利用繪圖處理器加速粗粒化分子動態模擬探討硬性高分子於不同側鏈分子結構下的微結構型態

Abstract

我們以繪圖處理器加速粗粒化分子動力學模擬針對硬性高分子的不同側鏈結構、主鏈組成、側鏈接枝密度與粒子大小以及主鏈剛硬性質對其本身的微結構型態影響。我們以聚噻吩在熔融態下的有序堆積為分子鏈構形的參數設計參考，發現當接枝密度為100%時，不同側鏈結構與組成對整體自組裝行為的演變有單層層狀、近晶狀、向列狀等等，而改變不同主鏈組成發現到不同側鏈結構在主鏈組成低於0.2時，其有序參數因粒子間表面能主導打破有序形態而均有驟降的情形。當我們固定主鏈組成為0.5把側鏈接枝密度降低加上改變不同側鏈結構，發現降低的側鏈接枝密度有助於主鏈之間的聚集導致產生有六方堆積與雙層層狀形態的出現，且50%接枝密度會較25%接枝密度組得到更緊密的主鏈堆疊行為，且兩者均因側鏈位於主鏈同側而有分子鏈聚集的形態。但在33%接枝密度下側鏈分佈於主鏈兩側而依然以單層層狀形態出現。此外我們更藉由在50%接枝密度下加大了側鏈粒子得到了多股螺旋的形態，以及不同側鏈構形對螺旋股數與行為上的差異。最後我們將主鏈的兩面角限制減弱以探討共平面性質消失對整體自組裝形態的影響得到有序結構上的破壞，至終也可得到單純由粒子不相容性主導的雙層層狀形態。

The GPU-accelerated coarse-grained molecular dynamics is adopted to investigate the effects of various side-chain architectures referring to compositions of main-chain, grafting densities of side-chains with different sizes of side-chain beads and rigidity of main-chains on the morphological behaviors of rod-like polymers. We set our parameters according to the well packing of poly(3-hexylthiophene)s in melting state. The self-assembly behaviors were observed in single-layered lamellae, Smectic C, and Nematic phase with different architectures of side-chains in 100% grafting density. The order parameters were decreased rapidly below the composition of main-chain by 0.2 with all architectures of side-chains due to the interfacial energy between different kinds of coarse-grained beads, main-chain and side-chain beads. When the fraction of main-chain was fixed in 0.5, the hexagonal cylinder and double-layered lamellae were found in 50% and 25% grafting density of linear side-chains. The aggregation phenomena of main-chains by 50% grafting density side-chains is more closely packed than 25% grafting density on different side-chain architectures. Besides, multi-stranded helixs were observed by increasing the bead size with different architectures of side-chains in 50% grafting density system. In the end, the spring constant of dihedral angles of main-chains were deduced to study the effects by breaking the coplanarity of main-chains on the morphological behaviors of rod-like polymers, and a destruction of ordered state has be found in this part.