ABC星狀共聚物在不對稱作用力下的相變化行為探討

Abstract

吾人利用耗散粒子動力學研究星狀共聚物在作用力參數不對稱時的微結構變化情形，並進一步將結果與PI-PS-P2VP實驗系統作比較。首先維持aAB與aBC值相等並調大aAC值，綜觀在在此條件下完成的相圖，發現大多形成的微結構都同樣可以在作用力對稱的系統中看到，但是因為A與C較為互斥的影響，使各種結構形成的區域隨之產生變化，主要是朝著B組成增大的方向移動。在三成份組成相近時發現到以fA / fB / fC = 0.25 / 0.25 / 0.5為主的區域形成[6.4.10; 8.4.10] (3.3.4.3.4) + [6.4.12]的角柱結構(polygonal cylinders)，[6.4.12]是在實驗系統中廣泛被觀察到的角柱結構，然而作用力參數設定為對稱的理論系統卻不容易看到。另外，當三成份組成為fA / fB / fC = 0.3 / 0.6 / 0.1時觀察到六方堆積殼層型角柱結構(hexagonally packed core-shell cylinders)，這是在PS-PI-PMMA實驗中所能看到的一種特殊結構。上述結構的形成證明了改變作用力參數對稱性可以漸漸觀察到過去在作用力對稱的系統中無法看到，卻是實驗能觀察到的結構，這個結果甚至可以作為對PI-PS-P2VP系統的結構預測。將本系統結果與PI-PS-P2VP實驗系統相比較之後，發現結構變化趨勢雖然與實驗系統已經相當接近，但仍無法使形成的結構達到完全對應，在推測造成差異的原因為作用力參數值需進一部作提高或改變aAB與aBC的相等關係後，吾人進一步嘗試藉由調整作用力參數之間的關係使同組成下形成的微結構與實驗系統接近，成功的觀察到完整的[6.4.12]角柱結構形成；然而針對只有在PI-PS-P2VP實驗系統中觀察到的一種特殊結構：PI與PS形成一層，而PI在層中形成垂直層平面的六方圓柱堆積(cylinders-in-lamellae)作測試時，僅得到在層中形成微胞狀的聚集。吾人由分析結果進一步推測與實驗系統較接近的aij值範圍，這個預測的結果將會成為繼續深入尋找能使模擬系統結果與實驗系統形成結構吻合的參數的基礎。

We employ dissipative particle dynamics (DPD) to examine the effects of asymmetric interaction parameter on the resulting structures of ABC star copolymers, and further, compare our results with PI-PS-P2VP star copolymers. Here, we assume two of the interaction parameters: aAB and aBC, are equal, and increasing the amount of aAC. It can be found that lots of morphology which formed in symmetric interaction parameter system can still be observed in our results. But due to the repulsive of A and C component, regions of morphology are vary toward the direction of increasing B composition (fB). When the composition of three components are fA / fB / fC = 0.25 / 0.25 / 0.5, a kind of polygonal cylinder which called [6.4.10; 8.4.10] (3.3.4.3.4) + [6.4.12] is observed. The [6.4.12] polygonal cylinder are always be observed in experimental system, but cannot be predicted in DPD when interaction parameters are symmetry. Additionally, a structure called hexagonally packed core-shell cylinders, which be found in PS-PI-PMMA star copolymers by Thomas et al., can also be observed in our system when fA / fB / fC = 0.3 / 0. 6 / 0.1 and 0.1 / 0.6 / 0.3, prove that we can use DPD to simulate some morphology which easily be found in experimental system while interaction parameters are asymmetry, even make a prediction for PI-PS-P2VP experimental system. Compare our results with PI-PS-P2VP star copolymers, although the resulting phase behaviors are similar, the morphologies result from two systems still cannot to match absolutely. According to adjust the relationship of interaction parameters and increasing all of them, we successfully find single [6.4.12] polygonal cylinder, but the structure called cylinders-in-lamellae which found by Matsushita et al. still cannot simulated by DPD. We suggest that the value of aAC must maintain a difference in aAB and aBC, and each interaction parameter also has to large enough to separate each component completely.