拉脹結構應用於機械致動液滴運輸裝置之設計

Abstract

液滴傳輸技術具備高精度、非接觸操作與低試劑消耗等優勢，已成為微流體系統與生化檢測領域之核心技術。本研究旨在開發一套基於機械致動與拉脹（Auxetic）結構的液滴傳輸平台，利用機械應變調控表面微結構變化以實現液滴的抓取與釋放。在系統建構上，選用聚二甲基矽氧烷（PDMS）摻雜石墨粉作為基材，利用1064 nm紅外雷射光熱效應實現低成本且高精度的微結構直寫加工，成功製備出具不同幾何參數之超材料樣本。 為解析液滴釋放的力學機制，本研究建立了無重力懸滴單軸應變模型」基於體積守恆與最小表面能原理，推導出抵抗變形的理論回復力，並證實液滴釋放的物理本質為彈性回復力與重力共同對抗表面釘扎力的競爭過程；實驗亦表明，相較於傳統座滴法（Sessile Drop），懸滴傾斜去釘扎實驗所測得的臨界力值更能準確預測懸掛液滴的釋放行為。針對原始PDMS表面因高接觸角遲滯導致釋放困難之問題，本研究採用溶劑溶脹誘導法製備滑移液體注入多孔表面（SLIPS）。實驗確立了浸泡10CS矽油30分鐘為最佳製程參數，此條件能在保留基材基礎抓取力的同時，有效屏蔽表面微觀缺陷。 結果顯示，經SLIPS改質後，樣本S2的水平釘扎力降至未處理狀態的51%，潤滑油膜成功將固—液摩擦轉化為低能障的液—液滑移，協助樣S2、S3與S4克服界面阻力，實現液滴的邊界去釘扎與完整釋放。然而，研究亦界定了此策略的物理極限：對於接觸線高度纏繞的樣本S1，受限於宏觀幾何鎖死（Macroscopic Geometric Interlocking）與接觸線積分效應，即便經過表面改質仍無法釋放。本研究整合了雷射加工、力學建模與表面改質策略，闡明了機械致動液滴釋放的微觀機制與工程邊界，為拉帳結構設計機械致動液滴運輸裝置提供了具體的理論依據。

Droplet transport technology, characterized by high precision, non-contact operation, and low reagent consumption, has emerged as a core technology in the fields of microfluidic systems and biochemical detection. This study aims to develop a droplet transport platform based on mechanical actuation and auxetic structures, utilizing mechanical strain to modulate surface microstructures for droplet capture and release. For system fabrication, polydimethylsiloxane (PDMS) doped with graphite powder was selected as the substrate. By leveraging the photothermal effect of a 1064 nm infrared laser, a low-cost and high-precision direct writing process was achieved, successfully fabricating metamaterial samples with varying geometric parameters. To elucidate the mechanics of droplet release, a "zero-gravity pendant drop uniaxial strain model" was established. Based on the principles of volume conservation and minimum surface energy, the theoretical restoring force resisting deformation was derived. The study confirmed that the physical essence of droplet release is a competition where elastic restoring force and gravity jointly overcome the surface pinning force. Experimental results also indicated that, compared to the traditional sessile drop method, the critical force values obtained from pendant drop tilt depinning tests provide a more accurate prediction of the release behavior of suspended droplets. To address the challenge of release failure caused by high contact angle hysteresis on native PDMS surfaces, a Slippery Liquid-Infused Porous Surface (SLIPS) was prepared using a solvent swelling-induced method. The experiment established that immersion in 10CS silicone oil for 30 minutes is the optimal processing parameter, a condition that effectively shields microscopic surface defects while retaining the substrate's fundamental gripping capability. Results showed that after SLIPS modification, the horizontal pinning force of sample S2 decreased to 51% of its untreated state. The lubricating film successfully transformed solid-liquid friction into a low-energy barrier liquid-liquid slip, enabling samples S2, S3, and S4 to overcome interfacial resistance and achieve boundary depinning and complete release. However, the study also defined the physical limits of this strategy: for sample S1, which exhibits a highly entangled contact line, release remained unachievable even after surface modification due to macroscopic geometric interlocking and the contact line integral effect. By integrating laser processing, mechanical modeling, and surface modification strategies, this research elucidates the microscopic mechanisms and engineering boundaries of mechanically actuated droplet release, providing a concrete theoretical basis for designing mechanically actuated droplet transport devices utilizing auxetic structures.