有趣的是加入一條極長鍊到上述的短鍊系統中後，本來很硬的長鏈會因為背景短鍊的碰撞而形成實驗上所看到的自我螺旋結構。我們歸納出此結構的發生是背景短鍊密度和長鍊硬度的平衡結果。來自短鍊的碰撞讓長鍊的等效硬度減少。為了更進一步了解這個現象，我們透過模擬探索了由長鍊硬度和背景短鍊密度所構成的相空間。結果顯示在長鍊極硬的情況下，若要形成完美的螺旋結構，需要有密度適當的背景短鍊。 ;Large scale patterns such as clustering can be observed in different self-propelled systems:from cell aggregations to fish schools.Several models have been proposed to describe these diverse systems which all show the collective behaviours.They conclude that, the alignment of velocities between two self-propelled elements explains the mechanism.
Inspired by the experimental observation of swarming bacteria self-assembled into rotating spiral-coil structures, we conduct a 2-dimensional semi-flexible self-propelled chain simulation. In the monodisperse system, the system comprises several short self-propelled chains with the same length. Under this condition, self-propelled chains with spatial interactions, shows cluster formation. We provide a novel way to describe the attraction between self-propelled chains by changing the stiffness of chains. With the increase of stiffness, the cluster size distribution exhibits larger clusters.
Interestingly, in the bidisperse system, an rigid ultra-long chain interacted with short chain backgrounds can form self-rotated and rotational structure. The onset of spiral-coil conformation is related to the balance of background density and stiffness of long chain. We investigate the spiral coil formation by varying long-chain stiffness and short-chain density. The collisions from the background decrease the effective stiffness of long chain. As a result, our finding can be demonstrated by phase diagram of those two parameters. Our results explain the self-assembled spiral coils in the stiff long bacterial swarm systems.
