以耗散粒子動力學研究自泳動桿狀奈米粒子在波浪狀管道中之行為分析

Abstract

本論文利用耗散粒子動力學研究被動和主動奈米桿狀粒子在波浪型隧道中的動態行為。被動粒子由於流體施加到物體上的流體動力和扭矩而運動，而主動粒子則可以自我推進。隧道形成在兩個正弦形狀的實心壁之間，上壁的波峰與下壁的波谷同步，發展了寬到窄和窄到寬的交替區域。我們研究了桿長（N）和作用力（F_a）對隧道不同區域內奈米桿狀粒子分佈的影響。對於被動奈米桿狀粒子，發現三種狀態的存在。當N較小時，奈米桿狀粒子均勻地分佈在整個通道中。但是，隨著N的增加，奈米桿狀粒子開始在固體壁附近堆積。此外，令人驚訝地發現，與寬到窄區域相比，奈米桿狀粒子傾向於在窄到寬區域中堆積，從而導致沿流動方向的不對稱分佈。當N足夠大時，不對稱性會變得非常明顯，但不會有進一步的變化。對於活性奈米桿狀粒子，隨著 F_a 或N的增加，壁積累情況會加劇。然而，隨著 F_a 的增加，從窄到寬和寬到窄區域之間的奈米桿狀粒子分佈的不對稱性卻很快減緩。此外，對於較長的奈米桿狀粒子在 F_a 較大時，我們觀察到位在上下波浪壁之間的特殊循環軌跡，但對於較短的奈米桿狀粒子在 F_a 較小時，則無法追蹤到此現象。

The dynamic behavior of passive and active nanorods in a wavy tunnel is investigated by dissipative particle dynamics. The passive particles move because of the hydrodynamic forces and torques exerted by the fluid onto the bodies and the active ones can self-propel. The tunnel is formed between two solid walls of sinusoidal shape and the crests of the upper wall are synchronized with the trough of the lower wall. Alternating wide-to-narrow and narrow-to-wide regions are developed. The effects of rod length (N) and the active force (F_a) on the distribution of nanorods within the various regions of the tunnel are studied. For passive nanorods, three regimes are identified. As N is small, the nanorods distribute uniformly throughout the channel. However, the nanorods begin to accumulate near the solid walls as N increases. Moreover, it is surprising to find that nanorods tend to pile up in the narrow-to-wide region as compared to the wide-to-narrow region resulting in an asymmetric distribution along the flow direction. When N is large enough, the asymmetry becomes rather significant but stops to escalate further. For active nanorods, the wall accumulation scenario is intensified as F_a or N increase. However, the asymmetry in the nanorod distribution between the narrow-to-wide and wide-to-narrow regions diminishes quite rapidly with increasing F_a. Furthermore, peculiar cycling trajectories sandwiched between the upper and lower wavy walls are observed for long rods at large F_a but they vanish for short rods with small F_a.