| 摘要: | 高能電子束會對高分子材料造成電子輻射損傷，使其斷鍵或與其他鏈段產生鍵結，導致晶體結構產生變化與損傷，不利於分析其原始結構隨時間的演變。本次研究探討不同反應速率的自由基清除劑，沒食子酸(gallic acid, GA)與抗壞血酸(ascorbic acid)，於減緩聚乙烯(polyethylene, PE)受到穿透式電子顯微鏡電子輻射損傷中的作用。本次研究藉由穿透式電子顯微鏡的電子繞射模式來觀測半結晶高分子PE中(110)、(200)、(020)和非晶的繞射環強度和晶格間距的變化來檢測自由基清除劑對於降低電子輻射損傷的效用。從繞射圖譜得知不同平面峰值的位移，瞭解電子輻射損傷對於晶體的影響；同時也能計算臨界電子劑量來比較有無自由基清除劑的電子輻射損傷減少程度。實驗結果顯示PE在繞射圖譜中的結晶平面間距隨著電子劑量增加而變大，表示分子間因電子輻射而產生斷鍵與交聯反應。PE的結晶訊號強度隨著總電子劑量累加而衰退；而非晶的訊號強度則隨著電子劑量增加而上升，代表結晶因電子輻射損傷而非晶化。更重要的是在加入AA和GA自由基清除劑後能夠增加材料承受的臨界電子劑量，分別由20.8 e-/Å2改變為24.5 e-/Å2和26.8 e-/Å2。此一結果顯示添加自由基清除劑能有效地減緩高分子的電子輻射損傷。我們期望未來能應用在軟質材料的動態觀測上，確保材料不受電子輻射損傷的影響並保留結構的完整性。;High-energy electron beams can cause radiation damage to polymer materials, leading to bond breaking or cross-linking. This damage limited the image resolution and in-situ observation. This study examines the effects of free radical scavengers with different reaction rates—specifically, ascorbic acid (AA), which reacts quickly, and gallic acid (GA), which reacts slowly—in reducing radiation damage to semicrystalline polyethylene (PE). Using electron diffraction, we observed a decay in the intensities of the diffraction rings and a shift in lattice spacings of PE for the (110), (200), (020), and amorphous phases. The critical electron dose was calculated to compare radiation damage reduction with and without free radical scavengers. The results show that the lattice spacings in PE increased with higher accumulated doses. The intensity of crystalline signals decreased as the electron dose accumulated, while the intensity of amorphous signals increased, suggesting that crystalline regions became amorphous phases due to the radiation damage. Most importantly, the addition of AA and GA changed the critical electron dose from 20.8 e⁻/Ų to 24.5 e⁻/Ų and 26.8 e⁻/Ų, respectively, indicating a reduction in radiation damage to PE. Moreover, PE with GA can react with more free radicals, leading to a higher tolerance of critical doses. These results demonstrate that free radical scavengers can effectively minimize the electron beam damage to polymers. |
