微奈米結構與表面改質對液滴濕潤狀態轉變及抗冰行為分析

Abstract

本研究針對液滴濕潤行為與抗冰性能，系統性比較不同微結構設計與表面改質方式在兩種表面基材（NOA65與sol-gel）上的影響，並評估單層與雙層微/奈米粗糙度結構的抗冰效能。透過製備一系列具有方柱微結構的樣品，分別應用物理吸附型防潑水劑（市售型防潑水劑Glaco）與化學矽烷化修飾（十八烷基三氯矽烷OTS）賦予表面疏水性，並進行接觸角、滑動角以及結冰實驗之量測與行為分析。 NOA65樣品經Glaco處理形成雙層微奈米結構表面，在室溫下展現出前進與後退接觸角皆超過150度且滑動角低於5度的超疏水特性。變溫實驗中，液滴於冷卻過程發生Cassie至Wenzel態轉變並出現冰橋，導致接觸角劇降；融冰後則觀察到液滴可自發回復高接觸角，顯示強烈去濕潤傾向。定溫實驗顯示，在高濕度條件下，NOA65雙層表面因塗層物理吸附不穩，冷凝水滲入結構間隙破壞氣墊層，導致抗冰時長無顯著優勢，反而單層塗佈Teflon樣品在乾燥環境中表現出2000秒以上不結冰的穩定行為，說明熱傳導係數與塗層一致性對抗冰效果具決定性影響。 Sol-gel基材透過共價矽烷化改質方式提升塗層穩定性，於高溫燒結下製備之雙層結構具備微柱與均勻奈米粒子覆蓋，展現高接觸角與滑動角小於5°的超疏水性能。在定溫結冰實驗中（表面溫度約為 −19.5 ± 0.2 °C），單層結構因低溫下濕潤狀態轉變，隨柱高增加導致接觸面積上升，結冰時間反而縮短，平面樣品平均結冰時間為973秒。相較之下，雙層結構於低柱高下可維持穩定氣墊層，有效延緩冰晶成核，平均結冰時間可達4521.5秒，顯示顯著抗冰潛力，但是當柱高超過臨界值後，氣墊層穩定性下降，延遲效益隨之減弱，平均結冰時間減為270.9 ± 213.1秒。 變溫實驗進一步揭示Sol-gel雙層表面具冰橋形成、去濕潤回復Cassie狀態與接觸角恢復的能力，且該回復行為與柱高緊密相關，較高結構有利於氣墊穩定與氣流導引，提升融冰後的接觸角與液滴脫附能力。

This study systematically investigates the effects of various microstructure designs and surface modification methods on droplet wetting behavior and anti-icing performance, using two types of substrate materials: NOA65 and sol-gel. The anti-icing capabilities of surfaces with single- and dual-scale micro/nanostructured roughness were evaluated. A series of samples with square micropillar structures were fabricated and subjected to hydrophobic treatment through either physical adsorption of a commercial water-repellent agent (Glaco) or chemical silanization with octadecyltrichlorosilane (OTS). Measurements of contact angle, sliding angle, and icing behavior were conducted to analyze surface properties and phase transitions. NOA65 samples treated with Glaco exhibited dual-scale micro/nanostructures, showing superhydrophobicity at room temperature, with both advancing and receding contact angles exceeding 150° and sliding angles below 5°. During dynamic icing experiments, droplets underwent a Cassie-to-Wenzel state transition accompanied by ice bridge formation, resulting in a sharp decline in contact angle. However, after melting, droplets were observed to spontaneous dewetting transition and recover high contact angles. In contrast, isothermal temperature freezing tests under even low humidity revealed that the physically adsorbed coating on NOA65 lacked stability; infiltrating condensate disrupted the air cushion layer, leading to no significant improvement in icing delay. Conversely, single-layer Teflon-coated samples demonstrated robust anti-icing performance in dry environments, with droplets remaining unfrozen for over 2000 seconds, highlighting the critical roles of thermal conductivity and coating uniformity in determining anti-icing effectiveness. The sol-gel substrate was modified via covalent silanization to enhance coating stability. The fabricated dual-scale structures, prepared through high-temperature sintering, featured micropillars uniformly covered with silica nanoparticles, exhibiting superhydrophobic properties characterized by a high dynamic contact angle and a sliding angle below 5°. In the isothermal icing experiments (surface temperature approximately −19.5 ± 0.2 °C), the single-layer structures exhibited a decrease in freezing time with increasing pillar height. This behavior is attributed to the wetting state transition under low temperatures, where larger pillar heights led to increased solid–liquid contact area and promoted heterogeneous nucleation. The average freezing time on the flat surface was 973 seconds. In contrast, the dual-layer structures demonstrated significantly enhanced anti-icing performance. At lower pillar heights, a stable air cushion was maintained, effectively delaying ice nucleation, with the average freezing time reaching up to 4521.5 seconds. However, when the pillar height exceeded a critical threshold, the air cushion became unstable, leading to increased contact and reduced freezing delay, with the average freezing time dropping to 270.9 ± 213.1 seconds. Dynamic icing experiments further revealed that sol-gel dual-layer surfaces exhibited ice bridge formation, dewetting recovery to the Cassie state, and contact angle restoration. These recovery behaviors were strongly correlated with pillar height. Taller structures favored air cushion stability and airflow guidance, enhancing post-melting contact angle and droplet shedding capability.