以相分離微成型法製備表面緻密且具圖案結構之PVDF薄膜與其抗結垢特性探討

Abstract

薄膜分離技術因具備操作簡便與節能等優勢，廣泛應用於水處理與工業分離程序。然而，薄膜在長時間操作中容易因為懸浮物沉積於表面而產生結垢，導致過濾性能下降與使用壽命縮短。為改善此現象，近年來在薄膜表面引入圖案結構成為新興策略，不僅可增加有效過濾面積，還改變周圍局部流場以減少結垢。相分離微成型法因具備製程簡單與高圖案保真度的優勢，已被廣泛應用於圖案薄膜之製備。但此方法由於鑄膜液圖案面無法直接接觸非溶劑，造成圖案表面延遲相分離並產生孔洞結構，反而可能形成懸浮物易附著區域，影響抗結垢性能。 回顧過往製備表面緻密且具圖案結構薄膜的方法，我們發現其中多數方法面臨圖案保真度差或製程過於複雜等限制。其中，以2wt% PEGDA-PDMS模具內含水分誘導相分離成膜之策略，雖能避免上述缺點，但薄膜機械強度卻不足。為此，本研究針對此限制，提出能兼顧表面緻密性、圖案保真度與結構強度的製膜策略。在薄膜材料選擇方面，選用具備耐酸性與化學惰性的聚偏二氟乙烯(polyvinylidene fluoride, PVDF)為鑄膜之高分子材料，並採用環保的磷酸三乙酯(Triethyl phosphate, TEP)作為溶劑，以水為非溶劑。實驗設計根據成膜機制提出兩項製程改良策略，其核心目標皆為促使鑄膜液與大量非溶劑迅速接觸，以誘導瞬間相分離，進而在薄膜表面形成緻密層與內部支撐結構。在第一項策略中，我們嘗試增加PDMS預聚物中PEGDA的含量，以提升模具含水能力，期望自圖案面誘導瞬間相分離。然而，我們發現當PEGDA含量過高時，會干擾PDMS預聚物的交聯反應，導致模具無法固化。因此改以文獻中已證實可固化之2wt% PEGDA-PDMS模具，製備表面緻密之圖案薄膜。第二項策略則在模具內含水分尚未擴散完全前，使鑄膜液非圖案面接觸非溶劑，自底部誘導形成支撐結構。實驗結果顯示，當縮短鑄膜液於空氣中靜置時間時，可同時保留圖案面緻密層與非圖案面手指狀支撐結構。在固定進料流率與初始滲透流率之純水過濾測試下，可維持穩定之滲透流率，成功提升薄膜之機械強度。 為進一步驗證薄膜之抗結垢效能，本研究以牛血清白蛋白(BSA)水溶液進行掃流式過濾測試，並搭配共軛焦雷射掃描顯微鏡(CLSM)觀察其沉積分布。實驗結果顯示，表面具有緻密層之薄膜相較於表面有孔洞的薄膜能顯著減緩通量衰退，並抑制BSA之沉積。而在薄膜表面引入箭頭型圖案亦有助於改變局部流場，減少污染物滯留，可有效降低懸浮物滲透與累積。兩者結合的設計，即具緻密層與箭頭圖案之薄膜，展現最佳的抗結垢表現。 綜上所述，本研究建立一套簡單可行的製程策略，成功製備出兼具圖案保真度、表面緻密層與機械強度的抗結垢薄膜，期望為功能性薄膜的結構設計與機制探討提供新的思路。

Membrane separation technology is widely used in water treatment and industrial processes due to its simplicity of operation and energy efficiency, but membrane fouling limits its performance. Patterned membranes have gained attention for their ability to increase the effective filtration area and alter local flow fields, thereby reducing fouling. Among various fabrication methods, phase separation micromolding (PSμM) offers advantages of simplicity and high pattern fidelity. Nevertheless, since the casting solution on the patterned side does not directly contact the nonsolvent, delayed phase separation occurs, resulting in porous surface structures that may promote foulant attachment and reduce antifouling efficacy. Previous studies attempting to fabricate surface-dense, patterned membranes often faced challenges such as poor pattern fidelity or complicated processes. Among them, using 2wt% PEGDA-PDMS molds to induce phase separation via internally stored water has achieved both dense skin layer and pattern fidelity. However, the resulting membranes suffer from poor mechanical strength. To overcome this limitation, this study proposes a fabrication strategy that integrates dense skin layer, pattern fidelity, and internal structural strength. Polyvinylidene fluoride (PVDF) was selected as the casting polymer due to its excellent acid resistance and chemical inertness, with environment friendly triethyl phosphate (TEP) and water used as the solvent and nonsolvent, respectively. Based on phase separation mechanisms, two process modification strategies were proposed, both aimed at enabling rapid contact between the casting solution and a large amount of nonsolvent to induce instantaneous phase separation, forming a dense surface layer and an internal supporting structure. In the first strategy, we attempted to increase the water-holding capacity of the mold by raising the PEGDA content, aiming to induce phase separation from the patterned surface. However, it was found that excessive PEGDA disrupted the crosslinking reaction of the PDMS prepolymer, leading to incomplete mold curing. Consequently, we adopted a 2wt% PEGDA-PDMS mold previously reported to exhibit stable crosslinking, which was used to fabricate patterned membranes with dense surfaces. The second strategy focused on modifying the membrane formation process. Before the water stored in the mold had fully diffused, the non-patterned side of the casting solution was brought into contact with nonsolvent, thereby inducing phase separation from the bottom to form a finger-like support structure. By shortening the air exposure time of the casting solution, both a dense skin layer on the patterned surface and mechanically supportive finger-like pores beneath the non-patterned surface were achieved. The resulting membranes maintained a stable permeate flow rate, confirming enhanced mechanical strength. To further verify the antifouling performance, cross-flow filtration tests using bovine serum albumin (BSA) solution were conducted, combined with confocal fluorescence microscopy to visualize protein deposition. Membranes with a dense surface layer exhibited significantly lower flux decline and reduced BSA accumulation compared to those with porous surfaces. Moreover, the incorporation of arrow patterns effectively altered the local flow field and minimized foulant retention. The membranes combining both dense skin layers and directional patterns demonstrated the most outstanding antifouling performance. In conclusion, this study establishes a simple and feasible strategy to fabricate antifouling membranes with a dense skin layer, high pattern fidelity, and sufficient mechanical strength. The proposed approach offers new insights for the structural design and mechanism exploration of functional membranes in advanced separation applications.