現今對於基材表面粗糙度如何影響液滴接觸角遲滯的相關研究尚未清楚，本論文透過靜電紡絲與機械力研磨等方式在基材表面上提供粗糙度並且各基材上液滴接觸角遲滯是透過水滴的前進角與後退角量測所獲得的，然而粗糙基材上的潤濕性質可以透過全氟矽烷的蒸氣沉積法或者溶膠-凝膠法加以改善。隨著表面粗糙度增加時，液滴前進角會隨之上升但是對於後退角的潤濕行為可分為三種類型：(1)、隨粗糙度增加後退角隨之下降，(2)、隨粗糙度增加後退角隨之上升，(3)、隨粗糙度增加後退角存在最小值。針對此三種潤濕行為變化之合理說法可由粗糙結構中氣囊(air pocket)穩定程度獲得解釋。 影響粗糙結構中氣囊穩定程度變化可以透過觀察鑽孔基材中液體滲入與氣泡浮出過程加以說明，在錐形單孔基材中，隨著液體潤濕性質提升與孔洞深度變淺，都使得液體滲入速率變快而氣泡越容易排至大氣中。其潤濕過程是液膜接觸線沿著孔壁變化而向下流，並在底端累積並將氣泡隨之舉起並排出。而在多孔基材上，液滴會隨著滲入程度快慢而導致接觸角量測上的變化，當液體本身滲入速率較慢時，此前進角量測時符合Cassie-Baxter理論而上升，但是液體終究會滲入於孔洞中，導致在後退角量測上因Wenzel理論而角度下降。 ;The influence of surface roughness on contact angle hysteresis is not well understood. In this study, surface roughness is systematically altered on some polymeric substrates such as polystyrene, polycarbonate and poly(methyl methacrylate) by polishing or electrospinning method and its effect on contact angle hysteresis is investigated via measuring advancing and receding contact angles of water. The wettability on these substrates is also modifed by vapor-phase deposition of perfluorooctyltrichlorosilane or sol-gel reaction. As surface roughness is increased, the advancing contact angle grows but three types of the receding contact angle (θr) behavior have been identifed：(i) monotonic reduction of θr, (ii) monotonic enhancement of θr, and (iii) presence of a minimum of θr. The plausible mechanism based on the stability of air pockets is proposed to explain our experimental findings. The effect of stability of air ockets on rough surface can be observed by liquid imbibition into holes on a substrate. The imbibition behavior of a drop on top of a small hole is dependent on various rate of imbibition and the depth of hole. As the liquid drop favors wetting on the substrate surface or the depth of hole becomes more shallow, spontaneous and rapid imbibition into the conical hole takes place and trapped air is removed upon immediate impregnation. The possible imbibition pathway is that the three-phase contact line move downward along the wall of the hole. Once the contact line reaches the bottom, liquid starts to accumulate. The air bubble rises up slowly and eventually burst as it is in contact with the drop surface exposed to the ambient atmosphere. Liquid cannot immediately impregnate into the holes due to the relatively slow rate of imbibition. Therefore, the advancing contact angles of liquid drop on the porous substrate correspond to the Cassie-Baxter state. However, the liquid eventually invades the holes after some time and the receding contact angles are in the Wenzel state.
