探討融熔態 ABCBA 線性五嵌段共聚物於非失措系統之自組裝行為

Abstract

本研究運用自洽平均場理論探討ABCBA線性五嵌段共聚合物於非失措系統下之自組裝行為，並且與對應之ABC線性三嵌段共聚合物進行比較，而我們著重在作用力參數與組成對型態的影響，其中非失措系統即為A、C兩成分間Flory-Huggins作用力參數為最大。首先，當系統在作用力參數為對稱條件（χABN=χBCN）且B為主成分時，我們觀察到在兩系統中皆有交替型結構穩定存在於相圖中。隨著成分間不相容性的下降，由於ABC線性三嵌段中A與C成分聚集能力相當，交替型結構仍然能自組裝形成。然而在ABCBA五嵌段系統中，因為位於末端之兩條A鏈段具有較高之自由度，因此傾向進入到B成分之中形成C結構在AB-mixed的domain型態，使得交替型結構在ABCBA於中低作用力中消失。接著我們進一步觀察作用力參數為非對稱條件（χABN≠χBCN），並且針對χBCN大於χABN的系統進行探討，發現到在非對稱作用力參數下交替型結構皆非最穩定之結構。在ABC三嵌段中，主要是以核-殼結構為主要觀察到的相，但在ABCBA五嵌段中則更多了C與AB-mixed的domain分離的結構。藉由一系列的探討我們不僅找到合適之作用力參數擬合實驗系統，這些模擬結果更可作為實驗與理論學者在拓展三成分共聚合物之參考並促成多元結構的發展。

The self-assembly of ABCBA linear pentablock terpolymer melts with non-frustrated interactions of χACN larger than χABN and χBCN are investigated and compared with the corresponding ABC linear triblock terpolymers by three dimensional (3-D) self-consistent field theory (SCFT). In particular, we focus on the effects of the compositions, the interaction parameters, and the number of blocks. Firstly, when the interaction parameters are symmetric (χABN=χBCN) and B is major, both ABC triblocks and ABCBA pentablocks can exhibit intriguing A- and C-formed microstructures in the B-matrix. With decreasing the segregation strength, these various alternating phases can still be observed in the ABC systems. However, due to the chain topology, the A blocks tend to mix with the B blocks in the ABCBA pentablocks, which results in the formation of C-formed structures in the AB-mixed domains. Next, when χABN≠χBCN, in particular at χABN<χBCN, the alternating phases can hardly be formed in these two systems. Aside from the core-shell types structures mainly found in the ABC triblocks, the phase segregation between C and AB-mixed domains can more be discovered in ABCBA. In conclusion, these results not only capture the self-assembling behavior of ISOSI pentablocks, but also provide concrete suggestions for designing the diverse microstructures in the linear ABC-type terpolymers of ABC and ABCBA at non-frustrated interaction parameter regimes.