表面濕潤性與凝結行為之研究：雙親性表面的設計與最佳化

Abstract

疏水表面（hydrophobic surface）具有低表面能可以有效促進液滴的滑落。然而，疏水表面的低成核密度可能限制其在高效水收集系統中的應用。借鑒於生存在乾燥環境的甲蟲，雙親性表面（biphilic surface）結合了疏水與親水區域的特性，被認為能夠具備增強成核密度與液滴滑移能力，因此在同時提升水收集效率與熱傳效率方面具有潛在優勢。 NOA65平坦雙親性表面與溶膠凝膠法製備的平坦雙親性表面成功被製備透過以NOA65 光固化膠與二氧化矽奈米質地表面作為基材後續再進行疏水改質與多巴胺親水改質而成。然而，相較於NOA65雙親性表面，溶膠凝膠法製備的雙親性表面在增強親水點位的設計優化時有著顯著結構上穩定的優勢。藉由控制多巴胺反應濃度與時間來調控疏水表面上親水點位的密度與觀察其沉積生長的過程來進行一系列表面濕潤現象與凝結機制的探討。 研究結果顯示，在0.25 g/L 多巴胺濃度下，溶膠凝膠法製備的雙親性表面的 Cassie/Wenzel 濕潤現象轉換發生於多巴胺反應時間為22.5分鐘的時候。在凝結過程中，透過統計與量化不同凝結時間下液滴的數量與尺寸來分析表面上液滴數量密度、累積水量與液滴表面覆蓋率。此外，透過光學顯微鏡觀察下，疏水表面進行多巴胺親水改質後發現其成核密度有顯著提升。液滴式/薄膜式凝結模式的轉換界線延遲至多巴胺反應時間為27.5分鐘的時候。水收集效率隨著多巴胺反應時間的增加而提升，但液滴自然滑落直徑的最小值出現在20分鐘多巴胺反應條件下。在熱傳表現分析下，熱傳導係數在Cassie/液滴式凝結模式下皆有增加其中最大增幅41.7% 發生在10分鐘的多巴胺反應條件下。透過整合接觸角測量、收集水量與熱傳表現的結果進一步加深對雙親性表面獨特特性與其應用性。

A hydrophobic surface with low surface energy can improve the droplet removal capability. However, the low nucleation density of a hydrophobic surface can limit its application on high water harvesting efficiency. Inspired by the beetle living in a dehydrated environment, a biphilic surface with hydrophobic and hydrophilic properties is considered to enhance nucleation density and droplet mobility, thus providing significant potential for improving water harvesting efficiency and heat transfer performance. In this study, NOA65 flat biphilic surface and sol-gel flat biphilic surface are successfully fabricated by using Norland Optical Adhesive 65 (NOA65) and silica nano-textured surface as substrates, followed by hydrophobic modification and dopamine- hydrophilic treatment. In comparison with the NOA65 biphilic surface, the sol-gel biphilic surface offers a significant advantage in structural stability, allowing for the design of optimized hydrophilic sites. By adjusting the dopamine concentration and reaction time, a series of investigations are conducted to examine surface wettability and condensation mechanism, with the objective of controlling the nucleation density and observing the growth of deposition on the hydrophobic surface. This study demonstrates that, at a fixed dopamine concentration of 0.25 g/L, the Cassie/Wenzel transition boundary of the sol-gel biphilic surface occurred at 22.5 minutes of dopamine reaction time. During the condensation process, the droplet number density, accumulative water volume, and surface coverage were analyzed by statistically quantifying the number and size of droplets at different condensation times. The nucleation density on dopamine-treated substrates shows a notable enhancement under microscopy observation. The dropwise/filmwise condensation transition boundary is extended to 27.5 minutes of dopamine reaction time. The water harvesting efficiency exhibits a positive correlation with dopamine reaction time, but the lowest natural departure diameter is recorded at 20 minutes of dopamine reaction time. The heat transfer analysis reveals that the heat transfer coefficient (HTC) increased under Cassie /dropwise condensation mode, with the maximum enhancement of 41.7% at 10-minute of dopamine reaction time. The integration of contact angle measurements, water harvesting efficiency, and heat transfer performance can provide a deeper understanding of unique characteristics and further applications of biphilic surface.