angle is. The wetting transition from the Cassie to the Wenzel state is also observed after the constant contact angle mode and the softer substrate will induce an earlier wetting transition due to the softer texture. By comparing the theoretical calculation of evaporation rate in different modes, we can examine whether the expected evaporation mechanism is suitable or not.
Second, the Cassie impregnating wetting state is investigated by placing the ethanol drop on different patterned PDMS surfaces. Due to the lack of the knowledge of the Cassie impregnating state, our main purpose is to find out the relationship between the structure of the surfaces and the impregnating region. It is observed that the rougher the substrate is, the larger the impregnating region is. However, so far we cannot specify this phenomenon and its impregnating region. Our preliminary inference is that the Cassie impregnating wetting state is only the metastable state passing to complete wetting and the metastable state is the result of the equilibrium of the imbibition rate and the evaporation rate of ethanol. Besides, the contact angle in the Cassie impregnating wetting state is also examined to see if the Cassie equation can describe and the study of the ethanol drop evaporation on patterned surface is discussed to further understand the Cassie impregnating wetting state.
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