光控奈米孔洞表面上的液滴運動

Abstract

近年來，光敏材料的發展快速，由於其異構化的特性可在不同刺激下進行轉換，而光照條件下之技術具有非接觸與非侵入，且可以控制光波長以及設計光照圖案之優點，但是目前為止大多著墨光敏材料於固態基質上之濕潤性變化，鮮少研究動態響應下的應用，因此本研究希望透過液滴流動的結果與分析，能夠對系統有更深的理解。 本篇論文使用螺吡喃做為光敏材料，採用聚二甲基矽氧烷(PDMS)作為固態基質表面，透過雷射使PDMS表面具有二氧化矽微結構，使其表面性質呈現超疏水，並將螺吡喃塗佈於超疏水表面上，發現該表面的濕潤性會隨著UV光以及可見光的切換改變螺吡喃的異構化性質。透過量測液滴於未照光以及照光表面的靜態接觸角變化，觀察到接觸角會隨著螺吡喃塗佈量、UV光照時間以及環境光照時間的影響。接著分析不同表面結構對於動態接觸角的影響，讓液滴於傾斜表面上滑落並量測其遲滯現象，隨著雷切速率越快的表面，遲滯角有變大的趨勢，並發現於未照光和照光區域有不同的遲滯現象。 我們進一步透過設計光照圖案，使液滴通過與中軸呈30度至70度的過渡線夾角並產生偏折，發現於45度之過渡線夾角時，液滴有最大的偏折角度。於環境光下，量測MC螺吡喃結構還原與偏折角以及遲滯角的關係，觀察到遲滯現象主要由後退角所影響，並計算液滴於偏折下的橫向速度，將其與理論模型做比較，發現實驗值明顯較大，表示不能只用遲滯角差異來解釋，還有其他因素之影響。最後我們透過改變傾斜角度使液滴進入光照區域之速度不同，而造成停止或減速的運動，也藉由讓液滴沿著光照邊界流動達到引導液滴運動的效果。

In recent years, the development of photosensitive material is rapid. Due to their photoswitchable characteristics, they can change their properties under different light stimuli, which can be used to control the surface wettability. However, previous studies are mainly focused the static wettability changes of photosensitive materials on solid substrates, and only few are mentioned the application under dynamic response. Therefore, we study the dynamical response of the droplet through analysis of droplet flow on photosensitive surface. In this paper, spiropyran is used as a photosensitive material and coated on the nanoporous PDMS surface. The nanoporous surface of PDMS is made by laser scanning. It is found that the wettability of spiropyran coated surface can be switched under UV and visible light. We measured the contact angle of droplet on surface with and without UV and measured that contact angle can be affected with spiropyran coating amounts、UV exposure time and ambient exposure. In order to study the dynamic response of droplet, we analyzed the effect of different surface structures on the dynamic contact angles. On freely rolling experiment, it is found that the hysteresis angle tends to be larger with the higher laser velocity, and different hysteresis phenomena are found in the surface without UV and surface with UV. We also designed the mask pattern to make droplet flow through the various transition angle to deflect droplet. It was found that the droplet had largest deflection angle when the transition angle was 45 degree. We measured the relationship between the reduction of SP and deflection angle and dynamic contact angle. It was observed the hysteresis phenomenon was almost affected by the receding angle. We calculated the lateral velocity of the droplet and compared with the theoretical model. Finally, we apply this method to dynamically control the droplet for deceleration and guidance.