具結構超疏水性表面的製備

Abstract

降低表面能及增加表面粗糙度為製作超疏水性表面的方法。我們經由半導體微影蝕刻技術製造出一系列的矽晶母片，包括各種尺寸的方形柱狀突起與網狀突起，並有不同的間距。經由浸泡的方式在有圖案的矽晶母片上長一層自聚性單分子膜。由接觸角的量測結果發現，柱狀突起圖形在1＜r＜1.4時，液滴處在Wenzel狀態，隨著粗糙度變大（r＞1.4），接觸角變成Cassie狀態。網狀突起圖形固體覆蓋率（Φs）分佈從0.2~1.0，隨著Φs增加前進角有減小的趨勢，和Cassie equation的理論值對應良好。不論表面的圖形為何，在適當的粗糙度下，接觸角都可以超過150°，達到超疏水狀態。我們同時利用壓印的方法去製造表面粗糙度，以PDMS作為壓印模具，壓印溶凝膠以產生具結構的二氧化矽表面，圖形尺寸從10μm至0.3μm。使用添加界面活性劑的溶凝膠，可以改善壓印的品質，如減少裂痕、尺寸的收縮程度變小且容易得到大面積的完整圖形。經由疏水性矽烷單分子膜的改質，這些二氧化矽表面可以達到和具有相同圖案矽晶母片的超疏水性。

Superhydrophobic surface are generally made by lowering the surface energy and increasing the surface roughness. We designed a series of silicon surface that were fabricated by photolithography and exposed to silanization reagents to form self-assembled monolayers (SAM). The surfaces contain square pillars and square holes of different sizes and separations. For the surface of square pillars, when the roughness is small (1＜r＜1.4), hydrophobicity is governed by Wenzel model; when the roughness is higher then 1.4, Cassie model dominates the hydrophobicity. The solid fraction (Φs) of holes is designed from 0.2 to 1.0. The water contact angles of those patterned surfaces fit well with Cassie model. Regardless of the features, surfaces with a properly roughness become superhydrophobic. We also used elastomeric mold to pattern desired features including pillars and holes (10μm~0.3μm). Sol gel precursor was used as a patterning layer. Adding the surfactant improved the outcome of the soft embossing process by less shrinkage, less cracker and larger perfect area. After the silicon oxide surfaces with special patterns were covered with hydrophobic SAM, the advancing contact angles of these surfaces are in good agreement with the silicone surfaces of the same feature. The soft embossing is a convenient method to replicate superhydrophobic surfaces.