多孔隙介電結構及表面特性在摩擦生電裝置下之研究

Abstract

在生產過程中或實驗上摩擦起電往往被視為耗費能量或機械運作帶來的負面的物理現象，需要增加去除靜電的過程以避免靜電累積造成損害。然而，在2012年王中林團隊提出一種新的能量轉換方式，正是透過摩擦起電將機械能轉換為電能，此摩擦生電的裝置優勢在於材料上有較高的選擇性，藉由機械或自然環境的震動產生之電訊號可作為感測器之偵測外，其訊號若使用電容加以儲存電能，可對其他小型電子裝置進行充電，甚至有機會取代傳統感測器需要外部電源供應之需求，為小型電子產品及感測器之技術提供一種新的發展潛力。 在本文的第一部分，我們使PDMS形成孔洞結構，透過實驗的方式系統性地測試多孔洞介電質在何種條件下有助於提升摩擦生電裝置之輸出電壓，從結果發現孔隙率、工作頻率、施力方式及分離速率對於在表面形成摩擦電荷多寡有密切的關係。相較於純PDMS，多孔洞PDMS在工作頻率為3Hz、施加壓力為62.5kPa時，其輸出電壓值Vp-p最高為18V，電壓值增強4.5倍。另外，當頻率由0.7Hz提升至3Hz時，純PDMS與多孔洞PDMS輸出電壓才有明顯的差異。本研究使用之多孔性PDMS的製備相較於化學溶劑溶解方式，提供一種低成本，可大面積製造的方法，並提供了對於提高孔洞材料在摩擦生電裝置下最佳工作參數之貢獻，可望對於機器人產業、穿戴式裝置中軟性感測器發展有所幫助。 第二部份透過對PDMS表面進行電漿處理，孔洞材料的電壓並未增強，然而卻發現電漿處理後使用75%乙醇清潔表面，原本接觸及分離的的電壓訊號會漸漸反向形成顛倒的訊號，也就是位移電流在上、下電極間流動的方向相反，最後我們透過此實驗結果推測PDMS的表面由於活性官能基吸附乙醇溶液中的離子以共價鍵的方式結合，改變了PDMS原有的帶電性。這種經由表面改質而形成相反帶電表面的特性可應用於設計表面電荷圖案和誘導帶電微粒之靜電自組裝等方面。 最後一部分，我們基於對摩擦生電裝置的研究提出了一種新的判斷方向性之感測器，僅需要透過摩擦生電效應即可辨識手指在彈性起伏結構上移動之方向，其設計可延伸應用於觸覺感測器和電子皮膚上。

The effects of triboelectrification are usually regarded as the negative physical phenomenon in fabrication processes or experiments. In order to avoid the damage caused by the accumulation of triboelectric charge, it is necessary to increase energy costs because of the additive process of removing static electricity. However, a new type of energy technology called triboelectric nanogenerator was demonstrated by Prof. Zhong Lin Wang’s group in 2012, which is available to convert mechanical energy into electrical energy by triboelectric effect. The advantages of the triboelectric devices are not only allowing high selectivity of materials but also providing a new way to design sensors. Furthermore, electricity can also be used as a power supply in small electronic devices and has the opportunity to replace the external power supply in traditional sensors. The researches have also shown that technology provides a new perspective on the fields of small electronic products and sensors. In the first part of the thesis, we fabricated porous PDMS and systematically measured the performance of the porous dielectric material. The results showed that the porosity, working frequency, the methods of applying force and the rate of separation have a strong relationship with the formation of triboelectric charge density on the surface. Compared with pure PDMS, the porous PDMS has a maximum peak to peak output voltage of 18V, which gives 4.5-time enhancement when the operating frequency is 3 Hz and the applied pressure is 62.5 kPa. In addition, when the frequency is increased from 0.7 Hz to 3 Hz, there is a significant difference between the pure PDMS and the porous PDMS output voltage. The preparation of the porous PDMS in this study provides a low-cost, large-area manufacturing method compared to the chemical solvent dissolution method. Furthermore, we also attempt to provide optimum operating parameters of porous PDMS under the triboelectric device, which makes it useful for the applications of soft sensors in the robot industry and wearable devices. In the second part, we modified PDMS surfaces using plasma treatment. The results of the voltage of the porous PDMS was not obviously increased. However, it was found that if the surface was cleaned with 75% ethanol after the plasma treatment, the voltage signals gradually reversed which means the displacement current flows in the opposite direction between the upper and lower electrodes. The results suggest that the ions in the ethanol solution anchored on the reactive functional groups of the PDMS surface and changed the charge property. The modification of the surface can be applied to designing a surface charge pattern and electrostatic self-assembly of charged particles on the surface. Finally, we propose a new sensor based on the single electrode mode of triboelectric nanogenerator which can detect the direction due to the designable surface structure. The contact area is proportional to the voltage signal which can identify the moving direction of the finger on the structure. The design can also be extended to the applications of tactile sensors and electronic skin.