探討”非失措”之ABCBA線性五嵌段共聚合物於熔融態之自組裝行為

Abstract

本研究運用自洽平均場理論探討非失措型之ABCBA線性五嵌段共聚合物於熔融態之自組裝，我們著重在Flory-Huggins作用力參數之影響，非失措型意指A與C兩者之Flory-Huggins作用力參數最大；隨著對稱型作用力(χ_AB N=χ_AC N=χ_BC N)下降，因為成分間相容性變好，相行為與ABC線性三嵌段共聚合物類似，所以diamond、hexagonally perforated lamellae和Fddd等連續性結構轉變為gyroid，另一方面，B做為主成分所形成之交替型球狀與柱狀變為有相同A/C配位數之CsCl、NaCl和C_A^4/C_C^4。接著我們觀察在χ_AC N≥χ_AB N=χ_BC N下之變化，當χ_AC N固定時，χ_AB N=χ_BC N之下降使的聚集減弱以及結構尺寸縮小，固定χ_AB N=χ_BC N時，因為χ_AC N下降導致A和C聚集減弱，與B接觸面積增加，所以導致interfacial energy上升以及entropic energy下降；接著將χ_AC N固定，我們發現χ_BC N大於χ_AB N時，BC介面之能量較高，為避免其能量太高，B/C介面曲率改變並使的結構轉變為C-core/B-shell之型態；最後利用合適之χ_AB N、χ_AC N和χ_BC N建構三角相圖後，可以看到A為主成分時，結構以C-core/B-shell之型態為主，這是因為高分子鏈拓樸從ABC擴展為ABCBA時，因為C鏈段被兩邊B相鄰，所以B/C介面形成曲面時，C鏈段從兩邊被拉長，曲率變化幅度更大，也讓其結構變化更多元。

In this study, we employ the self-consistent mean field theory to explore the effect of flory-huggins interaction parameter on self-assembly behavior of non-frustrated ABCBA linear pentablock terpolymer, where the flory-huggins interaction parameter of A and C (χ_AC) is the strongest, in the melt. As the symmetric interaction parameters (χ_AB N=χ_AC N=χ_BC N) decrease, the compatibility between different component becomes better, thus, the phase behavior is similar to ABC triblock and the continuous structures including diamond, hexagonally perforated lamellae, Fddd transfer to gyroid. On the other hand, the packing orders of alternating spheres and cylinders with unequal coordination numbers tend to transfer to those with equal coordination numbers. Then we move to the system ofχ_AC N≥χ_AB N=χ_BC N, observing that the decrease of χ_AB N=χ_BC N make the segregation weaker and structure size smaller at fixed χ_AC N. Also, the decrease of χ_AC N at fixed χ_AB N=χ_BC N induces the interfacial energy to increase and entropic energy to decrease due to the fact that the B/C and A/B interfaces become larger. Subsequently, we explore the condition ofχ_AB N≠χ_BC N at fixed χ_AC N and notice that whenχ_BC N>χ_AB N, the curvature of B/C interface increases for preventing the interfacial energy of B/C interface too large and the structrues transform to C-core/B-shell type. Finally, we construct a phase triangle by using appropriate interaction parameter and discuss the diagram completely. In this phase triangle, the C-core/B-shell structures ocuppy a broad region as A is the major component. The reason is that when the topology expands from ABC to ABCBA, becase C is stretched from two side, the varing of curvature of B/C interface becomes significant. Therefore, the morphological transition is more diverse.