陽極氧化鋁結構之介電溼潤應用

Abstract

本研究製備出不同孔洞直徑及深度的陽極氧化鋁（Anodic Aluminum Oxide；AAO），並利用其奈米結構加上低表面能分子的修飾，展現出明顯的介電溼潤（Electrowetting on Dielectric；EWOD）效應。AAO具備有序排列且垂直的孔洞、機械性強、性質穩定、製作成本便宜等特性，藉由鋁的陽極氧化製程控制時間、電壓等因素，可獲得不同粗糙度之結構，孔洞直徑為14~342nm，深度為0.5μm及2μm的AAO。以單分子層吸附的方式，將FAS-17吸附於AAO奈米結構表面，可增大起始接觸角及免除鋁表面官能基的殘留，達到疏水甚至超疏水結構。將水珠滴於疏水AAO結構上，外加交流電壓，隨著電壓增加觀察水珠形貌的改變，可發現AAO結構因電位能改變而由疏水性轉為親水性。由於目前非常少文獻探討EWOD在孔洞內空氣被限制住的結構，因此本實驗藉由製備不同深度的AAO探討孔內空氣壓力與介電溼潤的關係，也利用改變升降電壓的速率探討EWOD的回復性。

A two-step anodization process is emoployed to fabricate a self-organized nanoporous anodic aluminum oxide (AAO) on aluminum film. The resulting AAO structure displays adjustable thickness and pore size contingent on the processing parameters. For Electrowetting on Dielectric(EWOD) testing, the as-prepared AAOs with different morphologies are first surface-modified by fluoroalkysilane（FAS-17）to render desirable hydrophobicity. Subsequently, an AC electrical field is imposed across a droplet and the AAO sample in which the solid/liquid interface experiences a dramatic change in charge density, resulting in the switching of wettability from hrdrophobic state to hydrophilic one. We investigate the EWOD effects on a variety of AAO samples with various thickness and pore diameters. To understand the wettability transition, a capillary-pressure balance model is proposed to estimate the depth of water penetrating into the AAO pore channels.