| 摘要: | 材料內部晶界常以隨機方式出現與排列，晶界的產生影響材料本身的機械強度、導熱度或導電度等特性。本研究旨在透過剪切作用誘導層狀嵌段共聚物的排列，使高分子鏈沿特定方向排整，進而減少晶界的存在。我們選用聚苯乙烯-聚乳酸(polystyrene-block-polylactide, PS-b-PLA)作為材料，使其先自組裝形成層狀結構。再透過改良的滾壓鑄造(roll-casting)裝置，經由調整單圓柱的旋轉速度及兩圓柱的間隙距離，施加不同強度的剪切力於PS-b-PLA上。我們透過穿透式電子顯微鏡(transmission electron microscopy, TEM)對結構內的變化進行觀測，可以觀察到剪切後的層狀結構會沿著剪切力的方向進行排列。此外，我們透過小角度X射線散射(small-angle x-ray scattering, SAXS)與超高解析冷場發射掃描式電子顯微鏡(cold field emission scanning electron microscope, CFE-SEM)對層狀結構的取向度(degree of orientation, π)進行量化分析，進一步探討旋轉速度與間隙距離對剪切效果的影響。研究結果顯示，相較於未經剪切的樣品，以300 rpm剪切處理後的樣品取向度可由0.31上升至0.69。由於取向度越接近 1，代表整體排列越整齊，此結果證明剪切力能有效提升層狀結構的有序程度。此外，我們根據 SEM 影像，依樣品的垂直深度將其分為三個區域：未受剪切區、輕微剪切區與高度剪切區。隨著剪切力的增加，局部結構逐漸由隨機排列的層狀轉變為特定方向的對齊排列，從而確定剪切力影響的最大深度。根據研究結果，圓柱間距與轉速兩項參數對剪切力之強度與穿透深度具顯著影響，進而決定高分子鏈段能否有效沿剪切方向排列。本研究進一步確認，剪切力強度與旋轉速度呈正相關，而與圓柱間距呈負相關趨勢。然而，本研究同步發現剪切誘導行為並非單純受剪切力影響，而是由剪切力強度、鏈段鬆弛能力與溶劑揮發速率三因素相互影響。唯有當三者達成適當平衡，方可實現高定向性之結構排列，並達到消除晶界缺陷的目的。;It is well known that grain boundaries aligned in different directions exist within materials, potentially affecting mechanical properties or conductivity. This study aims to induce the alignment of lamellar block copolymer through shearing to achieve a preferred orientation, ultimately reducing the grain boundaries. Polystyrene-b-polylactide (PS-b-PLA) was used to self-assemble into the lamellar morphology. Different shear strengths were applied to the PS-b-PLA through a modified roll-casting apparatus by adjusting the rotational speed and the gap between the two adjacent roll-casting cylinders. We used high-resolution transmission electron microscopy (TEM) to observe the structural changes and found that the lamellar structure aligns along the shear direction. Subsequently, the degree of orientation (π) of the lamellar morphology was quantified by small-angle X-ray scattering (SAXS) and cold field emission scanning electron microscope (SEM), further demonstrating the influence of rotational speed and gap distance. After shearing, the degree of orientation significantly increased from 0.31 to 0.69 compared to the unsheared sample, indicating that shearing greatly improves the alignment of the lamellar structure. Furthermore, we divided the samples by depth into three regions: unsheared, slightly sheared, and highly sheared from the SEM images. As the shear force increases, the local structure changes from a random lamellar orientation to a specific directional lamellar alignment in each region, allowing us to determine the maximum depth the shear force affects. The results indicate that lamellar orientation becomes highly anisotropic at higher rotational speeds or smaller gaps, as these conditions correspond to greater shear strength. However, we further found that the shear-induced alignment behavior is not solely governed by shear strength; it’s also co-regulated by the interplay between polymer chain relaxation time and solvent evaporation rate. A highly oriented structure can only be achieved when these three factors are properly balanced. |
