以相轉變法製作多孔壓電駐極體薄膜之製程及特性分析

Abstract

本研究以開發多孔壓電駐極體薄膜製程為核心，選用兩種PVDF的共聚物PVDF-TrFE、PVDF-HFP為材料，採用非溶劑誘導相轉變(Nonsolvent Induced Phase Separation, NIPS)以及蒸氣誘導相轉變(Vapor-Induced Phase Separation, VIPS)方式製作具有海綿狀孔洞的薄膜。研究發現NIPS製程使用之非溶劑凝聚液與薄膜成形具有關聯性，並可透過添加物改變薄膜結構；以VIPS製程製作薄膜則發現溶劑為薄膜結構的重要變因，透過不同溶劑以及不同比例的混和溶劑的選擇可產生不同結構的薄膜。在完成多孔壓電駐極體薄膜製程開發後，亦將各種薄膜進行-16 kV及12小時的電暈極化駐電程序，並量測其壓電係數。以動態法量測壓電係數之結果顯示，以NIPS法製備高分子溶液中含有8 wt%乙醇並使用60 wt%乙醇為凝聚液所製成的薄膜、以VIPS法製備分別使用DMF、DMAC溶劑製成的薄膜，輸出響應媲美商用EMFi薄膜；準靜態法量測結果則發現NIPS法製備高分子溶液中含有2 wt%乙醇並使用60 wt%乙醇為凝聚液所製成的薄膜，於0.1 N的施力條件下輸出超過4000 pC/N，相較商用EMFi薄膜高出9.95倍，其餘樣本也皆具有約2000 pC/N以上的輸出效果，遠高於EMFi以及實心的PVDF薄膜，量測結果也顯示準靜態法電荷輸出與樣本電容大小具有相依性。從本研究可發現，無論是NIPS、VIPS皆可透過參數調控改變薄膜結構，並使其在低頻率範圍的量測具有良好的壓電輸出響應。

In this study, different processes to fabricate porous piezoelectric electret films are developed, including non-solvent-induced phase separation (NIPS) and vapor-phase induced phase separation (VIPS) methods. PVDF-TrFE and PVDF-HFP copolymers are used to create spongy structures with different pore sizes and geometry. It is found that the non-solvent-based NIPS process is a key factor in the formation of the porous film, and the film structure can be modulated by additives. On the other hand, it is also found that the solvent is an important factor in the porous film formation of the VIPS process. After poling these porous piezoelectric electret films prepared by different methods and parameters, a corona discharge polarization at -16 kV and 12 hours of treatment is conducted, and their piezoelectric coefficients are measured and compared. Using the dynamic method, it shows that the NIPS films prepared with 8 wt% ethanol in the polymer solution and 60 wt% ethanol as the coagulation solution can have a compatible piezoelectric constant with the commercial EMFi electret film. The VIPS films prepared by DMF or DMAC solvents also is comparable to the EMFi electret film. The quasi-static method shows that the piezoelectric coefficient of the NIPS film prepared by 2 wt% ethanol in the polymer solution and 60 wt% ethanol as the coagulation solution can exceed 4000 pC/N, which is about 9.95 times higher than that of EMFi films. In summary, it is found that both NIPS and VIPS can create a porous piezoelectric film with different porous structures and they can provide an excellent piezoelectric property for sensing applications.