- 學位論文
HMDSO/MCE 電漿披覆膜沉積層結構 與氣體分離效能之研究
Study on the structure and gas separation performance of HMDSO/MCE plasma deposited membrane
摘要
本研究採用hexamethyldisiloxane (HMDSO) 電漿輔助化學氣相 沉積 (plasma enhanced chemical vapor deposition, PECVD) 於Mixed cellulose esters (MCE) 基材，製備SiOxCyHz/MCE 電漿披覆膜作為氣 體分離薄膜，此法因為單體本身不需具有不飽和鍵結或其他反應性官 能基，又具有穩定的物化性，加上對基材具有良好的附著性且不影響 基材之整體性質，所以適合應用於製備電漿披覆膜。 研究中探討電漿功率及沉積時間變化對SiOxCyHz/MCE電漿披覆 膜孔洞大小及數目之影響。實驗結果發現隨著沉積時間的增長，基材 表面溫度隨之上升，導致離子轟擊 (ion bombardment) 及蝕刻效應 (etching) 增強，經由SEM 觀察，可發現沉積速率隨之下降。再經由 XPS 分析電漿披覆膜之化學鍵結組成，隨著電漿功率及沉積時間的上 升，沉積層內SiO4 比例上升而SiC4 下降，表示碳氫物種在高溫下不 易吸附於表面，沉積層碳氫含量變少，導致沉積層結構緻密化。 電漿披覆膜沉積層厚度變化對沉積層孔洞尺寸及數量變化之影 響，可藉由正子湮滅光譜 (Positron Annihilation Spectroscopy, PAS) 分析技術予以探討。研究中發現電漿沉積初期，基材因蝕刻效應所產 生的碳氫物種與電漿聚合物混合，導致沉積層堆疊較為鬆散，因此形 成較大的孔洞。隨著沉積時間的增長，電漿蝕刻基材的機率降低，沉 積層中HMDSO電漿聚合物比例增高，所以堆疊較緻密。正子湮滅光 譜顯示在電漿沉積層與基材之界面處， 同向電子偶素 (ortho-positronium, o-Ps) 具有較高的生命週期 (lifetime, τ3 ; 正比於 孔洞尺寸)，而隨著電漿沉積層增厚，o-Ps lifetime隨之下降完全符合 實驗結果。此外，隨著沉積時間的增長，基材溫度上升，造成電漿聚 合物的碳氫物種減少，所以堆疊較緻密，導致其o-Ps生命週期τ3 略小 於界面處，也能合理解釋上述現象。另外經由正子湮滅光譜分析技 術，可發現沉積層孔洞尺寸，隨電漿功率上升而變小，所獲得的結果 與XPS所得之結果是相符合的。 將電漿披覆膜應用於空氣中之氧氮分離，隨著電漿功率及沉積時 間的上升，造成沉積層緻密化，導致氧氮分離時透過端氧氣濃度增 高，氧氣透過量降低。
並列摘要
In this study, SiOxCyHz/Mixed cellulose esters (MCE) plasma deposited membranes were fabricated by hexamethyldisiloxane (HMDSO) plasma enhanced chemical vapor deposition (PECVD) on the MCE, which has some advantages, e.g., monomer doesn’t have double bond and deposition layer with good physical and chemical resistances. The effects of plasma power and deposition time on the deposition layer pore size and pore numbers of the SiOxCyHz/MCE plasma deposited membranes were studied. It shows that the substrate temperature increases with increasing the deposition time. Meanwhile, the enhancement of ion bombardment and etching effect results the deposition rate decreases during the plasma deposition process. The XPS data revealed that the composition of SiO4 of the deposition layer increased with increasing the plasma power and deposition time. The positron annihilation spectroscopy (PAS) coupled with a variable monoenergy slow positron beam was utilized to detect the depth profile of the pore size and multilayer structure of the plasma deposited membrane. It was found that the deposition layer (mixtures of HMDSO species and MCE species) had more hydrocarbon group, resulting in the deposition layer had a looser structure at the initial period of plasma deposition. However, the MCE species content of the deposition layer decreases as the deposition time further increases. The deposition layer becomes denser. From the PALS, the o-Ps lifetime (τ3 correspond to the pore size) decreases along the plasma deposition layer growth direction. These results correspond with the XPS very well. The plasma deposited membrane was applied for O2/N2 separation. The O2 permeance decreased and the O2 concentration in the permeate enhanced when the plasma power and deposition time increased.